الفهرس 
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Abstract
Introduction of new volatile anaesthetic agents with low solubility and low anaesthetic potency has emphasized the need for reducing anaesthetic agent consumption by lowering fresh gas flow. In addition to pure economic or ecological benefits, low-flow may have a positive impact on the quality of patient care.
Most modern anaesthesia are equipped with a circle rebreathing system which allows for a considerable reduction of fresh gas flow rates. The real benefits of rebreathing techniques become evident only when the fresh gas flow rate is reduced to less than half the minute ventilation of the patient, usually to less than 3.0 L/min.
Low-flow anesthesia can be defined as a technique where fresh gas flow is adapted to satisfy the patient’s need for oxygen (about 200ml/min) and for volatile anaesthesics, but where excessive FGF may be used to vent unwanted components (e.g. nitrogen or methane to the anaesthesia gas scavenging system. In addition , there is a special CO2 absorber which removes expired CO2 from the breathing circuit. Typically, based on FGF, the following categories can be listed:
High flow anaesthesa uses a fresh gas flow, which is close to the patient’s minute ventilation (on average 3 to 6 L/min in a normal adult).
- Low-flow anaesthesia uses a fresh gas flow of less than half the minute ventilation of the patient, which is most often less than 3.0L/min on average in a normal adult.
- Minimal flow anaesthesia, the fresh gas flow is reduced to 0.5 L/min.
- In closed system anaesthesia, fresh gas flow is adapted to equal the patient’s need for oxygen and anaesthetic agents.
Technical requirements for the safe performance of low-flow anaesthesia include: Monitoring of oxygen concentration and alarm settings to avoid hypoxic gas mixture, monitoring Anaesthetic gas concentration inside the breathing circuit, leak free anaesthetic circuit.
Extensive monitoring for minute volume, oxygen saturation, airway pressure and CO2 is an important component required for carrying out low-flow anaesthesia. The fresh gas decoupling function lets the anaesthtist reduce the fresh gas flow to operate in the low-flow or minimal flow mode without having to worry about the effect of the fresh gas flow on the applied tidal volume.
Advantages of low-flow and minimal flow anaesthesia include, Avoidance of the need for in-circuit-humidifiers, raise the temperature of inspired gas by up to 6 degrees Celsius, Reduction of cost by about 25% by reduction of fresh gas inflow to 1.5L/min, reduction of the environmental pollution with scavenged gas.
Meanwhile accumulation of small amounts of nitrogen, minute amount of methane, acetone, carbon monoxide and inert gases in the circuit may be problematic during performance of low-flow anaesthesia.
Degradation of volatile anaesthetics by carbon dioxide absorbents into toxic products such as (compound A) formation with sevoflurane causes renal toxicity in rats thus anaesthiologist advise to use a fresh gas flow of more than 2L/min when using sevoflurane.
Low-flow anaesthesia is safe and easy for routine use. The introduction of newer anaesthetic agents with low solubilities and relatively higher costs has caused a resurgence of interest in the technique. Its use results in costs savings, and other benefits such as a reduction of environmental wastage and preservation of heat and humidity of the patient. Some anaesthetists encourage the use of low-flow technique, as long as highly equipped anaesthesia machines are available, while others are still cautious about the practice of low-flow anaesthesia.