Pupil changes during cardiopulmonary bypass

Abstract

Pupil diameter is used during anaesthesia to assess depth of anaesthesia and indicate cerebral hypoxia. This is especially so during cardiac bypass when other autonomic signs cannot be monitored. We have used a pupillometer to determine the effect of cardiopulmonary bypass on the pupil. We have also investigated if any effect was caused by washout of opioid from the central nervous system by allocating patients to one of two groups: in one the bypass pump was preloaded with fentanyl, in the other with 0.9% saline. Cardiopulmonary bypass caused pupil dilatation of between 17% and 53%, which was unaffected by preloading the bypass pump with fentanyl. This effect lasted for the duration of the study, which ended 30 min after the start of cardiopulmonary bypass. Sympathetic nervous system reflexes and hypothermia may account for this observation, but further research is necessary to exclude other contributory factors.