Isoflurane promotes early spontaneous breathing in ventilated intensive care patients: A post hoc subgroup analysis of a randomized trial

Inhaled sedation versus propofol in respiratory failure in the ICU (INSPiRE-ICU2): study protocol for a multicenter randomized controlled trial

BACKGROUND

Patients undergoing invasive mechanical ventilation often require pharmacologic sedation to facilitate tolerance of this life-sustaining intervention, but sedatives currently used in routine care have substantial limitations. Isoflurane is an inhaled volatile anesthetic with pharmacologic properties potentially suitable to sedation of ventilator-dependent critically ill patients, but need for specialized drug administration equipment has limited its use historically to general anesthesia in the operating theatre. This trial will evaluate isoflurane, administered using a novel drug delivery system, for sedation of ventilator-dependent adult intensive care unit (ICU) patients in the United States (US).

METHODS

The Inhaled Sedation versus Propofol in Respiratory Failure in the ICU (INSPiRE-ICU2) is a phase 3, multicenter, randomized, controlled, assessor-blinded non-inferiority trial that will evaluate efficacy and safety of inhaled isoflurane delivered via the Sedaconda ACD-S, compared to intravenous propofol, for sedation of mechanically ventilated adult ICU patients. At 16 US hospitals, 235 enrolled patients requiring continuous sedation during invasive mechanical ventilation will be randomized in 1.5:1 ratio to inhaled isoflurane or intravenous propofol for sedation. Treatment duration is expected to be at least 12 h and may last up to 48 (± 6) h or until no longer needing continuous sedation, whichever occurs first. The primary endpoint is the percentage of time sedation depth is maintained within the targeted range (Richmond Agitation Sedation Scale - 1 to - 4), in the absence of rescue sedation, during the treatment period. Secondary superiority outcomes include opioid exposure, wake-up time, cognitive recovery after end-of-treatment, and preservation of spontaneous breathing effort.

DISCUSSION

The INSPiRE-ICU2 trial will help determine the potential role of isoflurane for sedation of ventilator-dependent adult patients in the ICU. Key trial design features, including adoption of the estimand framework and blinded assessments of sedation depth, pain, and cognitive recovery, will ensure a rigorous evaluation of isoflurane for ICU sedation. TRIAL REGISTRATION: ClinicalTrials.gov, NCT05327296. First registered on April 5, 2022.

Challenges in Transitioning from Controlled to Assisted Ventilation in Acute Respiratory Distress Syndrome (ARDS) Management

Acute respiratory distress syndrome (ARDS) presents significant challenges in critical care, primarily due to its inflammatory nature, which leads to impaired gas exchange and respiratory mechanics. While mechanical ventilation (MV) is essential for patient support, the transition from controlled to assisted ventilation is complex and may be associated with intensive care unit-acquired weakness, ventilator-induced diaphragmatic dysfunction and patient self-inflicted lung injury. This paper explores the multifaceted challenges encountered during this transition, with a focus on respiratory effort, sedation management, and monitoring techniques, and investigates innovative approaches to enhance patient outcomes. The key strategies include optimizing sedation protocols, employing advanced monitoring methods like esophageal pressure measurements, and implementing partial neuromuscular blockade to prevent excessive respiratory effort. We also emphasize the importance of personalized treatment plans and the integration of artificial intelligence to facilitate timely transitions. By highlighting early rehabilitation techniques, continuously assessing the respiratory drive, and fostering collaboration among multidisciplinary teams, clinicians can improve the transition from controlled to assisted MV, ultimately enhancing recovery and long-term respiratory health in patients with ARDS.

Volatile anesthetics for lung- and diaphragm-protective sedation

This review explores the complex interactions between sedation and invasive ventilation and examines the potential of volatile anesthetics for lung- and diaphragm-protective sedation. In the early stages of invasive ventilation, many critically ill patients experience insufficient respiratory drive and effort, leading to compromised diaphragm function. Compared with common intravenous agents, inhaled sedation with volatile anesthetics better preserves respiratory drive, potentially helping to maintain diaphragm function during prolonged periods of invasive ventilation. In turn, higher concentrations of volatile anesthetics reduce the size of spontaneously generated tidal volumes, potentially reducing lung stress and strain and with that the risk of self-inflicted lung injury. Taken together, inhaled sedation may allow titration of respiratory drive to maintain inspiratory efforts within lung- and diaphragm-protective ranges. Particularly in patients who are expected to require prolonged invasive ventilation, in whom the restoration of adequate but safe inspiratory effort is crucial for successful weaning, inhaled sedation represents an attractive option for lung- and diaphragm-protective sedation. A technical limitation is ventilatory dead space introduced by volatile anesthetic reflectors, although this impact is minimal and comparable to ventilation with heat and moisture exchangers. Further studies are imperative for a comprehensive understanding of the specific effects of inhaled sedation on respiratory drive and effort and, ultimately, how this translates into patient-centered outcomes in critically ill patients.

Volatile Anesthetic Sedation for Critically Ill Patients

Volatile anesthetics have multiple properties that make them useful for sedation in the intensive care unit. The team-based approach to volatile anesthetic sedation leverages these properties to provide a safe and effective alternative to intravenous sedatives.

Ventilatory Effects of Isoflurane Sedation via the Sedaconda ACD-S versus ACD-L: A Substudy of a Randomized Trial

Devices used to deliver inhaled sedation increase dead space ventilation. We therefore compared ventilatory effects among isoflurane sedation via the Sedaconda ACD-S (internal volume: 50 mL), isoflurane sedation via the Sedaconda ACD-L (100 mL), and propofol sedation with standard mechanical ventilation with heat and moisture exchangers (HME). This is a substudy of a randomized trial that compared inhaled isoflurane sedation via the ACD-S or ACD-L to intravenous propofol sedation in 301 intensive care patients. Data from the first 24 h after study inclusion were analyzed using linear mixed models. Primary outcome was minute ventilation. Secondary outcomes were tidal volume, respiratory rate, arterial carbon dioxide pressure, and isoflurane consumption. In total, 151 patients were randomized to propofol and 150 to isoflurane sedation; 64 patients received isoflurane via the ACD-S and 86 patients via the ACD-L. While use of the ACD-L was associated with higher minute ventilation (average difference (95% confidence interval): 1.3 (0.7, 1.8) L/min, p < 0.001), higher tidal volumes (44 (16, 72) mL, p = 0.002), higher respiratory rates (1.2 (0.1, 2.2) breaths/min, p = 0.025), and higher arterial carbon dioxide pressures (3.4 (1.2, 5.6) mmHg, p = 0.002), use of the ACD-S did not significantly affect ventilation compared to standard mechanical ventilation and sedation. Isoflurane consumption was slightly less with the ACD-L compared to the ACD-S (-0.7 (-1.3, 0.1) mL/h, p = 0.022). The Sedaconda ACD-S compared to the ACD-L is associated with reduced minute ventilation and does not significantly affect ventilation compared to a standard mechanical ventilation and sedation setting. The smaller ACD-S is therefore the device of choice to minimize impact on ventilation, especially in patients with a limited ability to compensate (e.g., COPD patients). Volatile anesthetic consumption is slightly higher with the ACD-S compared to the ACD-L.

Increased Respiratory Drive after Prolonged Isoflurane Sedation: A Retrospective Cohort Study

Low-dose isoflurane stimulates spontaneous breathing. We, therefore, tested the hypothesis that isoflurane compared to propofol sedation for at least 48 h is associated with increased respiratory drive in intensive care patients after sedation stop. All patients in our intensive care unit receiving at least 48 h of isoflurane or propofol sedation in 2019 were included. The primary outcome was increased respiratory drive over 72 h after sedation stop, defined as an arterial carbon dioxide pressure below 35 mmHg and a base excess more than −2 mmol/L. Secondary outcomes were acid–base balance and ventilatory parameters. We analyzed 64 patients, 23 patients sedated with isoflurane and 41 patients sedated with propofol. Patients sedated with isoflurane were about three times as likely to show increased respiratory drive after sedation stop than those sedated with propofol: adjusted risk ratio [95% confidence interval]: 2.9 [1.3, 6.5], p = 0.010. After sedation stop, tidal volumes were significantly greater and arterial carbon dioxide partial pressures were significantly lower, while respiratory rates did not differ in isoflurane versus propofol-sedated patients. In conclusion, prolonged isoflurane use in intensive care patients is associated with increased respiratory drive after sedation stop. Beneficial effects of isoflurane sedation on respiratory drive may, thus, extend beyond the actual period of sedation.