Englert, Joshua A.

Abstract Introduction Sedation is routinely administered to facilitate comfort and tolerance of life support for critically ill adults dependent on invasive mechanical ventilation. Isoflurane, a widely used anesthetic during surgery, has properties that may also benefit ICU patients requiring continuous sedation. However, efficacy as a sedative and safety in this population is not well established. Methods We conducted two identically designed multicenter randomized trials, INSPIRE ICU1 and INSPIRE ICU2, at hospitals across the US. Ventilator-dependent adults were randomly assigned in a 1.5:1 ratio to receive either inhaled isoflurane or intravenous propofol as the first-line sedative for up to 48 ± 6 hours, targeting a sedation depth between Richmond agitation-sedation scale (RASS) -1 (drowsy) to -4 (responsive only to physical stimuli). Isoflurane was administered via an anesthetic conserving device (Sedaconda ACD-S). In both arms, opioids were permitted at the lowest dose required to achieve freedom from pain. The primary outcome was the percentage of time at target sedation level, assessed as a noninferiority outcome with pre-specified margin of 15%. Secondary outcomes included opioid exposure, wake-up time after end of treatment, time to extubation, and proportion of time with spontaneous breathing effort. Results A total of 470 combined participants were included in the two trials. In each trial, 142 patients were randomly assigned to isoflurane and 93 to propofol. In INSPIRE ICU1, percentage of time within target sedation depth was 77.1 [53.2, 89.9] % with isoflurane and 80.9 [58.2, 96.4] % with propofol (difference -1.5 [-8.9, >99] %; p < 0.01 for noninferiority). In INSPIRE ICU2, percentage of time within target sedation depth was 72.6 [66.4, 78.9] % with isoflurane and 74.5 [67.5, 81.5] % with propofol (difference -1.9 [-9.4, >99] %; p < 0.01 for noninferiority). In both trials, patients assigned to isoflurane received significantly less opioid, measured as fentanyl equivalents, during the treatment period. In INSPIRE ICU2, participants receiving isoflurane were significantly likelier to exhibit spontaneous breathing efforts, but this finding was not replicated in INSPIRE ICU1. There were no significant differences in time to wake-up or time to extubation between groups in either trial. No episodes of malignant hyperthermia or propofol infusion syndrome were reported. Adverse events were comparable in type and frequency between groups. Conclusions In two US multicenter trials, isoflurane was noninferior to propofol for maintaining target sedation depth in adults undergoing invasive ventilation, and was associated with significantly lower opioid exposure. (NCT05327296, NCT05312385) This abstract is funded by: Sedana Medical

Mechanical ventilation is necessary to support patients with acute lung injury, but also exacerbates injury through mechanical stress–activated signaling pathways. We show that stretch applied to cultured human cells, and to mouse lungs in vivo, induces robust expression of metallothionein, a potent antioxidant and cytoprotective molecule critical for cellular zinc homeostasis. Furthermore, genetic deficiency of murine metallothionein genes exacerbated lung injury caused by high tidal volume mechanical ventilation, identifying an adaptive role for these genes in limiting lung injury. Stretch induction of metallothionein required zinc and the zinc-binding transcription factor MTF1. We further show that mouse dietary zinc deficiency potentiates ventilator-induced lung injury, and that plasma zinc levels are significantly reduced in human patients who go on to develop acute respiratory distress syndrome (ARDS) compared with healthy and non-ARDS intensive care unit (ICU) controls, as well as with other ICU patients without ARDS. Taken together, our findings identify a potentially novel adaptive response of the lung to stretch and a critical role for zinc in defining the lung’s tolerance for mechanical ventilation. These results demonstrate that failure of stretch-adaptive responses play an important role in exacerbating mechanical ventilator–induced lung injury, and identify zinc and metallothionein as targets for lung-protective interventions in patients requiring mechanical ventilation.