Background: The evidence base for the widely accepted standard regimen of succinylcholine for rapid sequence induction (1.0 mg kg^-1) remains unclear.

Methods: We performed a systematic review and meta-analysis of randomized trials comparing any succinylcholine regimen with the standard regimen (1.0 mg kg^-1) and reporting on intubating conditions and/or apnoea times. Results were expressed as absolute risk differences (ARD) for dichotomous data and mean differences (MD) for continuous data.

Results: We retrieved six trials with relevant data of 864 patients (ASA 1 or 2, aged 18-65 years, body mass index < 30 kg m^-2). Four regimens (0.3, 0.4, 0.5, 0.6 mg kg^-1) were compared with 1.0 mg kg^-1 in at least three trials each, and three (0.8, 1.5, 2 mg kg^-1) in one each. With 0.3 to 0.5 mg kg^-1, the likelihood of excellent intubating conditions was significantly decreased (ARD-22% to-67%). With 0.3 and 0.4 mg kg^-1, but not with 0.5, 0.6, 0.8, 1.5 and 2.0 mg kg^-1, the likelihood of unacceptable intubating conditions was significantly increased (ARD + 22% and + 32%, respectively). With 2.0 mg kg^-1, but not with 0.8 or 1.5 mg kg^-1, the likelihood of excellent intubating conditions was significantly increased (ARD + 23%). Apnoea times were significantly shorter with regimens ≤0.8 mg kg^-1 (MD-1.0 to-3.4 min) but were not reported with 1.5 or 2.0 mg kg^-1.

Conclusions: With succinylcholine regimens ≤0.5 mg kg^-1, excellent intubating conditions are less likely and apnoea times are shorter, compared with 1 mg kg^-1. With 0.3 and 0.4 mg kg^-1, unacceptable intubating conditions are more common. Succinylcholine 1.5 mg kg^-1 does not produce more often excellent conditions compared with 1 mg kg^-1, while 2.0 mg kg^-1 does, but the database with these regimens is weak and apnoea times remain unknown. Limited information size and strong statistical heterogeneity decrease the certainty of the evidence.