Characteristics and risk factors associated with mortality during the first cycle of prone secondary to ARDS due to SARS-CoV-2 pneumonia.

Introduction: Early identification of patients with failure to prone position allows other treatments which could decrease mortality. The objective of our study was: describe the characteristics, behavior of oxygenation and pulmonary mechanics in mechanically ventilated patients with ARDS due to SARS-CoV- 2 treated with prone position. Secondary objectives were identify independent determinants of mortality; particularly, number of prone cycles associated with mortality. Methods: It was a prospective study. All patients with <150 mmHg PaO 2 /FiO 2 ratio and prone position were included and classified according to the PaO 2 /FiO 2 behavior after the first prone cycle: 1) No increase, 2) Increase 50%. The number of prone cycles was also recorded. Baseline characteristics, severity scores, respiratory mechanics and PaO 2 /FiO 2 ratio behavior were compared between survivors and non-survivors.Statistical analysis was performed by Mann Whitney's, Chi² Test and Wilcoxon range tests. Independent factors associated with in-hospital mortality were identified by means of Cox regression. Results: 273 were treated with prone position over 18 months. The baseline PaO 2 /FiO 2 was 116 [97-135] mmHg (115 [94-136] in survivors versus 117 [98-134] in non-survivors; p=0.50). After prone position, 22 patients (8%) had the same value in PaO 2 /FiO 2 ratio ; 46 patients (16%) showed an increase equal less or equal 25%; in 55 patients (21%) there was an increase between 25 and 50% over baseline; and in 150 patients (55%) the rise was greater than 50%. Mortality was 86%, 87%, 72%, 50% respectively. (p<0.001). Having debuted with PaO 2 /FiO 2, ratio < 100 mmHg did not imply that the patient was refractory to the prone position.Of the 273 patients, 127 (46%) required 1 prone cycle, 57 (20%) 2 cycles, 50 (17%) 3 cycles, 17 (6%) had 4 cycles and 19 (7%) 5 or more cycles. Mortality was 55%, 70%, 70%, 82%, and 70% respectively (p<0.001). Factors independently associated with mortality were the percentage of increase in PaO 2/ FiO2 after 24 hours in prone, age, and the number of prone cycles. Conclusions: Older patients unable to improve PaO 2 /FiO 2 after 24 hours in prone and who require more than 1 prone cycle, may be candidates for other treatments for refractory hypoxemia.