There are numerous physiological changes that occur by the third trimester of pregnancy, many of which potentially make anesthesia more hazardous. The anesthesiologist must be familiar with the major physiological changes that occur with pregnancy and the potential anesthetic implications (Table 156.1).

The anesthesiologist must be in close communication with the obstetrician in determining the indication and true urgency for cesarean section. A distinction must be made between urgent and emergent or stat section, as those in the former category may allow time for regional anesthesia, while those in the latter nearly always require general anesthesia in the absence of a functioning epidural catheter. Although each individual case must be considered in consultation with the obstetrician, those falling in the urgent but not emergent category generally include (a) variable decelerations with prompt recovery of fetal heart rate (FHR), (b) dystocia, (c) previous classic cesarean and active labor, (d) active genital herpes and ruptured membranes, (e) ruptured membranes and abnormal fetal presentation (i.e., transverse, breech, multiple gestation), and (f) rapidly deteriorating maternal illness (pre-eclampsia, cardiac, pulmonary). Conversely, those indications generally falling into the emergent or stat category include (a) prolonged fetal bradycardia or persistent late decelerations (rule of 60s = FHR <60/minute or deceleration
lasting longer than 60 seconds), (b) massive maternal hemorrhage (placenta previa, placental abruption), (c) prolapsed umbilical cord, and (d) uterine rupture.