COVID 19 Is a new disease and a pandemic, it has affected almost every human on Earth either directly or indirectly.[5] Research in the field is ever increasing. There has been considerable confusion regarding the timing of intubation in COVID 19. Gattinoni et al.[6] in 2020, published a letter to the editor, where they mentioned that patients with COVID 19 acute respiratory distress generally presented with hypoxemia, unusual lung compliance and preserved lung gas volume in CT thorax imaging. That may lead to a substantial increase in minute ventilation and respiratory drive.[6] The increased respiratory drive present may amplify the risk of lung injury through P-SILI. If oxygen therapy, HFNC and NIV are unable to match or compensate for these increased respiratory efforts; patients may still need invasive mechanical ventilation even after resolution of hypoxemia.[6] This statement was also supported by observation obtained from hundreds of patients in Italy and the United Kingdom. In contrast, Tobin et al.[7] criticized that P-SILI is a recent invention and there was not sufficient literature in support. However, a recently published article showed a reduction in median oesophageal pressure in those patients of COVID 19 ARDS, who were on NIV support and had improved chest radiology.[8, 9] So, the confusion regarding the timing of intubation and invasive mechanical ventilation in Covid19 ARDS patients still lingers on.
Our survey found out that most physicians treating COVID 19 patients, believe that COVID ARDS is different from typical ARDS, thus it makes them decide differently regarding the indications for intubation. 56.2% of all the respondents were of the view that mortality in COVID 19 ARDS is higher when compared to other forms of ARDS. Chiumello et al.[10] in a study where they compared the CT findings of COVID 19 ARDS with historical controls found COVID 19 ARDS to be a subset of “typical” ARDS with better compliance, especially in early stages. Considering the COVID 19 ARDS population is very homogeneous compared to a heterogeneous population of typical ARDS, some differences were expected between the two populations. Overall, there was however not much difference and the mortality rates in the study were also similar in the two groups. The differences that were observed did not affect the decision for intubation. They primarily suggested some differences in the ventilatory settings and avoidance of recruitment maneuvers.
67.1% of respondents agreed on P-SILI, even though it’s something whose existence is disputed. It’s a form of lung injury which has been documented quite recently though there have been some studies in late 1980s suggesting about it.[11] Nearly 90% of the respondents agreed on use of spontaneous awake proning in case of hypoxia and also in for of using high flow nasal cannula (HFNC) if the hypoxia persisted. 56.3% preferred to give a trial of non-invasive ventilation (NIV) if HFNC was unavailable or failed. 47.9% of these were unsure about the impact of NIV on development of P-SILI. Many have shared cases where patients on NIV developed subcutaneous emphysema and pneumothoraces.
Around 30% of patients with acute hypoxemic respiratory failure are treated with non-invasive ventilatory support. P-SILI can be reduced by use of high PEEP, but it is difficult to provide through NIV due to higher amount of leaks and interruptions in NIV as during feeding, patient discomfort and position changes. NIV failure is associated with mortality rates around 50% which in our opinion is usually because of delayed intubation.[12] This is mainly because of prolonged exposure of injured diseased lungs to high tidal volumes and trans-pulmonary pressure swings.[13] Treatment failure with NIV is more expected in patients with more severe disease: Pao2/FiO2 < 200 mmHg before treatment and higher SAPS II score (> 35) are associated with higher risk of being intubated.[13] The real dilemma is how to know patient is going into NIV failure. There have been many proposed ways to decide on NIV failure like swing in Pes (Esophageal pressure - a surrogate of PL) or tidal volume more than 9-9.5 ml/kg. HACOR scoring which takes in to account heart rate, GCS, pH, P/f ratio and respiratory rate can also be used for this purpose.[14] For patients undergoing HFNC, a simple ROX index (ratio of SpO2/FiO2 to respiratory rate, evaluated continuously during treatment) has been tested and validated to predict treatment success and failure. Patients with ROX Index > 4.88 after two hours of treatment are likely to avoid intubation, while those with a ROX < 2.85, < 3.47 and < 3.85 after two, six and 12 hours of HFNC are at high risk of treatment failure and the need for endotracheal intubation and invasive mechanical ventilation.[15]
Nosocomial Pneumonia is a major complication in ICU patients.[16] VAP rates have not come down in recent times despite adherence to various prevention bundles. Most of the clinicians in our survey; in spite of their doubts in NIV to cause P-SILI, still persisted with it as they feared higher incidences of ventilator associated pneumonia (VAP) and other nosocomial infections if the patient got intubated. This fear was more driven due to shortage of adequately trained staffs in COVID ICUs. There are limited studies looking into the incidence of hospital acquired pneumonia in COVID ARDS patients. Whether use of NIV reduces risk of nosocomial pneumonia or not is not yet clear as per the available literature. The present of an endotracheal tube is expected to increase the risk of biofilm formation and colonization of the airways.[17] Diagnosis of VAP is very difficult in a patient of ARDS. These factors make it difficult for us to make a conclusion whether NIV is protective or not in development of VAP.