Low-flow anaesthesia in paediatric patients

Abstract

Editor—We were interested in the study regarding carbon monoxide (CO) rebreathing during low-flow anaesthesia (LFA) in paediatric patients.1Nasr V Emmanuel J Deutsch N et al.Carbon monoxide re-breathing during low-flow anaesthesia in infants and children.Br J Anaesth. 2010; 105: 836-841Abstract Full Text Full Text PDF PubMed Scopus (19) Google Scholar It is reassuring to note that modern anaesthetic circuits do not contribute to CO rebreathing in the context of LFA, as elegantly demonstrated by an in vitro control experiment. Although the technique is becoming increasing popular, even in paediatric practice, the absence of a single definition of LFA hampers further enquiry and consistent study design.2Baum JA Aitkenhead AR Low-flow anaesthesia.Anaesthesia. 1995; 50: 37-44Crossref PubMed Scopus (81) Google Scholar, 3Meakin GH Low-flow anaesthesia in infants and children.Br J Anaesth. 1999; 83: 50-57Abstract Full Text PDF PubMed Scopus (31) Google Scholar, 4Tohmo H Antila H Increase in the use of rebreathing gas flow systems and in the utilization of low fresh gas flows in Finnish anaesthetic practice from 1995 to 2002.Acta Anaesthesiol Scand. 2005; 49: 328-330Crossref PubMed Scopus (8) Google Scholar Meakin3Meakin GH Low-flow anaesthesia in infants and children.Br J Anaesth. 1999; 83: 50-57Abstract Full Text PDF PubMed Scopus (31) Google Scholar defined low fresh gas flow (FGF) as <1 litre min−1, and noted that when using modern circuits, the required flow is more dependent upon the circuit than patient weight, unless using basal flow. In the in vivo limb of their experiment, the authors chose a liberal definition of an LFA, which is half of minute ventilation.1Nasr V Emmanuel J Deutsch N et al.Carbon monoxide re-breathing during low-flow anaesthesia in infants and children.Br J Anaesth. 2010; 105: 836-841Abstract Full Text Full Text PDF PubMed Scopus (19) Google Scholar We feel that, by choosing a relatively higher FGF, they reduced the likelihood of detecting a clinically significant accumulation of CO. They also did not state the absolute flow rates used in the study, which reduces the applicability of their findings to the practice of anaesthetists who use the definition of <1 litre min−1. A further confounding factor to the study is the removal of 150 ml min−1 for the purpose of gas sampling. Although concentrations were recorded every 5 min, it is unclear if the sample stream was constant or intermittent. Additional information is required to enable the reader to critically appraise the impact of this methodology on the results. The CO increase noted was small and, although statistically significant, the authors acknowledge that the clinical significance of such small changes is unknown. It would be interesting to determine what CO levels are reached at the kind of very low flows (FGF <1 litre min−1) that are routinely practiced in children and relate these to critical levels of CO exposure known to produce clinical effects. None declared.