The isolated forearm technique in non‐paralysed patients

We are pleased that Professor Pandit persisted in performing and publishing his observational study of the isolated forearm technique (IFT) in unparalysed, spontaneously breathing patients [1], despite initial opposition. It is also encouraging to see that all patients in this trial were unconscious during their surgery. However, we disagree with his conclusion that neuromuscular blockade somehow causes changes in patient perception, such that consciousness (ie a positive IFT response) becomes more likely at deeper levels of anaesthesia. This is counterintuitive, given that muscle relaxants potentiate volatile agents and reduce the minimum alveolar concentration (MAC) [2]. Pandit’s conclusion would only be legitimate if he had included a neuromuscular blockade group in his study that received exactly the same anaesthetic technique and dose, and found that there were positive IFT responses in this group. We think that Pandit’s conclusion may be based on a misinterpretation of the published literature. He states that Baraka et al. [3], and Zand et al. [4] observed high levels of responsiveness in paralysed patients despite deeper anaesthesia. Pandit believes that the end tidal concentrations of inhalational anaesthetic agents in these two studies were in the region of 1 – 1.8 MAC, higher than in those of his spontaneously breathing patients who moved non-specifically (end tidal concentrations of approximately 0.9 MAC). This belief is incorrect. Both these studies were for caesarean section and virtually all the responses occurred between induction and delivery. In the study by Baraka et al. [3], the end-tidal anaesthetic concentrations were not measured, but were set on the anaesthetic machine and vaporiser (halothane 0.5% in 50% nitrous oxide). Zand et al. [4] used sevoflurane at a pre-set vaporiser inspired concentration of around 2% in 50% nitrous oxide. Although Zand et al. described an apparently adequate end-tidal anaesthetic concentration in excess of 1 MAC, during such an early stage of anaesthesia, the end tidal concentration will not not reflect brain concentration. Simulation of agent uptake (Gasman, http://www.gasmanweb.com/software. html) using these pre-set anaesthetic concentrations suggests that Baraka et al.’s patients [3] would have taken in excess of ten minutes to achieve a brain concentration of 1 MAC, and Zand et al.’s patients [4] would have taken at least five minutes. The induction to delivery interval was 7.5 minutes in Baraka et al.’s study [3], but not reported in Zand et al.’s study (although not likely to be very different). In both studies, therefore, the vast majority of isolated forearm responses would have occurred in the presence of an inadequate depth of anaesthesia. Another misconception occurs when using the isolated forearm technique in the absence of a command to signal their wakefulness,in thinking that paralysed patients who awaken do not move spontaneously. We have performed studies in which the command to move a hand was given every one to two minutes, and so almost immediately after a patient awakens, they are given a command to move the hand and have little opportunity to move spontaneously [5]. However, in non-trial situations when the isolated forearm technique is used without a tape recorder, we have observed many patients who moved a foot, an