Cerebral arteriovenous difference of oxygen during gradual and sudden increase of the concentration of isoflurane for induction of deliberate hypotension

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Abstract
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.