Per- and postoperative changes in the arterio-venous oxygen content difference (AVDO2) in patients subjected to craniotomy for cerebral tumours

Summary Sixteen patients with supratentorial cerebral tumours were subjected to craniotomy under thiopentone, fentanyl, nitrous oxide, halothane anaesthesia during moderate hypocapnia (PaCO₂ level 4.0 kPa). The arterio-venous oxygen content difference (AVDO₂) was measured peroperatively, and repeatedly during the first three hours after extubation.Peroperatively the level of AVDO₂ averaged 8.0 vol% during opening of the dura, and decreased to 7.0 vol% during closure of the dura (P<0.05). Immediately after extubation the AVDO₂ decreased to 4.3 vol% (P<0.05), and during the next 3 hours a gradual increase to 5.8 vol% (P<0.05) was disclosed. In individual cases the postoperative changes in AVDO₂ correlated fairly well with changes in mean arterial blood pressure (MABP), but other factors including duration of the operation, age of the patients, size of the tumour, level of PaCO₂ and adaptation to prolonged hyperventilation during operation are supposed to be responsible for the low levels of AVDO₂ observed in the postoperative period.