Pain management using a novel hybrid technique of perineural stimulation combined with regional anaesthesia through a stimulating perineural catheter for below knee amputation

Summary

Pain after amputation can be difficult to manage due to its complex aetiology. A multimodal approach to analgesia, including regional anaesthetic techniques, is advised. However, optimal pain management cannot always be achieved, and high doses of opioid analgesics may contribute to adverse effects. We describe the management of an elderly patient with significant co‐morbidities undergoing below knee amputation. Pre‐operatively, a popliteal sciatic stimulating perineural catheter and a femoral non‐stimulating perineural catheter were placed. When pain control was suboptimal on the first postoperative day, a combination of local anaesthetic and a brief period of peripheral nerve stimulation through the sciatic stimulating perineural catheter was used to augment pain control, thereby avoiding additional opioid use. Although nerve stimulation utilising specialised equipment, such as percutaneous stimulator electrodes, has been previously described in acute pain medicine, we demonstrate the use of a novel hybrid technique which combines nerve stimulation through a perineural catheter and local anaesthetic. Further research is warranted to explore the utility of this neuromodulation technique in clinical practice.

Introduction

Peripheral nerve stimulation or neuromodulation has been recognised as a chronic pain management technique for many years. However, the role of nerve stimulation in regional anaesthesia has been predominantly limited to nerve localisation. In the era of ubiquitous ultrasound use, the application of nerve stimulation techniques has declined significantly in clinical practice. However, emerging evidence suggests that there are potential analgesic benefits of percutaneous nerve stimulation, and interest in nerve stimulation now seems to be building in the context of acute pain management [1]. Percutaneous nerve stimulation involves placing specialised, small‐diameter (0.2 mm) electrode leads percutaneously, usually with ultrasound guidance, 1–3 cm away from the nerve. The lead is then connected to a portable nerve stimulator and stimulation may be continued for weeks or months [2].

Pain after amputation has complex aetiology involving both peripheral and central mechanisms of cortical re‐organisation, including the interplay between the ascending spinal projection neurons and injured inhibitory interneurons [3]. Considering the potential efficacy of percutaneous nerve stimulation as a potential means for neuromodulation, a combination of regional anaesthesia using local anaesthetic with nerve stimulation as a hybrid regional technique has been proposed [4]. In this report, we describe a case whereby a combination of local anaesthetic and peripheral nerve stimulation, delivered using the same perineural stimulating catheter, augmented the quality of post‐amputation pain control.

Report

A 73‐year‐old man weighing 80.9kg (body mass index of 27.4 kg.m⁻²) with a complex past medical history including diabetes with paraesthesia limited to the glove‐and‐stocking distribution and a recent history of systemic anticoagulation for a left ventricular assist device due to ischaemic cardiomyopathy, underwent below knee amputation for an ischaemic limb. The patient was receiving an infusion of unfractionated heparin which was stopped 4 h before surgery. Popliteal sciatic and femoral nerve blocks were chosen as the most suitable regional anaesthetic technique for postoperative analgesia, in accordance with the American Society of Regional Anesthesia guideline and the Canadian consensus advisory on regional techniques and anticoagulation [5, 6], which state that nerve blocks in close proximity to vessels which are compressible are deemed acceptable in the setting of recent anticoagulation.

Pre‐operatively, a popliteal sciatic perineural stimulating catheter (E‐Cath^® Stim, Pajunk, Geisingen, Germany) (Fig. 1) and femoral perineural non‐stimulating catheter (E‐Cath®, Pajunk, Geisingen, Germany) were inserted under ultrasound guidance and placement of the sciatic catheter was confirmed by peripheral nerve stimulation (current threshold of 1.5 mA with plantar flexion). A 1:1 mixture of ropivacaine 1% and bupivacaine 0.25% were injected via the sciatic (15 ml) and femoral (10 ml) nerve catheters at the time of insertion. A low dose of local anaesthetic was used to minimise the risk of local anaesthetic systemic toxicity given the patient’s poor cardiac function and co‐morbidities. Induction of general anaesthesia was with fentanyl 200 µg, remifentanil 20 µg and propofol 50 mg i.v. Anaesthesia was maintained with sevoflurane (end‐tidal concentration 1.7–1.9%) and ketamine 20 mg i.v. was administered intra‐operatively, but no other analgesics were given during the 3‐h operation. Postoperatively, regular paracetamol (975 mg 6‐hourly) and gabapentin (200 mg 12‐hourly) were prescribed, together with intermittent boluses of local anaesthetic (ropivacaine 0.2% 10 ml via the sciatic catheter and 6 ml via the femoral catheter, 2‐hourly).

Figure 1.

Equipment for nerve stimulation and local anaesthetic administration via the stimulating perineural catheter. The nerve stimulator lead can be disconnected and taped to the patient’s skin when not in use.

Initially, the patient’s pain was well controlled. However, it worsened in the afternoon of the first postoperative day with the patient reporting numerical rating score for pain (NRS) of 7/10 at his amputated stump, both at rest and on movement. The pain was described as sharp but with a component of dull aching, which caused the patient significant distress and discomfort. Due to his cardiac disease, we felt reluctant to increase the local anaesthetic bolus dose. We therefore discussed an off‐labelled usage of peripheral nerve stimulation via the perineural catheter, drawing on previous studies which had demonstrated the analgesic benefit of this technique as a screening tool before permanent peripheral nerve stimulation device implantation for chronic pain [7]. The patient consented to the use of peripheral nerve stimulation through his existing sciatic perineural catheter on a trial basis.

The intermittent boluses of local anaesthetic were temporary suspended via the sciatic perineural catheter, while the nerve stimulator was attached and stimulation was commenced. The nerve stimulator was set at 0.1 ms pulse duration with 2 Hz frequency, and the amplitude was gradually increased from 0.2 mA to 0.5 mA whereupon the patient felt slight warmth in his stump. This was continued for 60 min, thereafter his NRS score was reduced to 0/10 both at rest and on movement. When peripheral nerve stimulation was stopped the intermittent local anaesthetic bolus regimen was resumed until the third postoperative day upon removal of the nerve block catheters. His pain remained mild (maximum NRS 4/10) both at rest and on movement, and no additional opioids were required throughout his three‐week hospital stay.

Discussion

This case demonstrates the potential analgesic benefit of brief sciatic peripheral nerve stimulation following below knee amputation, following which pain management is often challenging. Given the complex aetiology of phantom and residual limb pain, and the likelihood that patients will be elderly with multiple comorbidities, it is important to achieve desirable pain control with minimal opioid and local anaesthetic dosing to reduce the risk of complications such as delirium and local anaesthetic systemic toxicity. In this case, we successfully applied a hybrid regional anaesthetic approach, combining peripheral nerve blockade using local anaesthetic with brief neuromodulation and were able to avoid the use of opioids altogether. We speculate that this hybrid regional anaesthetic technique is not only synergistic but complementary, as the local anaesthetic solution blocks neuronal transmission, while electrical stimulation may neuromodulate the unblocked fibres remotely. Non‐pharmacologic options such as transcutaneous electrical nerve stimulation (TENS) for neuromodulation have demonstrated reduction in phantom pain and stump pain and our case indicates a similar benefit of perineural electrical nerve stimulation [8]. The exact mechanism of perineural stimulation may be somewhat different as the electrodes in TENS are transcutaneous whereas in our case, the stimulating electrode (i.e. catheter) was in close proximity to the nerve.

Top‐up boluses of local anaesthetic via the sciatic nerve block catheter were not performed in view of patient’s cardiac comorbidity and consequent increased risk of local anaesthetic systemic toxicity. Drawing on a previous study on the analgesic effects of brief neurostimulation [7], an unconventional approach was instead adopted using the in‐situ perineural stimulation catheter. Rescue analgesia using neuromodulation following foot surgery and knee arthroplasty has been described [1, 2]. However, this was with specialised electrode leads that were inserted percutaneously a few centimetres away from the nerve [2]. This method contrasts to our technique which employs the same in‐situ nerve stimulation catheter used for peripheral nerve block, positioned perineurally. This catheter therefore functioned both as a conduit for local anaesthetic administration and an electrode for therapeutic nerve stimulation. Unlike specialised electrode leads used for percutaneous nerve stimulation for chronic pain, the electrode is built‐in as a single unit in the stimulating perineural catheter which is inserted in a standard fashion without the risks of lead fracture.

Neuromodulation utilising low‐frequency, low‐voltage stimulation has demonstrated analgesic effects in both dorsal root ganglion stimulation and plexus blockade, although its exact mechanism is unknown [9, 10]. While low‐frequency nerve stimulation is traditionally used for nerve localisation in regional anaesthesia, the novelty in our case is the adaptation of this technique to facilitate neuromodulation, in combination with regional analgesia using local anaesthetic to optimise pain management. The optimal settings for peripheral nerve stimulation via perineural catheter and its frequency are yet to be determined, and although this report is encouraging it is only a single case. Further research is therefore warranted to explore the potential clinical utility and safety of this novel hybrid technique with common regional anaesthetic equipment (i.e. stimulating catheter and nerve block stimulator) for patients at risk of complex pain.