Low-flow anaesthesia and carbon monoxide in paediatric patients.

Editor—We read with interest the paper by Nasr and colleagues regarding carbon monoxide (CO) rebreathing during low-flow anaesthesia (LFA) in infants and children and an earlier study by the same authors. We would like to call attention to two confounding issues. First, they have stated that an electrochemical sensor was used for measurement of CO in these studies in the range 0–2000 ppm, resolution 1 SD 2 ppm (Monoxor III, Bacharach Inc., Anderson, CA, USA). According to the manual for this device, it is designed to detect and display concentrations of CO in ambient air, flue gases, or combustion equipment, and its accuracy is +5% or +10 ppm, whichever is greater. The authors have reported that inspired concentrations of CO were mean 2.0 ppm (0–14 ppm) during LFA and 2.6 ppm (0–18 ppm) in the earlier study. It is clear that these values are too small to be placed in the limits of measurement error and questionable. Secondly, there is a disagreement between the results of the two papers. 2 The authors reported that LFA increased exhaled and inspired CO and increased COHb in children ,2 yr, in contrast to their earlier study where LFA increased CO and COHb in children .2 yr. This important difference has not been explained. We suggest that the authors had not used an appropriate device for the measurement of CO and the results of the studies are contradictory and unreliable.