Peripheral Neuromodulation. Peripheral Neurostimulation in Postoperative Pain and its role in preventing persistent post surgery chronic pain

Electroanalgesia is based on “gate control Theory” (activation of large motor fibbers inhibits transmition of pain signals from small fibbers).

New dispositives ultrasound guided, allow a lead to be inserted approximately 0.5 to 3.0 cm close to peripheral nerves.(1)

In 2018, the US Food and Drug Administration (FDA) approved the first PNS device designed  for percutaneous placement portability and short term use.

The main question that evidence should answer is if perisferic stimulation could replace or potentiate the use of perisferic catheter and integrate this dispositive to multimodal perioperative analgesia.(2)

The accessibility to ultrasound machines,the high prevalence of anaesthesiologists with skills in ultrasound-guided regional anaesthesia, the development of a  small stimulator that can be stick into the skin, the development of an insulated electrical lead specifically designed for percutaneous, extended use (up to 60 days) in the periphery now allow the wide application of PNS to treat postoperative pain.(1)

PNS use in the perioperative setting is still on its beginnings, and require high quality prospective clinical trials to definitively demonstrate efficacy and feasibility of this technology in the surgical environment. (2)

The only device with FDA clearance and published cases for the treatment of acute pain is the SPRINT PNS system (SPR Therapeutics, LLC, OH, USA). For both acute and chronic pain in the back and/or extremities for up to 60 days. This device include two components: a percutaneous electrical lead to deliver the stimulation to the target nerve and a battery-powered external pulse generator. (3)

One of the main reasons for the increased interest in PNS  it is the  potential to modulate pain signalling and decrease neuronal sensitization, with opioid sparing effect, reducing the incidence of hyperalgesia , allodynia and the neuropathic pain in the postoperative period reducing its persistence. It can be use alone or together with pharmacological approach performing also a nerve block. The option to switch between chemical or electric nerve stimulation in the postoperative period may have good results. (2)

Stratifying the risk of develop of persistent postoperative pain is essential to allow to PNS to be a cost effective preventative measure. Early PNS may avoid priming/sensitizing nervous system providing enhanced analgesia for patients developing or with previous neuropathic pain. PNS has the potential more than control the pain, it can improve recovery recruiting and strengthening affected muscles groups and nerve regeneration. (2)

Specific surgeries: In knee arthroplasty , neurostimulate sciatic and femoral nerve has allowed opioid sparring .No falls, motor blocks or infections.

PNS seem to be a promising useful techniques in foot surgery, placing an electrode near the sciatic nerve in hallux valgus surgery. (5)

In rotator cuff repair the use of neurostimulation in interscalene approach do not showed appreciable differences if the leads where placed in the suprascapular nerve.(6) In cruciate ligaments repair. A electrode could be placed at femoral nerve(5)

A randomized placebo controlled trail of 60 days in postoperative  patients after knee replacement showed relief or persistent postoperative pain and improved function. These results provide evidence from a multicentre, randomized, double-blind, placebo-controlled trial showing that percutaneous PNS is safe and can provide sustained benefits for patients with postoperative pain after TKA.(4)

As benefits PNS avoid the challenges of management local anaesthetics infusion pumps, eliminate the risk of medication toxicity and obtain a longer length of analgesia compared with peripheral catheter. Combined, these characteristics permit a far longer duration of use for PNS compared with continuous peripheral nerve blocks, possibly providing both preoperative and subsequently postoperative analgesia that outlasts the pain resulting from nearly all surgical procedures

Limitations of PNS:  Sadly the costs and accessibility of these dispositives are still unaffordable in ordinary conditions. (2) The leads are fragile and can be damaged or be broken during its exit and some part or it may persist inside the patient .(1)

There is no consensus on when and how much time  PNS must be use in postoperative.(2)

PNS use in managing acute pain and in the transitional period  is promising. It must overcome many obstacles  before it can be introduced into routine practice. We must determine which patients, which types of surgeries, and which nerves are the best candidates for this treatment. We need to determine if a PNS lead should be placed before surgery, immediately after surgery, during the subacute transitional pain period, or only after chronic pain develops. (2)

Ultrasound-guided percutaneous PNS may serve as an alternative approach free of some of the limitations associated with peripheral nerve blocks for this patient population. However the evidence is currently limited to small-scale feasibility studies. Further large-scale prospective, studies are necessary. (5)