An obstetrical care team is evaluating a patient at 39 weeks gestation who is undergoing a… — USMLE Step 2 CK

An obstetrical care team is evaluating a patient at 39 weeks gestation who is undergoing an induction of labor for gestational diabetes mellitus. She is currently receiving a continuous intravenous oxytocin infusion. Ten minutes ago, she reported a sudden onset of mild shortness of breath. Her vital signs are temperature $37.0^\circ\text{C}$ ( $98.6^\circ\text{F}$ ), blood pressure $122/78\text{ mm Hg}$ , heart rate $95\text{/min}$ , and respiratory rate $20\text{/min}$ . Oxygen saturation is $98\%$ on room air. An arterial blood gas analysis reveals:

* $\text{pH}$ : $7.44$
* $\text{PaCO}_2$ : $29\text{ mm Hg}$
* $\text{PaO}_2$ : $104\text{ mm Hg}$

The electronic fetal monitor demonstrates a baseline heart rate of $145\text{/min}$ with moderate variability. In the past 20 minutes, there have been five uterine contractions. Following three of these contractions, the fetal heart rate gradually decreased to a nadir of $125\text{/min}$ , with the nadir occurring after the peak of the contraction, before returning to the baseline. The cervix is 5 cm dilated and 80% effaced. Which of the following is the most appropriate next step in management?

Discontinue the oxytocin infusion and reposition the patientAnswer
B
Proceed to immediate cesarean delivery
C
Order computed tomography pulmonary angiography
D
Perform a transcervical amnioinfusion
E
Continue observation with continuous fetal monitoring

Answer

The most appropriate next step in management is to discontinue the oxytocin infusion and reposition the patient.

The correct answer is to discontinue the oxytocin infusion and reposition the patient. The electronic fetal monitor demonstrates recurrent late decelerations (occurring with more than 50% of contractions) in the setting of moderate variability. This combination represents a Category II fetal heart rate tracing, which signals transient uteroplacental insufficiency but indicates that the fetus is not currently acidemic. The standard initial management is intrauterine resuscitation. This includes discontinuing uterotonic agents (such as oxytocin) to reduce uterine workload and repositioning the patient (typically to the left lateral decubitus position) to relieve aortocaval compression and maximize uteroplacental blood flow.

Step-by-Step Solution

Evaluate the maternal vital signs and arterial blood gas analysis in the context of pregnancy.

The pH of 7.44 and PaCO2 of 29 mm Hg represent a normal, compensated physiologic chronic respiratory alkalosis due to progesterone-induced hyperventilation. The mild shortness of breath is a common physiologic finding.

To rule out maternal respiratory compromise, such as a pulmonary embolism, which would require immediate separate intervention.

Analyze the fetal heart rate (FHR) tracing to determine its category and the underlying pathophysiology.

The tracing shows a baseline of 145/min with moderate variability and recurrent late decelerations (occurring with >50% of contractions). This is a Category II tracing indicative of transient uteroplacental insufficiency.

Accurate interpretation of the FHR tracing dictates the urgency and type of obstetric intervention.

Select the appropriate evidence-based intervention for a Category II tracing with recurrent late decelerations.

The correct action is intrauterine resuscitation, which includes discontinuing the oxytocin infusion and repositioning the mother to the left lateral decubitus position.

These conservative measures maximize uteroplacental blood flow and fetal oxygenation and must be attempted prior to operative delivery.

Key Concept

Management of Category II fetal heart rate tracings with recurrent late decelerations requires initial intrauterine resuscitation, while normal physiologic respiratory changes in pregnancy should not be misinterpreted as pathology.

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