Current practice in the pre‐operative assessment of patients for elective repair of abdominal aortic aneurysm

Abstract

SummarySevoflurane, desflurane and isoflurane were compared using a circle system in 97 patients undergoing short surgical procedures. Using initial high flows, the time intervals to equilibration between inspired and end-expired agent concentrations were measured; equilibration was defined as F E = F I 0:8. The mean (SD) times obtained for sevoflurane, desflurane and isoflurane were 8.2 (2.1) min, 3.8 (0.7) min and 19.7 (6.5) min, respectively. These times were significantly different from each other (p < 0:0001). After equilibration total flows were reduced to 500 ml.min ÿ 1 ; at these flows the initial decline in end-expired agent concentration was minimal with desflurane, intermediate with sevoflurane and greatest with isoflurane. Both desflurane and sevoflurane are appropriate for efficient use of the circle system during short anaesthetics.Keywords Anaesthetics, volatile; sevoflurane, desflurane, isoflurane. Equipment; breathing systems, circle, closed. ...................................................................................... Correspondence to: Dr N. Soni Accepted: 17 November 1996 In contrast to other anaesthetic breathing systems in common use, the circle system has the unique advantage of permitting anaesthesia with low fresh gas flows, thereby conferring physiological, economic and environmental benefits [1, 2]. In clinical practice, the important considerations when using circle systems are firstly the initial period of high gas inflow required to denitrogenate the lungs and attain an adequate alveolar anaesthetic concentration and subsequently the effective maintenance of this concentration during low flows. There is no general agreement as to what constitutes an adequate alveolar concentration before flows can be reduced. Low-flow anaesthesia is commonly instituted only after about 20 min at high flows, but this precludes the efficient use of the circle system for the large proportion of anaesthetics which are of short duration. (The term 'efficient' refers to a low value for the ratio of fresh gas flow to expired minute volume. This is obtained by flows classified minimal (250-500 ml.min ÿ 1 ) or low (500-1000 ml.min ÿ 1 ), using the terminology proposed by Simionescu [3].It has been shown that, when desflurane is used in the circle system, an adequate alveolar concentration, as indicated by end-expired (F E 0 ) desflurane concentration, is rapidly achieved [4]. This allows reduction of fresh gas flow after a very short time, with the end-expired desflurane concentration effectively maintained at flows of 500 ml.min ÿ 1 . In contrast, isoflurane takes longer for endexpired and inspired (F I ) concentrations to equilibrate [4], and after flow reduction end-expired isoflurane concentrations are poorly maintained. Sevoflurane has not been studied in this context, although its physical properties [5] suggest that it should behave similarly to desflurane. This study compares sevoflurane, desflurane and isoflurane for efficient use of the circle system during short anaesthetics. Me...

Disparity in the risk stratification of major surgery

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The anaesthesia consult clinic: does it matter which anaesthetist sees the patient?

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Ideal peri‐operative management of patients with cardiovascular disease: the quest continues

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