The practice of obstetric anesthesia began in 1847 when Sir James Young Simpson introduced ether, or “twilight sleep,” into obstetric practice for the final stages of labor and delivery. Today obstetric anesthesia has evolved into a complex subspecialty. Although the majority of deliveries are uncomplicated, parturients are presenting with increasingly complex comorbidities such as cystic fibrosis and corrected congenital heart disease because of medical and surgical advances in the treatment of their underlying conditions. Modern regional anesthetic techniques have contributed to maternal and neonatal safety.
This chapter provides an overview of the physiologic changes seen with pregnancy, describes commonly used methods of labor analgesia, and provides an overview of anesthetics administered during pregnancy for cesarean section and non-obstetric surgery.
PREPARATION FOR PAIN DURING LABOR
The majority of parturients experience moderate to severe pain during labor and delivery, which they describe as being more intense than any other previous pain experience. Women who deliver for the first time describe the pain as more intense than that of subsequent labors. It is reported that the pain is exceeded only by traumatic amputation or causalgia.
The American Society of Anesthesiologists (ASA) states:
There is no other circumstance where it is considered acceptable for an individual to experience untreated severe pain, amenable to safe intervention, while under a physician's care. In the absence of a medical contraindication, maternal request is a sufficient medical indication for pain relief during labor.
Lack of proper psychological preparation can contribute to the pain experienced during labor and delivery. Prenatal classes may dissipate fear about the birthing process and give details about what to expect. Considerable evidence exists that preparation for childbirth can significantly modify the amount of pain experienced.
Psychoprophylaxis, of which Lamaze is the most well-known method, postulates that the pain arising from uterine contractions and perineal distension can be replaced with conditioned “positive” reflexes. This technique promotes a natural delivery and avoids routine medical interventions. A partner who functions as a coach helps the parturient concentrate on breathing techniques and on releasing muscle tension. Education about labor and delivery is believed to give the parturient a sense of control over the birthing process. It may reduce the request for analgesia and anesthesia. However, two-thirds of mothers following this technique still require some kind of analgesic. Following this technique does not guarantee painless labor and may contribute to a sense of failure and lowered self-esteem in those who do request analgesics.
Excessive pain may result in more harm to the fetus than the judicious use of analgesics and anesthetics. The pain and stress of labor contribute to elevated levels of circulating catecholamines, especially epinephrine. Epinephrine has beta-adrenergic tocolytic effects on the myometrium. Adequate labor analgesia reduces plasma epinephrine levels and may shift a dysfunctional to a normal labor pattern.