Variation in postinduction hypotension incidence and patient characteristics depending on the definition used

BACKGROUND: Postinduction hypotension is common during general anaesthesia and is associated with adverse postoperative outcomes. However, the number of definitions in use and their impact on incidence is unclear. OBJECTIVE: To determine how different literature-derived definitions impact the reported incidence of postinduction hypotension and to explore overlap and discrepancies in patient characteristics when applied to a prospective cohort. DESIGN: Systematic literature search combined with a prospective observational cohort study. SETTING: The literature search covered studies published between January 2013 and April 2024. The observational study was a single-centre study conducted between January 2019 and July 2023 at a university hospital in the Netherlands. PATIENTS: A total of 720 adult patients undergoing elective non-cardiac surgery under general anaesthesia were included and their blood pressure was measured continuously before and during induction. MAIN OUTCOME MEASURES: Primary outcomes were the incidence of postinduction hypotension according to the definitions obtained from the literature, and the degree of overlap and differences in patient characteristics among three commonly used thresholds: mean arterial pressure <65 mmHg, >30% decrease in mean arterial pressure from baseline, and systolic arterial pressure <90 mmHg. RESULTS: Ninety-two studies were identified, reporting 56 unique definitions. Incidence of postinduction hypotension in the cohort varied from 10 to 89% depending on the definition used. Mean arterial pressure <65 mmHg was the most frequently reported threshold. Substantial discrepancies existed between the thresholds of mean arterial pressure <65 mmHg, >30% decrease in mean arterial pressure from baseline, and systolic arterial pressure <90 mmHg, with 32% of patients classified as hypotensive by only one threshold. Patients experiencing >30% decrease in mean arterial pressure from baseline were significantly older, had more (cardiovascular) comorbidities, and had higher ASA physical status classifications. Patients with mean arterial pressure <65 mmHg or systolic arterial pressure <90 mmHg generally had lower baseline and pre-induction blood pressure than non-hypotensive patients. CONCLUSIONS: Current heterogeneity in postinduction hypotension definitions leads to substantial variations in reported incidence and identifies clinically different patient groups. A standardised definition is needed to improve comparability between studies and strengthen clinical application. Future research should focus on outcome-driven thresholds for postinduction hypotension. TRIAL REGISTRATION: Overview of Medical Research in the Netherlands (OMON), identifier NL7810.