We have often observed arm withdrawal on administering rocuronium. This study was performed to determine the cause and to prevent this movement by mixing rocuronium with lidocaine or sodium bicarbonate.

Sixty-two patients, ASA I-II, were randomized into three groups for this blind, prospective study. After induction of anesthesia by thiopental sodium 0.5 mg/kg, each group received rocuronium 0.6 mg/kg alone (group R), with 2% (2 ml) lidocaine (group L), or rocuronium with an equivalent volume of 8.4% sodium bicarbonate (group S). Patients' responses to the injection were graded using a 4-point scale and the pHs of the mixtures were measured.

The incidence rate of arm withdrawal was more reduced in groups L (47%) and S (45%) than in group R (80%) (P < 0.05). Severe withdrawal movement (grade 3) did not occur in group S (0%).

The incidence and the degree of withdrawal movement in response to the injection of rocuronium were significantly reduced by mixing an equivalent volume of 8.4% sodium bicarbonate with rocuronium.