Oxytocic drugs are used for several indications in obstetrics and obstetric anesthesia. These include:
- The contraction stress test to evaluate fetal well-being during the antepartum period
- Induction of labor
- Treatment of labor arrest
- Active management of labor
- Treatment of uterine atony and postpartum hemorrhage
An anesthesiologist is most likely to give an oxytocic drug for the indication of uterine atony and postpartum hemorrhage. Following vaginal delivery, there can be increased uterine atony in the setting of retained products, a long labor, high parity, macrosomia, polyhydramnios, excessive oxytocin augmentation during labor, and chorioamnionitis. In these settings bimanual massage is first attempted before administration of an oxytocic agent. Oxytocic drugs are also given routinely following C-section to prevent development of uterine atony. The uterus has α and β receptors, with α-receptor stimulation resulting in contraction and β2-receptor stimulation resulting in uterine relaxation. The first line agent is Oxytocin (Pitocin), administered as a dilute solution of 20-40 U/L, which causes fewer cardiovascular effects compared to direct IV injection that can cause tachycardia, vasodilation, and hypotension. Methylergonovine (Methergine) (0.2 mg IM), an ergot derivative, can also be given to improve uterine tone. It causes intense and prolonged contractions and therefore is only given after delivery as a single intramuscular injection. Its use is contraindicated in preeclamptic patients and patients with cardiovascular disease because it can cause severe hypertension. Carboprost (Hemobate), a synthetic analogue of Prostaglandin F2 (0.25 mg IM), is another alternative to stimulate uterine contractions. It is also administered intramuscularly and should be avoided in asthmatics because of its association with bronchospasm. Prostaglandin E1 (600 Ug oral/sl/rectal) is another alternative but can cause hyperthermia. In contrast, agents given to stop premature labor are called tocolytics, and include magnesium and the β2-adrenergic agonists ritodrine and terbutaline. If oxytocic agents fail to treat uterine atony and postpartum hemorrhage, more invasive techniques are likely indicated.