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ABSTRACTS NONITORING OF NEURONUSCULAR FUNCTION I5 INPORTANT DURING SQUINT SURGERY SAIAH Nich~le, NO, BORGEAT Alain, NO, WILDER-SNITH Oliver, ND. Oepartment of Anesthesiology, University Hospital of Geneva, 1211 Gen~ve 4, Switzerland. A3 Introduction. Squint surgery is associated with a high failure rate. Conventionally used anesthetic techniques for this type of surgery are based on high doses of volatile anesthetics and a single bolus of muscle relaxants in order to facilitate tracheal tntubat/on. Any subsequent variations in muscle tension must be the result of the direct muscular relaxant properties of the anesthetic gases used together with the depth of anesthesia. Large interindivtdual variations in the muscle tension up to 60 ?9 of the baseline value (]) have been demonstrated with such anesthetic techniques. The depth of anesthesia was monitored by EEG and/or end tidal volatile anesthetic concentrations in these studies. However, no reliable correlation between muscle tension and such measures of depth of anesthesia has been demonstrated to date (2). Thus such measures of depth of anaesthesia appear inadequate to stabilise muscle tensions during squint surgery and may in part explain its high failure rate. We investigated the relationship between the extensibility of oculo-motor muscles as measured by the elongation test and the degree of peripheral muscular relaxation as monitored by evoked muscular contractions of the ulnar nerve. Patients and methods. After institutional approval and informed consent, 5 patients (ASA f or II) aged 14 to 82 being operated upon. for retinal detachment were included in the study. Anesthesia was induced and maintained with propofol. Tracheal intubation was facilitated by suxamethontum; After complete recovery from neuromuscular blockade, vecuronfum was administered in fractionated doses in order to perform the oculo-motor muscle elongation test at different values of T 1 (100, 50 & 0 respectively). Rqsults. A11 patients showed variable positions of the eyes according to the degree of myorelaxation. We also found a direct correlation between oculo- motor muscle extensibility and the degree of peripheral muscle relaxation. Changes of between ] to 4 nun were noted according to the degree of muscular relaxation (from 0 to 100 X muscular blockade). Conclusions. These preliminary results show that close monitoring of muscular relaxation is mandatory during squint surgery in order to keep the same level of muscular relaxation (as assessed by evoked muscular contractions) during the entire surgical procedure and to thus avoid an insufficient / inadequate correction due to varying muscle tensions. References. 1. Romano P, Gabriel L. Intra-operative adjustment of eye muscle surgery. Correction based on eye position during general anesthesia. Arch Ophtalmol 103 : 351-353, 1953. 2. Chang T, Dvvorsky WA, White PF. Continuous electromyography for monitoring depth of anesthesia. Anesth Analg 57 : 521-525, 1988.