Influence of the anaesthetic depth on the inhibition of the oculocardiac reflex during sevoflurane anaesthesia for paediatric strabismus surgery

Abstract

Background: It remains controversial whether the anaesthetic depth as assessed by bispectral index (BIS) influences the oculocardiac reflex (OCR) during strabismus surgery. We investigated whether BIS-guided sevoflurane titration may help to optimize the anaesthetic depth for inhibition of the OCR during paediatric strabismus surgery.

Methods: Eighty-four patients (aged 2-12 yr) undergoing strabismus surgery were randomly allocated to one of the three groups (n=28 for each) according to target BIS value of 40, 50, and 60. The end-tidal sevoflurane concentration with 50% N2O/O2 was adjusted towards target BIS. The incidence of OCR and the lowest heart rate (HR) were recorded in relation to the end-tidal sevoflurane concentration.

Results: The incidence of OCR was higher in Group BIS-60 (71.4%) than in Groups BIS-40 (10.7%) (P<0.001) or BIS-50 (32.1%) (P=0.003), with no difference between Group BIS-40 and Group BIS-50. The lowest HR [beats min(-1), mean (sd)] during traction on the extraocular muscle was lower in Group BIS-60 [112.3 (sd 17.8)] compared with Group BIS-40 [129.3 (11.2)] (P<0.001), with no difference between BIS-40 and BIS-50 [121.4 (16.3)], and between BIS-50 and BIS-60. The end-tidal sevoflurane concentration was different between the three groups (P=0.001).

Conclusions: We confirmed that OCR is relevant to the depth of anaesthesia. BIS values of 40-50 seem adequate for the inhibition of OCR. The results suggest that BIS may be a valuable tool during sevoflurane anaesthesia for strabismus surgery in children.