What is complex regional pain syndrome (CRPS)?

What classes of drugs do gabapentin and amitriptyline belong to? What are their mechanisms of action? What impact might they have on your anesthetic? What other drugs or therapies could be used for treatment of CRPS?

Are there any techniques for this anesthetic that can reduce her chance of further neuropathic pain?

Complex regional pain syndrome is a painful syndrome of unclear etiology and pathophysiology. It is presumably dysfunction of small fibers of the skin and deeper tissues associated with regional sympathetic nerve dysfunction that manifests with increased cutaneous sensitivity (allodynia and hyperalgesia), skin discoloration, and impaired or excessive sweating. The condition commonly affects distal parts of the limbs in glove-and-stocking distribution (non-dermatomal) and is more frequent in females. Some patients may experience motor dysfunction, weakness, and myoclonus. In the advanced condition, the muscles, bone, and skin are wasted, and the joints become stiff with resultant loss of limb function.

Gabapentin is an antiepileptic and pain medication that was synthesized to mimic the structure of gamma-aminobutyric acid (GABA); however, it is not thought to act on those receptors. Activity is believed to be on voltage-gated calcium channels at which it decreases calcium currents after chronic (not acute) exposure. The drug also interacts with NMDA receptors, protein kinase C, and cytokines, but the exact nature of its action on pain modulation is not known. Pregabalin is a longer-acting version of this drug that has not been thoroughly tested in pediatric CRPS patients. Gabapentin has been shown to inhibit the development of hyperalgesia and C-fiber responsiveness. Concerning anesthesia effects, its use has been associated with a lower requirement for intraoperative and postoperative opiates. A small percentage of patients receiving gabapentin have been found to exhibit a prolongation of the QT interval when also taking other medications that affect repolarization. Amitriptyline is a tricyclic drug that inhibits norepinephrine and serotonin reuptake at the second-order neuron synaptic transmission. This drug has been effective in treating depression and improves sleep and some aspects of pain in patients with CRPS. It has a strong anticholinergic effect and may cause delayed atrioventricular conduction, prolonged QRS and QT syndrome, torsades de pointes, AV block, lower threshold for seizures, urinary retention, hyperthermia, increased intraocular pressure, extrapyramidal syndrome, and anticholinergic psychosis. Its atropine-like effect may cause sinus tachycardia and ventricular premature contractions particularly when combined with other anticholinergic or sympathomimetic drugs such as atropine, glycopyrrolate, pancuronium, meperidine, succinylcholine, sevoflurane, isoflurane, and desflurane. Numerous other medications could be used in patients with CRPS including acetaminophen, nonsteroidal anti-inflammatory drugs, steroids, opioid medications, other anticonvulsants, local anesthetics for nerve blocks, and intravenous ketamine (for extreme cases). Other therapies include application of heat and cold, topical analgesics, physical therapy (perhaps most important), transcutaneous electrical nerve stimulation (TENS), biofeedback, and spinal cord stimulation.

A predominant theory of chronic neuropathic pain syndrome is the hyperexcitability of the second-order neuron (i.e., central sensitization) in the dorsal horn caused by the injured nerve. It is reasonable to assume that the use of spinal or epidural anesthesia with local anesthetics in these patients could block the nociceptive impulses generated at the surgical site from reaching the dorsal horn neurons and hence minimize further excitation of the dorsal horn neuron and reduce the potential for flare-up of RSD pain postoperatively. For the same reasons, it would be reasonable to plan an anesthetic that included a multimodal pain management strategy, with acetaminophen, nonsteroidal anti-inflammatory drugs, gabapentin, and opioids as needed. In this case, it would be appropriate to administer a regional anesthetic prior to starting surgery.

Would you premedicate this patient? Would you provide regional anesthesia? If so, what kind of block would you perform and when would you perform the block? What kind of airway management do you plan? How would you induce anesthesia?

How would you maintain anesthesia in this patient?

After induction, the patient becomes hypotensive with BP = 70/40. How do you treat this?

The patient develops ventricular tachycardia after treating her low heart rate with glycopyrrolate.

She has prolonged emergence after her anesthetic. Is this unexpected?