Anaesthesia, 1984. Volume 39, pages 155-1 57

CASE REPORT

Continuous sciatic nerve block

B. E. S M I T H , H . B. J. F I S C H E R A N D P. V. S C O T T

Summary

A technique of continuous sciatic nerve block is described. The method was used to relieve pain from ischaemic gangrene qf the .foot for 2 days before below-knee amputation and, combined with a con- rinuous inguinal paravasculur block, to provide regional anaesthesia both for the surgery and for the

first 2 postoperative days.

Key words

Anaesthetic techniques; regional. continuous. Anatomy; sciatic nerve.

A man aged 77 years with atherosclerosis and maturity onset diabetes mellitus was admitted to hospital with ischaemic pain in the toes oftheright foot. Both oral and parenteral analgesics had lost their effect. A right lumbar sympathetic block (10.0 ml phenol 69;) reduced pain but had little effect on the circulation and temperature of leg and foot. The patient was discharged from hospital but returned in desperation 5 days later with incipient gangrene. He had continuous severe pain and was unable to sleep. The surgeon wondered whether extradural bupivacaine might not provide analgesia and possibly delay the need to amputate. Since the patient also had symptoms ofprostatism, it was thought preferable to attempt continuous sciatic nerve block by means of an in- dwelling catheter passed under local anaesthesia into the neurovascular space enclosing the nerve.

Method

Using the posterior approach, the right sciatic

nerve was identified with a 16-gauge intravenous infusion cannula (Medicut) connected by its metal trocar to one terminal of a low-powered nerve stimulator. The trocar was removed and 8.0 ml lignocaine 2% injected down the cannula, both as a test dose and to open up the neurovascular space. An extradural catheter (Portex, 16G, 1.1 mm outer diameter, helical eyes) was passed through the cannula and advanced into the space with ease for a distance of 6.0 cm. This manoeuvre evoked paraesthesiae in the distribu- tion of the sciatic nerve. The cannula was with- drawn over the catheter, which was protected with a bacterial filter (Portex); 10 ml bupi- vacaine 0.75% was injected through the filter.

Pain relief began within 10 minutes and was complete after 40 minutes by which time the right leg felt warmer than the left. There was some loss of motor power (dorsiflexion and plantar flexion). The sciatic nerve from then on was continuously bathed in 0.57/, bupivacaine at a rate of 3.0 ml/hour by means of a Vickers syringe pump. The

B.E. Smith. FFARCS. Registrar. H.B.J. Fischer, FFARCS, Consultant, P.V. Scott. FFARCS. Consultant. Department of Anaesthetics. Bromsgrove General Hospital. Bromsgrove. Worcestershire B61 OBB.

ooO3-2409/84/020155 + 03 $03.00/0 @ 1984 The Association of Anaesthetists of Gt Britain and Ireland 155

156 B.E. Smith. H.B.J. Fischer and P.V. Scott

perfused catheter remained in situ for the next 48 hours when the decision was taken to perform below-knee amputation.

Anaesthesia and surgery

The patient was sedated with 7.5 mg diazepam intravenously (Diazemuls) and the sciatic cath- eter topped up with 10 ml 0.75% bupivacaine. A second. extradural catheter was passed into the neurovascular space surrounding the femoral nerve 2.5 cm below the right inguinal ligament, using the technique already described. An in- guinal paravascular block' (3-in-1 block) was induced with 15.0 ml of a mixture containing

equal volumes of bupivacaine 0.5% and pri- locaine 1 .Ox. During surgery, intermittent intra- venous injections of etomidate were given to reduce awareness, the patient breathing air; monitoring included the electrocardiogram, auto- mated oscillotonometry (Dinamap), and con- tinuous end-tidal carbon dioxide measurements (Datex capnograph).

Postoperative management

In the recovery room, both femoral and sciatic catheters were connected by a four-way tap to a Vickers syringe pump, bupivacaine 0.5% being delivered at a rate of 6.0 ml/hour over the

Fig. 1. This anteroposterior radiograph of the right thigh was taken 6 hours after below-knee amputation of the leg and 54 hours after insertion of an extradural catheter into the neurovascular space enclosing the sciatic nerve. The space has been outlined with radiological contrast medium injected through the catheter. Note the classically-described anatomical relationship between the sciatic nerve and the lesser trochanter of the femur.

The circular marker is placed at the entry of a similar catheter into thc neurovascular space enclosing the femoral nerve. The catheter can just be seen

issuing from behind the marker at about the 12 o'clock position.

Continuous sciatic nerve block 157

succeeding 48 hours. The catheters were then removed. Pain relief throughout was complete, and there were no complications from systemic absorption of local anaesthetic or from the presence of the catheters.

Discussion

Sciatic block is not the easiest of regional tech- niques, but with practice in the use of a nerve stimulator2 a success rate of over 95% may be achieved (Smith, in preparation). Having iden- tified the nerve, it should prove no more difficult to place a catheter in the sciatic neurovascular space than to place a catheter in the spinal extradural space. Once this is done, unilateral regional anaesthesia of very high quality seems possible for a period of days, provided that the catheter remains lodged in the neurovascular space, as it did in this one case (Fig. I . )

In relieving the pain of ischaemia, sciatic block ‘causes almost complete vasoconstrictor para- lysis of the foot and is better, safer, and less painful than lumbar sympathetic block for this p ~ r p o s e ’ . ~ To have expected a continuous sciatic infusion of bupivacaine to halt the inexorable progress of gangrene in our patient was a for- lorn hope. On the other hand, he became com-

pletely pain-free both before and after his operation, and was able to sleep. We combined continuous sciatic block with a continuous 3-in-I block at the time of surgery to relieve post- operative pain and to encourage the best possible blood flow to the stump so as to promote healing.

Sciatic nerve block is advocated in a number of situations$ it may prove worthwhile, in some cases, to consider the use of a continuous tech- nique.

Acknowledgments

We thank Mr G.F. Grave, FRCS, Consultant Surgeon, for referring the patient, and D r C. Dale, MRCP(UK), FRCR, Consultant Radio- logist, for her excellent radiograph.

References I . WINNIE AP. Inguinal paravascular technique of

lumbar block. Surgical Clinics of North America

2. MONTGOMERY SJ, PRITHVI RP. NETTLES D, JENKINS MT. The use of the nerve stimulator with standard unsheathed needles in nerve blockade. Anesthesia and Analgesia, Currenr Researches 1913; 5 2 827-3 1.

3. ATKINSON RS, RUSHMAN GB, LEE JA. A synopsis of anaesthesia. 9th ed. Bristol: Wright, 1982: 714-5.

1975; 55: 881-6.