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Respiratory Management Following Spinal Cord Injury

2.50 Contact Hours   -   0.30 CCUs
A score of 80% correct answers on a test is required to successfully complete any course and attain a certificate of completion.
Author:    Pamela Downey (MSN, ARNP)

Outcomes

Although pulmonary complications are a common and well-known problem in SCI, there is little information about their management. Current practice is mainly based on clinical experience and expert opinion. Management of care with appropriate interventions and prevention of pulmonary complications of SCI will be discussed with, support for a return to the maximal level of functioning.

Objectives

After completing this course, the learner will be able to:

  1. Differentiate the muscles of inspiration and expiration and their levels of innervation from the spinal cord.
  2. Describe the mechanics of respiration.
  3. Identify changes in PFTs which occur at various levels of complete and incomplete SCIs.
  4. Describe the American Spinal Injury Association Impairment Scale (AIS) used to classify the degree of impairment in SCI.
  5. Relate pulmonary physiologic changes which occur following various levels of injury to the spinal cord.
  6. Describe the assessment of pulmonary function following SCI.
  7. Relate five interventions which can be utilized in the management of compromised pulmonary function following SCI to optimize the patient’s quality of life.

Introduction

Respiratory complications are the main cause of morbidity and mortality in the acute phase of spinal cord injury (SCI), with an incidence of 36% to 83%. Approximately two-thirds of patients with acute SCI will experience complications such as atelectasis, pneumonia, and respiratory failure, which will require mechanical ventilation.1,2The degree of respiratory dysfunction is related to the extent and level of the neurological injury, in such a way that high cervical and thoracic injuries are at the highest risk.3 Various studies have suggested an increasing trend in cervical injuries, in particular, C1–C4 injuries, with an increased rate of SCI resulting in mechanical ventilation dependency.4,5

Respiratory dysfunction that leads to respiratory complications in SCI may be related to 3 factors6:

  1. An impairment in vital capacity (VC) resulting in:
  • Reduction in respiratory muscle strength and fatigue
  • Reduction in inspiratory capacity
  • Atelectasis
  1. Retention of secretions resulting in:
  • Increased production of secretions
  • Ineffective coughing
  1. Autonomic dysfunction resulting in:
  • Increased secretions
  • Bronchospasms
  • Pulmonary edema

Although pulmonary complications are a common and well-known problem in SCI, there is little information about their management. Current practice is mainly based on clinical experience and expert opinion.7 Promptness of prevention and treatment, as well as, a multidisciplinary treatment approach by professionals experienced in the treatment of SCI, reduces respiratory complications.

Muscles of Respiration

Figure 1

Inspiration

  • Diaphragm
    • Major muscle which mediates inspiration
    • Innervated by the phrenic nerve (C3, C4, C5 cervical nerve roots).8
  • Accessory muscles of inspiration are the:
    • External intercostals
      • Innervated by thoracic nerve roots
  • Clavicular portions of the pectoralis major
  • Scalenes
    • Innervated by cervical nerve roots C2 to C7
  • Sternocleidomastoids and trapezius
    • Innervated via cervical nerve roots C1 to C4 and also cranial nerve XI

Patients with high SCI can sometimes utilize oral, pharyngeal, and laryngeal muscles for short-term ventilation by projecting boluses of air past the glottis (glossopharyngeal breathing), although these muscles are not traditionally thought of as muscles of respiration.

Expiration

  • Abdominal wall muscles:
    • Rectus abdominus
    • Obliques
    • Transversus abdominus
    • All of the above aforementioned abdominal muscles are innervated by the lower thoracic and lumbar nerve roots
  • Internal intercostals
    • Innervated by the thoracic nerve roots

Normally, expiration is passive and does not require use of these muscles. However, these muscles are crucial when forced exhalation is needed, such as during exercise or coughing. When the ability to generate forced exhalation for coughing is impaired, removal of airway secretions is ineffective. In addition, these muscles contribute to normal function of the diaphragm in three important ways9-13:

  1. The intercostal muscles help to stabilize the rib cage, preventing inward collapse of the rib cage during diaphragmatic contraction for inspiration.
    • In patients with cervical or thoracic SCI, ps of the intercostal muscles leads to inward motion of the rib cage during inspiration, thus decreasing the volume of air inspired for a given amount of diaphragmatic work.
  2. The integrated abdominal wall and thoracic cage musculature act as a fulcrum against which the diaphragm can contract. Loss of this fulcrum effect reduces the efficiency of the diaphragm.
  3. Flaccid ps of the abdominal wall muscles leads to relocation of the abdominal contents caudad, away from the diaphragm. The diaphragm is less steeply domed and, therefore, less efficient.

Review of Mechanics of Respiration

Movement of the Rib Cage during Inspiration (Figure 2)

  • The diaphragm contracts and flattens
  • The external intercostal muscles contract while the internal intercostal muscles relax
  • The ribs move upwards and outwards while the sternum moves up and forward
  • The volume of the thoracic cavity increases
  • Air pressure in the lungs cause them to expand to fill up the enlarged space in the thorax
  • Expansion of the lungs causes the air pressure inside them to decrease
  • Atmospheric pressure is now higher than the pressure within the lungs so air rushes into the lungs

Movement of the Rib Cage during Expiration (Figure 2)

  • The diaphragm relaxes and arches upwards
  • The internal intercostal muscles contract while the external intercostal muscles relax
  • The ribs move downwards and inwards while the sternum moves down to its original position
  • The volume of the thoracic cavity decreases
  • The lungs become compressed and the air pressure inside them increases as the volume decreases
  • The air pressure within the lungs becomes higher than the atmospheric pressure so the air is forced out of the lungs to the exterior

Figure 2

Movement of the Rib Cage During Respiration

How to remember what happens to the intercostal muscles during respiration:

  • Inhalation = RICE
    • R: Relax your
    • I: Intercostal muscles and
    • C: Contract your
    • E: External intercostal muscles
  • Exhalation = ERIC
    • E: External intercostal muscles
    • R: Relax and your
    • I: Intercostal muscles
    • C: Contract

The process of inspiration involves contraction of the diaphragm and the external intercostal muscles that allow the chest cavity to expand. At high levels of ventilator activity, the accessory muscles are recruited to aid in this process. Expiration is largely passive but can be augmented by the forceful contraction of the muscles of the abdominal wall.6,14

The degree of respiratory failure associated with traumatic injuries to the spinal cord depends on the level of the spinal lesion. In general, functional impairment worsens as the level of injury is more rostral (i.e. superior in relationship to areas of the spinal cord). In addition, a complete SCI, defined as the absence of motor or sensory function below the injury (classified as American Spinal Injury Association (ASIA) score A), results in greater functional impairment than incomplete injuries (ASIA scores B–D). Other factors that are associated with pulmonary complications are age, preexisting medical illnesses, and associated major traumatic injuries.

Pulmonary Function Tests (PFTs)

Spirometry (meaning the measuring of breath) is the most common of the pulmonary function tests (PFTs). It measures lung function, specifically the amount (volume) and/or speed (flow) of air that can be inhaled and exhaled.

Spirometry generates pneumotachographs, which are charts that plot the volume and flow of air coming in and out of the lungs from one inhalation and one exhalation.

Lung Volumes and Lung Capacities

There are four lung volumes and four lung capacities. A lung capacity consists of two or more lung volumes.

The lung volumes are:

  1. Tidal volume (VT): the volume of air moved into or out of the lungs during quiet breathing.
  2. Inspiratory reserve volume (IRV): the maximal volume that can be inhaled from the end-inspiratory level.
  3. Expiratory reserve volume (ERV): the maximal volume of air that can be exhaled from the end-expiratory position.
  4. Residual volume (RV): the volume of air remaining in the lungs after maximal exhalation.

The four lung capacities are:

  1. Vital capacity (VC): the volume of air breathed out after the deepest inhalation.
    • Forced vital capacity (FVC): the determination of the vital capacity from a maximally forced expiratory effort.
  2. Total lung capacity (TLC): the volume in the lungs at maximal inflation (the sum of VC and RV).
  3. Inspiratory capacity (IC): the sum of IRV and VT.
  4. Functional residual capacity (FRC): the volume in the lungs at the end-expiratory position.
    • Forced expiratory volume in one second (FEV1): the volume of air exhaled at the end of the first second of forced expiration.

Individuals with SCI exhibit reduced lung volumes and flow rates as a result of respiratory muscle weakness. Changes in spirometric measurements in SCI are dependent on injury level and posture.14,15

  • Spirometric values of FVC, FEV1, and IC increase with more caudal lesions.16
  • As the level of injury ascends, TLC is progressively reduced. The reduction in FRC occurs at the expense of ERV, with a compensatory increase in RV.
    • The loss of ERV can be explained by the denervation of the abdominal musculature and other muscles necessary for forced exhalation. Goldman et al.17 found that the abdominal wall in quadriplegic/tetraplegic patients is twice as compliant as in normal subjects.
    • There is recent evidence of the benefits of a semi seated position to the weaning process of patients dependent on a respirator and the effect of the seated position on lung volume and oxygenation in acute respiratory distress syndrome.18,19
  • However, it must be noted that quadriplegics/tetraplegics have better pulmonary mechanics in the supine position than when upright.20
  • In erect postures, the abdominal contents fall forwards unopposed, and the diaphragm flattens, thus impairing the rib cage expanding mechanism of the only major respiratory muscle available in quadriplegia/tetraplegia. The increase in VC in the supine position is related to the effect of gravity on the abdominal contents and a concomitant reduction in RV.

The time factor is important because pulmonary function of quadriplegic/tetraplegic patients should improve as the muscle flaccidity associated with the initial phase of spinal shock converts to the spasticity of paralyzed muscles. This increase in muscle tone affects both intercostal and abdominal muscles and results in a decline in the end-expiratory volume and more effective diaphragmatic contraction.

Injury to the cervical or thoracic spinal cord affects the spinal nerves that innervate respiratory muscles. The diaphragm, the major muscle of inspiration, receives its innervation from the third, fourth, and fifth cervical spinal segments (Figure 3).

  • Paralysis of diaphragmatic, intercostal, and abdominal muscles results from lesions occurring above the third cervical level and, in the absence of mechanical ventilatory support, is incompatible with life.
  • High cervical incomplete lesions (C2–C4) or cervical lesions below C5 (C5–C8) are likely to produce paralysis, weakness, or spasticity in the muscles used to perform forced respiration. In these patients, neural control of the diaphragm is preserved, and spontaneous ventilation is possible. However, in such quadriplegic/tetraplegic patients, respiratory function is substantially compromised, and ventilatory failure can occur days after injury.

Figure 3

The respiration of patients with diaphragmatic paralysis commonly exhibits a paradoxical movement of the abdomen: the abdominal wall retracts during inspiration and protrudes during the expiration phase.

  • This pattern, more frequent in cervical than thoracic SCI, is the result of a lack of spinal motor activation of the external intercostals combined with the excessive compliance of the abdominal wall due to weak muscle contraction.
  • Alterations in chest wall, lung and abdominal compliance in quadriplegia/tetraplegia are associated with an increase in the work of breathing and may contribute to respiratory muscle fatigue.

After the initial stage of spinal shock has passed, patients with quadriplegia/tetraplegia may develop abnormal spinal reflexes that involve the abdominal muscles. This spastic contraction reduces the elastic properties of the abdominal compartment of the respiratory system.

  • Spastic contractions of the abdominal muscles impose a substantial load on inspiratory muscles. This additional pressure must be overcome for inspiration to occur or dyspnea results.15

The main physiologic consequence of expiratory muscle paralysis is an impaired cough. The cough reflex is preserved in cervical and upper thoracic SCI. However, the inability to cough adequately is caused by a weakness of the major muscles of expiration thus resulting in an accumulation of secretions.15

In acute quadriplegia/tetraplegia, some patients develop an unexplained production of excessive and tenacious bronchial mucus. Speculation presupposes that the bronchial mucus hypersecretion is caused by the unopposed vagal activity, perhaps related to the initial disappearance of peripheral sympathetic nervous system tone.21 This parasympathetic imbalance which predisposes the patient to atelectasis, pneumonia, and potentially respiratory failure include22-25:

  • Bronchial spasm
  • Decreased mucociliary activity
    • Decreased mucociliary activity is also related to mechanical ventilation which is associated with the development of secretion retention.
  • Increased vascular congestion

Assessment of Level and Completeness of SCI

Pulmonary physiologic changes due to SCI are related to the extent of neurological impairment. The American Spinal Injury Association Impairment Scale (AIS) is used to classify the degree of impairment that is based on strength in key muscles and on a sensory examination (Table 1).26

Table 1
American Spinal Injury Association (ASIA) Impairment Scale (AIS)* A Complete cord injury. No motor or sensory function is preserved in the sacral segments S4-5. B Sensory incomplete. Sensory but not motor function is preserved below the neurologic level and includes the sacral segments (light touch or pin prick at S4-5 or deep anal pressure) AND no motor function is preserved more than three levels below the motor level on either side of the body. C Motor incomplete. Motor function is preserved below the neurologic level and more than half of key muscle functions below the neurologic level of injury have a muscle grade <3 (Grades 0 to 2). D Motor incomplete. Motor function is preserved below the neurologic level and at least half or more of key muscle functions below the neurologic level of injury have a muscle grade ≥3. E Normal. Sensation and motor function are graded as normal in all segments and the patient had prior deficits.

*Muscle function is graded using the International Standards for Neurologic Classification of Spinal Cord Injury.

*For an individual to receive a grade of C or D (i.e., motor incomplete status), he/she must have either:

  1. Voluntary anal sphincter contraction or
  2. Sacral sensory sparing with sparing of motor function more than three levels below the motor level for that side of the body.

*Patients without an initial spinal cord injury do not receive an AIS grade.

The patient’s strength in key muscle groups is assessed and graded. A muscle grade of 5/5 is normal, and a grade of 3/5 means the muscle can be moved against gravity.

  • The motor level is defined as the most caudal key muscle that is graded 3/5 or 4/5 with the segment cephalad to that level graded 5/5.
  • The sensory level is defined as the most caudal dermatome to have normal sensation for both pinprick and light touch.
  • For areas that lack key muscles to test, such as between T2 and L1, sensory findings are used to estimate motor levels.

Complete motor SCI includes: (see Table 1 above)

  • AIS A (no sensory or motor function preserved below the neurologic level)
  • AIS B (sensory but no motor function preserved below the neurologic level)

Incomplete motor SCI includes: (see Table 1 above)

  • AIS C where motor function in less than half of the key muscles below the neurologic level have a muscle grade less than 3
  • AIS D more than half the key muscles below the neurologic level have a muscle grade of 3 or more

With quadriplegia/tetraplegia, there is injury to at least one of the eight cervical segments of the spinal cord. With paraplegia, there is injury in the thoracic, lumbar, or sacral regions.

Pulmonary Physiologic Changes

Pulmonary physiologic changes following SCI include:

  • Airflow limitation and bronchial hyperresponsiveness
  • Changes in lung and chest wall compliance
  • Changes in ventilatory control
  • Impairment of ventilatory muscle performance

In describing the occurrence of these changes, it is useful to consider SCI in three phases:

  1. Immediately following the injury
  2. During the year thereafter
  3. More than one year after injury

Timing of Changes in Ventilatory Function

Immediately after SCI, flaccid paralysis occurs and affects all muscles caudal to the level of injury. This physiologic state is known as spinal shock. Subsequent improvements in pulmonary function are due primarily to27-31:

  • Enhanced recruitment of accessory ventilatory muscles
  • Evolution from flaccid to spastic paralysis
  • Functional descent of the neurologic injury level as spinal cord inflammation resolves
  • Retraining of deconditioned muscles

Starting from several days to up to four to six weeks, spinal reflexes return and eventually become exaggerated as the syndrome of spasticity develops.

The timing of respiratory failure was examined in 72 patients with traumatic cervical SCI.32 Among those who required mechanical ventilation, 90% of the episodes of respiratory failure occurred within the first three days after SCI. Improvement in respiratory muscle performance after SCI largely occurs in the first year following injury.31,33-35

Impairment of Ventilatory Muscle Function

The extent of ventilatory muscle impairment depends upon the degree and location of the injury, as well as, the duration of time since the injury. The higher the level and more complete the injury, the more likely that there will be respiratory muscle dysfunction (Table 2).

Table 2
Respiratory Complications with SCI
Spinal Cord LevelMuscle InvolvementEffect on RespirationClinical Consequence

C1-3Complete paralysis of all respiratory musclesVital capacity only 5-10% of normal. Absent cough.Apnea and immediate death.
C3-6Varied Impairment of diaphragmatic contractionVital capacity 20% of normal. Weak and ineffective cough.Ventilation necessary in acute stages. Majority will be weaned from mechanical ventilation.
C6-8Diaphragm and accessory cervical inspiratory muscles intact. Intercostals and abdominal muscles intact. Expiration entirely passive. Secretion retention. No respiratory failure unless co-existing lung/chest injury/illness.
T2-4 Vital capacity 30-50% normal. Weak cough. 

Ventilatory muscles innervated below the level of a complete SCI are completely nonfunctional (AIS A or B), while the degree of ventilatory muscle compromise is variable in patients with incomplete injuries (AIS C or D) (see Table 1 above).

  • Complete injury above C3 causes:
    • Near total ventilatory muscle paralysis because the phrenic nerve, which innervates the diaphragm, arises from the third to fifth cervical roots.
    • Denervation of the intercostal, abdominal muscles, sternocleidomastoid, and trapezius muscles.
    • Due to complete paralysis of the respiratory muscles, patients with SCI above the C3 root have acute ventilatory failure and do not survive unless manual ventilation is rapidly instituted at the accident scene. In addition to ventilatory dysfunction, these patients are unable to cough without assistance.
  • Injury involving C3 through C5 cause:
    • Variable impairment of diaphragmatic strength
    • Variable impairment of the accessory muscles of ventilation (e.g., scalenes, sternocleidomastoid, trapezius).
    • Respiratory failure requiring mechanical ventilation is common during the first few days to weeks after the injury, either due to respiratory muscle weakness and fatigue or precipitated by atelectasis or pneumonia. As the initial muscle flaccidity transitions to spasticity and accessory muscles are recruited and strengthened, spontaneous ventilation is often adequate for weaning from mechanical ventilation. In addition to ventilatory dysfunction, these patients have an impaired cough due to loss of expiratory muscle strength.
  • Injury at C6 through C8
    • Patients with complete cervical SCI but with intact diaphragm function are able to inhale via the diaphragm and accessory muscles in the neck. Exhalation occurs primarily through the passive recoil of the chest wall and lungs, because the primary muscles of exhalation (internal intercostals and muscles of the abdominal wall) are paralyzed. The clavicular portions of the pectoralis major muscles provide only a small contribution.36,37 Thus, cough is impaired and even if these patients do not have initial respiratory failure, they are at an increased risk of respiratory muscle fatigue in the setting of respiratory system loading (e.g., pneumonia or excess secretions).8,12,13,38
  • Patients with injuries of the Thoracic Spinal Cord have:
    • Intact diaphragm function
    • Less impairment of overall ventilator muscle function despite some loss of intercostal muscle strength and impaired stabilization of the rib cage due to abdominal wall paralysis
    • The main respiratory impairment for these patients is an inefficient cough mechanism.

Changes in Lung and Chest Wall Compliance

Lung and chest wall compliance, when measured 1 to 12 months after SCI, is reduced in patients with quadriplegia/tetraplegia, compared with normal subjects.39 The decrease in compliance has been attributed to the accompanying reduction in lung volumes and possibly changes in surfactant that can occur with ventilation at reduced lung volumes.35 Although the abdomen is highly compliant in quadriplegia/tetraplegia, the rib cage compartment of the chest wall is stiff because of intercostal muscle spasticity and ankylosis of the rib articulations with the spine and sternum. It is believed that ankylosis of rib articulations results from an inability to inspire to total lung capacity due to inspiratory muscle weakness.35,39-42

Airflow Limitation and Bronchial Hyperresponsiveness

Subjects with quadriplegia/tetraplegia demonstrate reversible expiratory airflow limitation, which is usually only apparent when a bronchodilator is administered, as the predominant abnormality is a restrictive ventilatory defect. Loss of postganglionic sympathetic innervation to the airways is a potential mechanism contributing to airflow limitation, although the functional significance of direct sympathetic airway innervation is thought to be minor or absent. The reversibility of this airflow limitation was demonstrated by the administration of inhaled ipratropiu bromide, an anticholinergic agent, which caused an increase in expiratory airflow.43,44 This reversibility suggests that unopposed vagal cholinergic (bronchoconstrictor) activity also contributes to airflow limitation. An alternate explanation is reduced airway smooth muscle relaxation secondary to lack of inhalation to a normal total lung capacity.43-47

Abnormalities of sympathetic or parasympathetic nervous system activity may also be responsible for airway hyperresponsiveness noted after SCI causing quadriplegia/tetraplegia.48

Changes in Ventilatory Control

Individuals with quadriplegia/tetraplegia have an abnormally small increase in ventilatory drive in response to hypercapnia.49,50 As an example, a study of nine quadriplegic/tetraplegic subjects and eight able-bodied controls found that the ventilatory response to hypercapnia among quadriplegics/tetraplegics was approximately one-fourth that of the controls.50 The mechanism for a blunted response to hypercapnia is not fully explained by respiratory muscle weakness, as patients with comparable respiratory muscle weakness due to other causes do not exhibit the same blunted response.

One hypothesis is that the blunted response is related to a decrease in blood pressure in the sitting position. This was examined in a study of 12 subjects with quadriplegia/tetraplegia that found a normal ventilatory response to hypercapnia in the supine position and a reduced response in the sitting position.51 The ventilatory response was normal in the supine position, but decreased in the sitting position. The ventilatory response correlated better with blood pressure changes than with improved chest cage mechanics associated with the supine position.

Sleep-disordered breathing has been reported in individuals with SCI and is predominantly obstructive or a combination of obstructive and central.

Assessment of Pulmonary Function

Some of the techniques for performing PFTs need to be modified in the patient with a SCI. In addition, changes in respiratory muscle performance following SCI result in abnormal PFT results that can be predicted based on the level and completeness of SCI and other factors.

Standardized techniques for performing PFTs and calculating predicted values need to be adjusted due to the practical challenges posed by SCI patients. For example:

  • Measurement of Height
    • Height is used to calculate predicted pulmonary function values in the able-bodied, but precise measurement of height in SCI patients can be problematic since most cannot stand.
    • Measurement of supine length is preferred over arm-span or recalled standing height for use in the calculation of predicted pulmonary function values for patients with SCI.
  • Use of Modified American Thoracic Society (ATS) Standards
  • Many SCI patients, particularly those with complete quadriplegia/tetraplegia cannot meet the acceptability and reproducibility standards for spirometry set by the ATS.52 ATS standards require that exhalation last for more than six seconds, but in a study of 278 adults with SCI, the most common reason for unacceptable trials was failure to exhale maximally for a minimum of six seconds.53
  • ATS criteria also require a prompt onset of exhalation, but subjects with complete quadriplegia/tetraplegia are more likely than others with SCI to have a delay at the start of a forced expiratory maneuver, resulting in an excessive back-extrapolated volume.
  • When ATS standards are modified to allow expiratory efforts less than six seconds, as long as, a 0.5 second plateau is achieved (presumably at RV), and a greater degree of excessive back-extrapolated volume, as long as, the volume-time curves and flow volume loops are otherwise acceptable, then the FVC and FEV1 are reproducible.53 This finding indicates that despite respiratory muscle weakness, the FVC and FEV1 can be assessed longitudinally at all levels and neurologic completeness of SCI.
  • Mouthpiece for Pressure Measurements
    • In order to achieve accurate measurement of maximal inspiratory and expiratory static pressures, the mouthpiece may need to be adjusted.
    • Measurement of maximal inspiratory pressure after SCI is generally acceptable using a conventional mouthpiece with a flange that fits inside the mouth.
    • However, measurement of maximal expiratory pressure muscle with a flange style mouthpiece results in the underestimation of maximal expiratory respiratory muscle strength.54
    • For reliable results, a tube style mouthpiece that fits outside and around the mouth should be substituted.54
  • Effect of Posture
    • Posture has a significant impact upon lung mechanics in the majority of patients with SCI. Typically, patients with SCI have an increase in VC when changing from a seated to supine position, whereas the normal response to recumbency is a slight decrease in VC.
    • A change from the seated to the supine position results in a decrease in FRC because the abdominal contents push up upon the diaphragm. However, the muscle fibers of the diaphragm are longer at end expiration when supine and, thus, at a more favorable portion of their length-tension curve, resulting in a greater downward (caudad) excursion of the diaphragm during inspiration. Together, these effects result in an improved IC and VC when supine.
    • On the other hand, gas exchange abnormalities are more likely in the supine position due to airway closure and any atelectasis that could arise from tidal breathing at lower respiratory system volumes (at a reduced FRC).
    • When choosing a position to optimize respiratory system function, the advantage of a greater VC and IC must be weighed against the possibility of gas exchange problems due to airway closure and atelectasis (e.g., arising from tidal breathing at lower respiratory system volumes).
  • Expected Values for Spirometry
    • Among individuals with chronic cervical cord injury, spirometry typically shows a restrictive ventilatory defect with FVC and FEV1 values approximately 55% of the values predicted for able-bodied subjects.
  • Expected Values for Lung Volumes
  • Lung volumes following complete cervical cord injury show a marked reduction in ERV, a mild to moderate reduction in TLC and FRC, and preservation of RV.
  • The main lung volume abnormality after incomplete cervical or thoracic SCI is a moderate reduction in ERV.
  • Longitudinal Assessment of Pulmonary Function
    • Several case series have observed that after SCI, the greatest rate of improvement in pulmonary function occurs in the first three months and is followed by furthermore gradual improvement up to about one year following the initial injury.8,30,31,34 Over many years, a gradual decline in pulmonary function is observed.
    • A borderline effect of greater injury duration on decline in FEV1 was noted in patients with more severe injury, i.e., cervical SCI that was motor complete (AIS A and B) or motor incomplete AIS C. It has been hypothesized that the effect of greater injury duration on pulmonary function is attributable to a slow but progressive decrease in lung and rib cage compliance.55-57
    • Greater lifetime cigarette smoking (pack years) is associated with lower values for FVC and FEV1 both initially after SCI and during long-term follow-up.
  • Maximal Inspiratory and Expiratory Pressures
  • In general, when the level of SCI is below C5 and thus spares the phrenic nerve, maximal expiratory force is impaired more than maximal inspiratory pressure, which remains near or within the normal range.
  • Bronchial Hyperresponsiveness and Bronchodilator Response
    • Individuals with quadriplegia/tetraplegia, but not with low paraplegia, demonstrate airway hyperreactivity on bronchoprovocation testing with methacholine, histamine, and ultrasonically nebulized distilled water.58-60 Therefore, it is possible that patients with SCI may be more likely to be diagnosed with conditions that may be associated with airway hyperreactivity.
    • Approximately, 40 to 50% of SCI patients exhibit significant responses to bronchodilator administration, even in the absence of demonstrable airflow limitation at baseline.43,45 However, the clinical benefit of routine use of bronchodilators to maximize the pulmonary function of patients with quadriplegia/tetraplegia, but no history of asthma or COPD, has not been established.
  • Other Etiologies of Abnormal PFTs
    • When interpreting PFT results in a patient with SCI, it is important to remember that factors other than neurologic level and completeness of injury can affect pulmonary function.
    • These other factors include55,61,62:
      • Cigarette smoking
      • Co-morbidities such as asthma, COPD, and tracheal stenosis from prior intubation
      • Obesity
      • Other chest trauma sustained at the time of the SCI

Management of Compromised Pulmonary Function Following SCIs

Monitoring Diaphragmatic Function

The objective of monitoring diaphragmatic function in patients with acute SCI is to help in the decisions on managing the airway.

The two most important markers that predict the need for intubation are the level of the injury and the ASIA classification.

  • Complete lesions above C5 require intubation in virtually 100% of cases.3,63,64 In these patients, elective intubation is recommended. Urgent intubation when the patient develops respiratory distress increases the risk of neurological damage due to improper manipulation of the neck or by hypoxia.63
  • In select patients with complete cervical lesions or in those with incomplete or lower lesions, conservative management is preferred. In these cases, lung function should be strictly monitored.
    • Indicators for intubation include6,65:
  • A reduction in VC to below 15 mL/kg
  • A maximum inspiratory pressure below −20 cm H2O
  • An increase in pCO2
    • Monitoring by pulse oximetry is inadequate and requires arterial gasometry or capnography.65

The goals for patients who are intubated are to:

  • Predict the time when weaning can begin
  • Detect those patients who may become ventilator dependent

The studies on phrenic nerve conduction, although essential for assessing the possibility of using diaphragmatic pacemakers, do not properly differentiate between patients who can be weaned and those who become ventilator dependent. Pathological studies do not distinguish between neuropraxia, atrophy, and axonotmesis. Similarly, normal results do not guarantee a sufficient diaphragmatic force.66 For similar reasons, diaphragmatic fluoroscopy does not predict the possibility of weaning from the respirator and should not be used as a prognostic marker.66

In recent years, interest has grown in the use of ultrasound as a noninvasive, bedside approach to evaluating diaphragm function.67,68 Vivier et al.69 found that the relation between diaphragm thickness measured by inspiration and expiration using ultrasound correlated adequately with the work of breathing during noninvasive ventilation. Kim et al.70 recently demonstrated that diaphragm dysfunction diagnosed by M-mode ultrasound predicted weaning failure. However, the use of diaphragm ultrasound in patients with acute spinal cord injury has not been prospectively studied.

As with monitoring the need for intubation, spirometry with measurement of the VC and the maximum negative inspiratory pressure are the best bedside markers for initiating weaning.6,66,71

More direct measures of diaphragmatic function such as transdiaphragmatic pressure and negative inspiration force diaphragm needle electromyography are invasive and of little use in clinical practice.6,66 Noninvasive studies such as the estimation of diaphragm dysfunction using airway occlusion pressure during magnetic stimulation of the phrenic nerves are correlated with the duration of ventilatory support but their use in clinical practice is unknown.72

Ventilation Modes

To ventilate a patient with acute SCI, the peculiarities that exclusively affect these patients must be considered.

  • In high cervical and thoracic injuries, ventilation will depend almost exclusively on the functioning of the diaphragm, which will be responsible for providing 90% of the VT.65
  • The loss of expiratory musculature function causes an impairment in the ability to produce effective coughing, leading to the subsequent accumulation of secretions.65,71
  • The increased production of secretions secondary to autonomic dysfunction, in addition to the above, facilitates the onset of atelectasis.24,65,71

Although patients with acute traumatic SCI can usually be said to have “healthy” lungs,71 up to 60% of the patients may have sustained associated chest trauma.

In this continuing education course we will focus on the management of patients with acute SCI and “healthy” lungs. In contrast to the abundance of the literature on mechanical ventilation in acute pulmonary lesions, the literature on the management of specific complications of acute SCI is very limited and of low quality.

The preservation of diaphragmatic function should be a primary objective in all patients undergoing mechanical ventilation. Diaphragmatic dysfunction is a common cause of weaning failure.73 The consequences of this dysfunction in patients who depend almost exclusively on the diaphragm to maintain effective inspiration are clear.

Although the negative effect of mechanical ventilation on the respiratory musculature has been known for many years, the specific diaphragmatic impairment was recently reported by Vassilakopoulos and given the name “ventilator-induced diaphragmatic dysfunction” (VIDD).73,74

Diaphragmatic atrophy occurs early after only 18 hours of inactivity and appears to be related to an increase in muscle proteolysis.75,76 Diaphragmatic atrophy increases with ventilation time and causes a progressive reduction in diaphragmatic function.

VIDD has been linked to diaphragmatic inactivity caused by controlled ventilation. It has been shown in animal models that assist modes attenuate VIDD.77 These findings have not been confirmed in humans, and no difference has been found in the onset of VIDD between patients ventilated with pressure control and those ventilated with pressure support.78

Patients ventilated with pressure control is often used. Pressure support ventilation (PSV) is often avoided due to the lack of evidence for a better prognosis and the risk of inadequate ventilation and exhaustion in patients with reduced respiratory reserve. The objective is to maintain some level of diaphragmatic contraction, ensuring total respiratory support. Achieving this objective requires adequate interaction between the patient and the respirator and the avoidance of asynchrony.

Asynchrony can occur at any time in the respiratory cycle. With a perfect patient-ventilator interaction, the respirator should trigger in synchrony with the electrical impulses originating in the central nervous system.79 Up to 25% of patients present some type of asynchrony while on mechanical ventilation.80 Most of the ventilators in use today trigger inspiration by a signal measured within the ventilator circuit. The signal may be a fall in the pressure of the airway (pressure trigger) or a variation in the flow signal (flow trigger). Although it was initially believed that the flow trigger produced a better patient-respirator interaction, with current respirators, no differences have been found.81-83

In recent years, a new modality of ventilation has been reported: neutrally adjusted ventilator assist (NAVA).84 In this modality, the signal used by the respirator to deliver assistance is not the flow or the airway pressure, but rather the diaphragmatic electromyogram signal collected from electrodes placed on an esophageal catheter. Despite its promising theoretical advantages, to date there is little evidence of the superiority of NAVA compared with other ventilatory modalities.85

Common practice in some clinical settings is to use the flow trigger. The lowest level possible is used that avoids the auto trigger. In case an ineffective trigger is detected, the presence of auto-PEEP (positive end-expiratory pressure) must be ruled out. Overcoming intrinsic PEEP in a patient with muscular weakness is imperative because intrinsic PEEP is one of the most frequent causes of an ineffective trigger. Lengthening the expiratory time, using bronchodilators, adding external PEEP, and reducing the sensitivity of the trigger are alternatives that can improve synchrony.

Traditionally, the use of tidal volumes between 15 and 20 mL/kg has been recommended, with the goal of avoiding or treating atelectasis. This recommendation is based on the theory that high volumes improve the production of surfactant, prevent the collapse of the airway, promote recruitment, and are better tolerated by the patient.7,24,65,71 The clinical evidence for this recommendation is based on retrospective studies and case series.

One of the most referenced studies to justify this method for ventilating patients with SCI was published in the journal Spinal Cord in 1999.86 Peterson retrospectively reviewed 42 patients with SCI and found that those who were ventilated with >20 mL/kg were weaned 21 days earlier than those ventilated with <20 mL/kg (37.6 days versus 58.7 days). Several limitations in this study include:

  • The patients studied were not acute.
  • Although the authors indicated that the two patient groups had similar characteristics, they do not explain the reason why they were ventilated with different volumes when their typical practice was to use high volumes.
  • The endotracheal cuff was kept to allow for partial leak and to facilitate vocalization. As such, it is difficult to assess which tidal volume was effective.

Only one clinical trial has compared these two approaches.87 The study, reported exclusively as a poster, included only 16 patients ventilated 2 weeks after the injury. There were no differences between ventilating with 10 mL/kg and 20 mL/kg.

To facilitate the removal of secretions, the postural drainage and manually assisted coughing techniques are considered essential. The use of mechanical devices such as intrapulmonary percussive ventilation71 and mechanical insufflation-exsufflation (MIE)24 have not been prospectively assessed in acute patients undergoing mechanical ventilation. Retrospective studies suggest their efficacy for reducing the number of hospitalizations in chronic patients88 and for reducing the weaning time.24 In a survey on the use of MIE, only 49% of the centers that responded acknowledged using the technique routinely.89

Regarding PEEP, the standard recommendation is to use 0 cm H2O (ZEEP). The theory behind this recommendation is that it can increase air trapping in patients with expiratory muscle impairment. Considering that expiration is a passive phenomenon, it is difficult to justify this reasoning. The use of PEEP increases the residual functional capacity and may prevent the collapse and cyclic closure of alveoli, one of the causes directly related to the onset of ventilator-associated lung injury (VALI).90 Lacking evidence to support it, recommending the use of ZEEP no longer seems reasonable for the ventilation of patients with spinal injuries, at least in the acute phase.

Standard practice in some settings with acute SCI patients undergoing mechanical ventilation and who have “healthy” lungs is to use an assisted, pressure-controlled, ventilation mode, adjusted to achieve tidal volumes of 10 to 12 mL/kg with 5 to 7 cm H2O of PEEP, with the pressure plateau always below 30 cm H2O. The goal is to maintain total ventilator support, allowing the patient to initiate most of the cycles and attempting to adjust the inspiratory time to adapt it to the neural inspiratory time. This same ventilation modality is continued once weaning has begun in the resting periods between trials of spontaneous respiration. In all cases of acute pulmonary lesion, the lung protective ventilation strategy is followed.

In the event of recurrent atelectasis that does not resolve despite assisted coughing, bronchodilators, postural drainage, and hydration, the VT can be increased by 100 mL/day up to 15 to 20 mL/kg, as long as the plateau pressure is maintained below 30 cm H2O.

Weaning: When and How

Patients with cervical SCI have compromised respiratory functions and require mechanical ventilation based on the location and degree of the injury, both of which also affect their success in weaning from the respirator, which approaches 40% in patients with cervical injuries above C4, with increasing success in injuries below C5.91 The respiratory modality most commonly used in weaning is Progressive ventilator-free breathing (PVFB or T-tube),92 with noninvasive mechanical ventilation and tracheotomy also playing a role. Other adjuvant treatments include the use of phrenic/diaphragmatic pacemakers in patients who do not have spontaneous breathing and drug treatments whose actual benefit is still untested.

The start of weaning and the strategy to employ are determined by the following three factors:

  1. Degree of respiratory function at the time weaning is started
  2. Level of the injury
  3. Respiratory pathophysiology of the SCI

Therefore, the patient’s respiratory function needs to be assessed before and during weaning.93 The best parameters to use for assessing the patients respiratory function are66:

  • Arterial gasometry or capnography
  • Effectiveness of cough and diaphragmatic electromyography (which is not very useful in clinical practice)
  • Lung function tests especially VC

Before the start of weaning, it is advisable to optimize the patients breathing by94:

  • Administering bronchodilators
  • Aspirating tracheal secretions
  • Positioning the patient in the supine or Trendelenburg position

Once the patient’s breathing has been optimized, the various weaning modalities should be assessed. The three general approaches to weaning are95:

  1. Progressive ventilator-free breathing (PVFB) or t-tube
    • PVFB weaning consists of a respirator-free time that is gradually increased and achieves an increase in muscle force in patients with high and low cervical injuries.
    • The procedure is started with a FiO2 of 10% above the respirator baseline and with only 5 minutes of disconnection per hour, which is gradually increased throughout the day depending on the patient’s degree of tolerance, thereby avoiding exhaustion.
    • The intervals of connection to the respirator therefore must be sufficient for the diaphragm to recover before the next test (approximately 2 hours).
    • The withdrawal of mechanical ventilation can be proposed when the patient tolerates 48 hours without respiratory support.
    • Several studies have shown greater success with the T-tube.92,96
      • In a recent study performed on patients with prolonged mechanical ventilation, Jubran et al.97 concluded that weaning by PVFB through tracheostomy is faster compared with PS, without affecting 6–12 month survival. When assessing this study in terms of patients with cervical SCI, it is important to consider that one of the exclusion criteria is a bilateral phrenic nerve injury.
  2. Pressure support (PS)
  3. Synchronized intermittent mandatory ventilation (SIMV)
    • Weaning patients from mechanical ventilation using SIMV takes longer and does not improve the success rate. Currently SIMV is not advocated.96,98

Regardless of the weaning modality, all studies have observed that the time for the withdrawal of the respirator in patients with SCI ranges from weeks to months.99,100

Extubation is considered when, after 48 hours without ventilator support, the patient meets several requirements101:

  • A negative inspiratory pressure <−20 cm H2O
  • The ability to generate a flow peak of cough > 2.71/s

Checks before extubation include:

  • There are no required surgical or X-ray diagnostic procedures close to extubation that require sedation
  • Patient is cooperative without sedative drugs
  • Patient is afebrile and with stable vital signs
  • Saturation > 95% and pCO2 < 40–45 mmHg after >12 h breathing ambient air
  • FiO2 no more than 25% and PEEP < 5 cm H2O
  • X-rays with no abnormalities or an obvious improvement
  • Few bronchial secretions
  • Negative inspiratory pressure < −20 cm H2O
  • Vital capacity > 10–15 mL/kg of ideal weight
  • A normal fluid balance
  • No contraindications for performing physical therapy (fractured ribs, etc.) or for the use of noninvasive mechanical ventilation (facial fractures, etc.)

The Role of Noninvasive Mechanical Ventilation (NIMV)

The use of NIMV has been proposed for patients with SCI as respiratory support both in acute conditions and in respirator weaning and as a long-term night support for patients in whom hypoventilation is detected.

Indications for the use of NIMV include:

  • The patient must be cooperative
  • The patient must have an intact bulbar musculature
  • The patient must be medically stable

Bach and Saporito101,102 and Tromans et al.103 describe the use of NIMV in acute conditions:

  • To avoid connecting patients to respirators who have a VC < 50% of its normal value
    • If the VC falls below 1200 mL, continuous support will be necessary.
  • Limitations to these two studies include:
  • Both studies were retrospective and had a limited number of cases. Further studies are therefore needed to support the use of NIMV as a substitute for invasive mechanical ventilation.
  • NIMV may aid in respirator weaning and prevent postextubation failure, thereby reducing reintubation-related complications.104,105
    • If rehabilitation is included with NIMV support, the rate of success increases considerably.
    • Chronic SCI with reduced VC may benefit from support from nighttime NIMV in patients in whom nighttime saturation is repeatedly <95% and CO2 > 50 cm H2O, which unequivocally indicates hypoventilation.
  • In these patients with chronic hypoventilation, nighttime oximetry monitoring or capnography, indicates the need for nighttime NIMV and the patients who will benefit from respiratory electrostimulation.

NIMV can be used with two ventilator modalities:

  1. Continuous positive airway pressure (CPAP), where a continuous inspiratory pressure is provided.
  2. Bilateral Positive Airway Pressure (BPAP), which provides support through two pressures (inspiratory and expiratory).
  • BPAP is more advantageous than CPAP because it keeps the alveoli open by providing a minimal PEEP.103
  • If, after administering BPAP, the VC presents a reduction >25%, weaning is discontinued.-*

Both modalities may be used with or without supplemental oxygen and with an interface that can be nasal, oral or naso-oral.

Limitations to the use of NIMV include:

  • Abdominal distension
  • Aerophagia
  • Barotrauma (very uncommon)
  • Although the patient may have functionally preserved bulbar musculature innervation, NIMV may not provide sufficient force to hold the nasal or oral piece in place.

Respiratory Electrostimulation: Phrenic and Diaphragmatic Pacemakers

Phrenic or diaphragmatic pacemakers, whose use started in the 70s by Glenn et al. 106, are one of the forms of respiratory support that may be used in the withdrawal of the volumetric respirator as an alternative to long-term respiration in patients with SCI, thereby improving their quality of life.

Electrostimulation of the phrenic nerve consists of triggering diaphragmatic contractions through direct electrical stimulation of the phrenic nerve in the neck and chest. Candidates for electrostimulation include patients with:

  • Functional phrenic nerves and diaphragm
  • No severe airway disease or pulmonary parenchyma
  • Spinal injuries above C4

It is therefore necessary, prior to implantation, to perform phrenic nerve conduction with bilateral, simultaneous diaphragmatic fluoroscopy. After its placement using thoracotomy, a period of conditioning is needed in order to improve the muscle tone of the diaphragm, which may have atrophied due to lack of use.

The daily duration of the electrophrenic respiration may be 16 hours to 24 hours, with nighttime ventilator support to support physiological recovery of the diaphragmatic muscle, in anticipation of the next day.

  • Advantages of electrophrenic respiration include:
    • Lower cost due to fewer episodes of infection when comparing it to conventional ventilation.107
    • Greater survival with a better quality of life due to improved sociability, convenience, and mobility.108

External diaphragmatic pacemakers are a modality that is more applicable to the ICU.109 This modality uses electrodes that are implanted directly using endoscopy within the diaphragmatic muscle and which are connected to an external stimulator implanted in the skin. This system can be used early on for the management of weaning in the ICU thus lessening the likelihood of complications by avoiding the need for major surgery.

In regard to quadriplegic/tetraplegic patients who have inadequate function of the phrenic nerves and in whom the implantation of phrenic/diaphragmatic pacemakers is not possible, there are experimental studies in animals that attempt to restore ventilation without respirator with high-frequency spinal cord stimulation (HF-SCS) of the intercostal muscles. DiMarco and Kowalski110, in a study conducted on dogs, achieved periods of up to 6 hours without a respirator preventing muscle fatigue.

In some groups, approximately 40% of the patients are supported at all times with these devices. It is important to note that diaphragmatic pacemakers only supplement the inspiratory function and do not replace the expiratory functions such as coughing or the removal of secretions. It is here where rehabilitation and external mechanical assistance have considerable importance.

It is known that patients with cervical SCI have increased resistance in the airways due to a loss of sympathetic control.

  • For quadriplegic/tetraplegic patients, there are studies with medications that attempt to counteract this effect thus facilitating weaning. These medications include:
    • Bronchodilators (salmeterol) which appears to improve respiratory function, inducing an anabolic effect on the respiratory musculature.111
    • Methylxanthines (theophylline) may be effective in facilitating respirator weaning in quadriplegic/tetraplegic patients by improving muscle force.112
    • Testosterone derivatives which increase muscle mass and force.113
  • All of these medications have had conflicting results

Tracheostomy

Tracheostomy is a common procedure in patients with traumatic SCI, especially in cervical SCI or thoracic level with associated injuries.

  • Effective therapy in patients with cervical SCI consists of:
    • Early intubation
    • Tracheostomy
  • For patients with incomplete injuries, evidence of respiratory failure should prompt immediate airway intervention, half of whom will require tracheostomy.114
  • Risk factors for post injury tracheostomy include3,115-117:
    • Active pneumonia
    • Age (>45 years)
    • Comorbid lung diseases
    • High level injury severity score
    • Preexisting comorbid illness
    • Rostral ASIA A level (C2–C4)
    • Severity of impaired consciousness
    • Smoking history
  • Specific to a cervical SCI cohort, the extent of injury was the most important factor in determining the need for a tracheostomy.118
    • In a retrospective study, patients with high-thoracic SCI have more respiratory complications (including the need for tracheostomy), even after adjustment for age, sex, and Glasgow Coma Scale, compared with patients with low-thoracic SCI or thoracolumbar fractures. In this study, respiratory complications significantly increased the mortality risk in less severely injured patients.119
    • Winslow et al.120 noted that respiratory complications are as important as the level of injury in contributing to the prediction of length of stay.

The literature has suggested that early insertion of a tracheostomy facilitates pulmonary management and an earlier discharge from the intensive care unit (ICU).

  • In a retrospective study, early tracheostomy (<day 7) in traumatic SCI patients was associated with121:
    • A shorter duration of mechanical ventilation
    • A shorter length of ICU stay
    • Decreased laryngotracheal complications
  • Limitations of this study include:
  • Lack of demonstrating that early placement of a tracheostomy prevents the risk of ventilator-associated pneumonia or affects the mortality rate.
  • A retrospective review of patients with cervical SCI verified that tracheostomy when compared with endotracheal intubation longer than 7 days122:
    • Decreased the mortality rate and pulmonary complications
    • Early tracheostomy facilitated quicker extubation and shorter hospital stays
    • As a result of this study, early tracheostomy was recommended if at least two of the following three factors are present:
  • The Injury Severity Score (ISS) > 32
  • The patient has a complete SCI
  • PaO2/FiO2 ratio <300 3 days after mechanical ventilation was initiated
  • Sims and Berger suggest that early tracheostomy be considered in hospitalized trauma patients123:
    • A condition requiring intubation on arrival
    • A history of cardiac disease
    • Requiring halo fixation and who present with a high ISS

Both surgical and percutaneous tracheostomies (PTs) can be safely performed in the ICU.

  • PT is a feasible and safe procedure in patients with cervical spine fracture and available anatomical landmarks without neck extension.124
  • Advantages of PT include125:
    • PT is a much quicker method
    • Injury to the adjacent neck structures is minimized
    • PT has fewer late infections of the stoma which could be an important advantage in patients who have undergone anterior cervical spine fixation and who require prolonged ventilator support.126
  • Currently, there is a paucity of retrospective studies evaluating the period of time that should separate these procedures to determine the safety of early tracheostomy after anterior cervical spine fixation, but a period of 1-2 weeks is often used.91,127-129
  • The long-term sequelae of lateral tracheostomy in patients with anterior cervical fusion await further investigation.130

Tracheostomy appears to facilitate weaning by decreasing the work of breathing, especially in patients with limited respiratory reserve.92 Compared to the native airway, the tracheotomy cannula constitutes an additional resistive component.

  • In a physiological study performed on difficult-to-wean patients, it was found that diaphragmatic effort is lower during a T-piece trial with a deflated cuff than when the cuff is inflated.131
  • Other authors have recently shown that a deflated cuff during weaning strategies not only improves the time to decannulation but also decreases respiratory infections and improves swallowing

Conservative Management of Respiratory Dysfunction

Respiratory complications are the main cause of morbidity and mortality in the acute phase of SCI, with an incidence of 36% to 83%.1,2 Although pulmonary complications are a common and well-known problem in SCI, there is little information about their management. Current practice is mainly based on clinical experience and expert opinion.7

The pillars of early treatment of respiratory dysfunction in SCI are intensive management of secretions and atelectasis, which has been shown to improve the outcomes in patients with SCI.71 The most important objective of treatment is the expansion of the lungs and the clearing of secretions. The techniques commonly used to help remove secretions include:

  • Aspiration
  • Assisted coughing
  • Assisted postural drainage
  • Percussion and vibration

Increasing ventilation in patients on mechanical ventilation include133:

  • High tidal volumes
  • Noninvasive positive air pressure support
  • Respiratory exercises used for muscle training

Interventions for mobilizing secretions are essential for preventing mucus plugs, atelectasis, pneumonia, and respiratory failure and should be started early after the injury.

To optimize results when using respiratory therapy techniques, it is essential to have:

  • Proper pain management to facilitate patient cooperation
  • Since bronchospasms are continuous in patients with cervical SCI due to autonomic changes in the acute phase, with a predominance of vagus nerve tone, the following interventions may be advocated:
    • Bronchospasms respond well to beta-2 agonists and inhaled anticholinergic agents134, with beneficial effects on FEV1, FVC, and peak expiratory flow.135 Their use is widely recommended and should be started before bronchospasms are apparent.6,133
    • There is no question that bronchoscopy with alveolar lavage is an effective method for removing secretions, but it is not exempt from complications such as tracheobronchial irritation, edema, and aspiration. The technique should be reserved for patients who do not respond to more conservative measures or for taking microbiological samples.
  • The multidisciplinary treatment approach for professionals experienced in the treatment of SCI reduces respiratory complications and the need for performing fibrobronchoscopy.24,71

Postural Drainage

The goal of postural drainage and passive positioning techniques if the patient is immobilized is to use gravity to facilitate the movement of secretions from the most peripheral regions of the lungs to the main airway, where the secretions can be more easily removed using coughing or other methods of aspiration.

  • The positioning of the patient with the affected lung area in the upper position allows for gravity to help in the drainage.
  • Each position (Trendelenburg, supine, prone, and left and right lateral) should be held for at least 5 to 10 minutes, depending on tolerance.

Percussion and Vibration

Percussion and vibration consist of external manipulations of the chest to mobilize secretions.

  • Percussion consists of rhythmically tapping on different areas of the chest with a cupped hand. The floating ribs should be avoided, and the intensity and duration of the percussion should be adjusted to the patient’s comfort level.
  • Vibration consists of the application of vibration with the hands to the chest wall and soft tissues of the chest during the expiratory phase.
  • These techniques may be combined with postural drainage.
  • Contraindications include:
    • Acute hemoptysis
    • Chest burns and wounds
    • Fractured ribs
    • Increased intracranial pressure
    • Instability of the cardiovascular system
    • Pulmonary embolism
    • Significant pleural effusion
    • Tension pneumothorax
    • Unstable spine

Assisted Coughing Techniques

The goal of assisted coughing techniques is to help generate effective cough strength. They are often used with postural drainage, intermittent positive-pressure breathing (IPPB), and insufflator. Several techniques which may be used include:

  • Manually Assisted Coughing
    • This maneuver consists of chest compressions coordinated with the patient’s breathing. This attempts to imitate the normal cough thus helping to mobilize secretions from the lowest areas of the lungs.
    • The therapist who performs the technique places the palm of the hand below the patient’s rib cage, between the xiphoid process and the navel, exerting pressure upwards and inwards in sequence with the patient’s voluntary expiration or cough. The external pressure acts in the place of the paralyzed intercostal and abdominal muscles.
  • The effectiveness of manually assisted coughing can be improved with the prior administration of nebulized saline to thin the secretions.
  • The cough can also be increased with prior lung insufflation. It is possible to generate higher expiratory flows by using larger lung volumes.
    • Contraindications to manually assisted coughing include:
  • Internal abdominal complications
  • Recent placement of a vena cava filter
  • Rib fractures
  • Unstable spine in traction
  • Mechanically Assisted Coughing (Mechanical Insufflation-Exsufflation)
    • This procedure is begun by applying positive pressure to the airway (insufflation) using a mechanical device (Cough-Assist) to immediately afterwards transform this positive pressure into negative pressure (exsufflation).
    • This sudden change of pressure in a short period of time (<0.02 s) generates an air flow capable of pulling respiratory secretions to the exterior.
    • Each session consists of 6 - 8 cycles (1 cycle usually consists of 2 seconds of insufflation and 3 seconds of exsufflation) with pressures approximately ±40 cm H2O, generating an expiratory flow of approximately 10 L/s, which is followed by 5 - 10 minutes of rest to avoid hyperventilation. Pressures below ±30 cm H2O are ineffective.136
    • Mechanical insufflation-exsufflation can be applied through tracheotomy, facemask, or mouthpiece, and is more effective than manually assisted coughing and reduces the need for deep endotracheal aspiration, which makes the technique less irritating for the lungs and more comfortable for the patient.
    • Advantages in the use of an insufflation-exsufflation device during intensive and post-intensive care are137:
  • Reduction in the number of bronchoscopies
  • Reduction in the number of respiratory complications
  • Reduction in weaning time
  • Contraindications to the use of an insufflation-exsufflation devices include:
    • History of barotrauma
    • Presence of pulmonary bullae

Respiratory Muscle Training (RMT)

There is no clear evidence of the benefit of RMT in patients with SCI.

  • In a systematic review of 8 studies (3 randomized, controlled clinical trials), it was concluded that there is only level 4 evidence to support the use of inspiratory muscle training (IMT) in improving the respiratory function of patients with SCI.138
  • Recently, Mueller et al.139 in a randomized, controlled clinical trial compared various RMT methods in quadriplegic/tetraplegic patients. They concluded that training of the inspiratory force is more beneficial than training of the respiratory muscle resistance in improving respiratory function, voice, chest mobility, and quality of life in patients with quadriplegia/tetraplegia during the first year of the injury.

IMT consists of the use of resistance during inspiration to improve the strength and resistance of the inspiratory musculature that is unaffected (or partially affected) by the SCI.

  • The technique uses devices with spring-loaded valves that allow for expiration and resist inspiration. These devices can be connected to the tracheotomy tube or to a mouthpiece.
  • Weights placed on the abdomen or incentive spirometers can also be used in IMT to resist inspiration.
  • A typical IMT program requires the patient to generate an additional inspiratory pressure for 15 - 30 minutes 2 - 3 times a day.140 The optimum inspiratory pressures are not yet known, although excessive pressures may cause respiratory fatigue and hypercapnia.141

With regard to the expiratory musculature, the strengthening of the pectoralis major muscle may be useful (C5–C7 innervation, its function may be partially preserved), because the clavicular part helps expiration.

  • Given that the VC in high SCI is influenced by the position of the patient (the diaphragm tends to remain partially collapsed due to the effect of gravity), it may help to place an141
    • Abdominal girdle which can improve respiratory function in the sitting position by placing the diaphragm in a more efficient position.
    • Electrical surface stimulation can be placed directly on the abdominal muscles or applied to the lower thoracic medulla which can improve coughing and expiratory muscle function.

Although there is scant evidence from the physiological point of view, it does make sense to use RMT, at least in the ventilator weaning phase. The treatment is started only when the patient is able to tolerate periods of spontaneous respiration.

  • Initially, the resistance is set to 7 - 10 cm H2O for a maximum of 1 minute, twice a day.
  • The resistance, frequency and duration are gradually increased as the inspiratory force improves.142

Noninvasive Ventilatory Support

Noninvasive ventilatory support is used to provide positive pressure in the airway during expiration and/or inspiration. There are various types of positive-pressure support but the most widely used include:

  • CPAP
  • BPAP
  • IPPB
    • Although this type of NIMV may occasionally be used to ventilate patients with high SCIs, it is typically used in respiratory weaning and as a long-term night support for patients with hypoventilation.
    • The IPPB mode can be administered with mechanical devices or with an Ambu bag.
    • IPPB is useful fr lung expansion by introducing large volumes of air.
  • The pressure level should be started at 10 - 15 cm H2O and gradually increased, never exceeding 40 cm H2O.7
  • It is a NIMV method rarely used in patients with SCI.
  • It may be an alternative to tracheostomy in patients with high quadriplegia/tetraplegia.
  • requires that the patient be conscious and cooperative.
  • The preferred method for ventilatory support is administration through a mouthpiece during the day and through a nose mask during the night.

Noninvasive ventilation can also be supplied through negative-pressure body ventilators such as the iron lung, the pneumobelt, and other devices.143 They are very rarely used but may provide some advantage as an option for temporary or permanent ventilation of patients with high quadriplegia/tetraplegia, as well as, facilitating speech, mobility, and so forth.144

Case Study

Scenario/Situation/Patient Description

Per EMS (1900): 18-year old Thomas Hutton dove face first, at approximately 1800, into the 3 foot end of a cement swimming pool after drinking beer all afternoon with his friends. He hit his forehead on the bottom of the pool. His friends pulled him out of the pool while calling 911. He has not regained consciousness since.

Upon arrival in the emergency department, EMS reports:
GCS: 3
BP: 150-170/70-80
HR: 140-160, sinus tachycardia
RR: 40-50, rapid, shallow
SaO2: 87-90%

You observe: Patient is on a backboard with a semi-rigid cervical collar in place.

20 gauge peripheral IV placed in left antecubital with 1000ml Normal Saline infusing at 100ml/hr. Patient on 100% rebreather mask with oral airway inserted.

Interventions/Strategies
Continue backboard and semi-rigid collar.
Continue monitoring GCS.
Place EKG leads to cardiac monitoring.
Place pulse oximetry.
Place BP cuff.
Insert another 20 gauge IV into right antecubital while drawing stat Hgb/Hct, blood ETOH levels, serum electrolytes, coagulation studies, cell blood counts: send to lab.
Bedside fingerstick for blood glucose level.
Draw ABG for stat results.
Insert urinary catheter and send stat urine drug screen to lab.
Inspect, palpate, percuss and auscultate the following systems where feasible: neurologic, integumentary, pulmonic, cardiovascular, abdominal, urinary.
Imaging studies:
Chest x-ray: AP and lateral
Cervical spine x-rays: AP, lateral and odontoid
Head and neck CT
Continue to try to locate family to ascertain information pertaining to allergies, current medication and immunization status, past medical and surgical history.

Discussion of Outcomes
GCS continues at 3.
Chest x-rays show pulmonary infiltrates.
Cervical spine x-rays indicate an extension teardrop fracture at C2 with neck CT confirming the diagnosis.
Head CT shows fracture of frontal bone with hematoma at base of occiput.
All laboratory tests WNL except blood alcohol level 0.42, ABG’s show acute respiratory acidosis: pH 7.26, PaO2 75, PaCO2 56, HCO3 24, BE -4.

Strengths and Weaknesses
Continuing GCS of 3 with imaging studies indicative of a severe head injury and an extension teardrop fracture at C2: a neurologist and neurosurgeon should be consulted.
Chest x-ray indicating pulmonary infiltrates and respiratory acidosis coupled with continuing hypertension, rapid, shallow respirations, and lower than expected SaO2 per oximetry: emergent intubation indicated.

Conclusion

Pulmonary physiologic changes due to SCI are related to the extent of neurological impairment. The American Spinal Injury Association Impairment Scale (AIS) is used to classify the degree of impairment that is based on strength in key muscles and on a sensory examination.

Immediately after SCI, flaccid paralysis affects all muscles caudal to the level of injury (i.e. spinal shock). Subsequent improvements in pulmonary function are due primarily to functional descent of the neurologic injury level as spinal cord inflammation resolves, enhanced recruitment of accessory ventilatory muscles, retraining of deconditioned muscles, and the evolution from flaccid to spastic paralysis.

The extent of ventilatory muscle impairment depends upon the degree and location of the injury, as well as, the duration of time since the injury. The higher the level and more complete the injury, the more likely that there will be respiratory muscle dysfunction. Complete injury above C3 produces near total ventilatory muscle paralysis because the phrenic nerve, which innervates the diaphragm, arises from the third to fifth cervical roots.

When obtaining spirometry, American Thoracic Society (ATS) standards may need to be modified to accept expiratory efforts less than six seconds in duration, as long as a 0.5 second plateau is achieved (presumably at residual volume), and a greater degree of back-extrapolated volume (e.g., ~7.5% of forced vital capacity), when volume-time curves and flow volume loops are otherwise acceptable.

Among individuals with chronic cervical cord injury, spirometry typically shows a restrictive ventilatory defect with FVC and FEV1 values approximately 55% of the values predicted for able-bodied subjects.

SCIs often lead to restrictive respiratory changes. VC is an indicator of overall pulmonary function. Patients with severely impaired VC may require assisted ventilation. It is best to proceed with intubation under controlled circumstances rather than waiting until the condition becomes an emergency.

Lung volumes following complete cervical cord injury show a marked reduction in ERV, a mild to moderate reduction in TLC and FRC, and preservation of RV. The main lung volume abnormality after incomplete cervical or thoracic SCI is a moderate reduction in ERV.

f supine length is preferred over arm-span or recalled standing height for use in the calculation of predicted pulmonary function values for individuals with SCI.

Posture has a significant impact upon lung mechanics in the majority of patients with SCI. Typically, individuals with SCI have an increase in VC when changing from a seated to supine position, whereas the normal response to recumbency is a slight decrease in VC.

Greater lifetime cigarette smoking (pack years) is associated with lower values for FVC and FEV1 both initially after SCI and during long-term follow-up.

f SCI is below C5 and thus spares the phrenic nerve, maximal expiratory force is impaired more than maximal inspiratory pressure, which remains near or within the normal range.

quadriplegia/tetraplegia may demonstrate mild expiratory airflow limitation, which only becomes apparent during reversibility testing with inhaled bronchodilators such as beta2-agonists and the anticholinergic agent ipratropium bromide. However, the clinical benefit regarding the routine use of bronchodilators in quadriplegia/tetraplegia for purposes of maximizing pulmonary function has not been established.

Mechanical ventilation can adversely affect the structure and function of the diaphragm. Early tracheostomy following short orotracheal intubation is probably beneficial in selected patients.

Weaning should start as soon as possible, and the best modality is progressive ventilation-free breathing (PVFB/t-tube), due to its efficacy and ease of performance. Appropriate candidates can sometimes be freed from mechanical ventilation by electrical stimulation. The conservative management of respiratory dysfunction in SCI patients can be used to help remove secretions by various techniques and to increase ventilation by respiratory exercises and noninvasive positive air pressure support.

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This course is applicable for the following professions:

Advanced Registered Nurse Practitioner (ARNP), Certified Registered Nurse Anesthetist (CRNA), Clinical Nurse Specialist (CNS), Licensed Practical Nurse (LPN), Licensed Vocational Nurses (LVN), Registered Nurse (RN), Respiratory Therapist (RT)

Topics:

Advance Practice Nurse Pharmacology Credit, CPD: Practice Effectively, Critical Care / Emergency Care, Neurology


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