Neither epidural blocks nor the combined spinal-epidural technique are risk-free. Because many of these risks have serious consequences, the of Obstetricians and Gynecologists (ACOG) has issued the following statement: "Persons administering or supervising obstetric anesthesia should be qualified to manage the infrequent but occasionally life-threatening complications of major regional anesthesia... Mastering and retaining the skills and knowledge necessary to manage these complications requires adequate training and frequent application."
Abnormally low blood pressure, referred to as hypotension, occurs in about 10% of women receiving epidural blocks. Fortunately, there are usually no harmful effects. Hypotension occurs because the epidural block affects not only the sensory fibers that carry pain signals, but also the nerve fibers that control muscle contractions inside blood vessels. This causes blood vessels to relax, resulting in lower blood pressure. If severe, this can affect blood flow to the fetus. To reduce this risk, most women receive fluids intravenously prior to the epidural placement.
The medications used in epidural blocks sometimes escape into the blood stream. In high enough concentrations, this can lead to serious consequences in the mother and fetus. The mother may exhibit bizarre behavioral changes that can eventually lead to convulsions. She may also experience severe cardiovascular symptoms, including cardiac arrest (heart attack). Fortunately, local anesthetic toxicity occurs in less than 0.5% of patients, and most reactions are mild. However, convulsions due to toxicity from local anesthetics can result in neurologic injury or death of the mother and/or newborn. Treatment includes stopping medication, making sure the mother and baby are getting enough oxygen, and stopping convulsions.
Allergies to anesthetics used in epidural blocks are rare. Most women who describe "allergic reactions" are actually experiencing bothersome side effects including a rapid and pounding heart rate. A true allergy involves development of a rash and/or shortness of breath due to swelling of the airway.
High spinal occurs when the anesthetic travels up the spinal cord. In addition to suppressing pain messages in the sensory nerves, the anesthetic may affect the diaphragm, resulting in respiratory distress. This can result from too much medication, incorrect placement in the spinal space, or inappropriate positioning of the patient immediately after injection. This can happen with a spinal or epidural anesthetic. Unless the diaphragm is paralyzed, the patient can usually breathe adequately. Occasionally, endotracheal intubation (placing a tube through the mouth or nose to maintain the airway), or placing the mother in a well-ventilated area is necessary.
The primary concern for many patients is whether an epidural block can result in long-term paralysis or nerve injury. This is exceedingly rare, occurring in less than 1 in 10,000 patients. If nerve damage is suspected, a thorough and immediate examination should be performed in consultation with a neurosurgeon. Bruising can occur without major consequence. Some patients complain of low back pain after an epidural block. However, the risk of low back pain after labor is the same with or without an epidural.
A severe headache following any regional block analgesia is probably a spinal headache. This occurs when the covering of the spinal cord is punctured and fluid leaks out, a situation termed "wet tap." The decreased fluid allows the brain to settle and the patient experiences pain. This occurs in only 1 to 3% of patients. However, the risk for spinal headache is close to 70% if a "wet tap" is recognized at the time of epidural placement. Treatment begins with oral analgesics, caffeine, and plenty of fluids. If this does not provide relief, an epidural blood injection may be performed. This involves drawing about 15 mL of the patient's blood and injecting it into the epidural space. The blood coagulates over the hole in the dura (the covering of the spinal cord) and prevents further leakage. Patients generally feel relief within one or two hours.