Clinical applications of low flow and closed circuit anesthesia

Abstract

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. Nevertheless, by this degree of fresh gas flow reduction, being very close to the patient's gas uptake, the advantages of the rebreathing technique can be achieved nearly extensively. Closed System Anesthesia, however, the anesthetic technique by which just these volumes of oxygen, nitrous oxide, and volatile anesthetics are applied, which are taken up by the patient at the particular time, can't be performed satisfactorily even if highly sophisticated equipment is used. 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.