LOW AND MINIMAL FLOW INHALATIONAL ANESTHESIA

Purpose: To describe the pharmacokinetic behaviour and practical aspec ts of low (0.5-1 l.min(-1)) and minimal (0.25-0.5 l.min(-1)) flow anae sthesia. Methods: A Medline search located articles on low flow anaest hesia, and computer simulated anaesthetic uptake models are used. Prin cipal findings: Most, 85-90%, of anaesthetists use high fresh gas flow rates during inhalational anaesthesia. Low/minimal flow anaesthesia w ith a circle circuit may avoid the need for in-circuit humidifiers, ra ise the temperature of inspired gases by up to 6 degrees C, reduce cos t by about 25% by reduction of fresh gas flows to 1.5 l.min(-1) and re duce environmental pollution with scavenged gas. Knowledge of volatile anaesthetic pharmacokinetic behaviour facilitates the use of minimal/ low flow rates, Small amounts of nitrogen or minute amounts of methane , acetone, carbon monoxide, and inert gases in the circuit are of no c oncern, but the degradation of desflurane (to carbon monoxide by dry a bsorbent) and sevoflurane (to compound A by using a fresh gas flow of > 2 l.min(-1)) must be avoided. With modem gas monitoring technology, safety should be no more of a concern than with high flow techniques. Conclusion: The use of fresh gas flow rates of < 1 l.min(-1) for maint enance of anaesthesia has many advantages, and should be encouraged fo r inhalational anaesthesia with most modern volatile anaesthetics.