Isoflurane, Sevoflurane and Desflurane consumption in an anaesthetic gas reflector system with target controlled administration (MIRUS™) versus a semi-closed circle system with automatic end tidal concentration control (Aisys Carestation™) using an artificial lung model

The effect of fresh gas flow (FGF) on isoflurane concentrations at given vaporizer settings during low-flow anaesthesia was investigated. Ninety patients (American Society of Anaesthesiologists physical status I or II) were randomly allocated to three groups (FGF 1 l/min, FGF 2 l/min and FGF 4 l/min). Anaesthesia was maintained for 10 min with vaporizer setting isoflurane 2 vol% and FGF 4 l/min for full-tissue anaesthetic uptake in a semi-closed circle system. Low-flow anaesthesia was maintained for 20 min with end-tidal isoflurane 1.5 vol% and FGF 2 l/min. FGF was then changed to FGF 1 l/min, FGF 2 l/min or FGF 4 l/min. Measurements during the 20-min period showed that inspired and end-tidal isoflurane concentrations decreased in the FGF 1-l/min group but increased in the FGF 4-l/min group compared with baseline values. No haemodynamic changes were observed. Monitoring of anaesthetic concentrations and appropriate control of vaporizer settings are necessary during low-flow anaesthesia.

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Controlled Emergence From Anesthesia Using the Closed-Circle System

Anesthesia & Analgesia ◽

10.1213/00000539-197453060-00011 ◽

1974 ◽

Vol 53 (6) ◽

pp. 869-875

Author(s):

ALFRED FEINGOLD

Keyword(s):

Closed Circle ◽

Closed Circle System

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Evaluation of estimates of alveolar gas exchange by using a tidally ventilated nonhomogenous lung model

Journal of Applied Physiology ◽

10.1152/jappl.1997.82.6.1963 ◽

1997 ◽

Vol 82 (6) ◽

pp. 1963-1971 ◽

Cited By ~ 18

Author(s):

Thierry Busso ◽

Peter A. Robbins

Keyword(s):

Gas Exchange ◽

Lung Model ◽

Gas Composition ◽

Breathing Patterns ◽

Alveolar Volume ◽

Gas Concentration ◽

Pulmonary Capillaries ◽

Partial Pressures ◽

End Tidal ◽

Alveolar Gas Exchange

Busso, Thierry, and Peter A. Robbins. Evaluation of estimates of alveolar gas exchange by using a tidally ventilated nonhomogenous lung model. J. Appl. Physiol. 82(6): 1963–1971, 1997.—The purpose of this study was to evaluate algorithms for estimating O2 and CO2 transfer at the pulmonary capillaries by use of a nine-compartment tidally ventilated lung model that incorporated inhomogeneities in ventilation-to-volume and ventilation-to-perfusion ratios. Breath-to-breath O2 and CO2 exchange at the capillary level and at the mouth were simulated by using realistic cyclical breathing patterns to drive the model, derived from 40-min recordings in six resting subjects. The SD of the breath-by-breath gas exchange at the mouth around the value at the pulmonary capillaries was 59.7 ± 25.5% for O2 and 22.3 ± 10.4% for CO2. Algorithms including corrections for changes in alveolar volume and for changes in alveolar gas composition improved the estimates of pulmonary exchange, reducing the SD to 20.8 ± 10.4% for O2 and 15.2 ± 5.8% for CO2. The remaining imprecision of the estimates arose almost entirely from using end-tidal measurements to estimate the breath-to-breath changes in end-expiratory alveolar gas concentration. The results led us to suggest an alternative method that does not use changes in end-tidal partial pressures as explicit estimates of the changes in alveolar gas concentration. The proposed method yielded significant improvements in estimation for the model data of this study.

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Expiratory and arterial partial pressure relations under different ventilation-perfusion conditions

Journal of Applied Physiology ◽

10.1152/jappl.1983.54.6.1745 ◽

1983 ◽

Vol 54 (6) ◽

pp. 1745-1753 ◽

Cited By ~ 6

Author(s):

A. Zwart ◽

S. C. Luijendijk ◽

W. R. de Vries

Keyword(s):

Partial Pressure ◽

Dead Space ◽

Gas Analysis ◽

Lung Model ◽

Breathing Patterns ◽

Tracer Gas ◽

Physiological Dead Space ◽

Arterial Partial Pressure ◽

The Difference ◽

End Tidal

Inert tracer gas exchange across the human respiratory system is simulated in an asymmetric lung model for different oscillatory breathing patterns. The momentary volume-averaged alveolar partial pressure (PA), the expiratory partial pressure (PE), the mixed expiratory partial pressure (PE), the end-tidal partial pressure (PET), and the mean arterial partial pressure (Pa), are calculated as functions of the blood-gas partition coefficient (lambda) and the diffusion coefficient (D) of the tracer gas. The lambda values vary from 0.01 to 330.0 inclusive, and four values of D are used (0.5, 0.22, 0.1, and 0.01). Three ventilation-perfusion conditions corresponding to rest and mild and moderate exercise are simulated. Under simulated exercise conditions, we compute a reversed difference between PET and Pa compared with the rest condition. This reversal is directly reflected in the relation between the physiological dead space fraction (1--PE/Pa) and the Bohr dead space fraction (1--PE/PET). It is argued that the difference (PET--Pa) depends on the lambda of the tracer gas, the buffering capacity of lung tissue, and the stratification caused by diffusion-limited gas transport in the gas phase. Finally some determinants for the reversed difference (PET--Pa) and the significance for conventional gas analysis are discussed.

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The Influence of CO2 Production and Physiological Deadspace on End-Tidal CO2 During Controlled Ventilation: A Study Using a Mechanical Model

Anaesthesia and Intensive Care ◽

10.1177/0310057x8901700415 ◽

1989 ◽

Vol 17 (4) ◽

pp. 482-486 ◽

Cited By ~ 8

Author(s):

M. A. Stockwell ◽

W. Bruce ◽

N. Soni

Keyword(s):

Carbon Dioxide ◽

Mechanical Model ◽

Carbon Dioxide Production ◽

Lung Model ◽

Co2 Production ◽

Controlled Ventilation ◽

End Tidal Carbon Dioxide ◽

Carbon Dioxide Levels ◽

End Tidal ◽

End Tidal Co2

A mechanical lung model was used to investigate the effect of varying carbon dioxide production and deadspace on the end-tidal carbon dioxide levels achieved during mechanical ventilation when using the Bain, Humphrey ADE, and circle systems. Both factors had significant influence on end-tidal cardon dioxide concentration and could result in values in excess of those considered acceptable in clinical practice. The implications of the results are discussed.

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Factors affecting expired waveform for carbon monoxide

Journal of Applied Physiology ◽

10.1152/jappl.1984.56.3.708 ◽

1984 ◽

Vol 56 (3) ◽

pp. 708-715

Author(s):

D. Z. Rubin ◽

S. M. Lewis ◽

C. Mittman

Keyword(s):

Carbon Monoxide ◽

Normal Subjects ◽

Lung Model ◽

Repeated Testing ◽

Factors Affecting ◽

Sensitivity Tests ◽

Standard Parameter ◽

Expired Gas ◽

End Tidal ◽

Computer Simulation Studies

We previously presented a method based on a computer lung model for determining the distribution of both specific ventilation and specific diffusing capacity. These argon and carbon monoxide (CO) washin and washout studies were obtained in 12 normal subjects and 24 patients with varying degrees of obstructive lung disease. In addition to end-tidal and mixed expired gas concentrations, the expired waveform for both gases was sampled. In patients we found that this method failed to adequately describe CO dynamics during the early part of expiration; predicted concentrations were higher than actual data. Modifications of the original model that satisfy all data are presented. This new model suggests that CO uptake occurs in spaces with ventilatory properties of dead space. The accuracy and reliability of these observations were established by computer simulation studies as well as by repeated testing in one subject. These proved to be highly reproducible over a period of 5 mo. Standard parameter sensitivity tests showed parameters to vary by less than 10% and to be stable even when realistic levels of noise were added to the data. We conclude that studies involving ventilation of insoluble gases are insufficient to describe gas exchange in the lung. The addition of an exchangeable gas adds significant understanding of lung function, particularly in disease.

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Distribution of ventilation and diffusing capacity in the normal and diseased lung

Journal of Applied Physiology ◽

10.1152/jappl.1981.51.6.1463 ◽

1981 ◽

Vol 51 (6) ◽

pp. 1463-1470 ◽

Cited By ~ 2

Author(s):

S. M. Lewis ◽

D. Z. Rubin ◽

C. Mittman

Keyword(s):

Normal Subjects ◽

Lung Model ◽

Uniform Structure ◽

Model Parameters ◽

Diffusing Capacity ◽

Single Breath ◽

Steady State Method ◽

Noise Measurements ◽

End Tidal ◽

And Diffusion

Conventional tests of diffusing capacity (DL) consider the lung to be a uniform structure with regard to both ventilation and diffusion. These assumptions are incorrect even in normal subjects. We present a method for determining the distribution of both specific ventilation (SV) and DL from the washin and washout of C18O and simultaneous washout of argon. Both end-tidal and mixed-expired data are fit to a two-compartment lung model; parameters that define SV and DL are assigned to each compartment. From data generated by a model, the parameters recovered were found to be relatively insensitive to realistic levels of noise. Measurements in one subject were highly repeatable. We examined 15 normal subjects and 16 subjects with varying degrees of obstructive lung disease. In both groups the better ventilated spaces generally showed a higher DL. The sum of the total two-compartmental DL's correlated with, but was found to exceed, the value obtained using the steady-state method and generally exceeded the single-breath result. We conclude that this method has potential advantages over conventional methods and is worthy of further study.

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