Nitroprusside in preeclampsia. Circulatory distress and paradoxical bradycardia.

Abstract

In severe preeclampsia, short-term peripartum management of hypertension with hydralazine is complicated by relatively prolonged hypotensive episodes, resulting in fetal distress. We hypothesized that nitroprusside's rapid onset and brief antihypertensive action would permit more controlled blood pressure reduction. Nitroprusside was infused into 10 invasively monitored subjects until mean arterial pressure either 1) was gradually reduced 10-20% or 2) fell abruptly. Subjects fell into two groups, defined by whether the hypotensive effect of nitroprusside was accompanied by a fall in heart rate (group A, n=$) or a rise (group B, n=2). Group B showed the expected sinoaortic baroreceptor reflex elevations in heart rate (+17 ±6 beats/min) in response to moderate falls in mean arterial pressure (-32±9 mm Hg) elicited by moderate doses (1.03±0.23 /tg/kg/min). However in group A, steep reductions in mean arterial pressure (-75±22 mm Hg, p<0.0001), significantly greater than in group B (p<0.05), occurred at much lower doses (0.35±0.23 /ig/kg/min;/?<0.05) and were accompanied by falls in heart rate (-21±7 beats/min). The apparently paradoxical falls in heart rate and extreme hypotensive responses in group A indicate severe circulatory compromise, corresponding to the cardiac and vasomotor depression that characterizes severe hemorrhage and other forms of acute/severe hypovolemic hypotension. This hemodynamic pattern represents a cardiopulmonary baroreceptor reflex presumably related to the Bezold-Jarisch reflex. The appearance of this pattern in the present study probably reflects the imposition of nitroprusside's prominent venous dilator action on the relatively reduced blood volume that generally characterizes severe preeclampsia. (Hypertension 1991;18:79-84) P reeclampsia, a hypertensive disorder unique to pregnancy, occurs in about 7% of pregnancies that continue beyond the first trimester. 1Severe preeclampsia is distinguished from the mild form of the disease by the magnitude of hypertension (severe, systolic pressure greater than 160 mm Hg or diastolic pressure greater than 110 mm Hg) and the existence or severity of proteinuria, visual symptoms, pulmonary edema, epigastric pain, or other accompanying disturbances.1 -2 Severe preeclampsia is a major cause of maternal and fetal morbidity and mortality. Its etiology has not been established.The reduced sinoaortic baroreceptor reflex sensitivity that characterizes severe preeclampsia results in hemodynamic instability.3 This instability, manifested as markedly enhanced responses to antihypertensive drugs, is of concern with hydralazine because of the relatively long and variable intervals to its maximum effect and its relatively long durations of action. When cumulative doses of the drug exert their full effects without baroreceptor reflex buffering, severe hypotension and fetal distress frequently results. -5Intravenous nitroprusside has become the drug of choice for parenteral treatment of most hypertensive crises in nonpregnant adults and has largely supplanted di...

A Comprehensive Review of Hypertension in Pregnancy

“…Cyanide metabolizes to thiocyanate which can lead to toxicity in 24–48 hours. Adverse effects include excessive vasodilation and cardioneurogenic (i.e., paradoxical bradycardia) syncope in volume-depleted preeclamptic women [132]. …”

Update on the Use of Antihypertensive Drugs in Pregnancy

“…84 Adverse effects include excessive vasodilation and cardioneurogenic (ie, paradoxical bradycardia) syncope in volume-depleted preeclamptic women. 85 The risk of fetal cyanide intoxication remains unknown. Given the long experience with hydralazine and alternative use of parenteral labetalol or oral calcium channel blockers, this drug is considered as a last resort.…”

Anestesia na Pré-Eclâmpsia

“…In severe pre-eclampsia it produces intense arterial hypotension and paradoxical bradycardia 56 , even in low doses (0.3 µg.kg ). This therapy requires arterial catheterization to monitor maternal blood pressure 1 .…”