Early symptoms are those of stimulation, but as serum levels rise, depression follows. Symptoms may include light-headedness, dizziness, tinnitus, metallic taste, and numbness of the tongue and mouth. Patients may show bizarre behavior, slurred speech, muscle fasciculation and excitation, and ultimately, generalized convulsions, followed by loss of consciousness.
hese manifestations generally develop later than those of cerebral toxicity. Moreover, no symptoms may develop because signs are usually induced by higher serum drug levels. he notable exception is bupivacaine, which is associated with neurotoxicity and cardiotoxicity at virtually idenricalilevels (Mulroy, 2002). Because of its toxicity risk, use of a 0.75-percent solution of bupivacaine for epidural injection has been proscribed by the FDA. Similar to neurotoxicity, cardiovascular toxicity is characterized first by stimulation and then by depression. Accordingly, hypertension and tachycardia are soon followed by hypotension, cardiac arrhythmias, and impaired uteroplacental perfusion.
• Management of Local Anesthetic
Seizures and severe ventricular arrhythmias can follow large doses of local anesthetics that are given inadvertently. Labor and delivery units should be stocked with a 20-percent lipid emulsion solution (Intralipid). It is administered as a rapid intravenous bolus followed by an infusion upon the first sign of local anesthetic systemic toxicity (Neal, 2012). Controlling seizures and securing the airway are essential to prevent aspiration and hypoxemia. Benzodiazepines, such as midazolam or lorazepam, may be used to help control seizures, particularly if lipid emulsions are not available. Magnesium sulfate also controls convulsions (Chap 40, p. 736). Abnormal fetal heart follow and stem from maternal hypoxia. With proper manage ment, including supportive measures, the fetus usually recovers.
herefore, it is best for the fetus and mother to delay delivery until the mother is stabilized.
With proper treatment of local anesthetic systemic toxicity (LAST) with lipid emulsions, vital signs usually return to normal. The woman, however, should be monitored, placed in the lateral decubitus position to avoid aortocaval compression, and provided continued supportive care. Vasopressors can be used to support blood pressure. With cardiac arrest, emergency cesarean delivery is considered if maternal vital signs have not been restored within 5 minutes (Chap, 47, p. 931). As with convulsions, however, the fetus is likely to recover more quickly in utero once maternal cardiac output is reestablished.
Pain with vaginal delivery arises from stimuli from the lower genital tract. These are transmitted primarily through the pudendal nerve, the peripheral branches of which provide sensory innervation to the perineum, anus, vulva, and clitoris. The pudendal nerve passes beneath the sacrospinous ligament just as the ligament attaches to the ischial spine. Sensory nerve fibers of the pudendal nerve are derived from ventral branches of the S2 through S4 nerves.
The pudendal nerve block is a relatively safe and simple method of providing analgesia for spontaneous delivery. As shown in Figure 25-2, a tubular introducer is used to sheathe and guide a 15-cm-long 22-gauge needle into position near the pudendal nerve. The end of the introducer is placed against the vaginal mucosa just beneath the tip of the ischial spine. he in troducer allows 1.0 to 1.5 em of needle to at the injection site. he infection may spread posteriorly to the hip joint, into the gluteal musculature, or into the retropsoas space (Svancarek, 1977).