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Pupil changes during cardiopulmonary bypass
G C Fletcher1, A J Asbury, J H Brown
1Department of Anaesthetics, Western Infirmary, Glasgow.
Insights
Cardiopulmonary bypass causes significant pupil dilation during anesthesia, regardless of fentanyl preloading. This effect persists post-bypass, suggesting other physiological factors influence pupil size.
Area of Science:
- Anesthesiology
- Cardiovascular Surgery
- Neuroscience
Background:
- Pupil diameter is a critical indicator for assessing anesthetic depth and detecting cerebral hypoxia, particularly during cardiac bypass when other autonomic monitoring is limited.
- Cardiopulmonary bypass (CPB) presents unique challenges for monitoring patient status due to altered physiological conditions.
Purpose of the Study:
- To investigate the impact of cardiopulmonary bypass on pupil diameter.
- To determine if fentanyl washout from the central nervous system contributes to changes in pupil size during CPB.
Main Methods:
- A pupillometer was employed to measure pupil diameter in patients undergoing CPB.
- Patients were divided into two groups: one with fentanyl preloaded into the bypass pump, and a control group with saline preloading.
Main Results:
- Cardiopulmonary bypass induced pupil dilatation ranging from 17% to 53%.
- This pupil dilatation was not significantly affected by preloading the bypass pump with fentanyl.
- The observed effect persisted for the study duration, ending 30 minutes after CPB initiation.
Conclusions:
- Cardiopulmonary bypass demonstrably causes significant pupil dilatation.
- Fentanyl preloading does not mitigate CPB-induced pupil dilatation, suggesting opioid washout is not the primary cause.
- Further research is required to fully elucidate the mechanisms, potentially involving sympathetic nervous system reflexes and hypothermia, underlying CPB-induced pupillary changes.
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.