In general, light sedation is often administered with spinal anesthetics, and such administration decreases the incidence of postoperative respiratory complications as compared to the use of general anesthetics. In one study, nearly two thirds of complications related to general anesthetic use involved postoperative respiratory events. Conversely, the most common complications associated with spinal anesthetics are postdural puncture headache (PDPH) and backache.

PDPH is the most common complication in patients receiving spinal anesthesia, with incidences as high as 25% reported in some studies. Small-bore, 25-gauge, pencil-point needles decrease the incidence of PDPH. The greatest incidence of PDPH occurs when large-bore epidural needles accidentally
puncture the dura. PDPH is believed to result from a loss of cerebrospinal fluid, which places traction on the meninges and, thus, on the brain. Patients with a PDPH typically present with orthostatic, position-related headaches. Valsalva maneuvers, such as coughing and sneezing, exacerbate the head pain. The patients may complain of nausea, vomiting, dizziness, visual and auditory changes, paresthesias, weakness, and cranial-nerve palsies. The pain typically resolves in several days. Conservative measures, such as rest, hydration, and caffeine can alleviate symptoms. More long-standing symptoms can be managed through an autologous epidural blood patch, with success rates approaching 90% for the first blood patch and up to 98% with repeat patches.

In general, the delivery of anesthesia of any kind is associated with postoperative backache, but the incidence is higher following spinal anesthesia. Epidurals have been associated with a higher incidence and a longer duration of backache than have spinal blocks. The etiology of such backache is unknown, but local anesthetic irritation, direct trauma, and ligamentous strain related to muscle relaxation have been postulated.

Although systemic toxicity is continually a concern with epidural anesthesia, systemic toxicity does not occur with spinal anesthesia, because drug doses are generally considered too low to cause toxic reactions, even if injected intravenously.

Total or high spinals occur when excessive amounts of medication are injected intrathecally. The anesthetic spreads to the entire spinal cord and the brain stem, resulting in total sympathetic blockade with resultant bradycardia, hypotension, and respiratory depression. Ponhold and Vicenzi found that the patient’s operative position helps determine the incidence of bradycardia and, thus, of sympathetic blockade. Patients in the Trendelenburg position were more likely to develop bradycardia than were those in the supine or hammock position. Respiratory arrest can also occur as the primary and accessory respiratory muscles are paralyzed, and the lower-respiratory brain centers are affected. Adequate supportive measures with antimuscarinics, vasopressors, intravenous fluids, and ventilation can effectively treat highspinal blocks.

Neurologic injury is a feared complication of both spinal and epidural anesthesia. The incidence of serious injury to the cauda equina roots and paraplegia is extremely low, but persistent paresthesias and limited motor
weakness are the most common injuries among neurologic complications. Barash and Stoelting state that, “Injury may result from direct needle trauma to the spinal cord or spinal nerves, from spinal cord ischemia, from accidental injection of neurotoxic drugs or chemicals, from introduction of bacteria into the subarachnoid or epidural space, or very rarely from epidural hematoma.”

Transient neurologic symptoms (TNS) can result from clinical administration of high concentrations of local anesthetics, causing pain to radiate down the back and lower extremities. The pain occurs within 24 hours after spinal anesthesia and generally lasts 48 hours. As the number of procedures done using spinal anesthetics has increased over the past decade, so has awareness and concern about TNS. Hyperbaric lidocaine is a major culprit in causing TNS, and the lithotomy position and knee arthroscopy position increase the rate of TNS. Although the dose of a solution does not appear to affect the incidence of TNS, anesthesiologists believe that hyperbaric solutions surrounding neurologic components pool in dependent locations and fail to mix adequately with cerebrospinal fluid, causing cauda equina syndrome. Anesthesiologists speculate that neural stretching compromises blood flow and can exacerbate sciatic-type symptoms. Pollack et al. compared various concentrations of lidocaine and found no difference in their associated incidences of TNS. TNS is, however, a rare complication. In a retrospective study examining the risk of neurologic symptoms in 4,767 subjects, Horlocker et al. showed the safety of spinal anesthesia.

Spinal hematoma and other central nervous system (CNS) hematomas are potentially disastrous complications of spinal anesthesia in patients receiving anticoagulation therapy, which is commonly administered to various patients, including those with atrial fibrillation and hypercoagulable disorders; those with orthopedic fractures; and those who are bedridden and debilitated. Antiplatelet-drug use and traumatic or prolonged needle placement also can lead to CNS hematomas. The American Society of Regional Anesthesia and Pain Management has developed practice guidelines for treating neuroaxial anesthesia. The extremely low incidence of neuroaxial hematomas precludes prospective randomized studies. Using these guidelines and understanding the relevant pharmacology permits well-informed clinical decision-making (http://www.asra.com/publications/consensus-statements-2.html).