Effect of Sildenafil on Pulmonary Circulation and Cardiovascular Function in Near-Term Fetal Sheep During Hypoxemia

Nifedipine disturbs fetal cardiac function during hypoxemia in a chronic sheep model at near term gestation

BACKGROUND

Nifedipine is a widely used drug in pregnancies complicated by maternal hypertensive disorders that can be associated with placental insufficiency and fetal hypoxemia. The evidence regarding fetal myocardial responses to nifedipine in hypoxemia is limited.

OBJECTIVE

We hypothesized that nifedipine would not impair fetal sheep cardiac function under hypoxemic environment. In particular, we investigated the effects of nifedipine on fetal ventricular functional parameters and cardiac output.

STUDY DESIGN

A total of 21 chronically instrumented fetal sheep at 122 to 134 gestational days (term, 145 days) were included in this study. Fetal cardiac function was evaluated by measuring global longitudinal strain, indices describing ventricular systolic and diastolic function, and cardiac outputs using two-dimensional speckle tracking and tissue and spectral pulsed-wave Doppler echocardiography. Fetal carotid artery blood pressure and blood gas values were invasively monitored. After baseline data collection, fetal hypoxemia was induced by maternal hyperoxygenation. After hypoxemia phase data collection, 9 fetuses received nifedipine infusion, and 12 fetuses received saline infusion. Data were collected 30 and 120 minutes after the infusion was started. After 120 minutes of data collection, maternal and fetal oxygenation were normalized, and normoxemia phase data were collected, while infusion was continued.

RESULTS

Hypoxemia decreased fetal carotid artery mean arterial pressure from 40 (8) mm Hg to 35 (8) mm Hg (P<.007), and left ventricular global longitudinal strain showed less deformation than at baseline (P=.001). Under hypoxemia, nifedipine caused a reduction in right ventricular global longitudinal strain (P<.05), a decrease in right ventricular isovolumic relaxation velocity and its deceleration (P<.01) indicating diastolic dysfunction, and a drop in right ventricular cardiac output (P<.05). Nifedipine did not alter fetal left ventricular functional parameters or cardiac output. When normoxemia was restored, fetal right ventricular functional parameters and cardiac output returned to baseline level.

CONCLUSION

In hypoxemic fetus, nifedipine impaired right ventricular function and reduced its cardiac output. The detrimental effects of nifedipine on fetal right ventricular function were abolished, when normoxemia was restored. Our findings suggest that in a hypoxemic environment nifedipine triggers detrimental effects on fetal right ventricular function.

Effects of nifedipine and sildenafil on placental hemodynamics and gas exchange during fetal hypoxemia in a chronic sheep model

INTRODUCTION

We hypothesized that nifedipine and sildenafil would have no detrimental effects on placental hemodynamics and gas exchange under fetal hypoxemia.

METHODS

In 33 chronically instrumented fetal sheep, placental volume blood flow (Q_Plac) and umbilical artery (UA) vascular impedance were measured by Doppler ultrasonography. Fetal carotid artery blood pressure and blood gas values were monitored. After baseline data collection, maternal and fetal hypoxemia were induced. Following hypoxemia phase data collection, 12 fetuses received sildenafil and 9 fetuses nifedipine infusion, and 12 fetuses served as controls receiving saline infusion. Data were collected 30 and 120 min after infusion was started. Then maternal oxygenation was normalized and normoxemia phase data were collected, while infusion was continued.

RESULTS

Hypoxemia significantly decreased fetal pO₂ and blood pressure. In the sildenafil group at 30- and 120-min hypoxemia + infusion phases, fetal blood pressure and Q_Plac were significantly lower and pCO₂ higher than at baseline without returning to baseline level at normoxemia + infusion phase. In hypoxemia, nifedipine did not affect fetal blood pressure or placental hemodynamics. Both in the sildenafil and nifedipine groups, fetal pO₂ remained significantly lower at normoxemia + infusion phase than in the control group. Umbilical artery vascular impedance did not change during the experiment.

DISCUSSION

In fetal hypoxemia, sildenafil had detrimental effects on placental hemodynamics that disturbed placental gas exchange. Nifedipine did not alter placental hemodynamics in hypoxemia but disturbed placental gas exchange upon returning to normoxemia. Umbilical artery vascular impedance did not reflect alterations in placental hemodynamics.

Oxycodone concentrations in the central nervous system and cerebrospinal fluid after epidural administration to the pregnant ewe

The main sites of the analgesic action of oxycodone are the brain and spinal cord. The present study describes the concentrations of oxycodone and its metabolites in the brain and spinal cord after epidural administration to the ewe. Twenty pregnant ewes undergoing laparotomy were randomized into two groups to receive epidural oxycodone: infusion group (n = 10, 0.1 mg·kg^-1 bolus followed by continuous infusion of 0.05 mg·kg^-1 ·h^-1 for five days) or repeated boluses group (n = 10, 0.2 + 2x0.1 mg·kg^-1 bolus followed by a 0.2 mg·kg^-1 bolus every 12 hours for five days). After five days of oxycodone administration, arterial blood samples were collected, the sheep were killed, and a CSF sample and tissue samples from the cortex, thalamus, cerebellum and spinal cord were obtained for the quantification of oxycodone and its main metabolites. The median plasma and CSF concentrations of oxycodone were 9.0 and 14.2 ng·mL^-1 after infusion and 0.4 and 1.1 ng·mL^-1 after repeated boluses. In the infusion group, the cortex, thalamus and cerebellum oxycodone concentrations were 4-8 times higher and in the spinal cord 1310 times higher than in plasma. In the repeated boluses group, brain tissue concentrations were similar in the three areas, and in the spinal cord were 720 times higher than in plasma. Oxymorphone was the main metabolite detected, which accumulated in the brain and spinal cord tissue. In conclusion, first, accumulation of oxycodone and oxymorphone in the CNS was observed, and second, high spinal cord concentrations suggest that epidural oxycodone may provide segmental analgesia.