Gender differences in cerebrovascular reactivity to carbon dioxide during sevoflurane anesthesia in children: Preliminary findings

Background: Cerebrovascular reactivity to carbon dioxide CO₂R) is affected by age, gender and anesthetic agents. While gender differences in CO₂R are described in adults, there are no such data in children. Aim: To examine the gender differences in CO₂R in children during sevoflurane anesthesia. Methods: Five girls and five boys <15 years of age and ASA physical status I, undergoing general anesthesia for elective surgery were enrolled. Under steady-state anesthesia with <1.0 MAC sevoflurane, middle cerebral artery blood flow velocity changes were monitored using Transcranial Doppler ultrasound while endtidal carbon dioxide (EtCO₂) was adjusted from 40 to 30 mmHg (hypocapnia) and then from 40 to 50 mmHg (hypercapnia). CO₂R was calculated between EtCO₂ ranges 30-40 and 40-50 mmHg. Cerebrovascular resistance (eCVR) was estimated as MAP/Vmca and the change in eCVR (δeCVR) between EtCO₂ 30 and 40 mmHg and between EtCO₂ 40 and 50 mmHg was calculated. Results: There was no gender difference in CO₂R. However, both CO₂R and δeCVR were lower in the EtCO₂ 40-50 mmHg range compared to EtCO₂ 30-40 mmHg range only in girls (P = 0.01 and P = 0.01, respectively). Vmca increased significantly with increase in CO₂ (P < 0.001) for both boys and girls. The coefficient of nonlinear correlation (r) between Vmca and EtCO₂ was 0.88 in girls vs 0.66 in boys. Conclusion: While there were no gender differences in CO₂R within the individual EtCO₂ ranges examined, girls but not boys had a significantly lower CO₂R and δeCVR in the higher EtCO ₂ range during <1.0 MAC sevoflurane anesthesia.