The effect of cardiac output changes on end‐expired volatile anaesthetic concentrations – a theoretical study

Kennedy, R. C.; Baker, A. B.

doi:10.1111/j.1365-2044.2001.02212.x

Cited by 4 publications

(8 citation statements)

References 12 publications

(18 reference statements)

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“…13 To produce a difference in arterial sevoflurane partial pressures as large as we measured, the cardiac output in the control group would need to be approximately three times that in the nitrous oxide group-or an order of magnitude greater than the estimated difference in cardiac output in our study. 23,24 Inclusion of nitrous oxide in the gas mixture reduces the inspired concentration and cumulative dose of volatile agent because of its "MAC (minimum alveolar concentration) sparing" effect. The magnitude of this effect in our study, as indicated by the baseline concentrations in the two groups, was a 22% reduction in arterial ( fig.…”

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confidence: 99%

Nitrous Oxide Diffusion and the Second Gas Effect on Emergence from Anesthesia

et al. 2011

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Background: Rapid elimination of nitrous oxide from the lungs at the end of inhalational anesthesia dilutes alveolar oxygen, producing "diffusion hypoxia." A similar dilutional effect on accompanying volatile anesthetic agent has not been evaluated and may impact the speed of emergence. Methods: Twenty patients undergoing surgery were randomly assigned to receive an anesthetic maintenance gas mixture of sevoflurane adjusted to bispectral index, in airoxygen (control group) versus a 2:1 mixture of nitrous oxideoxygen (nitrous oxide group). After surgery, baseline arterial and tidal gas samples were taken. Patients were ventilated with oxygen, and arterial and tidal gas sampling was repeated at 2 and 5 min. Arterial sampling was repeated 30 min after surgery. Sevoflurane partial pressure was measured in blood by the double headspace equilibration technique and in tidal gas using a calibrated infrared gas analyzer. Time to eye opening and time extubation were recorded. The primary endpoint was the reduction in sevoflurane partial pressures in blood at 2 and 5 min. Results: Relative to baseline, arterial sevoflurane partial pressure was 39% higher at 5 min in the control group (P Ͻ 0.04) versus the nitrous oxide group. At 30 min the difference was not statistically significant. Time to eye opening (8.7 vs. 10.1 min) and time to extubation (11.0 vs.13.2 min) were shorter in the nitrous oxide group versus the control group (P Ͻ 0.04). Conclusions: Elimination of nitrous oxide at the end of anesthesia produces a clinically significant acceleration in the

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confidence: 99%

Nitrous Oxide Diffusion and the Second Gas Effect on Emergence from Anesthesia

et al. 2011

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“…In this context, cardiac output was found to be a major determinant of the rate of uptake and distribution of inhalation anaesthetic [6]. Kennedy and Baker reported that a large fall in cardiac output would accompany an increase in C E and indicated that the uptake was reduced [14, 15]. Therefore, under the condition of a fixed C I , a large fall in cardiac output would lead to an increasing C E , approaching C I , and a decreasing body uptake of inhalation anaesthetic agent.…”

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confidence: 99%

Application of MVBC equation to predict mixed venous blood concentrations of sevoflurane in cardiac anaesthesia

Hung

et al. 2005

Anaesthesia

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SummaryWe have proposed an equation for estimating the real-time mixed venous blood concentration (MVBC) of isoflurane in cardiac anaesthesia. However, information related to the application of our method to sevoflurane is lacking. We studied 12 patients undergoing cardiac surgery and anaesthetised with sevoflurane. At different time points, pulmonary arterial blood samples were collected for gas chromatography-mass spectrometry (GC-MS) to determine the real mixed venous concentrations of sevoflurane. The inspired and expired concentrations of sevoflurane, measured by a gas monitor, were used for the MVBC calculations. Using Bland-Altman analyses, we found that the calculated MVBCs accurately represent the actual concentrations of sevoflurane in pulmonary arterial blood, as shown by a near-zero percentage bias with a 0.14% precision between the two concentrations. The results demonstrated that our equation could be a useful method for estimating the pulmonary blood concentration of sevoflurane. Recently, we combined Fick's law and Lin's concept to derive a mixed venous blood concentration (MVBC) equation for the real-time estimation of isoflurane concentration in mixed venous blood [1]. We showed that the MVBC equation is more accurate than the effective blood concentration (EBC) equation proposed by Lin for estimating isoflurane blood concentration [1]. However, the accuracy of our MVBC method to estimate concentrations for other volatile anaesthetics agents in mixed venous blood is still unknown.Sevoflurane has been used in cardiac surgery because of its relative lack of airway irritation and myocardial depression, and its protective effect against myocardial ischaemia-reperfusion injury [2][3][4][5]. Sevoflurane has several physical properties significantly different from those of isoflurane [2,3]. We were interested in the applicability of our MVBC method for patients receiving sevoflurane anaesthesia during cardiac surgery. In addition, the variability of our MVBC method seemed wide (i.e. approximately 1%) in our previous study [1]. Since anaesthesia was maintained with a variable concentration of isoflurane (1-2%) during surgery, we hypothesised that the higher variability is due to the fact that the inhaled concentrations (C I ) of isoflurane had not been fixed. Because the uptake of inhalation anaesthetic [6] and the MVBC calculation (see MVBC equation under Methods) are both dependent on the C I , variation may cause a decrease in the accuracy of the method.In this study, we investigated the ability of our MVBC equation to estimate the blood concentration of sevoflurane during the first 2 h of cardiac surgery with fixed C I anaesthesia. Gas chromatography-mass spectrometry (GC-MS) was used to measure the blood concentration of sevoflurane. The relationship between the measured Anaesthesia, 2005, 60, pages 882-886

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“…The model is similar to those of Mapleson 6,7 , containing nine compartments: circuit; lung/blood, heart, brain, kidney, liver, muscle, fat, and poorly perfused tissues. The model has been extended to include a number of volatile agents 2 and has recently been described in greater detail [1][2][3][4] . The model does not include compartments to mimic blood transit time 7,8 .…”

Section: Methodsmentioning

confidence: 99%

“…Other parameters of the model, including the size of tissue compartments and relative blood flows were as originally described by Heffernan et al 5 . Blood/gas and tissue/blood partition coefficients are those we have used previously 2,9 . The model is initialized for the chosen agent and then values for compartment sizes, cardiac output and ventilation used in the model are adjusted for the weight of the patient.…”

Section: Methodsmentioning

confidence: 99%

“…Our results suggest this model predicts end-tidal (eT) isoflurane and sevoflurane at least as well as models used in target controlled infusion (TCI) systems predict blood propofol concentrations. We have used this model to explore the theoretical questions, such as relationship between cardiac output and volatile uptake 2 and to develop practical tools to guide the administration of inhalational anaesthetic agents 3,4 .…”

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Predictive Performance of a Model of Anaesthetic Uptake with Desflurane

Kennedy

2006

Anaesth Intensive Care

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We have previously shown that a model of anaesthetic uptake and distribution, developed for use as a teaching tool, is able to predict end-tidal isoflurane and sevoflurane concentrations at least as well as commonly used propofol models predict blood levels of propofol. Models with good predictive performance may be useful as part of real-time prediction systems. The aim of this study was to assess the performance of this model with desflurane. Twenty adult patients undergoing routine anaesthesia were studied. The total fresh gas flow and vaporizor settings were collected at 10-second intervals from the anaesthetic machine. These data were used as inputs to the model, which had been initialized for patient weight and desflurane. Output of the model is a predicted end-tidal value at each point in time. These values were compared with measured end-tidal desflurane using a standard statistical technique of Varvel and colleagues. Data was analysed from 19 patients. Median performance error was 78% (95% CI 8-147), median absolute performance error 77% (6-149), divergence 10.6%/h (-80-101) and wobble 8.9% (-6-24). The predictive performance of this model with desflurane was poor, with considerable variability between patients. The reasons for the difference between desflurane and our previous results with isoflurane and sevoflurane are not obvious, but may provide important clues to the necessary components for such models. The data collected in this study may assist in the development and evaluation of improved models.

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The effect of cardiac output changes on end‐expired volatile anaesthetic concentrations – a theoretical study

Cited by 4 publications

References 12 publications

Nitrous Oxide Diffusion and the Second Gas Effect on Emergence from Anesthesia

Nitrous Oxide Diffusion and the Second Gas Effect on Emergence from Anesthesia

Application of MVBC equation to predict mixed venous blood concentrations of sevoflurane in cardiac anaesthesia

Predictive Performance of a Model of Anaesthetic Uptake with Desflurane

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