Articles: closed-circuit-anesthesia.
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Acta Anaesthesiol Belg · Jan 1990
Respiratory diagnostic possibilities during closed circuit anesthesia.
An automatic feed back controlled totally closed circuit system (Physioflex) has been developed for quantitative practice of inhalation anesthesia and ventilation. In the circuit system the gas is moved unidirectionally around by a blower at 70 l/min. In the system four membrane chambers are integrated for ventilation. ⋯ Disregulations of metabolism, e.g. in malignant hyperthermia, are seen in a pre-crisis phase (increase of oxygen consumption and of CO2 production), and therapy can be started extremely early and before a disastrous condition has developed. Registration of compliance is only one of the continuously available parameters that guarantee a better and adequate control of lung function (e.g. atalectasis is early detected). The newly developed sophisticated anesthesia device enlarges tremendously the monitoring and respiratory diagnostic possibilities of artificial ventilation, gives new insights in the (patho)physiology and detects disturbances of respiratory parameters and metabolism in an early stage.
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Acta Anaesthesiol Belg · Jan 1990
Comparative StudyClinical applications of low flow and closed circuit anesthesia.
Minimal Flow Anesthesia, an extreme technique of semiclosed use of rebreathing systems performed with a fresh gas flow of 0.5 l/min, can be managed with already available anesthesia machines. As a standardized fresh gas volume with fixed composition is used, due to the exponential decrease of the patient's gas uptake, the gas composition within the breathing system may change markedly during the time course of anaesthesia. ⋯ The need for continuous adjustment of the fresh gas controls, the insufficient accuracy of the dosaging systems and the impossibility to calculate precisely the uptake figures in the individual case are essential obstacles for the routine use of this method. An account of the clinical realization of both techniques is given and the specific advantages and disadvantages are considered: although modern anesthesia machines are designed especially for the use of even lowest fresh gas flow rates, quantitative Closed System Anesthesia will not become a technique for routine clinical practice until apparatus with computer-aided closed loop feedback control of the fresh gas supply will be available.
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Opinions vary on the monitoring requirements associated with low flow to closed circuit anesthesia. Fresh gas flow rate affects variables of anesthesia ventilation such as the time constant of the breathing system, the inspired concentrations of O2, N2O and anesthetic vapor and the potential for rebreathing. ⋯ However, none of these safety monitors is beyond the scope of the "essential requirements" proposed for anesthesia workstations by international standard-writing groups, such as CEN or ISO. It may hence be concluded that fresh gas flow rate does affect variables to be monitored, but it does not affect essential monitoring requirements.
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Anaesth Intensive Care · Nov 1989
The influence of CO2 production and physiological deadspace on end-tidal CO2 during controlled ventilation: a study using a mechanical model.
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 carbon 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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In a laboratory model, humidity output was investigated in relation to the design of a circle absorber system. A 70-kg subject was simulated with fresh gas flows of 0.5, 2 or 5 litre min-1. Different circle systems, absorption canisters and tubings were studied. ⋯ Coaxial tubing only moderately increased the humidity. If a fresh gas flow of 0.5 liter min-1 was used, optimum moisture contents were attained, irrespective of the circle system tested. Low fresh gas flows, a small canister and an Eger A type circle system, were factors which increased humidification.