Question

A 35-year-old woman, gravida 2, para 1, at 38 weeks gestation is evaluated in the obstetric triage unit for the onset of active labor. Her surgical history is significant for an open myomectomy two years ago for a 10-cm intramural fibroid, during which the surgeon noted that the uterine cavity was entered. Her temperature is $37.1^\circ\text{C}$ ($98.8^\circ\text{F}$), blood pressure is 112/70 mm Hg, pulse is 108/min, and respirations are 22/min. Arterial blood gas analysis on room air shows a pH of 7.44, $\text{PaCO}_2$ of 28 mm Hg, and $\text{HCO}_3^-$ of 20 mEq/L. The fetal heart rate tracing initially shows a baseline of 145/min with moderate variability and no decelerations. Tocodynamometry shows contractions every 3 to 4 minutes. A cervical examination reveals the cervix is 5 cm dilated and 90% effaced, with the fetal presenting part at -1 station.

Thirty minutes later, the patient suddenly reports a sharp, tearing, and continuous lower abdominal pain that does not remit between contractions. The fetal heart rate tracing abruptly demonstrates a baseline drop to 80/min that persists for 4 minutes without recovery. A repeat cervical examination reveals that the fetal head is no longer palpable.

Which of the following is the most appropriate next step in the management of this patient?