Outcomes in randomized trials of tracheal intubation in the critically ill: A systematic review

Background: Critically ill patients undergoing tracheal intubation experience a high rate of peri-intubation adverse events. The lack of consensus on outcome selection hinders comparisons across studies. Therefore, we conducted this review to systematically identify outcome measures reported in randomized controlled trials investigating tracheal intubation in critically ill adults. Methods: We searched PubMed, Embase, and Cochrane Central Register of Controlled Trials from inception through July 5, 2025, for randomized controlled trials published in high-impact journals enrolling critically ill adults undergoing tracheal intubation. We described primary and secondary outcomes, categorized them into four domains (clinical, physiological, procedural, and other), and documented associations between interventions and primary outcomes. Results: We identified 43 randomized controlled trials, with 15 primary and 46 secondary outcomes. Hypoxemia was the most frequently reported primary outcome (12 studies, 28%), followed by first-pass success (11 studies, 26%), cardiovascular instability/collapse (3 studies, 6.9%). Common secondary outcomes were hypoxemia (26 studies, 60%) and mortality (21 studies, 49%), followed by intubation difficulty (20/43, 47%), cardiovascular instability/collapse (17/43, 40%), and the use and duration of organ support (16/43, 37%). Hypoxemia was the most common outcome in studies testing preoxygenation techniques (10 of 43, 23%), whereas first-pass success was predominant in those assessing laryngoscope types (7 of 43, 16%). Conclusions: Tracheal intubation trials have predominantly prioritized short-term physiological stability and procedural success, with minimal attention to patient-centered recovery outcomes. Adoption of a core outcome set is essential. Clinical trials registration: International Prospective Register of Systematic Reviews (CRD420251081056).