Articles: closed-circuit-anesthesia.
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Acta Anaesthesiol Scand · Aug 1989
Carbon dioxide distribution in Mapleson A and D systems: an experimental study.
The distribution of CO2 in the Mapleson A and D rebreathing systems was investigated experimentally during controlled ventilation and with the expiratory valve closed during inspiration. Maximal and minimal levels of CO2-concentration obtained from capnograms along the tubing were used to construct "gas profiles". For both systems, high tidal volumes and low fresh gas flows resulted in a high degree of gas separation with a pool of alveolar gas near the expiratory valve, and longitudinal gas mixing was minimal. ⋯ The end of the tubing nearest the patient was found to act as a reservoir for alveolar gas in the Mapleson A system and fresh gas in the Mapleson D system. Fresh gas utilization in the Mapleson D system was somewhat less efficient than in the Mapleson A system due to the fresh gas admixture to exhaled alveolar gas in the patient-near end of the tubing during expiration. The replacement of the usual expiratory valve of the Mapleson A system by a valve which is closed during inspiration makes the A system an alternative to the D system for controlled ventilation.
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Few studies have described the pharmacokinetics and pharmacodynamics of isoflurane (I) during the postoperative recovery room stay. In this study the influence of balanced anesthesia with I on the postoperative course was investigated by studying pulmonary washout of I and its effect on arterial oxygen saturation. METHODS. ⋯ All patients were extubated after a mean of 22 min at a mean etI of 17% of washout. After extubation, pulse oximetry indicated hypoxygenation in 18 patients (= 36%) during 2 periods (Fig. 4): (1) at a mean cIet of 0.1 Vol.-% (= 15% of washout) after a mean of 8 min; and (2) at a mean cIet of 0.08 Vol.-% (= 12% of washout) a mean of 19 min following extubation. Further episodes of hypoxygenation occurred as much as 40 min post-extubation. (ABSTRACT TRUNCATED AT 400 WORDS)
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Acta Anaesthesiol Scand · Jul 1989
Removal of halogenated anaesthetics from a closed circle system with a charcoal filter.
Halogenated anaesthetics may be removed from a closed circle system by means of a charcoal filter. With this technique dispersion to the atmosphere and a possibly destructive effect of the halogenated volatiles on the protective layer of ozone is avoided. Removal of halothane or isoflurane with a charcoal filter was studied in a closed circle system connected to an artificial lung. ⋯ However, the slopes deviated significantly from the theoretically predicted slopes, possibly because of adsorption to hoses and bags and unequal distribution of the volatiles in the system. Halothane was eliminated more slowly than isoflurane. This study demonstrates that halogenated volatiles are eliminated in an exponential way following charcoal filtration and the rate depends on the ventilation and type of volatile.
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In clinical practice, the addition of positive end-expiratory pressure (PEEP) into a standard anesthesia circle circuit decreases the delivered tidal volume (DTV) to a patient. We studied the magnitude of the delta DTV/delta PEEP relationship in two commonly used anesthesia systems. In addition, the magnitude of the delta DTV/delta PEEP relationship varies with both pulmonary compliance and volume of gas contained in the patient's breathing system between the ventilator and PEEP valve site, and this was also evaluated. Routine monitoring of expired tidal volume should be used whenever PEEP is added to an anesthesia circuit.