The degree of respiratory depression according to the effect-site concentration in remimazolam target-controlled infusion

BACKGROUND Remimazolam is not only associated with a lower incidence of respiratory depression than propofol but also in itself has the risk of respiratory depression. OBJECTIVE We investigated respiratory depression following remimazolam infusion, targeting different effect-site concentrations using target-controlled infusion. DESIGN A prospective, double-blind, randomised controlled study. SETTING Tertiary hospital, Suwon, South Korea, from April 2022 to November 2022. PARTICIPANTS One hundred and seven patients scheduled for general anaesthesia were randomised into three groups targeting remimazolam effect-site concentrations of 500 (RMZ-500) ( n = 36), 1000 (RMZ-1000) ( n = 35) and 1500 ng ml −1 (RMZ-1500) ( n = 36). INTERVENTIONS Remimazolam was solely infused for 10 min according to target effect-site concentrations. According to the degree of SpO 2 decrease, oxygen desaturations were managed with the following respiratory supports: jaw-thrust for SpO 2 less than 97%, 100% oxygen delivery for SpO 2 less than 93% and assisted ventilation for SpO 2 less than 90%. MAIN OUTCOME MEASURES The incidence of each respiratory support, along with respiratory variables (at baseline, 5 min and 10 min after remimazolam infusion) and loss of consciousness were observed for 10 min after remimazolam target-controlled infusion. RESULTS Both RMZ-1000 and RMZ-1500 required more frequent respiratory support than RMZ-500 (both P < 0.001), with nearly identical frequencies between RMZ-1000 and RMZ-1500. In terms of respiratory support, the incidence of assisted ventilation was significantly lower in RMZ-500 (2.8%) than RMZ-1000 (48.6%) and RMZ-1500 (50%) ( P < 0.001). RMZ-1000 and RMZ-1500 achieved loss of consciousness in all patients; RMZ-500 only achieved loss of consciousness in 86.1% of patients ( P = 0.010). In patients who maintained spontaneous respiration, tidal volume decreased by 41 to 48% and respiratory rate increased by 118 to 158% at 5 and 10 min, significantly compared to baseline in all groups ( P < 0.001). CONCLUSIONS Remimazolam infusion, like that of other benzodiazepines, led to respiratory depression, which was more prominent at higher target effect-site concentrations. Therefore, appropriate countermeasures should be developed to prevent oxygen desaturation. TRIAL REGISTRATION CRIS (https://cris.nih.go.kr), identifier: KCT0006952