Effect of decreasing PEEP on hyperinflation and collapse in COVID-19: A computed tomography study

BACKGROUND

High positive end-expiratory pressure (PEEP>10 cmH2O) is commonly used in mechanically ventilated hypoxemic patients with COVID-19. However, some epidemiological and physiological studies indirectly suggest that using a lower PEEP may primarily and beneficially decrease lung hyperinflation in this population. Herein we directly quantified the effect of decreasing PEEP from 15 to 10 cmH2O on lung hyperinflation and collapse in mechanically ventilated patients with COVID-19.

METHODS

Twenty mechanically ventilated patients with COVID-19 underwent a lung computed tomography (CT) at PEEP of 15 and 10 cmH2O. The effect of decreasing PEEP on lung hyperinflation and collapse was directly quantified as the change in the over-aerated (density below -900 HU) and non-aerated (density above -100 HU) lung volumes. The net response to decreasing PEEP was computed as the sum of the change in those two compartments and expressed as the change in the "pathologic" lung volume. If the pathologic lung volume decreased (i.e., hyperinflation decreased more than collapse increased) when PEEP was decreased, the net response was considered positive; otherwise, it was considered negative.

RESULTS

On average, the ratio of arterial tension to inspiratory fraction of oxygen (PaO2:FiO2) in the overall study population was 137 (119-162) mmHg. In 11 (55%) patients, the net response to decreasing PEEP was positive. Their over-aerated lung volume decreased by 159 (98-186) mL, while the non-aerated lung volume increased by only 58 (31-91) mL. In nine (45%) patients, the net response was negative. Their over-aerated lung volume decreased by 46 (18-72) mL, but their non-aerated lung volume increased by 107 (44-121) mL.

CONCLUSION

In 20 patients with COVID-19 the net response to decreasing PEEP, as assessed with lung CT, was variable. In approximately half of them it was positive (and possibly beneficial), with a decrease in hyperinflation larger than the increase in collapse.

REVersal of nEuromusculAr bLocking Agents in Patients Undergoing General Anaesthesia (REVEAL Study)

Background: Neuromuscular blocking agent (NMBA) monitoring and reversals are key to avoiding residual curarization and improving patient outcomes. Sugammadex is a NMBA reversal with favorable pharmacological properties. There is a lack of real-world data detailing how the diffusion of sugammadex affects anesthetic monitoring and practice. Methods: We conducted an electronic health record analysis study, including all adult surgical patients undergoing general anesthesia with orotracheal intubation, from January 2016 to December 2019, to describe changes and temporal trends of NMBAs and NMBA reversals administration. Results: From an initial population of 115,046 surgeries, we included 37,882 procedures, with 24,583 (64.9%) treated with spontaneous recovery from neuromuscular block and 13,299 (35.1%) with NMBA reversals. NMBA reversals use doubled over 4 years from 25.5% to 42.5%, mainly driven by sugammadex use, which increased from 17.8% to 38.3%. Rocuronium increased from 58.6% (2016) to 94.5% (2019). Factors associated with NMBA reversal use in the multivariable analysis were severe obesity (OR 3.33 for class II and OR 11.4 for class III obesity, p-value < 0.001), and high ASA score (OR 1.47 for ASA III). Among comorbidities, OSAS, asthma, and other respiratory diseases showed the strongest association with NMBA reversal administration. Conclusions: Unrestricted availability of sugammadex led to a considerable increase in pharmacological NMBA reversal, with rocuronium use also rising. More research is needed to determine how unrestricted and safer NMBA reversal affects anesthesia intraoperative monitoring and practice.

Lung response to prone positioning in mechanically-ventilated patients with COVID-19

BACKGROUND

Prone positioning improves survival in moderate-to-severe acute respiratory distress syndrome (ARDS) unrelated to the novel coronavirus disease (COVID-19). This benefit is probably mediated by a decrease in alveolar collapse and hyperinflation and a more homogeneous distribution of lung aeration, with fewer harms from mechanical ventilation. In this preliminary physiological study we aimed to verify whether prone positioning causes analogue changes in lung aeration in COVID-19. A positive result would support prone positioning even in this other population.

METHODS

Fifteen mechanically-ventilated patients with COVID-19 underwent a lung computed tomography in the supine and prone position with a constant positive end-expiratory pressure (PEEP) within three days of endotracheal intubation. Using quantitative analysis, we measured the volume of the non-aerated, poorly-aerated, well-aerated, and over-aerated compartments and the gas-to-tissue ratio of the ten vertical levels of the lung. In addition, we expressed the heterogeneity of lung aeration with the standardized median absolute deviation of the ten vertical gas-to-tissue ratios, with lower values indicating less heterogeneity.

RESULTS

By the time of the study, PEEP was 12 (10-14) cmH2O and the PaO2:FiO2 107 (84-173) mmHg in the supine position. With prone positioning, the volume of the non-aerated compartment decreased by 82 (26-147) ml, of the poorly-aerated compartment increased by 82 (53-174) ml, of the normally-aerated compartment did not significantly change, and of the over-aerated compartment decreased by 28 (11-186) ml. In eight (53%) patients, the volume of the over-aerated compartment decreased more than the volume of the non-aerated compartment. The gas-to-tissue ratio of the ten vertical levels of the lung decreased by 0.34 (0.25-0.49) ml/g per level in the supine position and by 0.03 (- 0.11 to 0.14) ml/g in the prone position (p < 0.001). The standardized median absolute deviation of the gas-to-tissue ratios of those ten levels decreased in all patients, from 0.55 (0.50-0.71) to 0.20 (0.14-0.27) (p < 0.001).

CONCLUSIONS

In fifteen patients with COVID-19, prone positioning decreased alveolar collapse, hyperinflation, and homogenized lung aeration. A similar response has been observed in other ARDS, where prone positioning improves outcome. Therefore, our data provide a pathophysiological rationale to support prone positioning even in COVID-19.