Depolarizing muscle relaxant, frequently used for rapid sequence endotracheal intubation in clinical field, has serious complication that occur intermittently, such as, hyperkalemia, increased intraoccular pressure and sudden cardiac arrest, especially in infants and adolescents. So the priming principle, i.e., the administration of a subparalyzing dose of a nondepolarizing muscle relaxant (priming dose) prior to the intubating dose, was developed for rapid sequence endotracheal intubation with nondepolarizing muscle relaxant. However, the priming dose sometimes causes complications, such as, swallowing difficulty or pulmonary aspiration, and this can cause patient discomfort or fatal complications. In this study we examined proper atracurium priming dose and evaluated possible complications of priming doses.

One hundred patients, scheduled for elective surgery were randomly allocated into five groups according to the priming dose used (group 1; 0, group 2; 0.03, group 3; 0.06, group 4; 0.09, group 5; 0.12 mg/kg). Patients received a midazolam and fentanyl injection, the base line TOF ratio was measured, and an intubating dose was given. We also examined changes in vital sign for 20 minutes after injection and noted the time when the twitch height became zero (onset time).

In group 1, the onset time was 107 ± 22.9 sec, and in groups 4 and 5, the onset times were 85.0 ± 15.6 and 69.9 ± 19.3 sec, respectively. But, in group 5, some patients showed tachycardia and swallowing difficulty.

The optimal priming dose of atracurium was determined as 0.09 mg/kg, in most cases, however patients sensitivity to the atracurium should be considered.