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

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.

Risks and benefits of deliberate hypotension in anaesthesia: a systematic review

“…Fifty-seven articles were found relevant to this topic: 14 randomized clinical trials 6,10,47,49,50,52,60, 69,72,83,153,179,180,197 , 4 controlled clinical trials 2,110,184,186 , 1 case-controlled study 105 181,190,193,194,199 , 3 retrospective case series 28,127,189 and 2 case reports 68,96 .…”

Efeitos do óxido nitroso em hipotensão controlada durante anestesia com baixo fluxo

“…Newman et al 22 stated that for cerebral aneurysm clips applied to patients, isofl urane has benefi cial effects on the cerebral oxygen presentation-requirement ratio. Haraldsted et al 23 also stated that the maximum limit of MAC value at which these benefi cial effects were seen is 2.5.…”

Cerebral blood flow during induced hypotension

“…In humans, trimetaphan-induced hypotension to a mean arterial pressure of 40 mm Hg caused EEG amplitude depression during 0.5 % halothane anaesthesia whereas there was no EEG depression with 1 % isoflurane [13]. Despite a similar depression in cerebral metabolic rate, isofluraneinduced hypotension was associated with higher cerebral blood flow than that during hypotension induced with a peripheral vasodilator during anaesthesia with propofol and alfentanil [14], and also blood flow was surplus to metabolic requirements when hypotension was induced with isoflurane [15]. Information on the cerebral effects of the newer anaesthetic agents is limited.…”