CHANGES IN THE CEREBRAL ARTERIOVENOUS OXYGEN-CONTENT DIFFERENCE BY SURGICAL INCISION ARE SIMILAR DURING SEVOFLURANE AND ISOFLURANE ANESTHESIA

Purpose: To investigate changes of cerebral arteriovenous oxygen conte nt difference (AVDO(2)) induced by surgical incision and to determine carbon dioxide (CO2) reactivity of the cerebral circulation during sev oflurane and isoflurane anaesthesia. Methods: Twenty-one ASA 1-2 patie nts undergoing elective surgery for supratentorial tumours were random ly allocated to receive either 1.3 MAC sevoflurane/N2O anaesthesia (n = 10) or equi-MAC isoflurane/N2O anaesthesia (n = 11). Before and afte r incision, haemodynamic measurements and AVDO(2) determinations were performed. After opening the dura, AVDO, was determined before and aft er the respiration rate was increased by 50%. Results: Incision produc ed an increase in mean arterial pressure from 69 +/- II to 97 +/- 22 m mHg (mean +/- SD) (P < 0.0005) and from 71 +/- 6 to 89 +/- 12 mmHg (P < 0.0001) in the sevoflurane and isoflurane groups, respectively, wher eas 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 AVDO(2) 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 AVDO(2), was larger i n 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 posti ncisional AVDO(2) value of the sevoflurane group was corrected for pre -incisional PaCO2. Carbon dioxide reactivity, calculated as the percen t change in AVDO(2) 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 isoflur ane group (P = NS). Conclusions: Sevoflurane and isoflurane are associ ated with similar impairment of cerebral flow-metabolism coupling at i ncision, while CO2 reactivity is maintained during both anaesthetics.