Effects of various anesthetic techniques and PaCO_2 levels on cerebral oxygen balance in neurosurgical patients

Objective: To assess the effects of various anesthetic techniques and PaCO2 levels on cerebral oxygen supply/consumption balance during craniotomy for removal of tumors, and to explore an anesthetic technique for neurosur-gery and an appropriate degree of PaCO2 during neuroanesthesia. Methods: One hundred and fourteen patients with supratentorial tumors for elective craniotomy, ASA grade I - II , were randomly allocated to six groups. Patients were anesthetized with continuous intravenous infusion of 2% procaine 1. 0 mg · kg-1 · min-1 in Group I , inhalation of 1. 0% - 1. 5% isoflurane in Group II , and infusion of 2% procaine 0. 5 mg·kg · min-1 combined with inhalation of 0.5% -0.7% isoflurane in Group III during the period of study. The end-tidal pressure of CO2(PET CO2 ) was maintained at 4.0 kPa in these 3 groups. In Group IV, V and VI, the anesthetic technique was the same as that in Group I but the PETCO2 was adjusted to 3. 5, 4. 0 and 4. 5 kPa respectively for 60 min during which the study was performed. The radial arterial and retrograde jugular venous blood samples were obtained at the onset and the end of this study for determining jugular venous bulb oxygen saturation ( SjvO2 ) , arteriovenous oxygen content difference (AVDO2) and cerebral extraction of oxygen (CEO2). Results: In Group I and I SjvO2, AVDO2 and CEO2 remained stable. Although SjvO2 kept constant, AVDO2 and CEO2 decreased significantly (P <0. 05) in Group II. Moreover, AVDO2 and CEO2 in Group II were significantly lower than those of Group III (P<0. 05). In Group IV, 60 min after hyperventilation, SjvO2 and jugular venous oxygen content ( CjvO2 ) decreased markedly (P < 0. 01 ) while CEO2 increased significantly ( P <0.01) . In addition, SjvO2, CjvO2 and CEO2 in Group IV were significantly different from the corresponding parameters in Group V and Group VI (P <0. 05) . In view of sustained excessive hyperventilation, SjvO2 was less than 50% in 37.5% patients of Group IV. Conclusion: Anesthesia with intravenous infusion of procaine combined with isoflurane inhalation proved to be more suitable for neurosurgery than procaine intravenous anesthesia or isoflurane inhalation anesthesia alone. PaCO2 at 4.0 -4. 5 kPa in patients undergoing craniocerebral surgery during neuroanesthesia would be beneficial in both decreasing ICP and maintaining cerebral oxygen supply/consumption balance.