The fresh‐gas flow sequence at the start of low‐flow anaesthesia

I was interested to read that Sobreira and colleagues (Sobreira et al. Anaesthesia 2001; 56: 379–80) have confirmed our previously reported findings [1], that Mapleson's theoretical computer spreadsheet model [2] is essentially accurate in predicting the first 20 min of low-flow anaesthesia. However, in our study (n = 30 in each group) the rate at which end-tidal values of inhalational agents (PE′an) reach 1 MAC is inversely related to their solubility. Hence, at 1 min, mean PE′an were 0.48, 0.89 and 1.09 MAC units for isoflurane, sevoflurane and desflurane, respectively. In contrast, values of PE′an at 1 and 2 min reported by Sobreira et al. (n = 7 in each group) were higher for sevoflurane followed by isoflurane and desflurane. Whilst it is difficult to compare studies involving different patients, sample sizes and experimental protocol directly, it is nevertheless useful to point out subtle differences in the results.