An obstetrician is called to the labor unit to evaluate a fetal heart rate tracing for a 2… — USMLE Step 2 CK

An obstetrician is called to the labor unit to evaluate a fetal heart rate tracing for a 28-year-old patient. The patient is a gravida 3, para 2 at $40$ weeks gestation. She was admitted $4$ hours ago in spontaneous labor and was subsequently started on an intravenous oxytocin infusion for labor augmentation due to a secondary arrest of dilation. Her temperature is $37.0^\circ\text{C}$ ( $98.6^\circ\text{F}$ ), blood pressure is $115/75\text{ mmHg}$ , and pulse is $88/\text{min}$ . The tocodynamometer demonstrates $7$ uterine contractions in a $10$ -minute period. The fetal heart rate tracing reveals a baseline of $135/\text{min}$ , minimal variability, and visually apparent, gradual decreases in the fetal heart rate that begin after the peak of each contraction and return to baseline after the contraction ends. Which of the following is the most appropriate next step in the management of this patient?

A
Immediate preparation for cesarean delivery
B
Placement of an intrauterine pressure catheter and amnioinfusion
Discontinuation of the oxytocin infusionAnswer
D
Administration of an intravenous fluid bolus and continued observation
E
Administration of intravenous ephedrine

Answer

Discontinuation of the oxytocin infusion

The patient is experiencing uterine tachysystole, defined as more than

5

contractions in a

10

-minute period. This excessive uterine activity limits the relaxation time between contractions, decreasing blood flow to the intervillous space and causing uteroplacental insufficiency. This is reflected on the fetal heart rate tracing as late decelerations, which are characterized by a gradual decrease in the fetal heart rate that begins after the peak of the contraction. The most appropriate initial step in intrauterine resuscitation for oxytocin-induced tachysystole is the immediate discontinuation of the oxytocin infusion. Additional resuscitative measures may include maternal repositioning, intravenous fluid bolus, and supplemental oxygen administration.

Step-by-Step Solution

Analyze the fetal heart rate (FHR) tracing.

The FHR shows late decelerations (gradual decreases starting after the contraction peak) with minimal variability.

Identifying the type of deceleration determines the underlying pathophysiology, which in this case is uteroplacental insufficiency.

Evaluate the uterine contraction pattern.

The tocodynamometer shows 7 contractions in a 10-minute period.

Normal labor has 5 or fewer contractions in 10 minutes. More than 5 indicates uterine tachysystole.

Determine the cause of the late decelerations and the appropriate intervention.

The tachysystole is likely driven by the oxytocin infusion, leading to compromised blood flow to the intervillous space and subsequent fetal hypoxia.

To restore uteroplacental blood flow, the immediate next step must address the tachysystole by stopping the offending agent.

Key Concept

Management of uterine tachysystole with late fetal heart rate decelerations requires immediate intrauterine resuscitation, starting with the discontinuation of uterotonic agents like oxytocin.

Question

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Topics

More questions from this topic