A comparison of cardiac index in normal term pregnancy using thoracic electrical bio-impedance and oxygen extraction (Fick) techniques

OBJECTIVE

To correlate cardiac index in normal late third-trimester pregnancy using the thoracic electrical bio-impedance technique with that obtained from the oxygen extraction technique.

METHODS

Eight carefully screened normal pregnant women underwent assessment of cardiac index using both the thoracic electrical bio-impedance technique and the oxygen extraction technique. Measurements were obtained in various positions.

RESULTS

The correlation was good between the thoracic electrical bio-impedance and oxygen extraction techniques in the left lateral (r = 0.915) and right lateral (r = 0.863) positions, and the intercepts at the midpoints of the oxygen extraction data in these positions suggested good absolute correlation as well. Correlation between thoracic electrical bio-impedance and the Fick cardiac index was poor in all other positions.

CONCLUSIONS

Thoracic electrical bio-impedance cardiac index assessment is influenced by maternal position and must be used with caution in clinical research protocols. This technique appears to be inappropriate for general clinical use during pregnancy.

Intrapartum fetal pulse oximetry in the presence of fetal cardiac arrhythmia

We report our experience with a reflectance pulse oximeter in intrapartum monitoring of a fetus with atrial flutter and heart block. During labor fetal arterial oxygen saturation ranged between 50% and 85%. Spontaneous vaginal delivery occurred with good maternal and neonatal outcome.

Asthma in pregnancy. National Asthma Education Program Working Group on Asthma and Pregnancy. National Institutes of Health, National Heart, Lung and Blood Institute

This manuscript is a summary of a comprehensive report dealing with asthma and pregnancy issued by the working group on Asthma and Pregnancy, National Institutes of Health (NIH), National Heart, Lung, and Blood Institute. The report was developed by a panel of obstetricians, pharmacologists, internists, allergists, and pulmonologists, who met over an 18-month period under the auspices of the NIH. Undertreatment of pregnant asthmatics, partially because of unfounded fears of adverse pharmacologic effects on the developing fetus, remains the major problem in the management of asthma during pregnancy in the United States. The four key components of asthma management during pregnancy are: 1) objective assessment of maternal lung function and fetal well-being, 2) avoidance or control of environmental precipitating factors, 3) pharmacologic therapy, and 4) patient education.

Severe pulmonary hypertension in pregnancy following successful repair of ventricular septal defect in childhood

BACKGROUND

Because of advances in surgical repair, an increasing number of women born with structural cardiac disease now live to reproductive age. Patients treated successfully in childhood are followed for varying periods of time, then may be lost to follow-up or told that no follow-up is necessary because their condition is stable. However, the hemodynamic changes that accompany pregnancy may result in cardiovascular decompensation, even after years of apparently good health.

CASES

We have recently cared for two women who had undergone repair of congenital heart disease in childhood. Although they thought that their repair was complete and they had been asymptomatic until the pregnancy, both presented with symptoms and signs of severe pulmonary hypertension, subsequently confirmed on cardiac catheterization. One patient elected to terminate her pregnancy, and the other died in the immediate puerperium.

CONCLUSION

Despite normal physical function and an absence of abnormal physical findings, a thorough cardiac evaluation including echocardiography should be considered for pregnant patients with a history of repaired congenital heart disease, especially if the original defect is known to lead to pulmonary hypertension.

Acute hemodynamic and respiratory effects of amniotic fluid embolism in the pregnant goat model

OBJECTIVE

Our purpose was to determine the acute-phase central hemodynamic and respiratory effects of raw, filtered, filtered and boiled, and meconium-containing amniotic fluid.

STUDY DESIGN

Pregnant goats (Capra hircus) in the last one third of pregnancy were given freshly collected autologous amniotic fluid in a volume of 2.5 ml/kg of body weight. Observations were then made at 10, 30, 60, 120, and 180 minutes after amniotic fluid embolism. Pulmonary artery catheters and femoral artery lung water catheters were placed for specimen and data collection.

RESULTS

Marked pressor responses were observed in both the pulmonary and systemic circulations with all amniotic fluid infusions. The pressor response was similar with raw, filtered, and filtered and boiled amniotic fluid. The pressor response seen with amniotic fluid containing meconium was significantly greater than that seen with the other forms. No significant effects were observed on cardiac or respiratory function except in the meconium group, where transient left ventricular dysfunction was accompanied by an acute increase in extravascular lung water and dysoxia.

CONCLUSIONS

The Capra hircus model is appropriate for the further study of amniotic fluid embolism. The acute pressor effects are transient and involve both the systemic and pulmonary circulations. Left ventricular dysfunction and dysoxia were observed only with embolism of amniotic fluid containing meconium.

Preliminary experience with intrapartum fetal pulse oximetry in humans

Electronic fetal heart rate (FHR) monitoring is commonly used to assess fetal well-being during labor. Nonreassuring patterns in many cases are associated with normal fetal acid-base condition, leading to unnecessary operative intervention. Fetal pulse oximetry has several potential advantages over FHR monitoring because it assesses not only pulse, but also arterial oxygen saturation and tissue perfusion. We describe our preliminary experience with the Nellcor N-400 Fetal Oxygen Saturation Monitor and FS-10 Oxisensor in 73 subjects during active labor at term. The mean (+/- standard deviation) duration of monitoring was 161.4 +/- 106.0 minutes, with sensor contact achieved 67.3 +/- 22.5% of the time during labor. Data were successfully recorded in all patients, with a reliable signal obtained 50.1 +/- 21.6% of the time during labor. The mean fetal oxygen saturation was 57.9 +/- 10.0%. The potential for research and clinical applications appears promising with further sensor and monitor development.

The effect of porcine somatotropin supplementation in pigs on the lipid profile of subcutaneous and intermuscular adipose tissue and longissimus muscle

The effect of porcine somatotropin (pST) on the lipid profiles of adipose tissue and muscle was investigated. Sixteen crossbred barrows were injected daily with either 3 mg of pST or a placebo. After slaughter, total lipid and fatty acid composition of raw subcutaneous (SC) adipose and intermuscular (IM) adipose tissue and longissimus muscle were determined. The SC adipose tissue from pST-treated pigs had a 7.5% decrease in total lipid content; specific fatty acids 16:0, 18:0, and 18:1(n-9)c decreased most. The IM fat from pST-treated pigs had lower levels of 16:0 and 20:0. There was no effect of pST treatment on the lipid profile of the longissimus muscle. The data suggest that pST treatment produces small but significant changes in the saturated fatty acid content of adipose tissue in pigs.

Successful pregnancy outcomes after amniotic fluid embolism

Two patients who survived cardiorespiratory arrest occurring in association with amniotic fluid embolism syndrome were seen during the subsequent pregnancy. Both had uneventful pregnancies and delivered at term without complications. These are the only case reports of pregnancy after amniotic fluid embolism, and they support a model of amniotic fluid embolism involving chemically abnormal amniotic fluid rather than an unusual sensitivity to normal amniotic fluid.

Maternal respiration and blood gases during aerobic exercise performed at moderate altitude

We studied whether maternal acid-base status during aerobic exercise performed at moderate altitude is affected by pregnancy. Seven primiparus women were tested at 37 wk gestation and 12 wk postpartum. Subjects were studied at rest, and during two cycle (50 W, 75 W) and two treadmill (67 m.min-1; 2.5% grade, 67 m.min-1; 12% grade) protocols. Exercise bouts lasted 6 min with a 10-min rest between sessions. Minute (VE) and alveolar (VA) ventilation, tidal volume (VT), and ventilatory equivalent for carbon dioxide (VE/VCO2) were significantly (P less than 0.01) greater when exercise was performed during pregnancy. Physiological dead space (VD) was not affected by pregnancy status and did not differ between rest and exercise. Decreases (P less than 0.01) in arterial pH during exercise averaged 0.04 units in both pregnancy and postpartum. Despite similar change in maternal pH, carbon dioxide tension (PaCO2) remained unchanged during exercise at 37 wk gestation but decreased at 12 wk postpartum. Decreases in arterial bicarbonate [HCO3-] associated with exercise were smaller during pregnancy. Our findings indicate that pregnancy did not compromise maternal acid-base status during aerobic exercise.

Premature rupture of the membranes: management controversies

Preterm premature rupture of the membranes continues to be a leading cause of perinatal morbidity and mortality in the United States. In the absence of amnionitis or fetal compromise, expectant management is a reasonable alternative to permit fetal weight gain and to allow for fetal lung maturation. When embarking on an expectant management course, a variety of clinical approaches are available to the practicing clinician.

Recent developments in pregnancy-induced hypertension

Pregnancy-induced hypertension (PIH) still remains an area in obstetrics of active research and investigation. Despite widespread academic attention, the cause of this disorder still remains unknown. The purpose of this paper is to review the important contributions to the literature during the period of July, 1990 through June, 1991. Elucidation of the pathophysiology of PIH has been enhanced by investigations of altered platelet calcium metabolism, the renin-aldosterone-angiotensin system, and other potent vasopressors. Recent reports of clinical management for eclampsia, liver rupture, HELLP syndrome, severe PIH in the second trimester, severe hypertension, and magnesium toxicity are presented.

Cardiac disease in pregnancy

The pregnant patient with normal cardiac function can accommodate many significant alterations in the cardiovascular system without difficulty. Pregnancy in a patient with significant cardiac disease, however, can be extremely hazardous, resulting in decompensation and even death. these conditions account for up to 30% of maternal mortality. This article reviews the interaction between cardiac disease and pregnancy.

Amniotic fluid embolism

Amniotic fluid embolism remains an enigmatic and often lethal condition. The pathophysiology is complex, however, from a clinical standpoint. Right or, more commonly, left heart failure is the dominant physiologic aberration. Disseminated intravascular coagulation is often present. The detection of squamous cells in the central circulation of living patients can no longer be considered pathognomonic for this condition.

Cardiac disease in pregnancy

Cardiac disease in pregnancy remains a major cause of indirect maternal death. An understanding of the impact of the physiologic changes associated with pregnancy upon structural cardiac disease is essential for proper counseling and management of these complex patients.

Position change and central hemodynamic profile during normal third-trimester pregnancy and post partum

Central hemodynamic response to position change was assessed in 10 normotensive primiparous patients between 36 and 38 weeks' gestation. Studies were repeated between 11 and 13 weeks post partum. Compared with the left lateral position, we observed a mean 9% fall in cardiac output in the supine position and an 18% fall when patients were standing. When standing, these patients had a 30% increase in pulse and a 21% fall in left ventricular stroke work index. The orthostatic response after pregnancy was much more labile than that during the third trimester. These findings have important descriptive implications for the understanding of the human response to orthostasis during pregnancy, as well as clinical implications for patients at risk of uteroplacental insufficiency and for working women during pregnancy.

Cardiac output responses of primigravid women during exercise determined by the direct Fick technique

We compared metabolic and cardiovascular responses to aerobic exercise with the direct Fick technique in women during and after pregnancy. Seven subjects were studied at 37 weeks' gestation and again 12 weeks postpartum. All were tested at rest and during four sequential exercise bouts consisting of 5 minutes at each of two cycle (50 and 75 W) and two treadmill (67 m x min-1 at 2.5 and 12% grade) protocols. Oxygen consumption (VO2) and heart rate were measured during the fifth minute of exercise. Arterial and mixed venous oxygen contents, obtained from catheters placed in the radial and pulmonary arteries, respectively, were used to calculate arterial-venous oxygen difference. Cardiac output and stroke volume were calculated from the Fick equation. Responses of VO2, cardiac output, and stroke volume were greater when exercise was performed at 37 weeks' gestation as compared with postpartum. In contrast, heart rate response (during cycling) and arterial-venous oxygen difference (during treadmill walking) were less when exercise was performed during pregnancy. Our results indicate that there is no compromise in maternal cardiac output during either cycle or treadmill exercise performed late in pregnancy as compared with postpartum conditions.

Central hemodynamic assessment of normal term pregnancy

Ten carefully screened primiparous patients between 36 and 38 weeks' gestation underwent pulmonary artery catheterization, arterial line placement, and central hemodynamic assessment in the left lateral recumbent position. Studies were repeated in the same patients between 11 and 13 weeks post partum. Compared with the nonpregnant state, there was a significant fall in systemic vascular resistance, pulmonary vascular resistance, colloid oncotic pressure, and colloid oncotic pressure-pulmonary capillary wedge pressure gradient by the late phase of the third trimester (p less than 0.05). Pregnancy was associated with a significant rise in cardiac output and pulse in all patients (p less than 0.05). There was no significant change in pulmonary capillary wedge pressure, central venous pressure, left ventricular stroke work index, or mean arterial pressure. Normally the late phase of the third trimester is not associated with hyperdynamic left ventricular function as assessed by the left ventricular stroke work index/pulmonary capillary wedge pressure ratio.