Oxygen Management

In recent times, the focus of medical research and licensed procedural experiments have widely explored the possibilities of alternative care plans. These alternative care plans have been adopted as supplemental or secondary regimens to the conventional plan to broaden modern medicine's reach. These new plans have gained medical acceptance in different parts of the world. As the COVID-19 pandemic raged, studies exploring using hyperbaric oxygen as a symptom relief in chronic COVID-19 infection increased significantly. The dark moment in medical history witnessed the introduction of many alternative care plans. However, supplemental oxygen helped record unprecedented success in managing COVID-19 symptoms, especially in older people.

Before the COVID-19 pandemic, supplemental oxygen therapy was widely accepted in inpatient emergency services. For instance, lower respiratory tract infections, including viral pneumonia, placed a considerable health burden on the pediatric population of third world countries. In many severe cases, the clinical symptoms documented for pediatric patients battling active respiratory syncytial (a multinucleated mass of cytoplasm that is not separated into individual cells) virus infection include low blood oxygen saturation and breathing difficulty. In the United States, these severe symptoms are commonly reported in the diagnosed cases pegged at 800,000 children annually. In these cases, the need for supplemental oxygen therapy is considered a criterion for inpatient admission. In a guideline study on diagnosing, managing, and preventing respiratory tract infections, Ralson et al. (2014) recommended oxygen supplementation as a primary treatment for these conditions.

In the therapy plan for cerebral ischemia, increasing cerebral perfusion and blood oxygen perfusion is considered a focal therapy goal. Bronchodilators and nitroglycerin are deemed unpopular in modern medicine. Hyperbaric oxygen therapy has been considered a new alternative to conventional care plans for cerebral ischemia patients. So far, supplemental oxygen therapy has been considered a credible alternative in medical conditions requiring an effective cell/tissue oxygen perfusion method. Some of these conditions requiring a low-risk, high-yield oxygen perfusion plan include severe blood loss, decompression sickness, acute traumatic ischemia, bronchiolitis, carbon monoxide poisoning, and pulmonary embolism.

Recently, hyperbaric oxygen's effectiveness in treating chronic tuberculosis has been explored. Scientific theories supporting these studies hold that the affected group of neurons in the penumbra zone (the area surrounding an ischemic event such as thrombotic or embolic stroke) might be reactivated and become biologically viable after several years. Supplemental oxygen therapy may help manage neurodegenerative diseases in patients with neuropsychological and electrophysiological abnormalities.

However, despite the promising potential of supplemental oxygen therapy in human medicine, a conservative approach to implementation is recommended as available scientific evidence on oxygen therapy remains insufficient. The possible adverse effects of high-concentration oxygen doses on the cellular level and end-organs remain largely unknown. There are also concerns about the potential long-term effects of this therapy in the pediatric population. Further advanced scientific investigations are required to establish a dosing guideline, document the cellular effects, and solve the uncertainties about oxygen supplementation. Currently, the scientific summaries on oxygen supplementation therapy in inpatient hospital care include:

• Supplemental oxygen therapy improved sensorimotor functions and enhanced P30 amplitude in the damaged hemisphere of chronic TB patients (Ravimohan et al., 2018).
• COVID-19 patients presenting with typical signs of pulmonary impairments reported significant medical benefits in studies prescribing supplemental oxygen therapy as an asymptomatic management option (Daher et al., 2021).
• Supplemental oxygen delivered under hyperbaric conditions increases the chances of brain tissue oxygen perfusion by ten-fold in patients with cerebral ischemia. Supplemental oxygen is also well-tolerated and considered safe under standard protocols.

Discovered independently by Carl Wilhelm Scheele and Joseph Priestly in 1776, oxygen has established a reference position in biomedical and physical science (Gottlieb et al., 2021). In physical science, oxygen is primarily recognized as an element, catalyst, and reactive agent. Beyond this recognition, biomedical science explored oxygen as a possible cheap drug for symptomatic relief in medical conditions characterized by poor blood oxygen saturation levels. Technological improvement in the development of compressed gas technology and pressure regulations solved the early problems with oxygen storage. Solving this problem also significantly improved medical investigations focused on a possible oxygen therapy plan.

Cells leverage the oxygen supply to produce energy from nutrients. The lung primarily supplies oxygen to cells in humans and other similar mammals. The supply function oxygenates the blood, aids cellular metabolism, and removes carbon monoxide waste from the cells. Medical impairments unbalancing this simple exchange compromises oxygen metabolism and subsequently disrupt cellular oxygen perfusion. For instance, oxygen uptake and excretion of carbon monoxide are compromised in ventilatory insufficiency. Carbon monoxide exhibits a superior tissue perfusion rate compared to oxygen, explaining why pulmonary insufficiency compromises the cellular uptake of oxygen and not the release of carbon monoxide.

The scientific basis for using high-concentration oxygen regimens in human medicine leverages the oxygen-cell exchange. Modifying this exchange impacts oxygen physiology for symptomatic relief. The common indications for the prescription of supplemental oxygen therapy include pulmonary embolism, cardiac failure, chronic obstructive pulmonary disease (COPD), pulmonary infection, septic shock, and congestive heart failure. There are also reports of the beneficial use of this therapy in cyanide poisoning, gas embolism, and burn injuries. With the exemption of pathology irreversible airway blockage causing difficulty in direct administration, there are absolutely no contraindications to supplemental oxygen therapy.

Humidified oxygen is not required in low-flow oxygen delivery and short-term high-flow oxygen administration courses (Calligaro et al., 2020). Therefore, humidified oxygen is not needed in pre-hospital settings. It is reasonable to use humidified oxygen in cases of upper respiratory discomfort due to dryness and in patients who require high-flow oxygen therapy for an extended period. Humidified oxygen can also be used in patients with an artificial airway requiring long-term oxygen management.

Clinical studies highlight the benefits of humidified oxygen in patients with viscous secretions. The British Thoracic Society guideline warns against the use of bubble bottles which allow a stream of oxygen to bubble through a container of water. These bubble bottles increase the risk of airway infections and prescribe no clinically significant benefits in patients. The decision to use humidified oxygen in the therapy course should be made individually. The attending specialist is advised to critically examine the risks and benefits of such a decision, as the clinical evidence supporting humidified oxygen therapy is insufficient to recommend wide use.

Poiroux et al. (2018) published a study investigating the effects of dry versus humidified oxygen. The study, with a participant pool of 354 subjects, examined the impact of these two methods on the quality of life of patients administered oxygen therapy under intensive care. The study data could not demonstrate that non-humidified oxygen was less effective in these patients than humidified oxygen after a 6–8-hour therapy course (Poiroux et al., 2018).

In modern medicine, oxygen is classified as a drug and should be administered based on good drug-prescribing and monitoring practices. The German S3 guideline of supplemental oxygen therapy recommends the prescription of oxygen by a trained physician, specifying a target range of oxygen saturation. Each prescription should be based primarily on the patient's evaluation by a senior clinician or specially trained healthcare professionals. In a grouped population study of oxygen prescription in patients, Harper et al. (2021) reported the proportion of inpatients with oxygen prescription ranging from 40 to 60%.

The British Thoracic Society Guideline recommends a standard oxygen prescription document for all healthcare facilities. Alternatively, facilities can opt for a designated oxygen section on all drug-prescribing documents or sections for oxygen prescription in an electronic prescribing system. Except for sudden illness or critical emergencies requiring quick interventions, a formal oxygen prescription should always be provided before an oxygen therapy course is initiated. These prescriptions should always be signed and specify the administration protocol details, including oxygen concentration, flow rate, target saturation range, and duration of administration. It is essential to ensure all nursing staff understand the aim of the therapy, including all healthcare professionals attending to the patients.

Clinicians are encouraged to disregard the old practice of specifying a fixed oxygen concentration or fraction of inspired oxygen. The method has no clear target for the therapy, making it hard for the nursing team to plan appropriately for monitoring and weaning when necessary. In emergencies, the lack of a formal oxygen prescription should not preclude the administration of supplemental oxygen. In pre-hospital cases, first responders and medical personnel should administer oxygen liberally if required to improve clinical symptoms. However, written documentation, including the duration of emergency administration, oxygen concentration, and flow rate, should be made in all instances of emergency medical interventions. Emergency oxygen administration should be based on the guidance provided on the card for patients with an oxygen alert card until blood gas measurements can be conducted.

In prescribing the delivery system, the attending specialist should consider oxygen requirements, breathing pattern, mouth opening, and risk of hypercapnia. Once therapy is initiated, the medical team should reassess the patient to detect possible signs of clinical deterioration at the early stage of treatment. It is essential in patients with no prior history of supplemental oxygen therapy. Early reassessments should also examine the risks of complications or the need for intensive care (Quinten et al., 2018). The reassessment interval should be determined by the severity of vital signs and the extent of hypoxemia. Patients who are started on oxygen therapy can be reassessed every 4 to 6 hours. The British Thoracic Society guideline recommends a 6-hour assessment interval for patients started on oxygen therapy and continuous monitoring depending on where the treatment was initiated.

Regardless of where therapy was initiated, continuous monitoring is recommended in track and trigger systems if multiple vital signs are outside the normal physiological ranges. In this case, the oxygen concentration required to achieve a target saturation range may depend primarily on the risk of a life-threatening complication or clinical deterioration (Arnolds et al., 2022). Suppose high-flow nasal cannula oxygen (HFNC) is initiated in a patient with no prior history of oxygen therapy under emergency conditions. In that case, the German S3 guideline also recommends continuous SpO₂, pulse, and respiratory rate monitoring. Other vital signs, including mental state, blood pressure, and body temperature, should also be monitored (Kang et al., 2020).

Recommendations on initiating oxygen therapy in emergency settings prioritize recognizing the clinical symptoms of conditions in which oxygen therapy is indicated. Medical personnel are expected to be capable of recognizing the clinical signs of inadequate tissue oxygenation. The pathophysiological mechanisms resulting in low tissue oxygenation are broadly categorized into two groups. The two groups include those impairing the oxygen-hemoglobin complex system and those causing arterial hypoxemia. Recognizing these mechanisms requires careful patient evaluation. However, more than one mechanism may contribute to poor tissue oxygenation in the same patient. The pathophysiological mechanism grouped under the failure of the oxygen-hemoglobin transport system include:

• Low hemoglobin concentration
• Poor tissue perfusion rate
• Hemoglobinopathies, high carboxyhemoglobin concentration, and other conditions implicated in the abnormal oxygen dissociation curve
• Histotoxic poisoning of the intracellular enzymes, including cyanide poisoning, paraquat poisoning, and septicemia
• In arterial hypoxemia, the pathophysiological mechanisms implicated include:
  • Right to left shunts
  • Low inspired oxygen partial pressure
  • Alveolar hypoventilation in sleep apnea, opiate poisoning, etc
  • Ventilation-perfusion mismatch in asthma, atelectatic lung zones, etc

The clinical symptoms of these pathophysiological mechanisms are nonspecific and can be challenging to recognize quickly. These symptoms include altered mental state, dyspnea, cyanosis, tachypnoea, arrhythmias, and coma. In all patients under evaluation for a possible oxygen therapy regimen, arterial oxygen saturation (SaO₂) and partial oxygen pressure (PaO₂) measurements are the principal indicators for initiating, prescribing, monitoring, and modifying supplemental oxygen therapy.

Arterial oxygen saturation and partial oxygen pressure can be normal in some patients presenting with clinical evidence of tissue hypoxemia caused by low cardiac output, anemia, and failure of tissues to use oxygen. In these cases, mixed venous oxygen partial pressure measured in pulmonary artery blood is considered a better index of tissue oxygenation as its value approximates to mean partial tissue pressure. The most widely used guidelines in assessing the patient for a possible immediate oxygen intervention include:

• Assess the airway and optimize airflow using airway positioning as necessary in the patient. Head tilts, chin lifts, and left lateral tilts might be required.
• Perform a thorough clinical assessment and documentation, including cardiovascular, respiratory, and neurological system assessments, at the beginning of every shift.
• Check and document oxygen equipment set up and any change in patient positioning at the beginning of each shift.
• Oxygen flow rate, patency of tubing, and humidifier settings should be checked and documented hourly.
• Heart rate, respiratory rate, respiratory distress, and oxygen saturation -using continuous pulse oximetry, should be checked hourly and recorded on the patient's observation chart.

An updated series of evidence-based patient assessment recommendations were included in the latest update of the British Thoracic Society guideline for supplemental oxygen use in adults. Recommendations relevant to the central theme of this course include:

• Chronically hypoxemic patients presenting a 3% or greater fall in oxygen saturation on their usual saturation range should be assessed using blood gas estimations in the hospital.
• In patients with comorbidities, including asthma, heart failure, and other illnesses, the appropriate therapy protocol should be initiated following the standard management plans for the diseases.
• In a pre-hospital setting or in patients under ambulatory care, oxygen saturation levels should be monitored until the patient's vitals are stable and a specialist does a full assessment. The concentration of oxygen administered should be adjusted upwards or downwards to maintain the appropriate saturation range.
• In emergencies, administer oxygen empirically without a formal prescription to restore airflow. The lack of formal oxygen prescription should not restrict oxygen administration in a formal setting. The oxygen concentration, the flow rate, adjustment, and the patient's response should be documented.
• Emergency service providers, first responders, and medical personnel on a rural visit should be equipped with portable pulse oximeters and oxygen cylinders and guide the use of oxygen as part of their emergency response equipment.

In acutely ill patients presenting for clinical intervention, oxygen therapy (if indicated) should be aimed at maintaining a patent airway. In patients with cardiac arrest, respiratory distress, or respiratory arrest, administer oxygen empirically. The American College of Chest Physicians and the National Heart, Lung, and Blood Institute recommended a list of conditions to classify clinical conditions requiring empirical initiation of oxygen therapy. These conditions include:

• Cardiac and respiratory arrest
• Hypoxemia (PAO₂ <7.8 kPa, SaO₂ <90%)
• Hypotension (Systolic blood pressure < 100 mmHg)
• Low cardiac output and metabolic acidosis (bicarbonate < 18 mmol/l)
• Respiratory distress (respiratory rate > 24/min)

The British Thoracic Society Guidelines for Oxygen Supplementation provided a harmonized protocol and evidence-based recommendations for administering supplemental oxygen. The summarized points on this guideline include:

Supplemental oxygen prescription and administration should be handled by trained clinicians with certification in patient assessment and symptom management. Therapy should start with documentation of respiratory rate, pulse rate, blood pressure, and body temperature and assess circulating blood volume and anemia. If patients present with a life-threatening complication, the clinician on duty is advised to seek clinical assistance from an intensive care specialist. In a pre-hospital care setting, the attending clinician should be prepared to call for an ambulance should an emergency arise.

Initial assessment and monitoring of hypoxemia and hypercapnia should include a track and trigger system. These systems provide updated real-time guidance on rapid changes in patient's vital signs. A track and trigger system might also guide therapy modification and clinical review on supplemental oxygen administration. Oxygen saturation should be tracked and monitored using pulse oximetry in all breathless patients started on supplemental oxygen. Keeping a real-time update of flow rate and volume of oxygen delivered in an observation chart is also recommended. Vital sign changes in patients at risk of hypercapnic respiratory failure should be strictly monitored.

The German S3 guidelines were developed within the Program for National Disease Management Guidelines (AWMF). As the first national guideline on supplemental oxygen therapy, the German S3 guideline directly addressed clinical concerns surrounding oxygen prescriptions and oxygen therapy in disease conditions. Target ranges of oxygen saturation levels recommended in this guideline are based on ventilation status risk of hypercapnic respiratory failure. There is also an overview of patient safety and comfort, indications requiring supplemental oxygen therapy, therapy monitoring, weaning, and other protocols covering oxygen use in inpatient admissions. The general recommendations adopted as practice points in the German S3 guideline on supplemental oxygen use include the following:

1. Positioning is considered a fundamental factor in therapy effectiveness. In conscious hypoxemic patients, an upright positioning may improve tissue oxygen saturation levels and disease prognosis. Clinical evidence links acute respiratory failure in morbidly obese patients with supine positioning. Pregnant women should be positioned on the left side to reduce the risk of aortocaval compression.
2. In non-hypoxemic patients, nonpharmacological options, including relaxation exercises, cooling of the face, airflow from a table fan, and walking aids, should be considered the primary therapy option in palliative care. Opioids are effective in the management of dyspnea in non-hypoxemic patients.
3. Respiratory rate is an important vital sign to be monitored in a hypoxemic patient on oxygen therapy. Respiratory rate is used in the track and trigger system and as a prognostic score. Patients are considered clinically stable at a National Early Warning 2 (NEWS2) score greater than 5, with the vital sign predominantly in the noncritical stage.
4. Pulse oximetry is recommended as a simple, non-invasive method of measuring the arterial oxygen saturation level in both inpatient and outpatient clinical settings. Oximetry measurements can significantly reduce the number of blood gas tests required. However, pulse oximetry is less accurate than measuring arterial blood oxygen saturation.

Patients may be prescribed home oxygen therapy in conditions requiring long-term oxygen therapy. Feasibility studies on home oxygen therapy plans indicated the need for medical supervision and periodic patient assessment. The plan, when indicated, reduces patients' hospital admission period and significantly eliminates the risk of hospital-acquired infections. Home oxygen therapy may be advised in some chronic conditions, including cardiac impairment and COPD. Home oxygen therapy improves disease prognosis and the clinical symptoms at presentation when administered correctly with no technical errors. The different, widely-recognized protocols of home oxygen therapy include the following (Shebl et al., 2022):

• Ambulatory Oxygen Therapy (AOT): is prescribed in physically active patients with severe resting hypoxia. All other chronic conditions resulting in severe low saturation levels and requiring long-term oxygen management can also be covered with a home delivery protocol.
• Nocturnal Oxygen Therapy: under this delivery protocol, oxygen is administered overnight and not during the daytime. Multiple studies, including the report by Lacasse et al. (2020), have investigated the clinical potentials of long-term continuous oxygen doses administered via a concentrator.
• Long-term Oxygen Therapy: is the most widely prescribed home oxygen delivery protocol. Supplemental oxygen is administered in patients with chronic hypoxemia. Stationary concentrators are popular with this protocol.
• Palliative Oxygen Therapy: protocol uses oxygen to relieve the sensation of persistent refractory breathlessness in advanced disease or life-limiting illness, irrespective of underlying pathology, where all reversible causes have been or are being treated optimally.
• Short Burst Oxygen Therapy (SBOT): protocol is indicated for the relief of breathlessness, not relieved by any other treatments. It is used intermittently at home for short periods, for example, 10–20 minutes at a time. Oxygen used in this way has traditionally been ordered for non-hypoxemic patients and used for subjective relief of dyspnea before exercise for oxygenation or after exercise for relief of dyspnea and recovery from exertion.

In LTOT, patients should not be assessed solely with pulse oximetry. The attending specialist should conduct an initial assessment using arterial blood gas sampling. During periods of apparent clinical stability, two arterial blood gas assessments should be performed at least 3 weeks before LTOT can be initiated. Capillary blood gas sampling can be used to remeasure PaCO₂ and pH at different oxygen flow rates for oxygen titration during this assessment. Patients should be reassessed after the oxygen titration is complete. Arterial blood gas helps to determine if the target oxygenation range has been achieved.

Patients who develop worsened hypercapnia or respiratory acidosis during an initial assessment may have comorbidity. Further clinical assessments and evaluation of physiological integrity are recommended. Suppose an unstable clinical state is confirmed if these patients experienced two repeated occasions of worsened hypercapnia or respiratory acidosis. In this case, the patient should only have domiciliary oxygen initiated with nocturnal ventilator support. The British Thoracic Society recommends the initiation of LTOT at a flow rate of 1 L/min and titrated up in 1 L/min increment until the SpO₂ is greater than 90%.

Without any contraindications, the LTOT flow rate should be increased by 1 L/min during sleep in non-hypercapnic patients. Ambulatory and nocturnal oximetry may be performed to allow a more accurate flow rate. Patients in clinically stable conditions with optimal neurological and cognitive functioning may be allowed to safely initiate, control, and monitor the flow rate increments. Until the target PaO₂ is achieved, flow rates may be increased at 20-minute intervals during an oxygen titration. Follow-up, including the blood gases and flow rate assessment, should be scheduled for 3 months after the initiation of LTOT. After this first schedule, the next follow-up should be at 6 to 12 months if the initial assessment is considered satisfactory.

Regarding the popular guidelines on home oxygen management, the equipment can be classified into three different groups.

Depending on the patient's age, oxygen requirements, therapeutic goals, tolerance, and humidification needs, various oxygen delivery methods are available for both inpatient and pre-hospital settings. These delivery systems are categorized into two broad classes- low-flow delivery methods and high-flow delivery methods. The low-flow delivery methods include:

• Simple face masks
• Nasal prongs
• Tracheostomy masks
• Non-rebreather face mask
• Isolette – (Used in neonatal intensive care units)

The high-flow delivery methods also include:

• Ventilators
• CPAP/BiPAP drivers
• High-flow nasal prong therapy 

The masks and valve design popular with these delivery systems allow the administration of inspired supplemental oxygen of 24 - 90%. The inspired concentration and, subsequently, the oxygen saturation attained depends on the ventilation minute volume and the flow rate. The high-flow mask systems can deliver an estimated 40 L/min of oxygen sufficient to meet the saturation level target in many inpatient settings. At this rate, the systems ensure the breathing pattern does not affect the FiO₂ as the delivery flow rate exceeds the physiological respiratory rate. With both the high-flow and low-flow delivery options, the most widely used masks in oxygen therapy include the following.

The concentration of oxygen administered and the flow rate of delivery are considered primary factors in the evaluation of the effectiveness of an oxygen therapy protocol. A recent study focused on nasal high-flow oxygen therapy in patients with hypoxia and reported how the effective inspiratory oxygen concentration depends on the patient's respiratory flow and breathing pattern (Schwabbauer et al., 2014). As with this study, recent studies on supplemental oxygen therapy have consistently explored high-flow oxygen therapy in conditions requiring oxygen.

In high-flow oxygen therapy, humidified oxygen is heated and delivered using specially designed nasal cannulas capable of providing supplemental oxygen at a rate of 40-60 L/min. Modern high-flow cannulas deliver oxygen at a rate higher than the patient's physiological respiratory flow. Consequently, a defined fraction of oxygen in inspired air (FiO₂) is delivered up to 1.0, independent of the patient's breathing pattern. In addition to rapidly boosting the saturation state, HFNCs also reduce the work of breathing and the risk of damage to the respiratory epithelium and respiratory discomfort. HFNCs are now widely used in intensive care units.

In a systemic review of a randomized-controlled quasi-experimental study, Marjanovic et al. (2020) compared the use of high-flow oxygen therapy versus conventional oxygen therapy in patients with acute respiratory failure admitted to the emergency department. The researchers indicated that high-flow oxygen decreased dyspnea and the respiratory rate in the study population (Marjanovic et al., 2020). In another systematic review conducted by Ou et al. (2017), study results indicated that the reintubation rate of critically ill patients was lower when high-flow oxygen was used compared with conventional oxygen delivery methods (Ou et al., 2017). High-flow oxygen also shortens hospital stays and lowers the intubation rate in immunosuppressed patients with acute pulmonary failure (Wen et al., 2019).

The German S3 guideline recommends that patients on high-flow oxygen therapy should be closely monitored and therapy discontinuation clearly defined. Patient monitoring should be done with pulse oximetry and observed for any clinical symptoms suggesting a therapy complication. In hospitalized patients with acute hypoxic pulmonary failure without hypercapnia, high-flow oxygen should be administered at a flow rate of 6 L/min via a nasal cannula or mask if the oxygen saturation level drops below 92%. Since HFNCs are not readily available outside the hospital, medical personnel and first responders should consider CPAP/NIV and reservoir masks as effective alternatives.

Oxygen delivery, therapy monitoring, and vital sign documentation are all fundamental requirements in supplemental oxygen care (O'Donnell et al., 2019). First responders, nurses, and medical personnel dispensing oxygen in clinical conditions where it is indicated are expected to sign the drug chart at every drug round. A periodic check on the delivery system's integrity is also recommended, especially in consciously sedated patients. These checks should also document the oxygen saturation range and provide the data necessary for weaning if needed.

The British Thoracic Society guideline prescribes a 5-minute periodic check for patients started on oxygen. The recommendation also includes patients who require an increased oxygen concentration and those whose oxygen therapy has been stopped. The delivery system should be modified to normalize the saturation range in stable patients with an oxygen saturation higher than the target saturation range. The nursing staff is expected to have a real-time update on the saturation range, and flow rate of patients started on oxygen.

Blood gas measurement should be done every 30 – 60 minutes in patients with a target saturation range of 88 - 92%. The recommendation should also be adopted in patients at risk of developing hypercapnic respiratory failure but with a normal PCO₂ on the initial blood gas measurement. Periodic checks in these patients should include the level of carbon dioxide. In stable patients with an oxygen saturation range normalized within the target range, blood gas measurements should not be repeated. Unless there are clear indications of clinical deterioration in signs and symptoms, blood gas measurement should not be repeated in patients with no risk of hypercapnic respiratory failure.

In stable patients responding to therapy, SPO₂ and the necessary variables should be monitored at least four times daily. Saturation levels should be monitored continuously in those with an active critical illness. Level 2 or 3 care in a critical care unit or high-dependency unit should also be considered. Once clinical stability is achieved and the oxygen saturation level normalizes, therapy should be continued or modified depending on the patient's condition. In patients with a saturation level below the target range, oxygen therapy should be increased and decreased if the saturation level is above the target range.

After every episode of therapy modification, the new saturation rate, flow rate, and delivery system should be recorded on the patient's personalized observation chart after 5 minutes. However, all modifications to an ongoing therapy should be approved by a senior specialist trained in supplemental oxygen therapy. All changes must be signed on the observations chart. In cases where a reduced oxygen concentration is approved as a therapy modification in a stable patient to maintain a target saturation, repeat blood gas measurements are not required. Patients with no risk of hypercapnic respiratory failure also do not need a recurrent blood gas measurement after an increased oxygen concentration to maintain the desired saturation range. However, the attending specialists should examine why the oxygen saturation level has fallen.

Repeated blood gas measurements should be carried out in patients at risk of hypercapnic respiratory failure and placed on an oxygen protocol to achieve a target range of 88 to 92%. After every increase in oxygen therapy, these measurements should be done at 30 – 60-minute intervals. Pulse oximetry is the recommended primary mode of monitoring in patients with no risk of hypercapnic respiratory failure. Provided the patient's vitals are stable and the desired oxygen saturation range is maintained (94 – 98%), repeated blood gas measurements are not required. Adjustments to the oxygen therapy should be guided against technical faults in the delivery system. Before a medical order for a flow rate increase, the medical personnel should check all parts of the oxygen delivery systems for technical faults and errors. The recommendation should be adopted in all patients regardless of clinical circumstances. Blood gas measurements should be repeated in all patients if the oxygen saturation fails to increase following a 5-10 minute period after increasing the oxygen therapy. A review of possible clinical concerns should be considered in this case.

On oxygen therapy discontinuation, the expert consensus in modern medicine states that oxygen delivery should be reduced when a patient is clinically stable, and oxygen saturation is above the target range or within the range for several hours. Oxygen therapy is effective in restoring tissue and arterial oxygenation in different clinical conditions. Study results reporting improvements in symptoms in patients on oxygen therapy support this. Documented signs of clinical stability in these patients include a normal respiratory rate and stable vital signs. During the short phase of recovery from an acute condition, some patients experience transient hypoxemia. Exercise-induced desaturation has also been reported in patients with acceptable oxygen saturations.

The German S3 guideline recommends discontinuing oxygen therapy in patients not at risk of hypercapnic respiratory failure. Patients being discontinued from oxygen should be within the target oxygenation range for several hours under a flow rate of 2 L/min. In patients at risk of hypercapnic respiratory failure, the lowest volume of oxygen administered before weaning should be 1 L/min or 0.5 L/min as necessary. A 24% Venturi mask set at 2 L/min as the lowest oxygen concentration before weaning can be considered in patients at risk of hypercapnic respiratory failure. If the target saturation range is maintained at this rate, repeat gas measurements are not required, and the patient can be eventually weaned off oxygen if stable.

The British Thoracic Society guideline recommends two consecutive observations on the target oxygen saturation level before oxygen therapy is stopped. Due to the possibility of impending clinical decline, the recommendation for the target oxygen range must be continually monitored. It may be suitable to adjust the target range after reviewing COPD patients who may have accommodated to have oxygen saturations <94% normally or in patients who may be appropriately discharged from the hospital with oxygen levels <94% but need an outpatient oxygen evaluation. Weaning off oxygen may be prescribed once the respective patient has ended the course of the initial prescription for oxygen supplementation.

Immediately after stopping oxygen therapy, the saturation should be monitored. If it is maintained at the target saturation level, a repeat check should be conducted one hour later. During this period, if the oxygen saturation and the physiological track and trigger score are considered satisfactory, the weaning process is successful, and the patient has safely completed the therapy course. In successfully weaned patients with underlying comorbidities, saturation levels and vital signs should be monitored as the patient is managed for these conditions.

If the target saturation level falls after stopping oxygen therapy, the weaning attempt is deemed unsuccessful (Rostin et al., 2019). In this case, the oxygen therapy is restarted with the lowest oxygen concentration maintained in the patient before weaning. Hold steady at this concentration and observe for 5 minutes. If this concentration restores the desired saturation level, continue oxygen therapy with this protocol and attempt weaning at a later date. However, the patients must fulfill all the necessary conditions, including stable vital signs, before weaning is initiated later.

Suppose a higher oxygen concentration is required to re-establish the target saturation range. In that case, the attending specialist should conduct a thorough clinical review examining the cause of deterioration before starting a new therapy protocol. The review should check for episodic hypoxemia or transient asymptomatic desaturation. Studies have reported patients experiencing episodic hypoxemia due to minor exertion or mucus plugging after properly discontinued oxygen therapy. A new oxygen protocol may be initiated in these patients. However, a new oxygen protocol is not required in cases of transient asymptomatic desaturation.

Home oxygen may be required after hospital discharge in patients with COPD who have completed a course of oxygen therapy. The S3 German guideline recommends continuing oxygen therapy even after discharge in patients who cannot be successfully weaned off oxygen. The decision to initiate long-term oxygen therapy after discharge should not be made only based on blood gas measurements conducted during the acute illness phase. A follow-up plan should also be initiated after discharge, and patients should be educated on the need for therapy adherence.

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