In 20 patients undergoing surgery for cerebral aneurysms, hypotension was induced with either gradual (over 5 min) or sudden increase of inspiratory concentration of isoflurane from 0.5% to 3%. Both modes elicited the same speed of induction of deliberate hypotension and similar decreases of cerebral arteriovenous difference of oxygen (AVDo2). The overall median values of mean arterial blood pressure decreased from 75.5 (range 64-90) mmHg (10 (8.5-12.0) kPa) to 55 (40-66) mmHg (7.3 (5.3-8.8) kPa) and the overall AVDo2 decreased from 6.75 ml/100 ml (3.8-9.4 ml/100 ml) to 5.85 ml/100 ml (2.6-8.1 ml/100 ml) within 10 min. It is concluded that irrespective of gradual or sudden increase of isoflurane concentration, cerebral blood flow is in surplus of metabolism and a favourable oxygen demand/supply ratio is maintained during induction of deliberate hypotension by isoflurane below 2.5 MAC.
Conjunctival oxygen tension (PcjO2) and routine cardiorespiratory parameters were measured in 8 patients during pulmonary surgery. In each patient we found a close relationship between PcjO2 and arterial blood oxygen tension (PaO2), and for all patients the correlation coefficient was 0.962. The mean values of the ratio between PcjO2 and PaO2 in each patient were ranging between 0.46 and 0.55. We conclude that PcjO2 measurements represent a useful and reliable method for evaluation of peripheral oxygenation and perfusion during pulmonary surgery. Furthermore, the method has been found useful for estimation of arterial blood oxygen tension in hemodynamically stable patients during anesthesia.
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 less than 0.05). Immediately after extubation the AVDO2 decreased to 4.3 vol% (P less than 0.05), and during the next 3 hours a gradual increase to 5.8 vol% (P less than 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.
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