Closed-circuit and high-flow systems: examining alternatives.

The nonrebreathing system has been with us since Morton demonstrated the administration of diethyl ether in 1846. Its current popularity is evidenced by the extensive use of the Bain system. The greatest advantage, its history of patient safety, is related to the circuit's simplicity and the knowledge that the delivered concentration equals the inhaled concentration. Most disadvantages of the nonrebreathing system are related to the required high delivery rates: operating room and environmental pollution, necessity of scavenging gases, cost of agents, energy loss through no-return operating room ventilation, inhalation of dry gases, and the inability of the anesthesiologist to quantitate patient uptake of oxygen and inhaled anesthetics. Partial rebreathing systems reduce the disadvantages related to high delivery flow rates but, owing to the required rebreathing, do not permit the anesthesiologist to know the inhaled anesthetic concentration. A carbon dioxide absorber is necessary. It is still impossible to quantitate uptake by the patient, and it is difficult to conclude that any real net advantage results from the use of partial rebreathing systems. When modern-day technology provides the practitioner with an appropriate anesthesia machine, it is likely that closed-circuit anesthesia will become the method of choice for anesthesia delivery. Although the economic, ecologic, and physiologic advantages of this system are important, its greatest asset is the ability to monitor important respiratory and cardiovascular variables in patients noninvasively. Important information provided to the anesthesiologist by the patient during closed-circuit anesthesia is lost through the pop-off valve when high-flow systems are used. During closed-circuit anesthesia the gas machine itself becomes a monitor. Practicing anesthesiologists will embrace closed-circuit anesthesia practice when-and if-they are convinced that it provides an opportunity for better and more efficient patient care than other systems.