Introduction: This study aimed to determine the age-specific bolus dose of remifentanil (ED50) to facilitate tracheal intubation without the use of neuromuscular blocking agents.
Methods: ASA 1–2 subjects were recruited into three groups of 0–3 months (group I), 4–12 months (group II), and 1–3 years (group III) of age. A sequential up-and-down design determined the remifentanil bolus dose, which was initially started at 3 mcg·kg−1 and adjusted in 1 mcg·kg−1 increments (range 1–6 mcg·kg−1). Following pretreatment with glycopyrrolate 10 μg·kg−1 and an induction dose of propofol 5 mg·kg−1, remifentanil was administered with a blinded study investigator commencing tracheal intubation after 60 s. After tracheal intubation, the time to return of spontaneous ventilation was measured. Logistic regression was used to predict the ED50 and ED95 of remifentanil.
Results: Sixty-four subjects were recruited. Tracheal intubation was successful at first attempt in over 90% of subjects in each age group. Satisfactory intubating conditions were achieved in 85%, 63%, and 75% of subjects in groups I, II, and III, respectively. The logistic regression results for ED50 (95% CI) were 3.1 (2.5–3.8), 3.7 (2.0–5.4), and 3.0 (2.1–3.9) mcg·kg−1, and ED95 (95% CI) were 5.0 (3.0–7.0), 9.4 (1.5–17.4), and 5.6 (2.9–8.4) mcg·kg−1 in groups I, II, and III, respectively. Infants aged 4–12 months (group II) showed a marked variability in dose response; however, the mean ED50 and ED95 were not different to groups I and III. Older children had a longer duration of apnea than infants, 331 vs 180 s (P < 0.05).
Discussion: The ED50 of remifentanil for tracheal intubation was higher in all age groups than previously reported. Ideal intubating conditions were achieved in 50% of subjects with remifentanil doses of 3.1–3.7 mcg·kg−1. Higher doses will be required for higher success rates and with anticholinergic pretreatment, doses of up to 6 mcg·kg−1 were tolerated, without adverse effects, in two patients. Further investigation of the variability in dose response in infants and assessment of the safety this technique is warranted.