Respiratory Management Following Spinal Cord Injury

Respiratory complications, acute and long-term, are the main cause of morbidity and mortality in patients who have had a spinal cord injury (SCI) (Bach et al., 2020a; Berlowitz et al., 2016; Garshick, 2021; Olivero et al., 2020; Reyes et al., 2020; Schilero et al., 2018a).

These complications include (but are not limited to) (Berlowitz et al. 2016; Garshick, 2021; Olivero et al., 2020; Reyes et al., 2020; Schilero et al., 2018a):

• Atelectasis
• Pneumonia
• Pulmonary edema
• Thromboembolism
• Respiratory failure

The degree of respiratory dysfunction is related to the extent and level of the neurological injury, and patients who have suffered a high cervical and thoracic injury are at the highest risk (Berlowitz et al., 2016; Garshick, 2020; Schilero et al., 2018a).

Respiratory dysfunction that leads to respiratory complications in SCI is complex and involves many factors; examples include (Garshick, 2021; Reyes et al., 2020):

• Abnormal/weak cough
• Airflow limitation
• Ventilatory muscle impairment/paralysis
• Bronchial hyperresponsiveness
• Excess bronchial mucous production
• Abnormal/decreased lung capacities and volumes
• Autonomic dysfunction

Pulmonary complications are a common and well-known problem in SCI, but there is relatively little information about their management. Despite years of experience and research, there are still many unknowns in the treatment of SCI (Fehlings et al., 2017), and treatment recommendations are, at times, based on clinical experience and expert opinion. Management of care with appropriate interventions, prevention of pulmonary complications associated with SCI, and support for a return to the maximal level of functioning will be discussed.

The following muscles are those involved in the action of inspiration or inhalation of air (see Figure 1) (Randleman et al., 2021):

• Diaphragm:
  • Major muscle which mediates inspiration
  • Innervated by the phrenic nerve (C3 to C6 nerve roots)
• Accessory muscles of inspiration are the:
  • External intercostals
  • Innervated by thoracic nerve roots, T2-T11
• Clavicular portions of the pectoralis major, C5 to T1
• Scalene:
  • Innervated by cervical nerve roots C3 to C8
• Sternocleidomastoids and trapezius:
  • Innervated via cervical nerve roots C2 to C4 and accessory nerve XI (Sternocleidomastoid) and C1 to C4 and accessory nerve XI (Trapezius)
  • 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

The following muscles are those involved in the action of expiration or exhalation of air (See Figure 1) (Randleman et al., 2021):

• Abdominal wall muscles:
  • Rectus abdominus
  • Obliques
  • Transversus abdominus
  • All these abdominal muscles are innervated by the lower thoracic and lumbar nerve roots, T6 to L3
• Internal intercostals:
  • Innervated by the thoracic nerve roots T1 to T11

Figure 1
Muscles of Respiration

The process of inspiration involves the contraction of the diaphragm and the external intercostal muscles that allow the chest cavity to expand (Costanzo, 2018). At high levels of ventilatory activity, the accessory muscles are recruited to aid in this process (Costanzo, 2018). Expiration is a passive process, and normally it does not require the active use of the abdominal and the internal intercostal muscles. However, the abdominal and internal intercostal muscles are recruited when a forced exhalation is needed, like during a cough or when exercising (Garshick, 2021). If a patient cannot generate a forced exhalation, i.e., a patient who has an SCI, an effective cough cannot be produced, and pulmonary secretions cannot be removed (Garshick, 2021). Also, the abdominal muscles and the internal intercostal muscles contribute to the normal functioning of the diaphragm, and when these muscles are not functioning, the efficiency of the diaphragm is negatively affected (Garshick, 2021).

Figure 2
Movement of the Rib Cage During 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 causes 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 moves 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

You can use this mnemonic tool to help you 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 degree of respiratory failure associated with traumatic injuries to the spinal cord primarily depends on the level of the spinal lesion, and cervical and high-level thoracic injuries impair the function of the diaphragm, the intercostal muscles, the abdominal muscles, and the accessory muscles that are the primary movers of inspiration and expiration (Wang et al., 2020).

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 in SCI patients are age, preexisting medical illnesses, smoking, and associated major traumatic injuries (Garshick, 2021).

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

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 a sensory examination (Table 1) (Hansebout & Kachur, 2018; Sánchez et al., 2020):

*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 (Naqvi & Sherman, 2021):

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

Respiratory dysfunction that causes pulmonary complications in SCI patients is complex and involves many factors, these include (Berlowitz et al, 2016; Garshick, 2021; Reyes et al., 2020):

• Abnormal/weak cough
• Airflow limitation
• Ventilatory muscle impairment/paralysis
• Bronchial hyperresponsiveness
• Excess bronchial mucous production
• Abnormal/decreased lung capacities and volumes
• Autonomic dysfunction
• Abnormal chest wall compliance

Performing PFTs and calculations of the predicted PFT values need to be adjusted/modified when doing PFTs in patients who have had an SCI (Garshick, 2021).

Garshick (2021) notes: “Many SCI patients, particularly those with complete tetraplegia, cannot meet the acceptability and reproducibility standards for spirometry set by the American Thoracic Society (ATS).” (Note: Specific recommendations for measuring PFTs in SCI patients was not addressed in the most current (2019) ATS PFT measurement recommendations).

• Measurement of Height (Garshick, 2021; Diggisie et al., 2018; Pothirat et al., 2015):
  • Height is used to calculate predicted pulmonary function values, but in non-SCI patients, height is measured while the patients are standing; this is obviously not possible for a patient who has had an SCI.
  • For patients who have had an SCI, height should be measured when the patient is supine.
  • Height can be estimated by using body measurements like arm span, but this technique may not be accurate, and measuring height while the patient is supine is preferred.
  • It is not recommended to rely on the patient’s recall of her/his height.
• Posture:
  • The vital capacity in SCI patients will often increase when they move from a sitting position to supine; the normal response is a decrease.
• Mouthpiece (Garshick, 2021):
  • Flange-style and tube-style mouthpieces can be used to measure PFTs, and for SCI patients, a flange-style may underestimate expiratory muscle strength; a tube-style mouthpiece should be used.
• Confounding factors (Garshick, 2021):
  • Research has found that factors like age and smoking history can affect PFT results in SCI patients.
• PFT results (Garshick, 2021; Raab et al., 2019; van Silfhout et al., 2016):
  • It is not uncommon for PFT results, e.g., FCV, to be abnormal in SCI patients.
  • Respiratory function is decreased immediately after the SCI, and then there is typically an improvement over the first few months-year after the injury.
  • What the long-term course of pulmonary function will be after an SCI – a decline, stability, or an improvement – is less clear.
  • Some authors have found that even several decades after an SCI, pulmonary function had not declined, while other authors have come to the opposite conclusion.
  • Understanding this issue and making conclusions is difficult because patients differ in their ability to train their respiratory muscles, changes in pulmonary function can vary depending on factors age, body mass, and cigarette smoking, and relatively little research has been done on this topic.

Non-invasive ventilation (NIV) is defined as the delivery of positive pressure ventilation without the use of an invasive device (an endotracheal tube or a tracheostomy) and by way of a noninvasive device like a face mask, a nasal mask, or nasal prongs (Hyzy & McSparron, 2021b).

Non-invasive ventilation can be delivered by a standard or portable ventilator, and the interface device can be (Hyzy & McSparron, 2021b):

1. An oronasal mask
2. A nasal mask
3. Nasal prongs
4. A full-face mask
5. A helmet

The two commonly used modes of delivery are bilevel NIV, commonly called bilevel positive airway pressure (BPAP – not BiPAP), and continuous positive airway pressure, CPCP (Hyzy & McSparron, 2021b).

Non-invasive ventilation is a well-established technique, and it can be used (Daoud et al., 2020; Hill & Kramer, 2022; Hyzy & McSparron, 2021a):

1. To treat patients who are not intubated or do not have a tracheostomy and who have acute or chronic respiratory dysfunction caused by a neuromuscular or chest wall disease, including SCI patients. This technique is commonly used to treat chronic respiratory dysfunction in SCI patients. It can be used to treat acute respiratory dysfunction in SCI patients, but there is little experience with this.
   1. There are no universally used criteria for patient selection for NIV in this clinical situation.
   2. Hill & Kramer (2022) recommend using objective data like an FVC that is < 50% of the predicted value, a maximum expiratory pressure <40 cm H₂O, an appropriate diagnosis, and subjective clinical findings. It is recommended to start NIV in these patients as soon as possible.
   3. In acute respiratory failure, there are no universally used protocols for NIV weaning. Weaning can begin when the patient’s respiratory and gas exchange status are normalizing, e.g., the respiratory rate is ≥ 12 and ≤ 22 breaths per minute, the patient is hemodynamically stable, and the peripheral oxygen saturation is ≥ 90% while on ≤ 60% FiO2 and as the patient can tolerate the procedure. There are no universally used protocols for NIV weaning I chronic respiratory failure.
2. To wean SCI patients who are endotracheally intubated and to wean SCI patients who have a tracheostomy and are ventilator-dependent and as an aid to tracheal decannulation (Ceriana et al., 2019; Guia et al., 2021; Ker et al., 2021; Schrieber et al., 2021; Toki et al., 2021).
   1. The use of NIV for weaning SCI patients is not new. Bach & Alba (1990) described a case series of 23 quadriplegics, ventilator-dependent patients with tracheostomies who were treated with NIV. Seventeen of the patients had their tracheostomies closed. The authors concluded that chronic SCI patients with a tracheostomy could be managed by NIV, and reports of other similar cases have been published in the medical literature (Kim et al., 2017; Rybczynski et al., 2019).

Non-invasive ventilation as a technique for weaning and (hopefully) decannulating SCI patients has many benefits, it can help avoid many of the complications of acute and long-term tracheostomy tube placement, and it has been used successfully (Guia et al, 2021; Ker et al., 2021; Toki et al, 2021). Most SCI patients who have ventilatory insufficiency should be considered for NIV weaning, and it is recommended to begin NIV weaning as soon as possible (Toki et al, 2021; Guia et al, 2021).

To be considered as a candidate for NIV weaning, patients should (Ker et al., 2021; Toki et al., 2021):

• Be fully awake, cooperative, and not using sedation.
• Not have a swallowing disorder.
• Be able to cough.
• Have no organ failure or infection.
• Have an oxygen saturation > 95% without supplemental oxygen.
• Have an arterial carbon dioxide partial pressure ≤ 40 mm Hg.
• Have a peak inspiratory pressure (PIP) < 35 cm H₂O.

This weaning technique has been successfully used, but it has not been well studied. It is noted that there are no established guidelines/protocols for the indications for and timing of NIV weaning (Hill & Kramer, 2022; Guia et al., 2021; Ker et al., 2021; Toki et al., 2021).

Phrenic or diaphragmatic pacemakers are a form of respiratory support that may be used for the partial or complete withdrawal of mechanical ventilation in patients with SCI thereby improving their quality of life (Wijkstra et al., 2022).

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 (Marion, 2022; Wijkstra et al., 2022):

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

It is, therefore, necessary before implantation to perform phrenic nerve conduction studies (Vashisht & Chowdry, 2021). The pacing electrodes can be placed in the chest, the diaphragm, or the neck. After implantation, a period of diaphragmatic conditioning is needed to improve the muscle tone of the diaphragm, which may have atrophied due to lack of use (Marion, 2022).

Patients will often be on electrophrenic respiration for part of or the whole day, and then during the night, the patient will receive ventilator support (Vázquez et al., 2013).

Advantages of electrophrenic respiration include (DiMarco, 2013):

• Fewer episodes of infection when compared to conventional ventilation.
• Greater survival with a better quality of life due to improved sociability, convenience, and mobility.

Regarding quadriplegic/tetraplegic patients who have an 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 have suggested that high-frequency spinal cord stimulation (HF-SCS) may someday be an alternative approach for SCI patients (DiMarco & Kowalski, 2019).

Approximately 50% of tetraplegic patients who are ventilator dependent will be able to achieve full-time ventilatory support with diaphragmatic pacing (DiMarco & Kowalski, 2019). 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.

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 (Foran et al., 2022; Hansebout & Kuchar, 2018):

• Early intubation
• Tracheostomy (Long-term management)

For patients with incomplete injuries, evidence of respiratory failure should prompt immediate airway intervention with endotracheal intubation. Patients who have been endotracheally intubated are at risk for respiratory and other complications, and in many cases, an elective tracheostomy is performed to prevent these issues when prolonged mechanical ventilation is likely (Foran et al., 2022; Mubashir et al., 2021; Handesbout & Kuchar, 2018) (Foran et al., 2022).

Tracheostomy can make weaning easier by decreasing airway resistance, it can make suctioning easier and more effective, it reduces the complications of long-term endotracheal intubation, and it is more comfortable than endotracheal intubation (Foran et al., 2022).

Risk factors that indicate the need for post-injury tracheostomy include (Hansebout & Kuchar, 2018; Long et al., 2022; Yu et al., 2022):

• Active pneumonia
• Old age
• Male gender
• Comorbid lung diseases
• High-level injury severity score
• Preexisting comorbid illness
• Low Glasgow Coma Scale score
• Smoking history

Specific to a cervical SCI cohort, the extent of the injury was the most important factor in determining the need for a tracheostomy (Branco et al., 2011).

In a retrospective study, patients with high-thoracic SCI have more respiratory complications (including the need for tracheostomy and intubation), even after adjustment for age, sex, and Glasgow Coma Scale (GCS), compared with patients with low-thoracic SCI or thoracolumbar fractures (Cotton et al., 2005). In this study, respiratory complications significantly increased the mortality risk in less severely injured patients.

Winslow et al. (2022) noted that respiratory complications are as important as the level of injury is contributing to the prediction of length of stay.

The literature has suggested that early tracheostomy (within the first 7 days) has many advantages, including (but not limited to) (Foran et al., 2022; Mubashir et al., 2021):

• Shorter duration of mechanical ventilation (MV)
• Shorter ICU stay
• Reduced risk of in-hospital mortality
• Decreased duration of sedation
• Decreased incidence of ventilator-associated pneumonia (VAP)

However, Mubashir et al. (2021) notes that evaluating the available evidence is difficult and “. . . it is challenging to make conclusive interpretations. Future prospective trials with a larger patient population are needed to fully assess short- and long-term outcomes of tracheostomy timing following acute SCI.”

Several recent systematic reviews also found that early tracheostomy does not reduce mortality and finds no effect on the duration of MV or intensive care stay in a general critical care population (Foran et al., 2022).

Both surgical and percutaneous tracheostomies (PTs) can be safely performed in the ICU (Kaczmarek et al., 2017). A PT is done by making a small incision and then a blunt dilation of the trachea to insert the tracheostomy tube.

Advantages of PT include (Kaczmarek et al., 2017; Ramakrishnan et al., 2019):

• PT is quicker to perform.
• It can be done at the bedside, obviating the need to transfer critically ill, ventilated patients to the operating room.
• A smaller incision with less bleeding.
• Injury to the adjacent neck structures is minimized.
• Lower rate of infection.

Patients who have had an SCI and will undergo spinal fusion surgery and a tracheostomy require special attention. The presence of a tracheostomy stoma could cause cross-contamination from the tracheostomy incision site to the spinal surgery incision site, and this has made the timing of the two procedures with each one an issue of concern (Galeiras et al., 2018). Performing the tracheostomy after the spinal surgery has typically been the approach, but the optimal time of separating the two procedures is not known. Although the research is limited, several studies found no infections or a very low rate of infection when a tracheostomy is done without waiting or with waiting several weeks after spinal surgery (Galeiras et al., 2018).

Tracheostomy reduces the work of breathing and reduces airway resistance, intrinsic positive end-expiratory pressure (PEEP), and peak inspiratory pressures (PIP) (Chen et al., 2019; Hyzy & McSparron, 2021a). Tracheostomy can also make ventilatory weaning easier (Hyzy & McSparron, 2021a).

Although pulmonary complications are a common and well-known problem in SCI, there is relatively little information about their management. Despite years of experience and research, there are still many unknowns in the treatment of SCI, and treatment recommendations are, at times, based on clinical experience and expert opinion (Fehlings et al., 2017).

Many patients who have an SCI cannot generate sufficient lower intrathoracic and expiratory pressure to produce an effective cough and clear secretions (Berlowitz et al., 2016; Nygren-Bonnier et al., 2018). This puts them at risk for atelectasis, impaired gas exchange, and infections (Nygren-Bonnier et al., 2018). One of the most important goals of treating respiratory dysfunction in SCI patients is managing secretions to prevent these complications (Reyes et al., 2020; Vázquez et al., 2013).

Many techniques can be used to manage and clear secretions, including (but not limited to (Bach et al., 2020; Blakeman et al., 2022; Luo, 2021; Spinou, 2020; Reyes et al., 2020; Vázquez et al., 2013):

• Postural drainage
• Assisted coughing
• Glossopharyngeal breathing
• Respiratory muscle training
• Percussion and vibration
• Airway suctioning

Deciding what treatments should be used should be done on a case-by-case basis, and the need will be, obviously, greater for some patients. Bach et al. (2020) indicated that if an SCI patient does not have a tracheostomy and is medically stable “. . . there is neither theoretic reason why, nor evidence that, routine chest oscillation, percussion, and vibration benefit them unless they have an acute pulmonary disease or are overwhelmed with peripheral secretions.”

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

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 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 it is 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.

Immediately after an SCI, flaccid paralysis can occur, affecting all the muscles that are caudal to the level of injury. This physiologic state is known as spinal shock or spinal paralysis. This state may continue for days or months, and during this time, pulmonary function is impaired. This is primarily due to impairment of the muscles of respiration but also due to a decrease in chest compliance, decreased airflow, hyper-responsiveness of the bronchial passages, and an abnormally blunted response to hypercapnia.

After the resolution of spinal paralysis, spastic paralysis occurs. During spastic paralysis, muscle tone is increased, and pulmonary function should improve. This happens several days or several weeks after the injury. Improvement in respiratory muscle performance after SCI largely occurs in the first year following injury.

Assessment of pulmonary function in SCI patients is done with PFTs. Performing PFTs and calculations of the predicted PFT values need to be adjusted/modified when doing PFTs in patients who have had an SCI. Many SCI patients will have abnormal PFTs, but there is an improvement over the first few months-year after the injury.

After an SCI, the long-term course of pulmonary function can be a decline, stability, or improvement.

Approximately 90% of patients who have had a traumatic SCI will need intubation, and up to 40% of patients who had a complete cervical lesion will become ventilator dependent. It is best to proceed with intubation under controlled circumstances rather than waiting until the condition becomes an emergency, as hypoxia in an SCI patient can adversely affect the patient’s neurological and many patients who have cervical spinal cord injury have a delayed onset of respiratory complications. Intubation is necessary for managing secretions, and SCI is often accompanied by many complications like trauma, coma, ARDS, and multi-organ system insufficiency. In these situations, non-invasive ventilation will not be effective. There are no specific criteria for ventilator settings that are specific to SCI patients.

If it is likely that the patient may be ventilator-dependent for a long time, tracheostomy is recommended. Tracheostomy can make weaning easier by decreasing airway resistance, it can make suctioning easier and more effective, it reduces the complications of long-term endotracheal intubation, and it is more comfortable than endotracheal intubation. Tracheostomy can be done at the bedside (PT) or in the OR.

In regard to criteria for weaning eligibility, Garshick (2020) wrote: “The accuracy of weaning predictors (eg, rapid shallow breathing index) in predicting weaning success has not been specifically addressed in this patient population, and we typically follow standard clinical criteria for weaning . . .” Schreiber et al. (2021) indicates that the probability of weaning success continues to be difficult to predict as there are no previous systematic review or meta-analysis has been conducted on the topic. Schreiber et al. (2021) also states that there are no societal guidelines or recommendations on weaning that are available and specific to this population of patients. Therefore, the typical weaning protocol is utilized. This protocol is alternating periods of exercise (the patient is disconnected from the ventilator) and rest (the patient is reconnected to the ventilator).

Conservative methods of preventing respiratory complications in SCI patients include:

• Postural drainage
• Assisted coughing
• Glossopharyngeal breathing
• Percussion and vibration
• Airway suctioning
• RMT

Phrenic or diaphragmatic pacemakers are a form of respiratory support that may be used for the partial or complete withdrawal of mechanical ventilation in patients with SCI. Electrostimulation of the phrenic nerve consists of triggering diaphragmatic contractions through direct electrical stimulation of the phrenic nerve in the neck and chest.

Non-invasive ventilation (NIV) is defined as the delivery of positive pressure ventilation without the use of an invasive device and by way of a noninvasive device like a face mask, a nasal mask, or nasal prongs. Non-invasive ventilation can be delivered by a standard or portable ventilator. The two commonly used modes of delivery are bilevel NIV, commonly called bilevel positive airway pressure (BPAP – not BiPAP), and continuous positive airway pressure, CPCP. Non-invasive ventilation is a well-established technique that it can be used to treat patients who are not intubated or do not have a tracheostomy. It can also be used for those who have acute or chronic respiratory dysfunction caused by a neuromuscular or chest wall disease, including SCI. In addition, it can also be used to wean SCI patients who are endotracheally intubated, those who have a tracheostomy and are ventilator-dependent, as well as for those requiring tracheal decannulation.

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