Trajectory of PaO <sub>2</sub> /FiO <sub>2</sub> Ratio in Shock After Angiotensin II
Patrick M. Wieruszewski, Patrick J. Coleman, Andrea R. Levine, Danielle Davison, Nathan J. Smischney, Shravan Kethireddy, Yanglin Guo, Jason Hecht, Michael Mazzeffi, Jonathan H. Chow
Abstract
Introduction High-dose catecholamines can impair hypoxic pulmonary vasoconstriction and increase shunt fraction. We aimed to determine if Angiotensin II (Ang-2) is associated with improved PaO 2 /FiO 2 and SpO 2 /FiO 2 in patients in shock. Methods Adult patients at four tertiary care centers and one community hospital in the United States who received Ang-2 from July 2018-September 2020 were included in this retrospective, observational cohort study. PaO 2 , SpO 2 , and FiO 2 were measured at 13 timepoints during the 48-h before and after Ang-2 initiation. Piecewise linear mixed models of PaO 2 /FiO 2 and SpO 2 /FiO 2 were created to evaluate hourly changes in oxygenation after Ang-2 initiation. The difference in the proportion of patients with PaO 2 /FiO 2 ≤ 300 mm Hg at the time of Ang-2 initiation and 48 h after was also examined. Results The study included 254 patients. In the 48 h prior to Ang-2 initiation, oxygenation was significantly declining (hourly PaO 2 /FiO 2 change −4.7 mm Hg/hr, 95% CI − 6.0 to −3.5, p < .001; hourly SpO 2 /FiO 2 change −3.1/hr, 95% CI−3.7 to −2.4, p < .001). Ang-2 treatment was associated with significant improvements in PaO 2 /FiO 2 and SpO 2 /FiO 2 in the 48-h after initiation (hourly PaO 2 /FiO 2 change +1.5 mm Hg/hr, 95% CI 0.5-2.5, p = .003; hourly SpO 2 /FiO 2 change +0.9/hr, 95% CI 0.5-1.2, p < .001). The difference in the hourly change in oxygenation before and after Ang-2 initiation was also significant ( p interaction < 0.001 for both PaO 2 /FiO 2 and SpO 2 /FiO 2 ). This improvement was associated with significantly fewer patients having a PaO 2 /FiO 2 ≤ 300 mm Hg at 48 h compared to baseline (mean difference −14.9%, 95% CI −25.3% to −4.6%, p = .011). Subgroup analysis found that patients with either a baseline PaO 2 /FiO 2 ≤ 300 mm Hg or a norepinephrine-equivalent dose requirement >0.2 µg/kg/min had the greatest associations with oxygenation improvement. Conclusions Ang-2 is associated with improved PaO 2 /FiO 2 and SpO 2 /FiO 2 . The mechanisms for this improvement are not entirely clear but may be due to catecholamine-sparing effect or may also be related to improved ventilation-perfusion matching, intrapulmonary shunt, or oxygen delivery.