[Intubation conditions and circulatory effects 90 seconds after a divided mivacurium dose with three different TIVA...

The aim of this study was to compare the intubating conditions of a mivacurium-induced neuromuscular block 90 s after a divided administration with three different methods of induction of anaesthesia.

After approval by the local ethics committee, we investigated 36 ASA I and II patients undergoing a 2-h scheduled, elective surgery, in whom a TIVA was induced by one of three different drugs, edomidate, methohexital or propofol. After stable anaesthesia was reached, 0.15 mg/kg and 0.1 mg/kg of mivacurium, spaced 30 s apart, was injected. Endotracheal intubation was performed 90 s after the first micacurium injection and the intubation conditions were graded (1: excellent, 2: good, 3: poor; 4: impossible). The neuromuscular function was stimulated every 20 s by a nerve stimulator in a train-of-four (TOF) pattern, and the time to complete distinction of a TOF response as well as the time of reoccurrence of the first twitch was taken. A minute prior to injection of the relaxant and every minute for 5 min, the systolic and diastolic blood pressure, mean arterial pressure (MAP) and heart rate were measured. The neuromuscular block was maintained with a mivacurium infusion on a level of one twitch response. After cessation of the mivacurium infusion we recorded the time of reappearance of the second, third and fourth twitch responses.

All patients could be intubated 90 s after mivacurium except for one, who was excluded for abnormal difficult intubation conditions. The etomidate group had significantly (chi 2 test) worse intubation grades than the methohexital group. In none of the groups did we observe any significant cardiovascular response due to the mivacurium injection, neither in blood pressure nor in heart rate. All groups showed similar onset of the maximal neuromuscular block (4 +/- 1.8 min) and recovery of the first TOF reaction (11.3 +/- 3.4 min). There was no difference in recovery from neuromuscular block maintained by infusion at the end of surgery.

A dose of mivacurium 3.57 times the ED95 does not produce any haemodynamic instability, if it is divided into two parts to induce a TIVA. After this dose, all patients could be safely intubated within 90 s. A prolongation of the neuromuscular block after higher mivacurium doses could not be seen, and this dose did not produce a more rapid onset of the maximal block in any group. The time for recovery from a mivacurium infusion did not differ among the groups. Etomidate, due to its short half-life, seems not ideal for induction of a TIVA together with mivacurium in the dosage used. Mivacurium meets the demands of good controllability as required for a TIVA and can be recommended for a 90-s injection-intubation interval as well as for maintenance of the neuromuscular block.