Effect of muscle relaxants on heart rate, arterial pressure, intubation conditions and onset of neuromuscular block in patients undergoing valve surgery.

Sixty six patients undergoing elective valve surgery were randomized to receive rocuronium bromide 0.6 mg/Kg (Group R, n=22), pancuronium bromide 0.1 mg/Kg (Group P, n= 22) and vecuronium bromide 0.1 mg/Kg (Group V, n=22), Measurements of heart rate and arterial pressure (systolic, diastolic and mean) were noted at the following stages: 1) baseline when haemodynamics were stable for 2 minutes after induction of anaesthesia (2) one, (3) three, (4) five minutes after administration of muscle relaxants, (5) One, (6) three, and (7) five minutes after intubation. In group R, the heart rate decreased 5 min after injection of muscle relaxant from 93.9 +/- 21.3 to 82.4 +/- 20.7 beats/min (p<0.001). However, it increased to 128.3 +/- 25.8 beats/min (p<0.001) following intubation and returned to baseline at 5 min after intubation. In group P, heart rate increased from 98.8 +/- 32.6 to 109.6 +/- 32.7 beats/min (p<0.001), 1 min after injection of pancuronium and this increase persisted throughout the study period. In group V, heart rate decreased from 99.9 +/- 22.3 to 83.8 +/-19.6 beats/min (p<0.001) at 5 min after injection of the drug. It increased to 118.6 +/- 22.4 beats/min (p<0.001), 1 min after intubation and returned to baseline at 5 min after intubation. The decrease in heart rate in group R and V was accompanied by a significant decrease in systolic, diastolic and mean arterial pressure. In group P, only the systolic pressure decreased significantly at 5 min after injection of the drug. Intubation was accompanied by a significant increased in systolic, diastolic and mean arterial pressure in all the groups. Excellent intubation conditions (intubation score 3-4) were observed with all the three drugs, however, there were number of patients in group P who showed diaphragmatic movement during intubation. Onset of action of muscle relaxant, was fastest with rocuronium (group R=132.7 +/- 0.3 sec, P=182.6 +/- 68.5 sec, V= 144.8 +/- 46.1 sec, Group P vs Group R). To conclude, pancuronium causes significant increase in heart rate and should be preferred in patients with regurgitant lesions having slower baseline heart rate. Vecuronium and rocuronium decrease the heart rate and should be preferred in patient with faster baseline heart rate. In terms of intubating conditions rocuronium and vecuronium provide best conditions, but onset is faster with rocuronium.