Keywordspreoperative evaluation, perioperative stroke, postoperative recovery, anesthesia, surgery, neuromuscular disorders, seizures, delirium, multiple sclerosis, movement disorders
Perioperative care of the patient with neurologic disease provides practitioners with a number of unique challenges ranging from timing of surgery, administration of medications, and anesthetic choices, to postoperative care. This chapter focuses on common neurologic disorders and the perioperative considerations that accompany them.
The incidence of Parkinson disease among all ages approximates 14 per 100,000 and increases to a median of 160 per 100,000 in persons over age 70 years. Therefore, thousands of parkinsonian patients will undergo various surgical procedures each year, and many will experience unique perioperative and surgical challenges related to their underlying disorder.
A key factor in caring for parkinsonian patients in any setting is establishing their specific medication regimen and the timing of these medications. Antiparkinsonian medications are almost exclusively oral, making challenging the “nil by mouth” (NPO) status prior to surgery and the timing and administration of perioperative medications. The patient’s typical medication regimen should be continued on the day of surgery as close as possible to the time of anesthesia. Levodopa has a short half-life, on the order of 1 to 3 hours; if the planned duration of surgery is long and general anesthesia is being employed, consideration should be given to placing a nasogastric tube and continuing levodopa intraoperatively. Missed doses may precipitate a parkinsonian crisis resulting in severe rigidity and akinesia, leading to prolonged intubation and recovery time. The possibility of resting or orthostatic hypotension, which is common in Parkinson disease and a side effect of many medications used to treat it, should also be considered, and anesthetic agents that commonly cause hypotension should be avoided.
When a patient is unable to take dopaminergic medications orally in the perioperative period, one strategy is to switch patients to a transdermal dopamine agonist, rotigotine, with a half-life of approximately 24 hours. However, this may be challenging for patients taking a complex oral regimen as conversion between various dopaminergic formulations varies widely from patient to patient.
Regional anesthesia has the added benefit of minimizing postoperative nausea and vomiting, which will allow for the timely resumption of oral medications. If general anesthesia is necessary, halothane should be avoided in patients taking levodopa as it sensitizes the heart to catecholamines. Propofol has been associated with worsening dyskinesias but has also been observed to improve tremor; it is often avoided in patients undergoing deep brain stimulation (DBS) surgery. Antiemetics are commonly administered intraoperatively and postoperatively, but dopamine antagonists such as prochlorperazine and metoclopramide can worsen parkinsonism and block the effects of levodopa therapy; therefore, they should be avoided in favor of ondansetron and domperidone.
Extubation of parkinsonian patients may be complicated. Up to one-third of patients have an obstructive ventilatory pattern related to upper airway dysfunction including laryngeal dysmotility and retained secretions. This dysfunction places parkinsonian patients at increased risk of aspiration. Parkinsonian patients are also at a substantially increased risk of developing postoperative confusion and hallucinations, in some cases due to underlying diffuse Lewy body pathology; therefore these patients must be monitored carefully in the postoperative setting and strategies to prevent delirium should be planned in advance. An elevated risk of urinary tract infections, aspiration pneumonias, and bacterial infections has been demonstrated in parkinsonian patients, leading to an increased length of hospital stay and increased perioperative morbidity. Improved surgical outcomes occur when medication regimens are optimized by a neurologist; with early mobilization; when postoperative complications are carefully monitored; and when conversations regarding long-term care and prolonged rehabilitation occur early in the hospitalization.
Special Considerations for Deep Brain Stimulation
DBS is now a well-accepted treatment for medication-resistant Parkinson disease. Given the potential risk of intracerebral hemorrhage with insertion of DBS leads, all antiplatelet medications should be discontinued for 7 to 10 days prior to surgery. Typically, antiparkinsonian medications are discontinued the night before surgery. General anesthesia is avoided so that the patient is awake and parkinsonian symptoms can be monitored intraoperatively. Postoperatively, patients should be kept normotensive to minimize the risk of hemorrhage, and antiparkinsonian medications should be resumed immediately.
Movement-Disorder Emergencies in the Perioperative Period
Perioperative movement-disorder emergencies commonly occur because a patient’s usual medication regimen is discontinued or because of new medications introduced in the perioperative period. Diagnosis requires a detailed knowledge of the patient’s preexisting conditions and a careful review of preoperative, intraoperative, and postoperative medications. Patients with Parkinson disease who have their levodopa discontinued suddenly for several days may experience parkinsonism-hyperpyrexia, characterized by fever, severe rigidity, autonomic instability, and an elevated serum creatine kinase level. Treatment includes restoration of dopaminergic therapy, and the management strategies discussed later.
Somewhat clinically similar to the parkinsonism-hyperpyrexia syndrome, neuroleptic malignant syndrome results from dopamine receptor blockade. Commonly implicated medications include neuroleptics, antiemetics (e.g., metoclopramide and prochlorperazine), and droperidol, which should be withdrawn promptly. In these syndromes, symptoms may last for days and be life-threatening. Treatment often requires care in the intensive care unit, with aggressive hydration and cooling. Dantrolene, bromocriptine, or amantadine is typically initiated, but the evidence for their efficacy is derived mainly from case reports.
A third and clinically distinct disorder, serotonin syndrome, results from excessive serotonin activity. It may occur as a consequence of drug interactions, overdose of certain medications, or therapeutic (or recreational) drug use. Manifestations may include hypertension, tachycardia, hyperthermia, diaphoresis, myoclonus, tremulousness, hyperreflexia, confusion, agitation, and even coma. Treatment involves discontinuation of offending agents and often requires care in the ICU, control of the blood pressure, and management with cyproheptadine or benzodiazepines. A final related condition, discussed later, is malignant hyperthermia, a rare genetic disorder triggered by inhalational anesthetics or succinylcholine.
Anesthetic and surgical complications related to multiple sclerosis (MS) are relatively rare, but certain preoperative, intraoperative, and postoperative considerations are important. There is not abundant evidence to suggest that anesthesia or surgery consistently leads to disease exacerbations, but physiologic stress is commonly considered a cause of exacerbations and is heightened in the perioperative period. Accordingly, patients should be counseled about the potential risk of MS exacerbation with surgery and monitored for such postoperatively.
Disease-modifying therapies (such as β-interferons, glatiramer acetate, fingolimod, dimethyl fumarate, and teriflunomide) aimed at reducing the frequency and severity of MS exacerbations should be continued in the perioperative period. In patients with low medullary and high cervical demyelinating lesions, ventilatory dysfunction should be anticipated, as respiratory effort may be impaired.
Consideration should also be given to choice of anesthetic and anesthetic technique in patients with MS. Systemic administration of certain local anesthetics (e.g., lidocaine) may unmask clinically silent MS plaques or transiently worsen preexisting symptoms. The presumed mechanism involves partial sodium channel blockade exacerbating preexisting conduction block across demyelinated plaques. The findings in a small case series suggested that spinal anesthesia is associated with a higher relapse rate in MS compared to general anesthesia, though the exact underlying mechanism is unknown. A larger, more recent retrospective study of 139 patients with various CNS diseases (including but not limited to MS) found no increase in neurologic relapses following neuraxial anesthesia. Epidural anesthesia may have a lesser risk than intradural anesthesia due to decreased concentrations of anesthetics penetrating the thecal sac. The American Society of Regional Anesthesia and Pain Medicine concluded that the evidence for neuraxial anesthesia affecting neurologic function in patients with preexisting CNS disorders is not definitive and that individual risk–benefit analysis should be employed when selecting a method of anesthesia.
Although general anesthesia has been linked to MS exacerbations, it has often been used successfully, and there is no evidence to suggest that any single intravenous or inhalational anesthetic is preferable to another. If a patient experiences an MS relapse in the immediate postoperative period, the intraoperative temperature recordings should be checked as hyperthermia may cause MS pseudoexacerbations (Uhthoff phenomenon, i.e., symptoms that are not caused by new MS lesions and improve with a return to normothermia).
Caution should also be exercised in patients with MS receiving intrathecal baclofen for spasticity, as abrupt withdrawal may precipitate a potentially life-threatening syndrome characterized by seizures, hallucinations, and autonomic instability. Management includes resumption of baclofen as soon as possible and treatment with high-dose benzodiazepines in the interim.
Patients with MS should be monitored closely in the postoperative period. The appearance of new demyelinating plaques or increased neurologic deficits related to existing plaques may result from the stress of surgery or infection. Such exacerbations may result in impaired respiratory function and in autonomic dysfunction causing labile blood pressure. Baseline neurologic dysfunction in patients with MS combined with the stress of surgery may result in longer recovery times and necessitate rehabilitation upon discharge, even in the absence of any clinical deterioration.
Delirium and Dementia
Delirium is a complex entity characterized by the relatively acute onset of disorientation and attentional deficits that follow a fluctuating course. The incidence of postoperative delirium in the elderly ranges from 10 to 60 percent and varies somewhat with the type of surgery performed ( Table 54-1 ). Due to its variable forms—hyperactive, hypoactive, and mixed—delirium is often under-recognized. Hyperactive delirium involves agitation, combativeness, and hypervigilance, as is commonly seen in alcohol withdrawal. This form is easily recognized by clinicians. The hypoactive form, which may present with lethargy, stupor, or even coma, is sometimes difficult to recognize, as patients are less obtrusive and do not seek care or attention. It is not uncommon for these patients to be misdiagnosed with severe depression or for their cognitive dysfunction to be unrecognized.
|Type of Surgery||Incidence Range (%)|
|Orthopedic (mainly hip)||32–55|
Research has focused mainly on identifying baseline characteristics that predispose to the development of postoperative delirium and on iatrogenic risks of developing delirium, with relatively less emphasis until recently on the management and the long-term consequences of postoperative delirium. Nearly 98 percent of cases of postoperative delirium occur within 3 days of surgery. An early study of patients undergoing repair of femoral neck fractures showed no difference in the incidence of postoperative confusion when comparing epidural to halothane anesthesia. A more recent meta-analysis compared anesthetic types and supported the notion that general anesthesia was not more likely to be linked with postoperative delirium than regional anesthetic techniques. However, the type of anesthesia does become relevant when considering the timing of a postoperatively altered mental status. Patients receiving regional anesthesia tend to maintain or recover cognitive function more quickly than those receiving general anesthesia. Especially in the first 24 to 48 hours, it is important to consider which type of anesthesia the patient received as this may account for differences in mentation.
Factors that are associated with the development of delirium are well-established ( Table 54-2 ). It is important to recognize the possibility of postoperative delirium in elderly patients and those with baseline cognitive impairment ranging from mild cognitive impairment to frank dementia. In patients undergoing elective surgery, it is especially important to obtain an accurate history of substance use as both intoxication and withdrawal may manifest as delirium following surgery. Even mild pre- to postoperative electrolyte shifts, such as subtle hypo- or hypernatremia, may result in postoperative delirium. Postoperative pain management poses a particular challenge. Both untreated pain and analgesic use may worsen delirium. There remains a tendency to utilize physical restraints postoperatively to prevent patients from disrupting their wounds; such restraints may increase the risk of delirium and therefore should be discontinued as soon as possible.
|Baseline cognitive impairment||Poor sleep hygiene|
|Urinary tract infection||Urinary catheters|
|Pneumonia||Multiple surgical procedures|
|Toxic derangements||Untreated pain|
|Withdrawal (alcohol, benzodiazepines)||Anticholinergics|
|Poor baseline nutritional status (low serum albumin)||Benzodiazepines|
|Uremic encephalopathy||Muscle relaxants|
Hypoxia and hypercarbia
|Antibiotics (cephalosporins and fluoroquinolones)|
|Electrolytes: hyponatremia/hypernatremia, hypercalcemia, hypermagnesemia, hypophosphatemia|
Postoperative delirium has been associated with a number of poor outcomes. Length of stay, postoperative complications, and mortality are known to increase in the setting of postoperative delirium. Such patients are more likely to be discharged to a rehabilitation or long-term nursing facility than those without delirium. Postoperative delirium has also been associated with an increased risk of developing dementia in elderly patients with no known baseline cognitive dysfunction, suggesting that delirium may in itself cause long-term neurologic damage.
Treatment of postoperative delirium involves early identification and exclusion of other potential causes of an altered mental state. This workup usually includes neuroimaging to assess for stroke, hemorrhage, or mass lesion; an electroencephalogram to evaluate for seizures; and possibly a lumbar puncture to evaluate for evidence of a cerebral inflammatory or infectious disorder. Treatment depends on identification and reversal of the underlying cause. In the postoperative period, delirium precautions should be instituted, including frequent reorientation, opening blinds to allow for natural light to enter, and maintaining normal sleep–wake cycles. Physical restraints should be discontinued as soon as is safe and replaced with close monitoring from nursing staff, sitters, or family members to ensure patient safety. Unnecessary lines and tubes, particularly urinary catheters, should be discontinued. Early postoperative mobilization, even range-of-motion exercises for bedbound patients, and simple acts such as making patients’ eyeglasses and hearing aids available are important in treating as well as preventing delirium. Psychoactive medications, particularly anticholinergics, should be discontinued whenever possible. Postoperative pain control should be with minimum levels of analgesics required for relief. If these nonpharmacologic interventions are insufficient, pharmacologic treatment should be considered only if patients pose a risk of direct harm to themselves or the staff, while taking care to avoid the benzodiazepine class of medications, which has a particularly poor cognitive side-effect profile. Common practice is to consider using a low dose of an antipsychotic medication, such as quetiapine, at bedtime.
Patients with dementia who undergo surgery require special consideration. It is crucial to establish the patient’s preoperative baseline cognitive and physical function with family and caregivers in order to assess accurately their postoperative level of functioning. Patients with dementia are often elderly and have numerous medical comorbidities as well as a poor nutritional status, dehydration, and baseline electrolyte abnormalities. These conditions should be optimized or corrected preoperatively in order to maximize recovery and shorten length of hospital stay. Acetylcholinesterase inhibitors used to treat dementia should be continued throughout the perioperative period, although this class of medications may prolong the effects of succinylcholine.
Patients with dementia are at an increased risk of numerous postoperative complications. In particular, they are at higher risk of postoperative renal failure, pneumonia, urinary tract infections, sepsis, and strokes compared to age-matched controls. They also have an increased risk of postoperative delirium related to their baseline cognitive impairment and comorbidities.
Postoperative care for patients with dementia mostly revolves around the prevention and treatment of delirium. Although surgery alone may be sufficient to precipitate delirium in a patient with dementia, other triggers should still be investigated. Patients with Alzheimer disease, and probably many other neurodegenerative conditions, are at increased risk of seizures, emphasizing the need to obtain an electroencephalogram for those with an unexplained altered mental state postoperatively. Postoperative pain control can be challenging as patients with severe dementia may not be able to verbalize whether they are in pain. Pharmacologic management of delirium in patients with dementia should be used as infrequently as possible. Benzodiazepines in particular should be avoided, and low-dose antipsychotics should be used sparingly—a US Food and Drug Administration black box warning links antipsychotics to increased mortality among elderly patients. In patients with Lewy body dementia, antipsychotics should be avoided due to their profound sedating and extrapyramidal effects, which may be irreversible. Patients with dementia and their families should be counseled early regarding the possibility of a prolonged postoperative hospital course and the potential for discharge to a rehabilitation or nursing facility; in the setting of elective surgeries, these considerations may impact the decision to proceed.
A detailed headache history is important when evaluating patients with postoperative headaches, as preexisting primary headache disorders, such as migraine and tension headache, are common and often exacerbated by the stress of surgery and the dehydration that accompanies the NPO status. There are numerous warning features in the history and physical examination that signal the possibility of a secondary headache phenomenon related to a structural brain injury ( Table 54-3 ).
Patients with migraine should have their prophylactic medications continued in the perioperative period. Their migraine-abortive agents should also be continued postoperatively, though caution should be exercised when prescribing triptan medications after vascular surgeries given their vasoactive properties. Intravenous hydration with normal saline and administration of antiemetics such as prochlorperazine may be useful for attacks even when the migraine is not accompanied by significant nausea and vomiting. A brief course of a nonsteroidal anti-inflammatory drug (e.g., naproxen or intravenous ketorolac) may be used in refractory cases.
As many as 4 percent of the population overuse analgesics for the treatment of pain including headache, and it is estimated that up to 1 percent of the general population have medication-overuse headache. While postoperative pain may require narcotics, treatment of headaches with short-acting narcotics sometimes exacerbates the primary headache disorder and prolongs the period of recovery. Nearly all agents given to abort headache may be associated with medication-overuse headache. Treatment for this condition is gradual discontinuation of the medication; however, symptoms of opiate withdrawal including headache, nausea, vomiting, tachycardia, and insomnia are common, and therefore these medications are best weaned outside the perioperative period.
Due to the high frequency of consumption, caffeine withdrawal has become a widely recognized source of headache. Cessation of caffeine intake in people with low-to-moderate daily caffeine consumption (235 mg, approximately 2.5 cups of coffee) was associated with high depression scores, fatigue, and headache in a controlled trial. Headaches from caffeine withdrawal may begin 24 hours after cessation and last up to 5 or 6 days. In patients with postoperative headache, a careful caffeine history should be taken and—when caffeine withdrawal is responsible—resumption of normal caffeine intake permitted.
Dural puncture with resultant intracranial hypotension remains a common cause of perioperative headache with an incidence ranging from 2 to 36 percent after spinal anesthesia and as high as 85 percent after accidental dural puncture with a large-bore needle during epidural anesthesia. Among such headaches, 90 percent will begin within 72 hours of the puncture and 66 percent within 48 hours. A headache immediately following the procedure should raise suspicion of an alternate etiology. The headache of intracranial hypotension is typically located in the frontal and occipital regions, is exacerbated by an upright posture, and is alleviated by recumbency. Accompanying symptoms may include nausea, vomiting, tinnitus, vertigo, paresthesias, diplopia, and cranial nerve palsies. MRI findings of intracranial hypotension include diffuse pachymeningeal enhancement, subdural fluid collections, engorged cerebral venous sinuses, and descent of the cerebellar tonsils ( Fig. 54-1 ).
Prevention of post–dural puncture headache involves using a smaller gauge or noncutting needle. Caffeine, gabapentin, theophylline, and hydrocortisone have some efficacy in the treatment of such headache. Epidural blood patch remains the mainstay of treatment; in a study of 504 patients, complete relief was noted in 75 percent, incomplete relief in 18 percent, and failure to relieve symptoms in only 7 percent. If the initial blood patch does not relieve symptoms, a second blood patch should be administered, often with an extended period of lying supine following the procedure.
Seizures and Epilepsy
Epilepsy has a cumulative incidence of approximately 3 percent in the general population and is therefore commonly encountered in the perioperative period. Perioperative seizures directly related to general anesthesia occur in only 2 percent of epileptic patients. A large retrospective study demonstrated that recent (within 1 week) preoperative seizures were associated with a significantly higher likelihood of postoperative seizures. Patients with epilepsy should be advised to take their antiepileptic medications on the morning of surgery, and these medications should be resumed as soon as possible postoperatively. Preferably, these drugs should be administered orally, although intravenous preparations of phenytoin, sodium valproate, levetiracetam, phenobarbital, lacosamide, and benzodiazepines are an alternative for those with limited oral intake. Oral and intravenous dosages are largely equivalent, but the frequency of administration may vary from one preparation to another, and some extended-release formulations may not be easily converted to an intravenous dose.
Both phenytoin and fosphenytoin can precipitate hypotension and arrhythmias with rapid intravenous infusion; however, fosphenytoin can generally be infused at a faster rate and with a lower risk of local adverse effects following extravasation, and therefore is the intravenous phenytoin preparation of choice. Phenytoin can be administered via feeding tube, but levels are altered by enteral feedings, making the intravenous preparation preferable in such instances.
Antiepileptic drug levels should not be checked routinely in the perioperative period unless there has been a recent change in seizure frequency or concern for drug toxicity. Antiepileptic medications have many drug interactions, particularly in the case of the cytochrome P450–inducing agents phenytoin, carbamazepine, phenobarbital, and primidone, which can result in decreased levels of many medications including some antibiotics, immunosuppressants, analgesics, and neuromuscular blocking agents.
It is widely believed that some general anesthetics can have both pro- and anticonvulsant properties depending on the dose and clinical situation. Enflurane, sevoflurane, and etomidate induce epileptiform activity on the electroencephalogram and should generally be avoided in patients with epilepsy. Concurrent administration of nitrous oxide may decrease the epileptogenic potential of sevoflurane. Intravenous anesthetics including barbiturates and propofol are used for the treatment of status epilepticus, but at induction have been reported to be excitatory and can rarely precipitate a seizure. Some opioids, particularly meperidine and to a lesser extent fentanyl, have been linked to seizures, especially with intrathecal use. Propofol and opioids can also cause myoclonus and tremulousness that may clinically mimic seizures. Neuromuscular blocking agents have not been linked to seizures; however, if seizures are suspected while these drugs are being administered, continuous electroencephalographic monitoring is required as clinical manifestations of seizures will be masked.
Evidence regarding the epileptic potential of local anesthetics is conflicting, although they likely can cross the blood–brain barrier. Studies investigating regional blockade in patients with epilepsy have concluded that perioperative seizures were not increased in frequency.
Postoperative seizures should be considered as an etiology for delayed awaking after anesthesia. A relatively high frequency of seizures has been found in patients with altered mental state or “spells” both in the intensive care unit and in general medical wards. If possible, an extended electroencephalogram should be obtained to exclude nonconvulsive seizures, but this should not delay treatment in cases where the suspicion of seizures is high.
Neuromuscular diseases present the neurologist, surgeon, and anesthesiologist with some important general considerations common to this group of disorders as well as challenges inherent to specific diseases. All patients with severe neuromuscular disease are at risk of increased ventilatory complications due to respiratory weakness, and preoperative pulmonary assessment with forced vital capacity and maximal inspiratory force should be performed. Complications in patients with respiratory weakness include an increased sensitivity to respiratory depression from opioids, barbiturates, and benzodiazepines, as well as difficulty in weaning from the ventilator. Patients with some neuromuscular disorders including the muscular dystrophies have an increased risk of life-threatening cardiac dysrhythmias along with depressed cardiac contractility, warranting a preoperative assessment with electrocardiography and echocardiography. Depolarizing neuromuscular blockers such as succinylcholine can lead to hyperkalemia and resultant cardiac dysfunction in these patients and should be avoided.
Motor Neuron Disease
The timing of surgical procedures and anesthetic choice in patients with amyotrophic lateral sclerosis is important given an often profound progressive underlying respiratory weakness. Procedures such as percutaneous endoscopic gastrostomy should be undertaken when the forced vital capacity is still more than 50 percent of the predicted value. There are reports of nondepolarizing neuromuscular blockade precipitating severe weakness in patients with amyotrophic lateral sclerosis. The underlying mechanism may involve defective neuromuscular transmission in new nerve sprouts reaching previously denervated muscles. However, due to the previously described effects of succinylcholine in many neuromuscular disorders, low doses of nondepolarizing blockers are preferred when neuromuscular blockade is necessary.
A relationship between spinal anesthesia and worsening of symptoms in amyotrophic lateral sclerosis had previously been suggested. More recent reports indicate that epidural anesthesia may be used safely in these patients without exacerbating neurologic symptoms. Given the potential complications and prolonged recovery times following anesthesia and surgery, a multidisciplinary preoperative approach with cardiac and pulmonary screening is warranted, with appropriate preoperative counseling of the patient and family members regarding these risks.
Peripheral Nerve Disorders
The prevalence of diabetic autonomic neuropathy, a complication of both type 1 and type 2 diabetes, ranges from 7.7 percent in newly diagnosed diabetics to 90 percent in those awaiting pancreatic transplant. Poor glycemic control and duration of disease are felt to be risk factors for the development and progression of the neuropathy. These patients are at increased risk of significant bradycardia during induction of anesthesia as well as intraoperative hypotension requiring vasopressor support. Although there are no specific guidelines for anesthetic choice, etomidate and opioids may minimize hemodynamic instability while thiopental and propofol may carry a higher risk of hypotension.
Charcot–Marie–Tooth disease, the most common hereditary motor and sensory polyneuropathy, has also been associated with autonomic dysfunction. Additionally, respiratory muscle weakness is found in a minority of patients. In a review of 86 patients with Charcot–Marie–Tooth disease undergoing surgery, few complications were seen. Although succinylcholine was previously felt to be contraindicated, Antognini did not find a significantly increased risk of poor outcomes with this drug but still recommended avoidance if at all possible on theoretical grounds.
Case series describe surgery as a potential trigger for acute inflammatory demyelinating polyradiculoneuropathy (AIDP; Guillain–Barré syndrome), a relatively common cause of acute paralysis. A recent retrospective analysis of 63 patients with AIDP found that 9.5 percent had undergone surgery within the prior 6 weeks and that the relative risk of developing AIDP in the 6-week postoperative period was 13 times higher than the baseline incidence in the population. The precise mechanism for this association is unknown, but one theory is that surgery alters the immune system, igniting a pathway leading to molecular mimicry against peripheral nerve components, perhaps in the setting of postoperative infection.
With both AIDP and chronic inflammatory demyelinating polyradiculoneuropathy (CIDP), perioperative forced vital capacity and maximal inspiratory force should be monitored serially to provide some indication as to whether a patient can be extubated safely. Patients with AIDP and CIDP are sensitive to nondepolarizing muscle relaxants, which may necessitate prolonged postoperative ventilation when administered. Reports of worsening neurologic function in patients with AIDP following epidural anesthesia exist. Local anesthesia has been linked to hypotension, bradycardia, and cardiac complications in patients with AIDP, presumably due to involvement of the autonomic nervous system. There are no firm recommendations regarding the preferred anesthetic technique for patients with AIDP and CIDP.
Patients with muscular dystrophies including Duchenne, Becker, and Emery–Dreifuss often undergo a series of surgeries in their lifetime involving tendon releases and correction of scoliosis. Due to the systemic nature of these disorders, a multidisciplinary perioperative approach involving a neurologist, pulmonologist, cardiologist, and anesthesiologist is often warranted. Many of these disorders are associated with cardiomyopathy and disorders of cardiac conduction. Respiratory function is often compromised because of ventilatory muscle weakness as well as poor mechanics secondary to skeletal abnormalities. For patients with Duchenne muscular dystrophy, the American College of Chest Physicians recommends a thorough preoperative pulmonary evaluation including measurement of forced vital capacity, maximal inspiratory force, and peak cough flow. Patients found to have a forced vital capacity of less than 50 percent of the predicted value should be considered for preoperative training of noninvasive positive pressure ventilation, given the risk of ventilatory compromise following surgery. Most muscular dystrophies are not linked to an increased incidence of malignant hyperthermia. Inhaled anesthetics such as halothane have been associated with rhabdomyolysis in the absence of succinylcholine in patients with elevated serum creatinine kinase levels at baseline.
Patients with other myopathies face similar risks associated with surgery and anesthesia. Reports of hyperkalemic cardiac arrest in children undergoing anesthesia have been linked to previously unrecognized myopathies. Central core myopathy, an autosomal dominant disorder, has been closely linked to malignant hyperthermia, via a common mutation in the ryanodine receptor gene ( RYR1 ). The prevalence of malignant hyperthermia has been estimated at 1 per 100,000 hospital discharges in all patients. This rare genetic condition is triggered by exposure to inhalational anesthetics or succinylcholine in susceptible individuals and is characterized by muscle rigidity, tachycardia, hyperthermia, hypercapnea, and metabolic acidosis. Malignant hyperthermia or a malignant hyperthermia-like syndrome has been described in a variety of myopathies and channelopathies (e.g., periodic paralysis). The mainstay of treatment for malignant hyperthermia other than supportive care remains dantrolene, which decreases skeletal muscle calcium release, thereby inhibiting muscle contraction. If anesthesia is required in patients with myotonic dystrophy, depolarizing muscle relaxant drugs should be avoided because they may cause myotonic spasm, and nondepolarizing drugs are given in reduced dosage to patients who are taking quinine for their myotonia.
Myasthenia gravis (MG) is the most common neuromuscular junction disorder, and consequently most of the research into the perioperative care of patients with such disorders has focused on MG. The preoperative care of patients with MG begins with appropriate counseling of the patient and family, emphasizing that the stress associated with elective surgery may temporarily worsen the disease, necessitate postoperative care in the intensive care unit, and lead to prolonged intubation. Since thymectomy is a treatment for MG, this surgery provides a natural avenue to study the perioperative care of patients with MG. A study of risk stratification of patients with MG undergoing thymectomy demonstrated that disease duration of greater than 6 years, a history of respiratory disease, daily pyridostigmine dose exceeding 750 mg, and a forced vital capacity of less than 2.9 liters predicted the need for postoperative ventilation. This predictive tool may not apply to patients with MG undergoing surgeries other than thymectomy. A preoperative neurologic examination focusing on facial strength, dysarthria, dysphagia, neck flexion, and formal pulmonary function testing, especially in those patients with bulbar weakness, allows for anticipation of postoperative ventilatory compromise and pulmonary complications including aspiration.
Numerous studies have investigated the effects of pyridostigmine on neuromuscular blockade in the perioperative period. There is not sufficient evidence to conclude that changing a patient’s pyridostigmine dose prior to surgery significantly impacts neuromuscular blockade or the duration of ventilation and thus the general recommendation is to continue the patient’s usual preoperative regimen. Most immunosuppressants in patients with MG do not interact with anesthetics; however, azathioprine extends the effect of succinylcholine and inhibits nondepolarizing neuromuscular blockers.
Elective surgeries should be undertaken when respiratory function is stable and patients are on the lowest possible doses of corticosteroids. In the case of more urgent surgery, presurgical plasma exchange should be considered as it decreases the duration of postoperative ventilation and stay in the intensive care unit in patients undergoing thymectomy. Intravenous immunoglobulin remains another option if plasma exchange is unavailable.
When possible, regional anesthesia is preferable to general anesthesia in patients with MG, as it minimizes the need for neuromuscular blockade and ventilation. Patients with MG have a decreased number of functional acetylcholine receptors and thus their response to neuromuscular blockade may be abnormal during general anesthesia. Patients may have a prolonged blockade when either succinylcholine or nondepolarizing neuromuscular blockers are used. The dosing of neuromuscular blockade should be individualized based on the severity of the patient’s myasthenia; however, 50 percent of a routine dose is likely adequate and an extended recovery time should still be anticipated.
Postoperative recovery in patients with MG may be prolonged. Electrolytes, particularly potassium, should be monitored closely, as hypokalemia may worsen weakness in MG. Whenever possible, postoperative analgesia should be minimized and opioids, benzodiazepines, and barbiturates should be avoided if possible due to their respiratory depressant effects. Patients with MG should have their medications reviewed frequently to ensure that they are not receiving drugs that may worsen weakness, such as aminoglycosides. If pyridostigmine cannot be given orally, the parenteral dose should be administered at roughly one-thirtieth of the enteral dose. Atropine should be given before or concurrent with intravenous pyridostigmine to prevent bradycardia and excessive bronchial secretions. Although no precise clinical criteria can determine the timing of extubation, clinical examination including evaluation of neck flexor strength can guide the decision. After extubation, aggressive pulmonary toilet and use of incentive spirometry should be encouraged. Early mobilization shortens the duration of recovery.
Postoperative myasthenic crisis is not uncommon in patients with MG, with an incidence ranging from 12 to 34 percent following thymectomy. The likelihood of postoperative crisis has been related to a prior history of myasthenic crisis, preoperative bulbar weakness, preoperative serum acetylcholine receptor antibody levels of greater than 100 nmol/L, and intraoperative blood loss of greater than 1 liter. Management should involve emergent assessment of the patient’s respiratory status, recognizing that intubation is usually necessary. Effective treatment options include prompt initiation of plasma exchange or intravenous immunoglobulin.