Low‐flow anaesthesia

Abstract

SummaryAlthough many anaesthesia machines are equipped with circle rebreathing systems, inhalational anaesthesia remains frequently performed using relatively high fresh-gasflows. The major advantages of rebreathing techniques can be achievedonly ifthe fresh-gas flow is reduced to I Imin-' or less. Although there are potential risks associated with low-flow anaesthesia, modern anaesthesia machines meet all the technical requirements for the safe use of low-flow techniques if they are used in conjunction with equipment for monitoring inhaled and exhaled gas concentrations; these monitors are already increasingly available and, in the near future, are likely to become an obligatory safety standard in many countries. For both economic and ecological reasons, the use of new inhalational anaesthetics, with low tissue solubility and low anaesthetic potency, can be justified only i f the eficiency of administration is optimised by using low-flow anaesthetic techniques.

Low and minimal flow inhalational anaesthesia

“…Without this reduction, progressively more nitrous oxide is left in the circuit as uptake decreases which results in a slow decrease in oxygen concentration, s7 The slow time constant for circuit composition changes at low flow rates allows longer for detection and response before dangerous levels of hypoxia develop should an hypoxic mixture be delivered from the flow meters than when using high flow rates ( Figure 5). 38 The routine use of inspired oxygen monitoring further reduces the potential for hypoxia.…”

Assessing the clinical or pharmaco‐economical benefit of target controlled desflurane delivery in surgical patients using the Zeus® anaesthesia machine*

“…Economic and environmental concerns have led to the development of semi-closed circuits for delivery of volatile anaesthetics in which a significant proportion of the volatile anaesthetic mixture is re-breathed [1], resulting in a difference between delivered and inspired concentrations depending on the fresh gas flow (FGF). At some times during a case, a high FGF is needed to enable rapid control of end-tidal anaesthetic concentrations (at the cost of greater expense and environmental pollution) and at other times a low FGF is acceptable when end-tidal concentrations are stable over sustained periods [2].…”

Avaliação da anestesia com baixo fluxo de gases, comparando ventilação com pressão controlada à ventilação com tempo controlado - pressão limitada e fluxo constante de gases: modelo experimental em coelhos

“…53, Nº 1, Janeiro -Fevereiro, 2003 a realmente inalada, necessitando de ajustes no vaporizador. Estes ajustes podem ser explicados pela maior inércia que ocorre no sistema respiratório do aparelho de anestesia, durante o baixo fluxo, por haver relação inversa entre fluxo e concentração, ou seja, quanto maior o fluxo menor a concentração ajustada no vaporizador para se oferecer uma mesma concentração deste agente anestésico 5,32 . A monitorização deste parâmetro deve ser efetuada para que concentrações muito baixas ou excessivas não possam ser ofertadas inadvertidamente aos pacientes.…”

“…Gas flow used in non-rebreathing system was above 4 L.min -1 and in rebreathing systems it was of 500 to 1000 ml.min -1 . 32 Revista Brasileira de Anestesiologia Vol. 53, Nº 1, Janeiro -Fevereiro, 2003 BONETTI, FANTONI AND AULER JR Animals remained for 20 minutes in each experimental moment.…”