A Preliminary Report on the Use of Peripheral Nerve Blocks for Lower Limb Amputations

Summary

Objective

To determine whether there are any advantages of using peripheral nerve blocks as an anaesthetic technique for patients undergoing lower limb amputations.

Methods

Ten cases that had emergency surgery at the Korle Bu Teaching Hospital were reviewed. Indices looked at were the effectiveness of the nerve block, cardiovascular stability during surgery and the duration of postoperative analgesia provided by the block.

Results

9 out of 10 cases had an above knee amputation (AKA) and 1 had a below knee amputation (BKA). 7 of the 10 cases were diabetics. A sciatic nerve block (SNB) combined with either a 3-in-1 block or a psoas compartment lumbar plexus block (LPB) was given to patients undergoing an AKA. A sciatic nerve block combined with a femoral nerve block was given to the patient undergoing a BKA. In 7 cases, anaesthesia provided by the block was good and in 3 cases it was fair. The patients were cardiovascularly stable during surgery. Postoperative pain relief provided by the blocks ranged from 5 hours to 30 hours.

Conclusion

Using peripheral nerve blocks for lower limb amputations is an effective technique of anaesthesia, providing cardiovascular stability as well as good postoperative analgesia.

Introduction

The need for lower limb amputations (below knee or above knee amputations) in Ghana is not uncommon. Patients requiring this procedure as an emergency are usually either diabetics with uncontrolled sepsis of the leg or patients with peripheral vascular disease with gangrene. The patients are often quite ill and general anaesthesia can be dangerous. Neuraxial (spinal or epidural) anaesthesia, rather than a general anaesthetic is often used but even this can be problematic as the patients may be septic with unstable cardiovascular systems and spinal/epidural anaesthesia may drop the blood pressure further. An alternative technique is to perform a regional block of the affected lower limb using a combination of a sciatic nerve block with either a femoral nerve block, a 3-in-1 block, or a psoas compartment lumbar plexus block. A combination of the two blocks means that relatively large doses of local anaesthetic agents are going to be used and one should bear in mind the maximum safe dose of the agent. Technically it is generally easier to perform spinal or epidural rather than peripheral nerve blocks for the lower limb. The onset of action of a peripheral nerve block is longer than a spinal (subarachnoid block), and the success rate of a satisfactory block is generally lower than for neuraxial blocks. However the cardiovascular stability and postoperative pain relief these regional blocks provide make them worthwhile techniques to perform especially in the very sick patient. This paper reports the use of these blocks in 10 patients who underwent lower limb amputations at the Korle Bu Teaching Hospital.

Patients and Methods

The 10 patients being reported on here were patients who were undergoing a below knee or above knee amputation done as an emergency on days that the author was on call. For patients undergoing an AKA, a number were given a sciatic block combined with a three-in-one block and the remainder were given a sciatic nerve block combined with a psoas compartment lumbar plexus block. The only patient undergoing a BKA was given a sciatic nerve block (SNB) combined with a femoral nerve block. The decision on whether to use the anterior or posterior approach for the sciatic nerve block and whether to use a 3-in-1 block or LPB depended mainly on whether or not the patient could easily be turned onto their side (the posterior approach for a SNB and a LPB will need the patient on their side).

As is normally done for regional techniques the procedure was explained to the patient (who would have already signed a consent form for surgery) and the procedure done only if the patient agreed to it. A mixture of lidocaine with adrenaline 5mcg/ml together with either bupivacaine or ropivacaine (depending on which one was available) was used. The approach for the sciatic block was either the anterior approach described by Chelly et al¹ or the posterior approach described by Labat.² For each block, the sciatic, 3-in-1, and LPB the patient was given either 15ml of lidocaine with adrenaline (5mcg/ml) plus 10ml of 0.5% bupivacaine, or 15ml of 0.5% ropivacaine plus 10ml of lidocaine with adrenaline. The concentration of lidocaine used ranged between 1–1.5%, depending on the weight of the patient and in order to keep within the safe maximum dose. For the femoral nerve block (in the patient for a BKA), a combination of 5ml of 2% lidocaine with adrenaline (5mcg/ml) plus 5ml 0.5% bupivacaine was used.

Stimuplex nerve stimulating needles (Braun) were used for the blocks. A 150mm needle was used for the anterior approach to the sciatic nerve and a 100mm needle was used for the posterior approach. A 100mm or 150mm needle was used for the psoas compartment lumbar plexus block. For the blocks, the current was set initially at 3–4 mA and gradually decreased as the nerve was localised. A stimulating current of anything between 0.3 and 0.7mA was accepted prior to the anaesthetic agent being injected. Prior to and during the procedure, ECG, pulse oximetry and non-invasive blood pressure were monitored. Resuscitation drugs and equipment were readily available. As a measure of the degree of postoperative analgesia provided by the blocks, the number of hours postoperatively before any further pain relief was required was determined.

Results

As seen in table 1, the ages of the patients ranged between 55 years and 84 years with a mean of 69.1yrs. 4 were males and 6 were females giving a male to female ratio of 1:1.5. Out of the 10 patients, 7 were diabetics, 2 had peripheral vascular disease and 1 had a malignant ulcer of the knee. 5 patients had a SNB combined with a 3-in-1 block, 4 had a SNB combined with a psoas compartment LPB and 1 had a SNB combined with a femoral nerve block. All the patients were on antibiotics. Five patients were on subcutaneous heparin or low molecular weight heparin as prophylaxis against deep vein thrombosis (DVT), and one patient was on both heparin and aspirin.

Table 1.

Patient data and nerve block given

Patient	Age	Sex	Diagnosis	Co-morbidity	ASA	Amputation Type	Block Used
KO	65	F	Diabetic ulcer right foot	DM/HT	III	AKA	Sciatic (ant.a) 3-in-1 block
AS	70	F	Gangrene Right foot	PVD/HT	III	AKA	Sciatic (ant.a) 3-in-1 block
MA	75	M	Gangrene Left leg	DM/HT/PVD	III	AKA	Sciatic (ant.a) 3-in-1 block
EA	67	F	Gangrene Right foot	DM/HT	IV	AKA	Sciatic (ant.a) 3-in-1 block
KA	84	M	Gangrene Left leg	PVD	III	AKA	Sciatic (ant.a) 3-in-1 block
EO	63	M	DKA (treated) Gangrene Left foot	DM	IV	BKA	Sciatic (post.a) Femoral block
IN	74	M	Gangrene Left foot	DM	III	AKA	Sciatic (post.a) LPB
AP	55	F	Malignant Ulcer left Knee	NIL	III	AKA	Sciatic (post.a) LPB
MD	72	F	Gangrene Left foot	DM/HT	III	AKA	Sciatic (post.a) LPB
SA	66	F	Gangrene Right leg	DM	III	AKA	Sciatic (post.a) LPB

DM - Diabetes Mellitus HT - Hypertension PVD - Peripheral vascular disease DKA - Diabetic ketoacidosis LPB - Lumbar plexus block AKA - Above knee amputation BKA - Below knee amputation ant.a - anterior approach post.a - posterior approach

The mean duration of surgery was 97.5minutes (range 50mins–210mins). The time interval between the end of surgery and the time the first dose of analgesic was needed ranged between 5hrs and 30.5hrs with a mean of 12.5hrs. Most patients had a low haemoglobin level ranging from 6.8g/dL to 11.1g/dL with a mean of 8.8g/dL. White cell count was raised in most cases ranging from 4.4x10⁹/dL to 23.3x10⁹/dL with a mean of 16.0x10⁹/dL. Fasting blood sugars done a few hours prior to surgery were reasonable, ranging between 4.8mmol/L and 12.1mmol/L with a mean of 8.3mmol/L. All the 10 patients were cardiovascularly stable throughout surgery. The systolic blood pressure of the patients ranged between 90mmHg and 200mmHg with a mean of 139.9mmHg. The diastolic pressure ranged between 45mmHg and 135mmHg with a mean of 79.1mmHg. The heart rate of the patients ranged between 72 beats/min and 125 beats/min with a mean of 98 beats/min.

Discussion

In the West African sub-region, diabetes related lower limb amputation is responsible for more than half of non-trauma related amputations.³ Foot ulcers are a major problem in diabetes. The prevalence of foot ulcers in diabetics ranges from approximately 1% in some European and North American studies, 3–8% in Sweden, to over 11% in some African countries.³ Diabetics with foot ulcers are a group of high risk patients with significant morbidity and mortality. Kengne et al³ reported a mortality rate of 22.2% in diabetics with foot ulceration admitted to the diabetes unit of the Yaounde Central hospital.

A study from the Lagos University Teaching Hospital (LUTH), covering a three year period⁴ found that 42.6% of the lower limb amputations carried out at the hospital were diabetes mellitus(DM) related. Foot ulceration accounted for 25.7% of DM related deaths.⁴

In the ten cases reported here, 7 of them were diabetics. Diabetic patients requiring lower limb amputation are often septic and this compromises their cardiovascular system. In addition to this, some diabetics have autonomic neuropathy which impairs cardiovascular compensation when they are subjected to physiological changes such as occur during a general anaesthetic. Very often spinal anaesthesia (subarachnoid block) or epidural anaesthesia is given to diabetics undergoing lower limb amputations, and these have advantages over general anaesthesia. However since these neuraxial blocks do block sympathetic nerves to varying degree, hypotension can occur, worsening the already compromised cardiovascular system. Fanelli et al⁵ found out that even in ASA I&II patients in whom a unilateral spinal block was performed for lower limb surgery, the mean arterial pressure decreased by about 15% from the baseline values, whereas in patients who were given a sciatic-femoral block there was no change in mean arterial pressure. Also the cardiac index decreased by 15–20% in the group who were given a unilateral spinal block whereas there was no change in the group given a sciatic-femoral nerve block. In the ten patients reported here, heart rate, systolic and diastolic pressures were remarkably stable throughout surgery.

In the patients presented here, 9 had an AKA and 1 had a BKA. Those that had an AKA, had a sciatic nerve block combined with either a 3-in-1 block as described by Winnie⁶ or a psoas compartment lumbar plexus block. The patient who had a BKA had a sciatic block combined with a femoral nerve block. The lower limb is supplied by the sciatic nerve together with nerves from the lumbar plexus. The thigh is supplied by the femoral nerve, the lateral cutaneous femoral nerve, and the obturator nerve (all from the lumbar plexus). In addition, a narrow posterior slip of the thigh is supplied by the posterior femoral cutaneous nerve (S2 / S3) which enters the thigh together with the sciatic nerve but then diverges from the sciatic nerve. The leg below the knee is supplied by the tibial and peroneal branches of the sciatic nerve, as well as the saphenous nerve which is a continuation/branch of the femoral nerve. Thus for a BKA, a sciatic nerve block together with a femoral nerve block is adequate whereas for an AKA, one needs to block the sciatic nerve together with nerves of the lumbar plexus. One can block the nerves of the lumbar plexus by using a 3-in-1 block in which case the volume of local anaesthetic used should be at least 20ml to enable the solution to spread up the fascial compartment.⁶ Alternatively, one could do a psoas compartment lumbar plexus block.

In 5 patients, the anterior approach to the sciatic nerve as described by Chelly and Delauney¹ was used. In the other 5, the posterior approach, described by Labat, was used. One advantage of the anterior approach is that the patient does not need to be turned on to the side, which is desirable if the patient has a painful condition such as a fractured tibia. The 3-in-1 block is simpler to do than the psoas compartment lumbar plexus block. However since the 3-in-1 technique relies on the spread of the local anaesthetic agent up the neurovascular sheath, it is probably a less predictable block than the psoas compartment lumbar plexus block in which the lumbar plexus is approached posteriorly. In two of the patients, sensation was still felt over the posterior aspect of the thigh. In these cases, presumably the posterior cutaneous nerve of the thigh escaped the block.

The agents used for the blocks were lidocaine mixed with either bupivacaine or ropivacaine. The rationale for using lidocaine was that the onset of the block would be quicker than using bupivacaine or ropivacaine alone. The addition of bupivacaine or ropivacaine was to prolong the duration of the block. Ropivacaine was used when available otherwise bupivacaine was used. Advantages of ropivacaine over bupivacaine are that it is less cardiotoxic than bupivacaine and the onset of action is quicker than bupivacaine.⁷ Fanelli et al⁸ when comparing ropivacaine, bupivacaine and mepivacaine for sciatic and femoral nerve blockade found that the onset of the block was significantly shorter with ropivacaine compared to bupivacaine, but the duration of postoperative analgesia was shorter with ropivacaine as compared to bupivacaine.

In this report, two of the three patients who were given ropivacaine had postoperative pain relief for 5 hours which was shorter than the periods of postoperative analgesia for the patients who were given bupivacaine. With the dosages used, none of the patients showed any signs of local anaesthetic toxicity. Smith and Siggins⁹ showed that with sciatic nerve blocks, using the same dosage, a higher concentration (with less volume) resulted in a block that had a quicker onset time and a longer duration of action. As seen in Table 2, most of the patients had several hours of postoperative analgesia which is another advantage of using peripheral nerve blocks. Coagulation profiles were not done in any patient, but being septic, some of the patients may have had deranged coagulation. Some of the patients were on subcutaneous heparin and one patient was on aspirin as well as heparin. Inspite of this, none of the patients had any complication that could be attributed to bleeding in the vicinity of the block.

Table 2.

Results of nerve block

Initial	Onset Time	Supplementation of Anaesthesia	*Quality of Block (sensory)	Duration of Surgery (mins)	Time Postop before 1st analgesia dose /Comments
KO	20 mins	Midazolam 2mg	Good. Complete block	105 mins	30.5 hours
AS	Not Recorded	Entonox Propofol 40mg	Fair. Partial block	65 mins	17 hours
MA	25 mins	Pethidine 25mg	Good. Complete block	50 mins	7 hours
EA	30 mins	Entonox Propofol 100mg	Fair. Partial block	50 mins	When reviewed after 12 hrs, patient had not needed any analgesia and was not in pain
KA	30 mins	Propofol 100mg Pethidine 40mg Midazolam 4mg	Fair. Partial block	150 mins	12 hrs. Patient had some pain in lateral and posterior part of thigh during surgery
EO	30 mins	Nil	Good. Complete block	75 mins	10.5 hours
IN	Surgery started 1hr after block due to power problems	Confused preop Midazolam 3mg Fentanyl 30mcg Entonox	Good. Complete block	60 mins	5.5 hours
AP	20 mins	Midazolam 1mg Fentanyl 50 mcg	Good. Complete block	120 mins	10.5 hours
MD	30 mins	Entonox	Good. Almost Complete block	210 mins	5 hrs. Small area of sensation post during surgery
SA	30 mins	Nil	Good. Complete block	90 mins	15 hours

^*Quality of block assessed by Anaesthetist

An exciting advance that has taken place over the past few years is ultrasound guidance in regional anaesthesia.^10,11 Advantages of this are a high success rate of the blocks since the nerves are imaged by ultrasound and one can use lower volumes of the agent and thus higher concentrations. Complication rates are very low. When blocking the lower limb using ultrasound guidance, one can hopefully visualize the posterior cutaneous femoral nerve and therefore block it, avoiding the situation which occurred in two of the patients where it appeared that the nerve escaped being blocked.

Conclusion

Peripheral nerve blocks can effectively be used for lower limb amputations, providing cardiovascular stability and good postoperative analgesia. The introduction of ultrasound guided regional anaesthesia is a promising advance, increasing the success rate and safety of peripheral nerve blocks.