The hemodynamic effects of intubation during nitroglycerin infusion in severe preeclampsia

Article Abstract:

Pregnant patients with severe preeclampsia, a disorder of pregnancy characterized by high blood pressure (hypertension), protein in the urine, and other abnormalities, is a condition that can become life-threatening. These patients may also experience serious complications as a result of endotracheal intubation (insertion and maintenance of a breathing tube). Intubation is necessary during general anesthesia for delivery of the infant by cesarean section. However, in these patients the reflexive responses to intubation include increased heart rate and blood pressure. This may be combatted by the infusion of nitroglycerin, an antihypertensive drug; but this, too, can have adverse effects in preeclamptic women. These occur when patients are hypovolemic (have reduced blood volume), a common occurrence in preeclampsia. To evaluate the effects of nitroglycerin on volume-expanded preeclamptic patients (who had been given fluids to restore blood volume to more normal levels), six patients, none of whom had received prenatal care, were studied. Nitroglycerin infusion was administered after volume expansion, which was followed by intubation and delivery of the infant. The average time between intubation and delivery was 4 minutes, 38 seconds. Hemodynamic data (data concerning blood flow and pressure) were obtained before, during, and after intubation. Results showed that four patients began to vomit during nitroglycerin infusion, necessitating dose reduction. In these patients, blood pressure was not successfully lowered by 20 percent (the therapeutic goal) before intubation began. The overall effectiveness of the approach was 33 percent, and the protocol was terminated because of this low success rate and the side effects. The infants' Apgar scores (a measure of physiological functioning) were eight or higher after five minutes. Intravenous nitroglycerin is not effective in treating the hypertensive response to intubation of volume-expanded, severely preeclamptic women. (Consumer Summary produced by Reliance Medical Information, Inc.)

Care and treatment, Evaluation, Preeclampsia, Nitroglycerin

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Baroreflex function in normal pregnancy

Article Abstract:

One of the ways blood pressure is regulated is by the sinoaortic baroreflex, a reflex mediated by receptors in the carotid sinus and the aortic arch that respond to stretching. When stretched, as they would be when blood volume increases, these receptors cause the heart rate to slow and the peripheral blood vessels to dilate, lowering the blood pressure. The reflex is 'reset' (the threshold that triggers it changes) in aging, during sleep, and, possibly, during pregnancy. This was investigated in nine healthy pregnant patients at term (from 36 to 39.4 weeks gestation) and again six to eight weeks after delivery. The baroreflex was measured with a cannula (fine tube) inserted into the radial artery (in the forearm) to measure arterial pressure while the patient lay on the left side; the pressure was then recorded during the infusion of phenylephrine, a substance that increases blood pressure. The baroreflex was the ratio of change (decrease) in heart rate per unit change in arterial pressure as the drug was infused. Results showed that pregnancy was associated with increased baroreflex sensitivity: the ratio was 0.9 beats per minute per millimeters of mercury (mm Hg), compared with 0.5 beats per minute per mm Hg after delivery. This implies a reduced sensitivity to stimuli of the type represented by phenylephrine, that is, to alpha-adrenergic stimuli. The sensitivity of the baroreflex is related to the capacity of the blood pressure system to compensate for increases in blood pressure. The results suggest that this capacity is attenuated during pregnancy and that pregnant patients are more sensitive to drugs that affect the vascular system. (Consumer Summary produced by Reliance Medical Information, Inc.)

Pregnancy, Blood pressure, Blood pressure regulation

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