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

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.