Obstetric Surveys

The reported incidence of neurologic deficits in obstetric patients varies widely depending on the source and the complications that are being measured. Many surveys have attempted to assess the incidence of neurologic complications of neuraxial anesthesia, but these surveys share common limitations, including low response rates, lack of control groups who did not receive neuraxial anesthesia, and inaccurate diagnosis ( Box 31.1 ). Moreover, bias is created when more attention is paid to patients who received neuraxial blockade than to those who did not. Some of the more relevant surveys are listed in Table 31.1 . Although each survey is distinct in its population, measurements, and reporting, some generalizations can be made. Most of the neurologic complications in these reports were transient, most occurred in patients who labored, and only a very small minority were attributable to neuraxial anesthesia. Peripheral nerve damage was more common than central cord or plexus damage.

One of these reports from Leeds in the United Kingdom involved 3991 women who delivered in one center in a 1-year period. Twenty-one women presenting with symptoms after neuraxial blockade were matched with 21 asymptomatic control patients who had also received neuraxial blockade and 21 additional women who had not. Only one woman who had not had a neuraxial block had symptoms, and she was found to have foot drop after a vacuum extraction. Typical peripheral neuropathies occurred among those who delivered vaginally; sacral numbness was most commonly detected after cesarean delivery. All changes were transient, and none could be attributed to neuraxial anesthesia. Similar neurologic deficits were detected among the randomly selected, asymptomatic 21 control patients who had not undergone an anesthetic intervention. In contrast, negligible deficits could be detected among the 21 asymptomatic control women who had undergone an anesthetic intervention. These results demonstrate that minor neurologic deficits are to be found postpartum quite frequently if sought, but only those who have had anesthetic intervention are likely to complain or be questioned.

A prospective survey among 6057 women who delivered in one year in Chicago corroborates the findings of the Leeds study. The incidence of lower limb nerve injuries was approximately 1% (24 lateral femoral cutaneous nerve, 22 femoral nerve, 3 peroneal nerve, 3 lumbosacral plexus, 2 sciatic nerve, 3 obturator nerve, and 5 radicular injuries). Significant risk factors identified by logistic regression analysis included nulliparity and a prolonged second stage of labor but not neuraxial anesthesia.

A UK national audit of neuraxial blocks, without controls, published in 2009, found that the risk for major complications was 6- to 14-fold higher for perioperative than for obstetric procedures. Among the obstetric patients, the risk was highest for combined spinal-epidural (CSE), intermediate for spinal, and lowest for epidural procedures. Finally, the Serious Complication Repository (SCORE) project sponsored by the Society for Obstetric Anesthesia and Perinatology collected data from 30 institutions and more than 250,000 neuraxial blocks in the United States over a 5-year period (2004 to 2009); the incidence of anesthesia-related nerve injury for obstetric patients was approximately 1 in 35,000 deliveries. Four cases of epidural abscess/meningitis and a single case of epidural hematoma were reported.

Several conclusions can be drawn from these surveys. Despite an increased cesarean delivery rate in the past several decades, obstetric palsies still occur, and the reported frequency of neurologic sequelae depends on how hard one seeks them. The risk for transient mild deficits after childbirth may be quite high. A true figure for anesthetic complications cannot be calculated, even from thorough surveys, because (1) the diagnosis is rarely accurate and (2) definitions, severity, and duration are often ill defined. Table 31.1 demonstrates a variation in the incidence of neurologic sequelae from 1 in 3 for mild symptoms with no neuraxial block to 1 in 200,000 for spinal hematoma.

Other Surveys

Modern surveys of neurologic complications of spinal and epidural anesthesia among nonobstetric populations may yield more reliable results but still lack sensitivity to detect all potential problems and are commonly conducted in relatively elderly and sick populations. Auroy et al., Moen et al., Cook et al., and Pitkanen et al. surveyed mixed populations and found a lower incidence of serious sequelae in obstetric than in nonobstetric patients. It is therefore invalid to extrapolate findings from one population to the other. The reported risk for neurologic problems varies greatly with the patient population, local practice and skill, completeness of detection, and inclusion criteria. Hence, it is difficult to put any firm figure on the risk for neurologic complications after neuraxial anesthesia in obstetric patients.

Compression of the Lumbosacral Trunk

Compression of the lumbosacral trunk by the fetal head at the pelvic brim ( Fig. 31.3 ) preferentially affects the more medial fibers that make up the peroneal rather than the tibial nerve. In addition to weakness that predominantly affects ankle dorsiflexion (foot drop), compression of the lumbosacral trunk produces sensory disturbance mainly involving the L5 dermatome (see Fig. 31.1 ). This palsy most often results from cephalopelvic disproportion and is therefore typically seen after prolonged labor and difficult vaginal delivery.

The principal nerves in the pelvis. The lumbosacral trunk (L4 to L5) and obturator nerve (L2 to L4) are vulnerable to pressure as they cross the pelvic brim, particularly in cases of cephalopelvic disproportion. The femoral (L2 to L4) and lateral femoral cutaneous (L2 to L3) nerves are particularly vulnerable in the lithotomy position, where they pass beneath the inguinal ligament.

(Modified from Cole JT. Maternal obstetric paralysis. Am J Obstet Gynecol. 1946;52:374.)

Obturator Nerve Palsy

The obturator nerve is susceptible to compressive injury as it crosses the brim of the pelvis and within the obturator canal (see Fig. 31.3 ). The mother may complain of pain when the damage occurs, followed by weakness of hip adduction and internal rotation, with sensory disturbance over the medial thigh (see Fig. 31.1 ). She may have an abnormal gait secondary to weakness of thigh adduction. Cases are reported after both labor and cesarean delivery ; three of 66 new nerve injuries detected in a prospective study by Wong et al. were obturator nerve injuries. The most likely cause of obturator nerve palsy is compression of the nerve between the pelvis and fetal head or forceps applied to the fetal head.

Femoral Nerve Palsy

The femoral nerve does not enter the true pelvis and is therefore not vulnerable to compression by the fetal head but rather is vulnerable to stretch injury as it passes beneath the inguinal ligament. The femoral nerve may be injured proximal to or at the inguinal ligament. Proximal injuries are associated with weakness of hip flexion, whereas more distal injuries spare the motor supply to the iliopsoas muscle. The patient with a femoral neuropathy may walk satisfactorily on a level surface but may be unable to climb stairs; the patellar reflex is diminished or absent. Although the incidence of femoral nerve palsy has decreased as a result of changes in obstetric management (e.g., fewer deliveries with prolonged second stage), it is still one of the most common obstetric nerve injuries. Approximately one-third of the postpartum palsies detected by Wong et al. were femoral nerve palsies. Dar et al. detected five cases in their small population, although the symptoms were transient. Damage may result from prolonged flexion, abduction, and external rotation of the hips during the second stage of labor and also during procedures conducted in an excessive lithotomy position. The hips should therefore never remain continuously flexed during the second stage of labor.

Meralgia Paresthetica

Meralgia paresthetica is a neuropathy of the lateral femoral cutaneous nerve, a purely sensory nerve also known as the lateral cutaneous nerve of the thigh. First described more than 100 years ago, meralgia paresthetica is commonly encountered in pregnancy and childbirth. It is the most common nerve injury of pregnancy. The palsy may arise both during pregnancy, typically at about 30 weeks’ gestation, and intrapartum, in association with increasing intra-abdominal pressure. The distribution is unlike that of a nerve root lesion (see Fig. 31.1 ), yet the disturbance is commonly misattributed to neuraxial blockade. Meralgia paresthetica manifests as numbness, tingling, burning, or other paresthesias affecting the anterolateral aspect of the thigh. The most likely cause is entrapment of the nerve as it passes around the anterior superior iliac spine beneath or through the inguinal ligament, where its vulnerability is increased by a gravid uterus or by retractors used during pelvic surgery. The compressive effect of edema may also contribute. The condition can be expected to resolve after childbirth.

Sciatic Nerve Palsy

Sciatic nerve palsy arises from compression of the nerve, usually in the buttock. It is not commonly mentioned in surveys or generally recognized as a complication of childbirth, possibly because it is mistaken for a lesion of the lumbosacral trunk. It gives rise to loss of sensation below the knee with sparing of the medial leg, and loss of movement below the knee. Posterior cutaneous nerve and gluteal function are preserved, implying damage distal to the lumbosacral plexus, where the gluteal nerves branch off the sciatic nerve ( Fig. 31.4 ). Three cases out of 66 new nerve injuries were detected by Wong et al. It has occurred during childbirth with neuraxial blockade, either from sitting in one position too long or from a hip wedge misplaced during cesarean delivery. It has also been reported after iliac artery balloon placement for cesarean delivery in a woman with placenta percreta.

The sacral plexus. The dorsal divisions of the anterior primary rami are shaded.

(From Silva M, Mallinson C, Reynolds F. Sciatic nerve palsy following childbirth. Anaesthesia. 1996;51:1144–1148.)

Peroneal Nerve Palsy

The common peroneal nerve is vulnerable to compression as it passes around the head of the fibula below the knee. It is also susceptible to damage while it still forms part of the sciatic nerve as it leaves the pelvis. When the peroneal nerve is damaged at the knee, there is sensory impairment on the anterolateral calf and the dorsum of the foot. Foot drop may be profound, with steppage gait and weak ankle eversion, but plantar flexion and inversion at the ankle are preserved. Peroneal nerve palsy may be caused by prolonged squatting, sometimes popular in “natural childbirth,” by excessive knee flexion for any reason, by compression of the lateral side of the knee against any hard object, even the patient’s hand, and by prolonged use of the lithotomy position. The incidence of peroneal nerve palsy is lower than that of lateral femoral cutaneous and femoral nerve palsy.

Compression as a Risk Factor for Peripheral Neuropathy

During pregnancy, nerve compression caused by edema may be a factor in the genesis of several peripheral neuropathies, such as carpal tunnel syndrome, Bell’s palsy, and meralgia paresthetica. Neuraxial blockade may indirectly contribute to compression injuries because it may decrease the ability of a woman to perceive that her legs are in a position that contributes to compression-induced neuropathy. Practices that providers should observe to lessen the risk for compression-induced neuropathy are listed in Box 31.2 .

Neurologic Sequelae of Dural Puncture

The subject of post–dural puncture headache is discussed in detail in Chapter 30 . Other neurologic sequelae of dural puncture include meningitis (see later discussion), cranial nerve palsies, and subdural hematoma. These often present as headache but are distinct from disorders that should be included in the differential diagnosis for postpartum headache, including tension/stress and migraine headaches, cortical vein and venous sinus thrombosis, preeclampsia, hypertensive encephalopathy, intracerebral or subarachnoid hemorrhage, internal carotid artery dissection, and posterior reversible encephalopathy syndrome. It can be difficult to distinguish post–dural puncture headache from other serious causes of headache because signs and symptoms overlap.

Trauma to Nerve Roots and the Spinal Cord

Insertion of a spinal needle or epidural catheter may be accompanied by paresthesia that is sometimes painful. However, such a paresthesia is neither sensitive nor specific for nerve injury. If a paresthesia is encountered, advancement of the needle or catheter should be halted. It is generally deemed appropriate to then continue spinal or epidural catheter placement after the paresthesia subsides. Continued paresthesias should prompt removal and redirection of the needle. Although a flexible catheter is unlikely to do lasting damage to a nerve root in the epidural space, nerve roots in the subarachnoid space are more vulnerable.

Trauma Associated with Spinal Anesthesia

Insertion of a spinal needle below the level of the spinal cord sometimes causes brief radiating pain or paresthesia, which may be associated with persistent paresthesia in the same dermatomal distribution. Prolonged symptoms involving more than one spinal segment suggest damage to the spinal cord itself. Damage to the terminal portion of the cord (the conus medullaris) without intracord injection has also been reported in healthy conscious parturients receiving spinal or CSE anesthesia using a pencil-point needle. Typically, the patient complains of pain on needle insertion before any fluid is injected, often followed by the normal appearance of CSF from the needle hub, easy injection of the local anesthetic agent, and a normal onset of neural blockade. On recovery, there is unilateral numbness, which is succeeded by pain and paresthesia in the L5 to S1 distribution and foot drop, and in some cases urinary symptoms; sensory symptoms may last for months or years. The MRI appearance is one of a small syrinx or hematoma within the conus on the same side as the pain on insertion and subsequent leg symptoms ( Fig. 31.7 ). In the majority of cases, the anesthesia provider believed the interspace selected was L2–L3. In one patient who subsequently died of other causes, hematomyelia was confirmed at autopsy. After a rash of cases of conus damage in the 1990s, the practice of spinal needle insertion may have been modified by aware providers, but an abnormally long cord may still be damaged with the best of techniques.

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