1. Discuss the anesthetic options for this patient

For this peripheral lower limb surgery, the anesthetic options include general anesthesia, neuraxial anesthesia, and peripheral nerve blockade. Which choice is best is not always straightforward, and will be highly dependent on patient comorbidities, specific contraindications (e.g., anticoagulation status), and technical feasibility. Patients undergoing amputations often have multiple concurrent disease processes, which can impart morbidity, such as cardiac complications, wound infections, and pneumonia [1]. Additionally, 30-day mortality rates range from 8% to 32% [2].

General anesthesia (GA) allows for acceptable operating conditions for amputation. However, deleterious cardiac and respiratory consequences may occur secondary to GA, especially in this frail patient population with limited end-organ reserve [3]. Although lower limb amputations are relatively short procedures with minimal blood loss, patients may require invasive monitoring, as a consequence of the GA coupled with their comorbidities. For patients considered “high-risk” (≥4 risk factors) as stratified by the revised cardiac risk index [4], GA was associated with increased 30-day mortality when compared with regional anesthesia (RA) [2]. Debate continues as to whether GA increases postoperative delirium compared to RA. Current literature has shown no significant difference in this regard; however, neuraxial anesthesia is associated with a lower incidence of postoperative pulmonary and cardiac complications [3, 5–6].

Neuraxial anesthesia is often thought of as a promising alternative to GA, especially for the frail and elderly. Health professionals often mention the smooth transition between the intraoperative and the postoperative phase, especially in terms of pain control. However, achieving correct placement of the spinal or epidural needle may be challenging. Additionally, patients often have contraindications to a neuraxial anesthetic. In the presented case, the heparin infusion would need to be discontinued prior to surgery, and normal coagulation and platelet levels documented, specifically if the heparin infusion was longer than five days duration. Organizations such as the American Society of Regional Anesthesia (ASRA) publish regularly reviewed guidelines regarding regional anesthesia and anticoagulation [7].

The choice of single-dose spinal, continuous epidural, or combined spinal–epidural (CSE) neuraxial anesthetic depends on expected operative duration, plan for postoperative analgesia, and patient-specific factors. Neuraxial anesthetics may have significant hemodynamic effects. Utilization of hyperbaric local anesthetic and positioning the patient’s operative side down for several minutes, for a preferentially one-sided block, may lessen the hemodynamic effects of the spinal anesthetic. Slow titration of local anesthetics via an epidural catheter is another option to achieve a surgical level of anesthesia with less hemodynamic variability. However, epidurals are less reliable when compared to intrathecal blockade and have the added risk of inadvertent post-dural puncture headache.

Several case reports have described the reactivation of previous neuropathic pain with neuraxial nerve blockade for amputation [8–9]. It is postulated that this is due to an imbalance of sensory inputs brought on by neuraxial blockade since symptoms disappear once the neuraxial block dissipates. Reports describing this phenomenon state that it is a rare occurrence in those who have had previous amputation and advise that neuraxial techniques should not be considered contraindicated [8, 10].

Selective peripheral nerve blockade may also be an alternative for surgical anesthesia. Peripheral techniques may be especially useful in patients with significant comorbidities where neuraxial anesthesia is contraindicated and GA is of significant risk. For below-knee amputation (BKA), blockade of the sciatic and saphenous nerves are necessary. For above-knee amputation (AKA), blockade of the femoral, sciatic, lateral femoral cutaneous (LFC), and obturator nerves are usually necessary. A lumbar plexus block is efficient in covering the femoral, LFC, and obturator nerves; however, it is a deep block thus not suitable when anticoagulation is an issue. The success of the “3 in 1 block,” to cover the same nerves, has been shown to be less reliable, especially regarding the obturator nerve [11]. Similarly, a fascia iliaca field block can provide blockade of the femoral and LFC nerves. However, the local anesthetic concentration is usually lowered because of the large volume required; thus it is commonly used to provide analgesia, but not surgical anesthesia. Finally, individual blockade of the femoral, LFC, and obturator nerves is possible; however, the total dose of local anesthetics for all blocks combined cannot exceed the allowable weight-dependent dose.

For this patient, the author would recommend a spinal anesthetic so long as the anticoagulation was interrupted and coagulation status returned to normal. Alternatively, a sciatic and saphenous/femoral nerve block would provide adequate surgical conditions. Additionally, the combination of a multimodal analgesic regimen combined with a sciatic nerve catheter could provide excellent postoperative analgesia following BKA. If the patient were to have an AKA, then one can consider the addition of a femoral nerve catheter for postoperative pain control.

2. Review the incidence of phantom limb pain after amputation and the role regional anesthesia plays in preventing the occurrence

Nerve transection occurs because of amputation; thus attention needs to be directed toward the prevention and management of neuropathic and phantom limb pain (PLP). In the existing literature, the incidence of post-amputation PLP and phantom limb sensations can range from 30% to 90%, with 75% of amputees experiencing it soon after surgery. Many patients continue experiencing PLP for an average of seven years afterwards [12].

There are many pharmacologic treatments in use for PLP; however, efficacy has mainly been extrapolated from use with other neuropathic pain syndromes. Acetaminophen, non-steroidal anti-inflammatory drugs (NSAIDs), opioids, anticonvulsants, NMDA receptor antagonists, antidepressants, and muscle relaxants are commonly prescribed. Trials specifically examining PLP show beneficial results from agents such as tramadol, morphine, gabapentin, and amitriptyline [13].

Despite many systemic medications available, PLP is not easily treated. It is also established that poor pain control postoperatively is a substantial risk factor for prolonged pain issues [14]. Thus, anesthesiologists and surgeons are turning toward peripheral nerve catheters, to improve analgesia and decrease PLP in the early and late stages of recovery [12, 15].

For BKAs, preoperative placement and use of a continuous sciatic catheter provides analgesia for acute incisional pain and PLP for the duration of the infusion post-amputation. Use of a postoperative local anesthetic perineural sciatic infusion can decrease the need for systemic analgesics, such as opioids [15], and decrease the incidence of side effects, such as delirium. However, the sciatic block does not cover the saphenous nerve distribution and additional systemic analgesics are required.

For AKAs, continuous infusion of local anesthetic to anesthetize the majority of the affected area can be accomplished through a femoral nerve catheter with or without a sciatic nerve catheter or single-injection block. Alternatively, during the amputation, the surgeon may place a catheter within the sciatic nerve sheath, passing the proximal end of the catheter out of the lateral skin of the thigh. When running two nerve infusions, one must calculate and remain below the toxic dose limit for the chosen local anesthetic. Thankfully, the concentration of local anesthetic required for analgesia is relatively low and dual local anesthetic catheter infusions are often permissible.

How long an indwelling catheter is maintained is dependent upon many factors, including block effectiveness, patient preference, expected duration of stay, and infection risk. Longer nerve blockade appears to further decrease the risk of PLP [12]. Elastomeric, non-mechanical, disposable local anesthetic infusion systems are available for continuous peripheral infusions, which allow appropriate patients to leave hospital with a perineural catheter in place, provided appropriate patient resources and follow-up are available.