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Cerebrovascular reactivity to carbon dioxide is preserved during hypocapnia in children anesthetized with 1.0 MAC, but not with 1.5 MAC desflurane

[La réactivité cérébrovasculaire au gaz carbonique est conservée pendant l’hypocapnie chez des enfants anesthésiés avec 1,0 CAM, mais non avec 1,5 CAM, de desflurane]

From the Department of Anaesthesia, The Hospital for Sick Children, University of Toronto, Toronto, Ontario, Canada.

Address correspondence to: Dr. Bruno Bissonnette, Department of Anaesthesia, The Hospital for Sick Children, 555 University Avenue, Toronto, Ontario M5G 1X8, Canada. Phone: 416-813-7445; Fax: 416-813-7543, E-mail: bruno{at}anaes.sickkids.on.ca

Purpose: Maintenance of cerebrovascular reactivity to CO₂ (CCO₂R) is important during neurosurgical anesthesia. This study was designed to determine the effect of different desflurane concentrations on CCO₂R in children.

Methods: Children undergoing urological surgery were enrolled. Anesthesia was induced with sevoflurane in air/oxygen. After intubation, sevoflurane was switched to desflurane. Analgesia was provided with an epidural neuraxial block. Mechanical ventilation was adjusted to an initial EtCO₂ of 30 mmHg. Exogenous CO₂ was used to achieve an EtCO₂ of 40 and 50 mmHg. Patients were randomized to the sequence of desflurane concentration (1.0 and 1.5 MAC) and the EtCO₂. Transcranial Doppler was used to measure middle cerebral artery blood flow velocity (Vmca). Five minutes were allowed to reach steady state after each change in EtCO₂ and 15 min after changing the desflurane concentration.

Results: Sixteen patients were studied. The mean age and weight were 3.5 ± 1.5 yr and 14.4 ± 3.1 kg, respectively. Mean arterial pressure remained stable throughout the study, while at an EtCO₂ of 50 mmHg, heart rate decreased at both desflurane concentrations (P < 0.05). At 1.0 MAC, Vmca increased from 30 to 40 mmHg (P < 0.05), but not from 40 to 50 mmHg EtCO₂. At 1.5 MAC, Vmca increased between 30 and 50 mmHg (P < 0.05).

Conclusion: CCO₂R is preserved during hypocapnia in children anesthetized with 1.0 MAC, but not with 1.5 MAC desflurane. The lack of further increase in Vmca at higher EtCO₂ concentrations implies that desflurane may cause significant cerebral vasodilatation in children. This may have important implications in children with reduced intracranial compliance.