The place of the isolated forearm technique in modern anaesthesia: yet to be defined

Authors


I agree with Dr Russell [1] that the isolated forearm technique (IFT) has come in for a lot of misinformed, unfair, and irrational criticism. The IFT is simple in concept, does not require complex and expensive equipment, and has been around for more than 30 years. We must therefore ask the obvious question: “Why isn't the IFT routinely used to eliminate awareness associated with general anaesthesia?” We might also consider the subsidiary question: “Why do anaesthetists seem to prefer to use EEG-based methods of estimating unconsciousness?” Are we just a lazy and conservative profession? Our practice is moulded by a wide variety of influences, but I would suggest that the false perceptions associated with the IFT – that have been so strongly enumerated by Russell – are only a small part of the reason for the lack of widespread uptake of the IFT. In my view the main reasons are that: (i) the conduct of the IFT requires significantly extra effort that is potentially dangerously distracting; and (ii) there does not exist a good epidemiological evidence base showing that use of the IFT results in a greater number of happier patients (or at least, a lower incidence of postoperative recall). I am not making a claim in favour of routine EEG monitoring to prevent intra-operative recall. In their present form, all EEG-derived anaesthesia-based monitors (ABM) have been shown to be quite poor at tracking the conscious state of the patient [2], but they probably have some role as a ‘belt-and-braces’ check for total intravenous anaesthetic techniques, and in high-risk patients who cannot tolerate > 0.7 MAC of volatile anaesthetic drug. In my personal clinical practice, when I am faced with the rare patient who has suffered a previous instance of intra-operative awareness – or who has an excessive fear of this complication – I tell him/her that I plan to use both a brain-wave monitor and the IFT to confirm that he/she is unconscious while under anaesthesia. This practice is based on common sense rather than epidemiological data, but is easily comprehended by patients, and provides some comfort for them.

Performing the IFT is a significant distraction and may be dangerous

All practising anaesthetists know that the operating theatre is full of stimuli that compete for their attention, and they work in an environment in which their capacity for multitasking is often stretched [3]. In moments of crisis, it is crucial that our limited attention capacity is focused on the most relevant life-threatening issues; however, awareness is more likely at just these times of crisis. Even when using an automated electronic voice command, the IFT, in its present form, is a significant added perceptual and motor load on the single-handed anaesthetist (Table 1). Positive IFT responses will commonly occur around the time of tracheal intubation [4] – especially when the intubation is particularly prolonged and difficult. At these times, the primary focus of attention should be on securing the airway and achieving adequate ventilation and cardiovascular stability – not in checking whether accidental deflation of the IFT cuff has caused paralysis of the hand muscles, etc. Similarly, when the anaesthetic concentration has to be reduced because of cardiovascular compromise from life-threatening haemorrhage, we should properly be concentrating on restoration of blood volume and clotting.

Table 1. The processes required to check for possible intra-operative awareness when using: (a) the IFT; (b) an EEG monitor; and (c) an end-tidal volatile anaesthetic gas (ETAA) monitor
(a) using the IFT:
 1) Set up the extra cuff, neuromuscular junction monitor, ± electronic patient auditory command system. (N.B. there are no automatic auditory alarms).
 2) Evaluate the times and doses of when the neuromuscular blocker was given and their relationship to how long the cuff has been inflated or deflated.
 3) Check adequate cuff inflation (50 mmHg above systolic blood pressure).
 4) Check lack of paralysis in the hand using the neuromuscular monitor.
 5) Give the patient a specific named command to move his/her hand.
 6) See if any movement occurs in relationship to the command.
 7) If a movement has occurred, manually check the patient's cognition status with further commands.
 8) Adjust the anaesthetic drug delivery accordingly.
 9) Remember to deflate/re-inflate cuff if long operation.
(b) using an EEG monitor:
 1) Place electrodes.
 2) Set the alarms.
 3) Glance at the raw EEG waveform to confirm the reliability of the BIS number.
 4) Adjust the anaesthetic drug delivery accordingly.
(c) using the ETAA monitor:
 1) Set the alarms.
 2) Glance at the vaporiser and anaesthetic monitor to check the gas waveform.
 3) Adjust the anaesthetic drug delivery accordingly.

Does it work?

The other main reason for the poor uptake of the IFT is the lack of relevant convincing studies. At least 20 papers have been published on the IFT technique, and these do indeed show an encouraging and consistent ‘proof of principle’. These papers report the responses of between 12 and 184 patients (mostly n = 20–40), under a variety of different general anaesthetic techniques. Often, these patients receive little or no volatile general anaesthetic drug [5] and are only studied around the time of tracheal intubation. There are few studies that investigate the usefulness of the IFT in large numbers of patients, over the whole course of surgery, and who are receiving a modern volatile-based ‘heavy’ anaesthetic technique [6]. In this instance, the incidence of IFT responsiveness seems to be very low, but rare events are often a manifestation of unusual, and unexpected, causative processes. To minimise intra-operative patient recall, the three options available to the anaesthetist are: (i) the IFT; (ii) some form of ABM (usually the bispectral index (BIS)) and; (iii) maintenance of end-tidal volatile anaesthetic concentrations > 0.7 MAC. From the results of several large-scale epidemiological studies, it would seem that either maintaining the end-tidal volatile anaesthetic concentrations > 0.7 MAC, or keeping the BIS < 60, will be associated with a low (but not zero) incidence of intra-operative explicit recall [7]. Like all the ABM systems except for the BIS, there is no accurate estimate of the incidence of intra-operative recall with the use of the IFT. To obtain reliable epidemiological estimates of this incidence (< 1:500) would require a study of many thousands of patients in whom the IFT was used and acted upon. The incidence of recall when using an IFT is likely to be very low, because higher concentrations of anaesthetic drug are needed to block responsiveness than those required to block memory [8]. However, this remains a speculative assumption until a large study is done. There may be numerous (known and unknown) possible reasons why the IFT might fail to detect responsiveness quickly enough for the anaesthetist to increase the anaesthetic to prevent recall entirely. For example, the anaesthetic drugs can occasionally induce a catatonic ‘locked-in’ state in the partially anaesthetised, but conscious, patient [5], or various unpredictable rare technical failures could occur (e.g. cuff failure, unexpectedly prolonged clearance of neuromuscular blocking drugs, limb ischemia, etc). We just won't know the incidence of these potential rare problems, until a large prospective trial is done.

Conclusions

At present we have no clear idea of either the actual benefits of the widespread use of the IFT, or its risks – when applied in modern day-to-day anaesthetic practice. The IFT deserves to be evaluated in appropriately designed, public-good funded, large scale studies.

Competing interests

No external funding and no competing interests declared.

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