Introduction
Most COVID-19 fatalities and mortalities are primarily due to acute viral pneumonia leading to acute respiratory distress syndrome. With the progress of the infection, increasing respiratory support is required, making intensive care essential. Respiratory support in such circumstances includes oxygenation (supplying oxygen to the body cells) with low-flow and high-flow systems, non-invasive ventilation, and other respiratory therapies such as nebulized medications and rescue therapies such as prone positioning. The condition of some individuals improves, and respiratory support can be gradually reduced; others continue to deteriorate, and a decision needs to be made concerning intubation and mechanical ventilation.
What Is Hypoxia?
Hypoxia is the state of the body in which sufficient oxygen is unavailable to the tissues to maintain adequate homeostasis, a state of inner stability by adjusting to the external environment. This results from inadequate oxygen supply to the tissues due to low blood or oxygen content in the blood (hypoxemia).
COVID-19 Patients With Minimal Oxygen Needs:
Low-flow Oxygen - For individuals with hypoxemic respiratory failure due to COVID-19, oxygenation with a low-flow system at a reduced rate than the individual’s inspiration through a nasal tube is appropriate as an initial strategy. The degree of virus transmission at low-flow rates is less likely. The risk of the transmission of viruses might increase by contaminating the surrounding environment and hospital staff. However, the rate of flow at which the risk of viral transmission increases is unknown. Thus the individuals wear nasal tubes, and a droplet mask, especially during transport or when the hospital staff is around.
COVID-19 Patients With Advanced Respiratory Support Requirement:
As oxygen requirements increase over 6 to 15 L/min with difficulty breathing, the treatment options are high-flow oxygen via a nasal tube and oxygen supplied through a non-invasive ventilation (NIV) device.
Non-invasive Techniques:
Non-invasive modalities are used in individuals with acute hypoxemic respiratory failure due to COVID-19 and higher oxygen demands than low-flow oxygen can provide. The decision to start with the non-invasive modalities, either high-flow oxygen via a nasal tube or non-invasive ventilation, should be made by weighing the risks to and benefits for the individual, the risk of exposure to the health care workers, and the level of patient tolerance. Both modalities have been used in critically ill individuals with COVID-19. While these modalities improve oxygenation and dyspnea (shortness of breath), studies showing their success at preventing progression to intubation have limitations, and a reduction in death has not been found. However, decreased mechanical ventilation rate has been reported after shifting to higher intubation thresholds, suggesting that some individuals might not need intubation if appropriately supported with non-invasive methods.
How To Choose Between Oxygenation via High-flow Nasal Cannulae and Noninvasive Ventilation?
The choice between non-invasive ventilation and high-flow oxygen in individuals with COVID-19 is based mainly on the comorbidities and the tolerability of the individual. Non-invasive ventilation should be used in individuals with some comorbidity for which it is efficient such as acute hypercapnic respiratory failure from an acute exacerbation of the chronic obstructive pulmonary disease, acute cardiogenic pulmonary edema, underlying sleep-disordered breathing (obstructive sleep apnea or obesity hypoventilation), or respiratory muscle weakness. Both modalities can be used In the absence of such comorbidities. Device tolerability and patient comfort are the determining factors. High-flow oxygen via a nasal tube is associated with lesser adverse events. It is a more comfortable and practical mode of support, during which individuals can continue to talk and eat, compared to non-invasive ventilation. In some instances, a transition between high-flow oxygen via a nasal tube and non-invasive ventilation for a shorter duration, such as sleep, acute episodes of acute pulmonary edema, and meals, can be carried out with seldom switches between both modalities until the individual improves or deteriorates.
How To Monitor Non-invasive Modalities?
The application of non-invasive modalities like high-flow oxygen via a nasal tube (HFNC) and non-invasive ventilation (NIV) is similar to that for individuals not suffering from COVID-19, with CPAP (continuous positive airway pressure) rather than BiPAP (bilevel positive airway pressure) to reduce the transmission risk of the virus. Respiratory, fluid, and nutritional status are closely monitored for individuals receiving non-invasive support. Awake pronation should be continued while the individuals are on non-invasive respiratory support. The prone position has been used in acute respiratory distress syndrome (ARDS) to improve oxygenation and prevent bodily injury due to changes in the air pressure in ventilated patients. Awake proning is used to postpone invasive ventilation and improve oxygenation, thus the results. In awake proning, the individual is made to lie on their stomach with the face down to improve breathing and oxygenation.
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Respiratory - For individuals with a non-invasive approach, the individual’s respiratory status is carefully watched for progression. The individuals are monitored every one to two hours and obtain an arterial blood gas (ABG) to ensure adequate and safe ventilation. The arterial blood gas test is a test that measures the amount of oxygen and carbon dioxide in the blood. After this, the ABG test is carried out daily or as needed. Once patients are on high-flow oxygen via a nasal tube or non-invasive ventilation and showing signs of quick progression, a low threshold to intubation can be used.
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Nutrition - The individuals are closely monitored for signs of dehydration and malnutrition. For those receiving non-invasive modalities for prolonged periods, nasogastric feeding is advised despite the risk of aspiration.
Duration:
Some individuals can deteriorate quickly within a few hours to days, while others tolerate the modalities for prolonged periods such as one week to 10 days. There are no set rules or factors predicting a course an individual takes. Individuals who require non-invasive modalities for more extended periods or those whose condition progresses with either of the modalities are at a high risk of requiring intubation and mechanical ventilation.
How To Control Infections in Non-invasive Modalities?
When non-invasive modalities such as HFNC or NIV are used, in addition to other standard precautions, airborne precautions should be taken, such as an airborne infection isolation room, a negative pressure room, and complete personal protective equipment.
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HFNC - A surgical mask should be placed on the patient during high-flow oxygen via a nasal tube when healthcare workers are around or when the individual is transported.
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NIV - A full facemask that might reduce particle dispersion is advised if the individual undergoes non-invasive ventilation. A helmet has also been proposed for delivering non-invasive ventilation to COVID-19 individuals and may be associated with reduced aerosol dispersion compared to full facemasks. However, there is little data available on helmet use. In order to check the dispersal of viruses, non-invasive ventilation is initiated with a CPAP (continuous positive airway pressure) to use mild air pressure to keep airways open for easy breathing while sleeping using the lowest pressures.
Supportive Therapy:
Critically ill individuals on non-invasive modalities should receive supportive care similar to intubated individuals.
Other Considerations:
For Individuals with increased oxygen needs, additional diagnoses should be made; such as in case of a sudden increase in oxygen requirement, the individual should be checked for pulmonary embolism, acute cardiogenic pulmonary edema, or myocardial infarction.
Conclusion
Acute hypoxemic respiratory failure is one of the important principal causes of hospitalization and death in severe COVID-19 infection. Most of the intubated COVID-19 individuals are fatal. High-flow oxygen via a nasal tube and non-invasive ventilation help avoid intubation in individuals with pneumonia not responding to conventional oxygen treatment. Careful selection of individuals with severe hypoxemia, close monitoring, and appropriate administration of non-invasive ventilation can increase the success rate, along with all standard precautions to protect healthcare personnel from the virus.
