Isoflurane vs. propofol for sedation in invasively ventilated patients with acute hypoxemic respiratory failure: an a priori hypothesis substudy of a randomized controlled trial

BACKGROUND: Acute hypoxemic respiratory failure (AHRF) is a leading concern in critically ill patients. Experimental and clinical data suggest that early sedation with volatile anesthestics may improve arterial oxygenation and reduce the plasma and alveolar levels of markers of alveolar epithelial injury and of proinflammatory cytokines. METHODS: An a priori hypothesis substudy of a multicenter randomized controlled trial (The Sedaconda trial, EUDRA CT Number 2016-004551-67). In the Sedaconda trial, 301 patients on invasive mechanical ventilation were randomized to 48 h of sedation with isoflurane or propofol in a 1:1 ratio. For the present substudy, patients with a ratio of arterial pressure of oxygen (PaO(2)) to inspired fraction of oxygen (FiO(2)), PaO(2)/FiO(2), of ≤ 300 mmHg at baseline were included (n = 162). The primary endpoint was the change in PaO(2)/FiO(2) between baseline and the end of study sedation. A subgroup analysis in patients with PaO(2)/FiO(2) ≤ 200 mmHg was performed (n = 82). RESULTS: Between baseline and the end of study sedation (48 h), oxygenation improved to a similar extent in the isoflurane vs. the propofol group (isoflurane: 199 ± 58 to 219 ± 76 mmHg (n = 70), propofol: 202 ± 62 to 236 ± 77 mmHg (n = 89); p = 0.185). On day seven after randomization, PaO(2)/FiO(2) was 210 ± 79 mmHg in the isoflurane group (n = 41) and 185 ± 87 mmHg in the propofol group (n = 44; p = 0.411). In the subgroup of patients with PaO(2)/FiO(2) ≤ 200 mmHg, PaO(2)/FiO(2) increase between baseline and end of study sedation was 152 ± 33 to 186 ± 54 mmHg for isoflurane (n = 37), and 150 ± 38 to 214 ± 85 mmHg for propofol (n = 45; p = 0.029). On day seven, PaO(2)/FiO(2) was 198 ± 69 mmHg in patients randomized to isoflurane (n = 20) and 174 ± 106 mmHg in patients randomized to propofol (n = 20; p = 0.933). Both for the whole study population and for the subgroup with PaO(2)/FiO(2) ≤ 200 mmHg, no significant between-group differences were observed for PaCO(2), pH and tidal volume as well as 30-day mortality and ventilator-free days alive. CONCLUSIONS: In patients with AHRF, inhaled sedation with isoflurane for a duration of up to 48 h did not lead to improved oxygenation in comparison to intravenous sedation with propofol. Trial registration The main study was registered in the European Medicines Agency’s EU Clinical Trial register (EudraCT), 2016-004551-67, before including the first patient. The present substudy was registered at German Clinical Trials Register (DRKS, ID: DRKS00018959) on January 7th, 2020, before opening the main study data base and obtaining access to study results.