Major Adverse Events Associated With Emergency Endotracheal Intubation in Adult Patients: A Systematic Review.

Emergency endotracheal intubation (ETI) is among the highest-risk procedures performed in acutely ill adults, yet the burden, spectrum, and determinants of major peri-intubation adverse events remain unevenly characterised across settings. This systematic review synthesises contemporary primary evidence on major adverse events complicating emergency ETI in adults. PubMed/MEDLINE, Embase, Scopus, Web of Science, and ClinicalTrials.gov were searched from January 2021 to July 2026 for peer-reviewed primary studies (randomised trials, prospective or retrospective cohorts, and case-control studies) reporting major adverse events after non-elective ETI in adults outside the operating theatre. Reviews, meta-analyses, protocols, abstracts, editorials, letters, and preprints were excluded. Data were extracted in duplicate; observational studies were appraised with the Newcastle-Ottawa Scale and randomised trials with the Cochrane RoB 2 tool. Findings were synthesised narratively in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) 2020. Fourteen studies comprising approximately 61,430 intubation encounters across 14 countries were included. At least one major adverse event was reported in 14-52% of emergency intubations, with composite event rates of 45.2% in a 29-country cohort and 32.3% in a national emergency department cohort. Cardiovascular instability was consistently the dominant event (20.0-43.4%), followed by severe hypoxaemia (9.3-18.5%) and peri-intubation cardiac arrest (1.0-5.4%). Risk rose steeply with each additional laryngoscopy attempt (adjusted odds ratio: 4.4 for two attempts and 13.9 for four) and with pre-intubation hypotension, hypoxaemia, acidaemia, and elevated lactate. Major adverse events were independently associated with mortality. Major adverse events complicate a substantial minority to majority of emergency intubations in adults and are driven principally by pre-existing physiological derangement and repeated attempts. Standardised outcome definitions and pre-intubation haemodynamic optimisation warrant priority attention.