Fourteen fallacies about the isolated forearm technique, and its place in modern anaesthesia

The isolated forearm technique (IFT) was described by Tunstall in 1977 1 to address the high incidence of awareness with recall (AWR) associated with general anaesthesia for caesarean section. The technique consisted of a padded cuff/tourniquet around the right upper arm. The cuff was inflated before giving any neuromuscular blocking drug (NBD) and was deflated shortly after delivery when anaesthesia was deepened. Since Tunstall used a suxamethonium infusion, the arm then became paralysed. The technique was modified to enable its use with non-depolarising NBDs 2 and later, the tourniquet's position was changed to the forearm so that the normal blood pressure cuff could be on the upper arm of the same side, leaving the other arm unimpeded for the pulse oximeter and intravenous cannula. With the tourniquet on the forearm, neuromuscular integrity under and beyond the cuff can be checked by peripheral nerve stimulation to the ulnar and median nerves at the elbow. Compared with an anaesthesia brain monitor (ABM), the modified IFT meets virtually all the requirements of the ‘ideal’ depth of anaesthesia monitor (Table 1) and is the only direct monitor of patient consciousness in the presence of NBDs. Despite this, because of the plethora of misleading statements in the literature leading to widespread misunderstanding, only a few have used it clinically 2-4 or in research 5-9. The majority of the misleading information consists of fallacies 10 repeated uncritically from publication to publication. 1 Patients’ responses do not correlate with the traditional clinical signs, peri-operative dreaming or postoperative memory 11, 12. The problem is not the IFT. Clinical signs are unreliable indicators of consciousness 8, 13-15 and it is not possible to differentiate cases of AWR using clinical signs 8, 15. The amnesic effects of anaesthetic drugs generally ensure lack of recall even if they do not always ensure unconsciousness 8, 13. Depending on the actual anaesthetic, 12–40% of patients dream during anaesthesia and the relationship, if any, to consciousness is unclear 16. 2 The technique can only be used for 20 minutes or ischaemic nerve block occurs 11, 12, 17, 18, with an unknown risk of nerve damage 19. The tourniquet only needs to be inflated long enough to allow the blood levels of NBDs to fall below the level required for muscle paralysis. Traditionally, although the tourniquet has been inflated for 20 minutes, Cameron 4 describes only 5 minutes’ inflation while I have used up to 40 minutes. I have never seen ischaemic nerve block with the tourniquet on the forearm, and the neuromuscular integrity of the hand can be easily monitored using a peripheral nerve stimulator as described above. An ischaemic nerve block recovers within minutes of tourniquet deflation. If even a small movement of the fingers can be observed on tetanic stimulation, this is usually enough to observe a response of the fingers to command. 3 The arm becomes paralysed when the tourniquet is deflated 18, 20. This rarely happens with judicious doses of most non-depolarising NBDs 2-4. Curare, alcuronium, fazadinium, atracurium and vecuronium have all been used with no problems. After pancuronium (0.1 mg.kg−1) the arm may become paralysed after tourniquet deflation 20, but with lower doses (0.05 mg.kg−1), sufficient power remains to allow visible hand movements 21. Rocuronium remains to be investigated although I have used 0.5 mg.kg−1 successfully for several patients. 4 It is not possible to distinguish between purposeful and reflex movements 22-25. This myth arose following two studies 22, 23 in which the authors observed the patients from a distance with no attempt to communicate directly with them. Simply observing hand movements is inadequate 8. Reflex versus purposeful responses can be easily differentiated by asking the patient, by name, “squeeze my fingers” 8, 26, 27. 5 Response to command does not really indicate consciousness 28, 29. There is a frequent misconception that if patients have no recall then the intra-operative responses must have occurred at a preconscious level. In reality, these patients are conscious but have no subsequent recall 8, 13. In non-paralysed patients, response to command unequivocally indicates consciousness. The IFT is simply a means to allow a paralysed patient the ability to respond 13. 6 It's too late – the patient is already awake 14, 30, 31. Initial IFT responses occur when the patient is conscious but not laying down long-term memory, or they are dissociated from their environment 32. However, even at this early stage, not only is it reassuring for patients to know that their conscious state is recognised, but reassurance at this stage may prevent 8, or even cure, post-traumatic stress disorder that occurred as result of being conscious during previous surgery, even if there is no conscious recall of that event 33. In one study, the IFT revealed 20–80% of patients responded to commands before or during intubation and the authors were then able to administer a further bolus of etomidate to re-induce unconsciousness – only one patient had recall 14. 7 Anaesthesia has to be too light/too deep when the IFT is used 24, 25. Some believe that to use the IFT, one must use minimal anaesthesia so that responses can be observed. This is not true; one uses one's normal anaesthetic and monitors its effectiveness with the IFT. On the other hand, some believe that in the presence of NBDs, if your anaesthetic has to prevent responses, then that is too deep. This latter view would seem to accept that as long as there is (one hopes) no memory, operating on awake patients who expect to be unconscious, and who may or may not be in pain at the time, is acceptable. 8 Patients hear the commands but are unable to respond 25. This happened once, in the very early days of the technique 2, and has not been reported since. After surgery, the patient reported hearing my voice asking her to open and close the fingers of her left hand, but she was unable to do so. The tourniquet was on the left upper arm, and stimulating the ulnar and median nerves at the elbow with a short tetanus resulted in strong flexion of the fingers. Two possible explanations are: (1) the patient was trying to move her dominant (right) paralysed hand; (2) there was a conduction block under the tourniquet on the left upper arm at the time of the commands. 9 Patients hear the commands but ignore them 24, 25. In my practice, this has occurred with two patients in the distant past when using a generic tape. One patient told me she ignored the command so as to enjoy a dream, the second thought I was speaking to someone else. After the second case the command was personalised with the patient's name and there have been no further such occurrences. 10 Patient cooperation is required 34. Patients who have suffered AWR in the presence of NBDs describe ‘searching their body’ for something to move to indicate their plight. Patient cooperation is unlikely to be a problem 8. 11 There is no commercial system 19. The only equipment required is a manually inflatable blood pressure cuff or a tourniquet, both of which are readily available. Talking to the patient does not require equipment. 12 It is too complicated, too cumbersome and laborious, and may distract the anaesthetist 19, 35. Admittedly the IFT requires a little fore-thought to apply the cuff/tourniquet but the technique is simple 2-4, 7, 8 and can be used in children 8, 36. Once the cuff is applied, at its most basic, the IFT is simple observation with the occasional command to the patient. 13 It is unreliable and of historical interest only 37, 38. It is far from ‘unreliable’. It is the only direct means of communicating with paralysed patients and is described as the ‘gold standard’ for both consciousness monitoring 39, 40 and the ‘critical testing of depth of anaesthesia monitors’ 41. 14 You cannot take the blood pressure/you cannot use an intravenous infusion. The blood pressure can be measured on either arm, as normal, and an intravenous cannula can be inserted in the opposite arm. Clinically, although there is no evidence that ABMs ensure unconsciousness during surgery 6, 42, 43, the National Institute for Health and Clinical Excellence recommends their use, on the grounds that they may reduce the incidence of recall 44. Clearly, some believe that lack of recall is an adequate definition of general anaesthesia 44, 45 but the ethics of operating on conscious patients with amnesia is questionable 13, 32, 46. Since NBDs prevent patient movement, a valuable indicator that anaesthesia is becoming lighter, reducing the dose of NBDs is an important step in minimising the risk of AWR. The IFT can play a major role in this strategy, not only allowing the arm to remain unparalysed between surgically necessary doses of NBDs, but also by allowing the differentiation between reflex and conscious movement 8. At critical points during anaesthesia (e.g. prolonged intubation attempts or situations deemed to require a reduction in anaesthetic agent) it is very reassuring to know that the patient is still unconscious. Even without a ‘formal’ isolated arm, when a patient moves during surgery, the ‘IFT concept’ (asking the patient to move some unparalysed part of his/her body) has a real-time role in the direct monitoring and assessment of patient consciousness, whether NBDs are used or not. When discussing anaesthesia with patients worried about awareness, they readily understand the IFT and are relieved that they will have a means of communication should intra-operative awareness occur 8. In research, the IFT should have a major role in the assessment of ABMs. Those few studies that have explicitly investigated how reliably an ABM tracks hypnotic drug concentrations during the maintenance phase of anaesthesia have found the relationship to be too weak and variable to be clinically useful 47. Although the IFT is the ‘gold standard for the ‘critical testing of depth of anaesthesia monitors’ 43 in the presence of NBDs, no depth of anaesthesia monitor has been validated against the IFT in paralysed patients, and those few monitors that have been so studied fail to identify consciousness with any reliability 6, 42, 43. Despite this, ABMs continue to proliferate and emerge on to the market without ever undergoing such critical testing. Only tens of patients are required to investigate how accurately an ABM output tracks IFT responses, compared with the thousands required to investigate AWR. Much time, effort, and money has been spent on AWR research but should we not also be actively seeking to establish the proportion of patients who are conscious during surgery? Admittedly, as Professor Sleigh points out in this issue of the Journal 48, there are no large scale comparison trials with the IFT to investigate the incidence of AWR but, since the IFT is the gold standard of consciousness monitoring 39, 40, if patients are kept unconscious then there will be no AWR. As Smith and Pell state 49 with regard to the lack of controlled trials involving parachutes, “individuals who require that all interventions be validated by a randomised control trial need to come down to earth with a bump.” No external funding and no competing interests declared.