Neuraxial Blocks In Infected Or Febrile Patients

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Single-shot spinal techniques and short-term epidural catheterization appear to pose little risk to patients who may become transiently bacteremic during surgery. Conversely neuraxial blocks in infected or febrile patients may increase the risk of neuraxial infection, and these blocks remain controversial. Most authorities believe that neuraxial blocks should not be performed in patients who are bacteremic and have not commenced antibiotic therapy. If antibiotics have been started and there has been a clinical response, such as defervescence of a fever, single-shot spinal anesthesia may be safe. However, indwelling catheters may increase the risk of neuraxial infection. Therefore, extreme care should be taken when considering these techniques in such patients. If an indwelling cathter is chosen, patients should be monitored vigorously for sign and symptoms of neuraxial infection.

Meningitis is a medical emergency. Its mortality approaches 30%, even with antibiotic therapy. Delays in diagnosis and treatment can significantly worsen outcome. Clearly, rapid diagnosis and prompt, appropriate treatment are paramount. All patients who receive neuraxial blocks and are febrile or infected should be considered to be at risk. Signs of meningitis include severe headache, fever, meningismus, and altered mental status. Diagnosis is confirmed via lumbar puncture. If spinal abscess is suspected, lumbar puncture should be avoided to prevent seeding of the CSF with bacteria.

Neuraxial Blocks in Patients with Preexisting Neurologic Disorders

Preexisting neurologic disorders present challenges to the anesthesiologist. Postoperative neurologic injuries can have a variety of causes, including surgical trauma, prolonged tourniquet ischemia, improper positioning, extended labor and anesthetic technique.™ Progressive neurologic diseases, such as multiple sclerosis, may worsen perioperatively by happenstance, regardless of the anesthetic technique or surgical procedure. Furthermore, it is often difficult to determine the cause of postoperative neurologic injury. For example, the most common site of neurologic injury in total shoulder arthroplasty is at the level of the trunks of the brachial plexus, the same location as needle entry for interscalene blocks. Although it is tempting to implicate interscalene block as a risk factor for postoperative neurologic injury after these procedures, evidence points to surgical issues.™ Clearly, a careful, thorough approach to diagnosis is mandatory when postoperative neurologic deficits are evaluated.

Because of the issues discussed earlier and the medicolegal implications of any increase in postoperative neurologic deficit, many clinicians completely avoid neuraxial block in patients with preexisting neurologic disorders. However, one can easily imagine patients with severe cardiopulmonary disease for whom neuraxial anesthesia and analgesia would be the technique of choice for a variety of surgical procedures. Thus, decisions regarding the choice of anesthetic techniques should be based on individual patient factors, considering overall medical status, the surgical procedure, and patient preference, in addition to preexisting neurologic deficits. Informed consent is of paramount importance in these instances.

Preexisting central nervous system disease may present a more difficult dilemma to the anesthesiologist in relation to neuraxial anesthesia and analgesia. In theory, the preexisting central nervous system disease implies neural compromise that may predispose patients to neural injury after neuraxial anesthesia. Vandam and Dripps™ identified 11 patients with exacerbations of preexisting neurologic complications after spinal anesthesia and recommended that spinal anesthesia not be given to those with central nervous system or spinal disease, regardless of whether the patient is symptomatic. Other authors agree.181 Although central nervous system diseases such as lumbar radiculopathy, spinal stenosis, multiple sclerosis, amyotrophic lateral sclerosis, and poliomyelitis require the anesthesiologist's consideration when the anesthetic plan is being determined, the presence of these diseases is not necessarily a contraindication to neuraxial anesthesia.1™ Unfortunately, the literature regarding the use of neuraxial blocks in these patients consists of case reports only. No controlled studies have appeared to define risk of further neurologic injury in these patients presumably because of the difficulties encountered in designing and carrying out such investigations. Without definitive studies for guidance, decisions regarding the use of neuraxial anesthesia should be made on a case-by-case basis. Thus, the anesthesiologist should be aware of the pathophysiology of the neurologic disease as well as the potential mechanisms and incidence of neurologic injury associated with neuraxial block.

Diabetes Mellitus

Peripheral and autonomic neuropathies are part of the classic diabetic triopathy, along with retinopathy and nephropathy. Neuropathy occurs in a large number of diabetic patients. Depending on the criteria for diagnosis and the patient population studied, the incidence may range from 15% to 100%. ™ In patients with a 25-year history of type 2 diabetes mellitus, 50% have neuropathy.®9 Even in patients without clinical symptoms of neuropathy, there may be electrophysiologic evidence of neuropathy, consisting of slowing of nerve conduction velocities. The electrophysiologic abnormalities can occur even in patients with histologically normal nerves.12™ Preexisting neurologic dysfunction may lessen local anesthetic requirements. Diabetes is associated with arteriosclerosis. This microangiopathy affects nerve blood vessels and decreases local anesthetic uptake. As a result, nerves have prolonged exposure to higher levels of local anesthetics. In theory, preexisting nerve damage and increased exposure to local anesthetics may lead to neurologic injuries in diabetic patients, despite a dose of local anesthetic that would be considered safe in the normal population.™

There is laboratory evidence for the theory just discussed. Kalichman and Calcutt[136] examined the effects of local anesthetics on nerve conduction block and injury in a rat model of diabetes. They reported that local anesthetic requirements were reduced and that there was increased risk of local anesthetic-induced nerve injury associated with diabetes. Clinicians may conclude from the study by Kalichman and Calcutt that neuraxial block has an increased risk of local anesthetic-induced nerve toxicity in diabetic patients compared with nondiabetic patients, and that local anesthetic concentrations and doses should be reduced in diabetic patients. Unfortunately, there are no human clinical studies to confirm or refute this conclusion.

Multiple Sclerosis

Multiple sclerosis is characterized by random, demyelinating lesions of the central nervous system. Peripheral nerves are not affected. Its etiology is not well defined. The course of the disease is variable, ranging from indolent to relapsing-remitting with chronic progression to rapidly progressive. The timing of exacerbations of the disease is unpredictable. However, multiple factors have been associated with exacerbations, including stress, surgery, fatigue, and fever.™ ™ Clearly, an increase in symptoms can occur by coincidence perioperatively, regardless of the anesthetic technique chosen. Since the 1930s, authors have advised against the use of spinal anesthesia in patients with multiple sclerosis.™ However, the evidence for avoiding neuraxial block in this population is not compelling.233

™ ™ The mechanism of neuraxial anesthesia-induced relapse of symptoms is not known but may be local anesthetic toxicity. Because of this, some authors recommend epidural anesthesia over spinal anesthetic block, since epidural anesthesia exposes the spinal cord white matter to much lower concentrations of local anesthetic than spinal anesthetic block.™ If a neuraxial block is chosen, it may be prudent to use a dilute concentration of local anesthetic. The use of peripheral nerve blocks is not associated with relapses of multiple sclerosis.1™

Spinal Stenosis

Spinal stenosis is a common degenerative disease of the vertebral column that often remains asymptomatic. The use of neuraxial blockade in these patients is controversial. Cauda equina syndrome and polyradiculopathy have been reported in patients with asymptomatic spinal stenosis who underwent neuraxial block.«"3 ™ ™ The mechanism of injury is unclear in these instances. However, the incidence of transient paresthesias is increased when spinal anesthetics are placed in patients with lumbar spinal pathology such as spinal stenosis,™ and transient paresthesias increase the risk of persistent paresthesias after spinal anesthetics.113 Unfortunately, no clinical studies have addressed the risk of neurologic injury associated with neuraxial anesthesia in patients with spinal stenosis.


Neuraxial anesthetic and analgesic techniques remain an important part of the anesthesiologist's armamentarium. Depending on specific patient factors and the setting in which these techniques are applied, they may offer significant advantages. Fortunately, neuraxial techniques are associated with a low incidence of significant complications. However, as overall perioperative safety improves, rare and potentially devastating complications from neuraxial anesthesia and analgesia become more significant. Anesthesiologists can minimize the risk of these complications by appropriately applying neuraxial techniques in carefully selected patients. Proper patient selection depends on detailed knowledge of any conditions that may predispose patients to complications from neuraxial techniques.

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