Remifentanil requirement for acceptable intubation conditions with two different doses of ketamine without a neuromuscular blocking agent in pediatric patients.

The optimal remifentanil concentration for improving intubation conditions when intubation is performed without neuromuscular blocking agents (NMBAs) but with ketamine as an induction agent remains unknown. Here, we aimed to identify the effective bolus doses of remifentanil required to achieve acceptable intubation conditions upon anesthesia induction with 1 or 2 mg/kg ketamine without NMBAs.In this prospective, double-blinded, randomized up-down sequential allocation study, we enrolled pediatric patients aged 3-12 years undergoing general anesthesia for inguinal hernia surgery. The patients were randomly allocated to one of two groups to receive either ketamine 1.0 mg/kg (K1 group) or 2.0 mg/kg (K2 group) intravenously until seven success-failure pairs were achieved. The remifentanil dose for each patient was determined using the modified Dixon's up-and-down method with an initial dose of 2.5 μg/kg and a step size of 0.5 μg/kg.In total, 51 patients (22 in the K1 group and 29 in the K2 group) were enrolled. The effective dose (ED)50s of remifentanil for obtaining clinically acceptable intubation conditions under anesthesia induction with ketamine but without NMBAs was 3.2 μg/kg in the K1 group and 1.6 μg/kg in the K2 group. High-dose remifentanil with 1 mg/kg ketamine was associated with more severe chest wall rigidity and lower mean blood pressure and heart rate than was low-dose remifentanil with 2 mg/kg ketamine.The ED50 of remifentanil required for clinically acceptable intubation conditions with anesthesia induction using 1 mg/kg ketamine without NMBAs in pediatric patients was twice that when using 2 mg/kg ketamine. The combination of 2 mg/kg ketamine and remifentanil was better at preventing chest wall rigidity.