Reflex pupillary dilatation in response to skin incision and alfentanil in children anaesthetized with sevoflurane: a more sensitive measure of noxious stimulation than the commonly used variables.

Background: Estimation of analgesia in anaesthetized children is often imprecise, and consequently, anaesthesiologists commonly evaluate children's response to surgical stimulation by movement or haemodynamic changes. In adults reflex pupillary dilatation has been demonstrated to be a very sensitive measure of noxious stimulation, correlated with opioid concentrations. The autonomic nervous control changes with age, raising the hypothesis that mechanisms involved in pupillary autonomic functions regarding both sympathetic and parasympathetic components may also differ between adults and children. In this pilot study, we tested the hypothesis that the pupillary reflex dilatation might allow assessment of noxious stimulation and analgesic effect of alfentanil in children under sevoflurane anaesthesia, as an alternative to haemodynamic and bispectral measures.
Methods: After sevoflurane induction, 24 children were maintained in steady-state conditions at 1.5 MAC of sevoflurane in O(2)-N(2)O (50-50). An intense noxious stimulation was provided by standardized skin incision on the lower limb. A bolus of alfentanil (10 microg kg(-1)) was administered either 1 min (n=16) or 2 min (n=8) after skin incision. Haemodynamic values, bispectral index (BIS) and pupillary diameter (PD) were recorded just before stimulation and at 30-60 s intervals during 4 subsequent minutes.
Results: In all children PD increased significantly after noxious stimulation [+200 (40)%, at 60 s]. In contrast, mean heart rate and blood pressure increased only 11 (7)% and 10 (8)% respectively, 60 s after stimulation. BIS did not change significantly. In all children, alfentanil injection induced a rapid decrease of PD and restored pre-incision values in 2 min.
Conclusion: PD is a more sensitive measure of noxious stimulation than the commonly used variables of heart rate, arterial blood pressure and BIS in children anaesthetized with sevoflurane.