2005 Annual Scientific Meeting - CLICK FOR PROGRAMME

The Isolated Forearm Technique

 Ian F Russell, Department of Anaesthesia, Hull Royal Infirmary

Failure to respond to command is currently the accepted indicator of the threshold between consciousness and unconsciousness. To date, only the Isolated Forearm Technique (IFT) can directly detect the change from unconsciousness to consciousness during “anaesthesia” in the presence of muscle relaxants: The IFT, first described by Tunstall [1,2] directly assesses the patient's ability to respond to a simple command during surgery. Despite many publications [3-7] which have successfully used the IFT the technique continues to be criticised on the grounds that:

1. Response to command does not correlate with the clinical signs of light anaesthesia, post op dreaming or recall

2.  The IFT can only be used for 20 minutes as the arm will become paralysed.

3.  It is difficult to distinguish purposeful arm movements from reflex movements.

4.  The response to command does not indicate that the patient is conscious.

5.  You cannot take the blood pressure

6.  You cannot use an i.v. infusion

7.  It’s too late – the patient is awake.

With the availability (at a very significant price) of “depth of anaesthesia” brain monitors is there any future for the IFT? There is no evidence in the current literature that the available brain monitors can reliably detect consciousness during surgery: these monitors do not yet have the high level of discriminative power to be definitive methods for identifying depth of anaesthesia end-points [8-9]. The best they can do is give you a number associated with a probability that your patient is unconscious. A target level of propofol when using TCI gives you the same information – a probability that your patient is unconscious! Is a TCI pump a brain monitor? The B-Aware [10] and Safe 2 [11] studies suggest that BIS monitoring may reduce the incidence of awareness but there are several problems with the applicability of these studies to clinical practice [12]. The IFT is the gold standard [13] against which all consciousness monitors should be assessed. No monitor has yet been properly assessed against the IFT in paralysed patients undergoing surgery. In my practice, a brain monitor backed up with the IFT has distinct advantages over either technique used alone! 

References:

1.          Tunstall ME. Detecting wakefulness during general anaesthesia for caesarean section. British Medical Journal 1977:1;1321.

2.          Tunstall ME. The reduction of amnesic wakefulness during caesarean section. Anaesthesia 1979:34;316-319.

3.          Russell IF. The Isolated forearm technique. Relationship between movement and clinical indices. In Bonke B, Fitch W, Miller K (eds). Memory and Awareness in Anaesthesia. Amsterdam; Swets and Zeitlinger, 1990, 316-319.

4.          Russell IF. Conscious awareness during general anaesthesia: relevance of autonomic signs and isolated arm movements as guides to depth of anaesthesia. In Jones JG (ed) Baillière’s Clinical Anaesthesiology vol 3. Depth of Anaesthesia, London, Baillière Tindall, 1989; 3: 511-532.

5.          Gaitini L, Vaida S, Collins G et al. Awareness detection during general anaesthesia using EEG spectrum analysis. Can J Anaesth 1995;42:377-381.

6.          Flaishon R, Windsor A, Sigl J et al. Recovery of consciousness after thiopental or propofol. Anesthesiology 1997;86:613-619.

7.          Byers GF, Muir JG. Detecting wakefulness in anaesthetised children. Can J Anaesth 1997;44:486-488.

8.          Drummond JC. Editorial. Monitoring depth of Anesthesia: with emphasis on BIS and MLAEP. Anesthesiology 2000; 93: 876-882.

9.          Kalkman CJ, Drummond JC. Monitors of Depth of Anesthesia, Quo Vadis. Anesthesiology 2002; 96: 784-787.

10.      Myles PS, Leslie K, McNeil J, Forbes A, Chan MTV. Bispectral index monitoring to prevent awareness during anaesthesia: The B-Aware randomised controlled trial. Lancet 2004; :363: 1757-1763

11.      Ekman A, Lindholm ML, Lennmarken C, Sandin R.  Reduction in the incidence of awareness using BIS monitoring. Acta Anaesthesiol Scand 2004; 48: 20-26.

12.      Siegmeth R, Bergman I, Absalom AR. Does depth of anaesthesia monitoring reduce the incidence of awareness? Bulletin, royal college of anaesthetists 2005; 29:  1463-1467.

13.      Jessop J, Jones JG. Conscious awareness during general anaesthesia. - What are we attempting to monitor. Br J Anaesth 1991;66:635-637.

 Tunstall’s original IFT

1.       Insert iv cannula in left forearm

2.       Apply BP cuff to left upper arm

3.       Apply padded tourniquet to right upper arm

4.       Inflate tourniquet

5.       Induce unconsciousness

6.       Administer suxamethonium and suxamethonium infusion

7.       Provide maintenance anaesthesia

8.       Ask patient regularly by name  to “Squeeze my fingers with your right hand”

9.       After delivery of baby deepen anaesthesia, deflate tourniquet, continue suxamethonium infusion

 The Suxamethonium infusion usually used for muscle relaxation resulted in the arm becoming paralysed when the tourniquet was deflated.

 Modified IFT for prolonged use

1.          Insert iv cannula in left forearm

2.          Apply BP cuff to right upper arm

3.          Apply padded tourniquet to right forearm

4.          Apply nerve stimulating electrodes to ulnar and/or median nerves at elbow

5.          Induce anaesthesia, inflate cuff, check neuromuscular integrity, give judicious dose of relaxant and intubate

6.          Provide maintenance anaesthesia

7.          After 20 minutes deflate tourniquet

8.          If more relaxant is required inflate tourniquet give top-up dose of relaxant

9.          After 20 minutes deflate tourniquet

10.      Repeat steps 8 – 9 as required

If there is a hand response then verify this by giving the patient a different command. Neuromuscular integrity should be checked at regular intervals.