You are caring for a parturient at 38 weeks gestation who is undergoing an urgent cesarean delivery with spinal anesthesia due to labor with a breech presentation and fetal macrosomia. Her medical history includes pulmonary hypertension, for which she is currently taking sildenafil three times daily. The obstetricians are having a difficult time delivering the large fetus and ask you to administer sublingual nitroglycerin, which you refuse. Your refusal is due to concern about which of the following adverse effects?

  • □ (A) Uterine hypertonicity

  • □ (B) Hypotension

  • □ (C) Bradycardia

Sildenafil is a selective inhibitor of cyclic guanosine monophosphate (cGMP)-specific phosphodiesterase type 5, and administration results in smooth muscle relaxation. Besides its use in erectile dysfunction, sildenafil is approved by the U.S. Food and Drug Administration for the treatment of pulmonary arterial hypertension. Nitroglycerin causes smooth muscle relaxation by releasing nitric oxide. Nitroglycerin is among those agents that can be used to induce rapid uterine relaxation, and its use for this purpose is well established. One of the primary mechanisms that terminates the effect of nitroglycerin is the metabolism of nitric oxide by cGMP.

It is well established that, in patients taking sildenafil, concomitant administration of nitrates can cause profound, even lethal, hypotension. For this reason, nitrate administration is contraindicated in the presence of sildenafil for at least 24 hours after the last sildenafil dose.

In the clinical scenario described, the patient is taking sildenafil to treat her pulmonary arterial hypertension. She is undergoing an urgent cesarean delivery due to being in labor with a breech fetus, and therefore it is highly unlikely that 24 hours has elapsed since her last sildenafil dose. Administration of nitroglycerin to this patient is likely to result in profound maternal hypotension. Tachycardia, not bradycardia, is likely to occur in this scenario because of the hypotension. Since she is receiving sildenafil, it is highly unlikely that uterine hypertonicity would occur. In this scenario, if uterine relaxation is required, the use of another agent besides sublingual nitroglycerin should be considered, such as a β2-receptor agonist or a calcium channel blocker.

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Answer: B