Low-flow anaesthesia at a fixed flow rate.
OBJECTIVE
This study attempts to assess the safety of low-flow anaesthesia (LFA) at fixed flow rates with particular reference to the incidence of a decline in FiO(2) below safe levels of 0.3 and to determine whether LFA can be used safely in the absence of an FiO(2) monitor.


METHODS
A total of 100 patients undergoing procedures under general anaesthesia at fresh gas flows of 300 ml/min of O(2) and 300 ml/min of N(2)O were monitored while maintaining the dial setting of isoflurane at 1.5% for 2 h. The changes in gas composition were analysed and even a single recording of FiO(2) of <0.3 was considered sufficient to render the technique unsafe in the absence of gas monitors.


RESULTS
The lowest recorded value of FiO(2) was 31% (v/v%). There was no incidence of adverse events necessitating the conversion from low flows to conventional flows.


CONCLUSIONS
We conclude that low flows of 300 ml/min of N(2)O and 300 ml/min of oxygen can be used safely for a period of 2 h without the use of monitors for gas analysis of oxygen and agent in adult patients weighing between 40 and 75 kgs.
Cherian
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Department of Anesthesiology and Critical Care, Jawaharlal Institute of Post graduate Medical Education and Research, Pondicherry, India. anushacherian@gmail.com
Badhe
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D000293:Adolescent; D000328:Adult; D000368:Aged; D000465:Algorithms; D000769:Anesthesia, Inhalation / Q000379:methods*; D018685:Anesthetics, Inhalation / Q000008:administration & dosage* / Q000493:pharmacokinetics; D001794:Blood Pressure / Q000187:drug effects; D005260:Female; D006339:Heart Rate / Q000187:drug effects; D006801:Humans; D007530:Isoflurane / Q000008:administration & dosage* / Q000493:pharmacokinetics; D008297:Male; D008875:Middle Aged; D009609:Nitrous Oxide / Q000008:administration & dosage* / Q000493:pharmacokinetics; D010100:Oxygen / Q000008:administration & dosage* / Q000493:pharmacokinetics; D012119:Respiration / Q000187:drug effects; D013990:Tidal Volume; D016896:Treatment Outcome; D055815:Young Adult
D018685:Anesthetics, Inhalation; D007530:Isoflurane; D009609:Nitrous Oxide; D010100:Oxygen