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COVID-19 pneumonia presents in most patients with significant hypoxemia but without substantial impairment of lung compliance that would increase the work of breathing (WOB) to levels requiring invasive mechanical ventilation. Thus, the ability to assess the WOB independent of the oxygen needs could help guide management and possibly avoid intubation. We previously developed and implemented in our ICU a WOB scale based on respiratory physiology ranging from 1 to 7 by assigning points to the respiratory rate level and the use of respiratory accessory muscles. We analyzed the use of our WOB scale in 10 patients admitted to our ICU with severe COVID-19 pneumonia. All patients had radiographic evidence of extensive lung disease with significant hypoxemia and multiple risk factors associated with poor outcome. Hypoxemia was successfully managed using high-flow nasal cannula. The WOB level was measured every 4 hours. The maximum WOB was 4.3 ± 0.9, contributed primarily by the respiratory rate with a score of 3.6 ± 0.5 but with infrequent use of respiratory accessory muscles. All 10 patients survived without need of intubation. For comparison, three other patients who needed intubation had a maximal work of breathing within the preceding 24 hours of 5.3 ± 1.2 with a respiratory rate score of 3.7 ± 0.6, as in non-intubated patients, but with more often use of respiratory accessory muscles. Our data suggest that patients with COVID-19 pneumonia can be supported for extended periods using HFNC despite tachypnea provided there is only infrequent use of respiratory accessory muscles, corresponding to a WOB scale ≤ 4, prompting closer assessment for possible intubation when WOB > 4. This approach would be especially advantageous under conditions of high disease intensity when avoidance of intubation is likely to result in a better outcome.

Introduction: A common misconception is that increased work of breathing (WOB) in hospitalized patients can be ruled-out when arterial O 2 tension (or saturation) is adequate and arterial PCO 2 is not elevated. Unrecognized WOB increase leads to respiratory muscle fatigue, cessation of respiratory function, and cardiac arrest. We previously developed a WOB Scale for bedside use adding points (maximum 7) based on respiratory rate (1 to 20 bpm = 1 point; 21 to 25 bpm = 2 points; 26 to 30 bpm = 3 points; and > 30 bpm = 4 points), nasal flaring (No = 0 points; Yes = 1 point), activation of the sternocleidomastoid muscle (No = 0 points; Yes = 1 point), and activation of abdominal muscles (No = 0 points; Yes = 1 point). A WOB Scale > 3 points typical identifies a patient in need of intervention to reduce or support WOB increase. However, widespread application of our WOB Scale - especially outside intensive care environments - would likely benefit from a simplified approach. Thus, we investigated developing a “reflex” approach whereby measurement of all four components would be contingent on the respiratory rate level. Methods: We analyzed 110 WOB Scale measurements in a mixed population of ICU and General Ward patients and assessed WOB Scale levels hypothesizing that a respiratory rate of 1 point (1 to 20 bpm) would be predictive of a low WOB Scale (i.e., not exceeding 3 points); thus, obviating the need to perform a complete WOB Scale evaluation. Results: The WOB Scale distribution showed that most patients had normal WOB with only 14 patients (12.7%) having a WOB Scale > 3 points (i.e., 1 point = 60; 2 points = 24; 3 points = 12; 4 points = 6; 5 points = 7; 6 points = 1; 7 points = 0). A respiratory rate level of 1 point (i.e., 1 to 20 bpm), occurred in 68 patients and only 3 (1.5%) had a WOB Scale > 3 points. Yet, when the respiratory rate level was 2 points (i.e., 21 to 25 bpm), which occurred in 28 patients, 3 (10.7%) had a WOB Scale > 3 points. Respiratory rate levels of 3 or 4 points (> 26 bpm) were associated with activation of at least one accessory respiratory muscle examined in 64% of the patients. Conclusions: A respiratory rate of 20 bpm or less predicted low WOB in most patients supporting a Reflex WOB Scale whereby respiratory accessory muscle activation is assessed only when the respiratory rate exceeds 20 bpm.

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With the emergence of COVID-19, healthcare worldwide is afflicted. While there is a spectrum of disease severity and presenting symptoms in infected patients, hypoxemic respiratory failure is the leading cause of mortality. Decision to intubate in rapidly deteriorating patients plays a significant role in determining patient outcome. In most patients, COVID-19 pneumonia initially causes worsening hypoxemia but minimal impairment of lung compliance which determines the work of breathing (WOB). Once adequate arterial oxygenation is established, a tool to determine WOB independent of oxygen needs can guide the decision to intubate for invasive mechanical ventilation (IMV). We monitored oxygen requirements and WOB in 14 patients admitted to our ICU with severe COVID-19 pneumonia. All patients had radiographic evidence of extensive lung disease, significant hypoxemia and multiple comorbidities. Hypoxemia was managed through non-invasive means, predominantly using highflow nasal cannula. To assess WOB, we used a scale developed by us assigning points to the respiratory rate and use of respiratory accessory muscles (range, 1 to 7) (Figure 1a). This was used at the time of initial evaluation and throughout the ICU stay. Out of 14 patients, 10 did not require intubation and recovered while 4 were intubated. We compared the maximum and average WOB of the non-intubated patients throughout their ICU stay with the WOB of intubated patients measured within 24 hours before intubation (Figure 1b). The maximal and the average WOB were higher in patients requiring intubation (mean ± SD, maximal 4.3 ± 0.9 vs 5.5 ± 1.0 pts, p = 0.028 and average 2.7 ± 0.6 vs 3.9 ± 0.5 pts, p = 0.002). Breakdown of the various WOB components demonstrated a statistically significantly higher maximal and average use of respiratory accessory muscles (assessed as their aggregate sum) and higher average respiratory rate in intubated patients. However, the maximal respiratory rate was not significantly higher. Our data illustrates the initial response to COVID-19 lung injury is tachypnea which can be sustained with adequate oxygenation. As lung injury progresses with more recruitment of respiratory accessory muscles, intubation for IMV becomes necessary. Our WOB scale becomes a useful tool to assist in the decision of when to intubate. It is simple to teach, apply and incorporate into routine patient assessment. We recommend routine and systematic WOB assessment to plan for orderly nonemergent intubations for IMV. Further refinement on the interventions recommended based on specific WOB level and other modifying factors is awaited.