UPPER AIRWAY-OBSTRUCTION DURING MIDAZOLAM SEDATION - MODIFICATION BY NASAL CPAP

We examined the depressant effect of midazolam on respiration in 21 he althy women undergoing lower abdominal surgery with spinal anaesthesia . Airway gas flow, airway pressure, and the sound of snoring were reco rded together with arterial oxygen saturation (SpO(2)) After spinal an aesthesia was established, subjects were deeply sedated with pentazoci ne 15 mg followed by incremental doses of midazolam 1 mg iv up to 0.1 mg . kg(-1). When SpO(2) decreased to <90% or snoring and/or apnoea wa s observed, continuous positive airway pressure applied through the no se (nasal CPAP) was increased until the respiratory deterioration war reversed. While one patient remained free of respiratory events, the o ther 20 patients were successfully treated with nasal CPAP restoring n ormal SpO(2) (95.5 +/- 1.7%) without snoring. Stepwise reduction of na sal CPAP determined the minimally effective CPAP to prevent snoring to be 5.1 +/- 2.1 cm H2O. Further reduction of nasal CPAP induced snorin g in 15 patients and obstructive apnoea in five patients with the latt er accompanied by a severe reduction of SpO(2) (824 +/- 6.1%). Patient s with apnoea were older than those who snored (P < 0.05). We conclude that upper airway obstruction contributes considerably to decreases i n SpO(2) during midazolam sedation for spinal anaesthesia.