The uptake of enflurane during anaesthesia

Devchand, D; Chakrabarti, M.K.; Lockwood, G. G.

doi:10.1111/j.1365-2044.1995.tb06036.x

Cited by 7 publications

(3 citation statements)

References 19 publications

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“…The breathing system is illustrated in Fig. 1 and has been described in detail previously [7]. Closure of the breathing system was demonstrated in every case by a continuous reduction in inspired oxygen concentration.…”

Section: Methodsmentioning

confidence: 99%

The uptake of sevoflurane during anaesthesia

Vagts

Lockwood

1998

Anaesthesia

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SummaryThe rate of uptake of sevoflurane during clinical anaesthesia (1.3 MAC) was measured by computer-controlled injection of liquid anaesthetic into a closed breathing system. The cumulative uptake of sevoflurane was 4.8 ml, 7.4 ml. 9.5 ml and 11.5 ml at 30, 60, 90 and 120 min, respectively. The ratio of inspired to end-expired sevoflurane was greater than similar measurements we have made for desflurane in the past, but the absolute rate of sevoflurane uptake was less than the rate of uptake of desflurane in these cases. The rate of uptake was equivalent to 0.59e ¹0.32t þ 0.039e ¹0.036t þ 0.105e ¹0.0034t ml.min ¹1 liquid sevoflurane. Plasma urea and creatinine measured on the first postoperative day were not significantly different from pre-operative values.

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Section: Methodsmentioning

confidence: 99%

The uptake of sevoflurane during anaesthesia

Vagts

Lockwood

1998

Anaesthesia

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“…The breathing system, lung model and calculations have been described previously [4,5]. The breathing system ( Fig.…”

Section: Methodsmentioning

confidence: 99%

The loss of sevoflurane from a closed breathing system

Vagts

Lockwood

1997

Anaesthesia

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SummaryWhen volatile anaesthetics are used in a closed breathing system it is usually assumed that inflow of anaesthetic to the system matches uptake by the patient. Early laboratory reports on the interactions between sevoflurane and soda lime cast doubt on that assumption. We have measured the loss of sevoflurane, desflurane and isoflurane from a closed breathing system and found no differences of consequences. We have used quantitative closed-system anaesthesia routinely for several years and have reported our experience with isoflurane, enflurane and desflurane. The use of sevoflurane in such a system is open to question for two reasons. Do the degradation products of sevoflurane in soda lime constitute a hazard to the patient? Does absorption and degradation of sevoflurane in soda lime invalidate the assumption that, if the breathing system is closed and the gas composition constant, then the amount of anaesthetic entering the breathing system equals the patient uptake? In this paper we consider only the second question: is closed-system anaesthesia using sevoflurane quantitative when soda lime is used to absorb carbon dioxide? Previous in vitro studies have demonstrated an alarming rate of disappearance of sevoflurane from flasks containing soda lime or Baralyme [1][2][3]. We have used a laboratory model to measure anaesthetic loss from a closed breathing system without soda lime, with soda lime but without carbon dioxide and with both soda lime and carbon dioxide. We have compared sevoflurane, desflurane and isoflurane. MethodsThe breathing system, lung model and calculations have been described previously [4,5]. The breathing system (Fig. 1) is based on the MIE 'Exeter'. A vaporising canister allowed infusions of sevoflurane to be delivered into the breathing system. The injection port was stoppered off when not in use. The breathing system was connected to a conventional open-system ventilator using a 'trunk'. This is a 22-mm, long corrugated tube within which plug flow is assumed to occur, maintaining isolation of the breathing system gas from the ventilator gas while transmitting intermittent positive pressure to the breathing system by a gas piston effect. The trunk and all other 22-mm corrugated tubes were disposable plastic. The trunk was 6 m long and the volume of the circle breathing system 3 litres without soda lime (the 550 g of soda lime charges displaces 330 ml). A disposable breathing filter and catheter mount connected the breathing system to the model lung, which was simply a large bottle (volume 22 440 ml) with no internal surfaces which could absorb volatile anaesthetics; compression of gas within the model lung during inspiration simulated expansion of true lungs. The model lung and breathing system were submerged under water and pressure tested for leaks at 50 cmH 2 O before and after every experiment.A Datex Ultima was used for gas analysis and spirometry. This adds 30 ml.min ¹1 air (used as an oxygen reference) to the sample which was then returned to the breathing system. A Manley v...

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“…21 Similar excesses of uptake over that predicted from the square-root-of-time theory have been reported by others for continuous-inflow versions of the Lowe method. 22 Anomalies of end-tidal partial pressure. The clinical aim was to maintain SAP close to the reference level.…”

Section: Are the Doses And End-tidal Partial Pressures Consistent Witmentioning

confidence: 99%

Quantitative study of Lowe's square-root-of-time method of closed-system anaesthesia

Silva

Mapleson

Vickers

1997

British Journal of Anaesthesia

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Intermittent injection of liquid anaesthetic into a closed breathing system is particularly suitable in countries with limited resources. A method of calculating appropriate times and magnitudes of the injected doses was described by Lowe but the method has never been assessed rigorously. Such an assessment was the purpose of this study. The technique was used in a double-blind, randomized comparison of halothane, enflurane and isoflurane in oxygen-air, with 20 ASA I or II patients in each group, undergoing superficial or abdominal surgery. The prescribed times of injection were adhered to, but the doses, after the first two, were adjusted to maintain systolic arterial pressure within 20% of the reference preoperative value. Partial pressures of the anaesthetics were monitored but concealed from the investigator-anaesthetist. The mean doses found necessary for each anaesthetic were within 33% of those calculated to produce 1.3 MAC. However, end-tidal partial pressure (just before each dose) stabilized at a steady level of only 0.97, 0.42 and 0.77 MAC for halothane, enflurane and isoflurane, respectively. Recovery from enflurane was much more rapid than that from the other agents but no patient admitted to any dreams. We conclude that the rate of uptake of anaesthetic declines more slowly than predicted and that the patients receiving enflurane were less deeply anaesthetized because the greater hypotensive effect of enflurane led to the use of smaller doses.

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The uptake of enflurane during anaesthesia

Cited by 7 publications

References 19 publications

The uptake of sevoflurane during anaesthesia

The uptake of sevoflurane during anaesthesia

The loss of sevoflurane from a closed breathing system

Quantitative study of Lowe's square-root-of-time method of closed-system anaesthesia

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