Changes in the cerebral arteriovenous oxygen content difference by surgical incision are similar during sevoflurane and isoflurane anaesthesia.

Abstract

To investigate changes of cerebral arteriovenous oxygen content difference (AVDO2) induced by surgical incision and to determine carbon dioxide (CO2) reactivity of the cerebral circulation during sevoflurane and isoflurane anaesthesia. Twenty-one ASA 1-2 patients undergoing elective surgery for supratentorial tumours were randomly allocated to receive either 1.3 MAC sevoflurane/N2O anaesthesia (n = 10) or equi-MAC isoflurane/N2O anaesthesia (n = 11). Before and after incision, haemodynamic measurements and AVDO2 determinations were performed. After opening the dura, AVDO2 was determined before and after the respiration rate was increased by 50%. Incision produced an increase in mean arterial pressure from 69 +/- 11 to 97 +/- 22 mmHg (mean +/- SD) (P < 0.0005) and from 71 +/- 6 to 89 +/- 12 mmHg (P < 0.0001) in the sevoflurane and isoflurane groups, respectively, whereas the heart rate increased from 60 +/- 9 to 72 +/- 8 bpm (P < 0.001) and from 65 +/- 6 to 70 +/- 7 bpm (P < 0.001), respectively. Arterial carbon dioxide tension (PaCO2) was increased from 33.6 +/- 2.3 to 34.6 +/- 1.8 mmHg (P < 0.05) with incision in the sevoflurane group. The AVDO2 was decreased from 6.5 +/- 1.6 to 5.3 +/- 1.6 vol% (P < 0.0005) in the sevoflurane group and from 6.7 +/- 1.1 to 6.0 +/- 1.1 vol% (P < 0.01) in the isoflurane group. The % change of AVDO2 was larger in the sevoflurane group than in the isoflurane group (-18.3 +/- 8.4% vs -9.1 +/- 9.0%; P < 0.05) but no difference remained after the post-incisional AVDO2 value of the sevoflurane group was corrected for pre-incisional PaCO2. Carbon dioxide reactivity, calculated as the percent change in AVDO2 per mmHg change in PaCO2, was 6.1 +/- 3.0%.mmHg-1 in the sevoflurane group and 5.9 +/- 2.4%.mmHg-1 in the isoflurane group (P = NS). Sevoflurane and isoflurane are associated with similar impairment of cerebral flow-metabolism coupling at incision, while CO2 reactivity is maintained during both anaesthetics.