Interpretations of responses using the isolated forearm technique in general anaesthesia: a debate

The isolated forearm technique (IFT) enables an otherwise paralysed patient to communicate awareness to the anaesthetist. We present a debate that focuses on how best to interpret IFT responses. On one side, Pandit argues that there is a range of response types from none through to movement initiated by the patient to alert the researcher. He also presents a de novo numerical scale by which IFT responses could be classed. Each response type reflects the underlying mental state (degree of unconsciousness), and he concludes that the effect of general anaesthesia on patients is not binary but heterogeneous. There can be mental states resulting from anaesthesia that produce adequate levels of conscious impairment sufficient for surgery to proceed, but in which a degree of wakefulness, including a capacity for later recall, is retained (a state previously termed 'dysanaesthesia'). A literature review of IFT (31 trials) is presented to support this assertion. In rebuttal, Russell and Wang argue that IFT response types are not so discrete, and that the IFT technique precludes higher levels of response. They argue that overinterpretation of IFT responses might in fact result in a greater risk of accidental awareness; a binary interpretation of the IFT response is the safest option. All authors agree that the IFT has a role in clinical practice and the study of anaesthetic mechanisms.