Cardiorespiratory Dynamics During Prone Positioning for Severe Ards: A Retrospective Cohort Study.

Objectives:To elucidate the changes in cardiorespiratory dynamics during neuromuscular blockade and prone positioning and determine the associations between changes in cardiorespiratory dynamics following prone positioning and mortality. Design:Single center retrospective cohort study of patients admitted to the medical ICU between June 1, 2020 and September 1, 2022 who received prone positioning while mechanically ventilated. Results:Our final cohort consisted of 136 patients. Prone position was associated with an improvement in A-a gradient of 113 mmHg (95% CrI 78 - 149) between the pre-proning values and 10 hours post proning. Norepinephrine dose did not significantly change before and after prone positioning (Estimated difference: 0.04 mcg/min 95% CrI -1.00 - 1.07). For the outcome of 7-d mortality, there was a high probability that the baseline factors of increasing age, male sex, and higher baseline A-a gradient were associated with increased risk of death. Increased total vasopressor requirement and increased in PCO2 were associated with worse prognosis while a decrease in instantaneous heart rate and a decrease in heart rate variability were associated with improved prognosis. Conclusion:The immediate changes in prone positioning primarily impact respiratory physiology, with limited influence on circulatory parameters. Predictors of short-term mortality after prone positioning include both respiratory and cardiovascular parameters suggesting that extrapulmonary effects, such as improvement in right ventricular heart function, might also contribute to the benefit of prone positioning.