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DEPTH OF ANAESTHESIA DOES NOT CHANGE ONSET OR OFFSET OF NEUROMUSCULAR BLOCK AT THE CORRUGATOR SUPERCILII MUSCLE AND THE ADDUCTOR POLLICIS MUSCLE

Université de Montréal, Department of Anesthesiology, Hôtel-Dieu, 3840 Rue St-Urbain, Montréal, PQ, H2Y 1T8

INTRODUCTION

This study investigated the influence of depth of anaesthesia on onset or offset of neuromuscular block (NMB).

METHODS
After approval of the local Ethics Committee and informed consent, 20 patients were included. Anaesthesia was induced and maintained using remifentanil/propofol-infusion. Intubation was performed without NMB. Hemodynamic monitoring consisted of an eosophageal Doppler probe (cardiac output) and non-invasive blood pressure. Patients were randomised into two groups. The propofol-infusion was adjusted to maintain BIS between 50 – 60 (Light, N=10), or between 30 and 40 (Profound, N=10). Remifentanil-infusion was adjusted to maintain a stable blood pressure and cardiac output. Neuromuscular monitoring consisted of phonomyography at the corrugator supercilii muscle and mechanomyography at the adductor pollicis muscle (TOF every 12 s). After establishment of the corresponding depth of anaesthesia, 0.2 mg/kg mivacurium was injected and onset, peak effect and offset of NMB measured. Data presented as mean (SD) and compared using t-test, P<0.05.

RESULTS
Age and weight did not differ between the groups. Onset time, peak effect and time to reach TOF-ratio of more than 0.8 in group ‘Light’ and ‘profound’ were 179 (46) s and 163 (40) s, 83 (21) % and 80 (19) %, 13 (4) and 14 (4) min, respectively at the corrugator supercilii muscle without any significant difference. The same parameters at the adductor pollicis muscle in group ‘Light’ versus ‘Profound’ were 227 (63) s versus 249 (68), 100 (0) versus 99 (1), 25 (5) min versus 28 (8) min, respectively. Although time to reach TOF-ratio of more than 0.8 was longer in the ‘profound’ group, it was not significant. Onset, offset and peak effect of NMB were significantly shorter and less pronounced at the corrugator supercilii muscle than at the adductor pollicis muscle. Mean cardiac output and blood pressure did not differ between the groups.

DISCUSSION
This is the first study investigating the influence of depth of anaesthesia onset, peak effect and offset of NMB after a bolus injection of a neuromuscular blocking agent. There was no significant difference of those parameters between patients in profound or light anaesthesia.

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