Trajectory of PaO/FiO Ratio in Shock After Angiotensin II.

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/FiO and SpO/FiO 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, SpO, and FiO were measured at 13 timepoints during the 48-h before and after Ang-2 initiation. Piecewise linear mixed models of PaO/FiO and SpO/FiO were created to evaluate hourly changes in oxygenation after Ang-2 initiation. The difference in the proportion of patients with PaO/FiO ≤ 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/FiO change -4.7 mm Hg/hr, 95% CI - 6.0 to -3.5,  < .001; hourly SpO/FiO change -3.1/hr, 95% CI-3.7 to -2.4,  < .001). Ang-2 treatment was associated with significant improvements in PaO/FiO and SpO/FiO in the 48-h after initiation (hourly PaO/FiO change +1.5 mm Hg/hr, 95% CI 0.5-2.5,   =  .003; hourly SpO/FiO change +0.9/hr, 95% CI 0.5-1.2,  < .001). The difference in the hourly change in oxygenation before and after Ang-2 initiation was also significant ( < 0.001 for both PaO/FiO and SpO/FiO). This improvement was associated with significantly fewer patients having a PaO/FiO ≤ 300 mm Hg at 48 h compared to baseline (mean difference -14.9%, 95% CI -25.3% to -4.6%,   =  .011). Subgroup analysis found that patients with either a baseline PaO/FiO ≤ 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/FiO and SpO/FiO. 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.