Clinical Validation of Non-Invasive Cardiac Output Monitoring in Healthy Pregnant Women

Validation of a noninvasive cardiac output monitor in maternal cardiac disease: comparison of NICOM and transthoracic echocardiogram

BACKGROUND

The physiological changes to the cardiovascular system during pregnancy are considerable and are more pronounced in those with cardiac disease. In the general population, noninvasive hemodynamic monitoring is a valid alternative to pulmonary artery catheterization, which poses risk in the pregnant population. There is limited data on noninvasive cardiac output monitoring in pregnancy as an alternative to pulmonary artery catheterization.

OBJECTIVE

We sought to compare transthoracic echocardiography with a noninvasive cardiac output monitor (NICOM, Cheetah Medical) in pregnant patients with and without cardiac disease.

STUDY DESIGN

This was a prospective, open-label validation study that compared 2-dimensional transthoracic echocardiography with NICOM estimations of cardiac output in each trimester of pregnancy and the postpartum period. Participants with and without cardiac disease with a singleton gestation were included. NICOM estimations of cardiac output were derived from thoracic bioreactance and compared with 2-dimensional transthoracic echocardiography for both precision and accuracy. A mean percentage difference of ±30% between the 2 devices was considered acceptable agreement between the 2 measurement techniques.

RESULTS

A total of 58 subjects were enrolled; 36 did not have cardiac disease and 22 had cardiac disease. Heart rate measurements between the 2 devices were strongly correlated in both groups, whereas stroke volume and cardiac output measurements showed weak correlation. When comparing the techniques, the NICOM device overestimated cardiac output in the control group in all trimesters and the postpartum period (mean percentage differences were 50.3%, 52.7%, 48.1%, and 51.0% in the first, second, and third trimesters and the postpartum period, respectively). In the group with cardiac disease, the mean percentage differences were 31.9%, 29.7%, 19.6%, and 35.2% for the respective timepoints.

CONCLUSION

The NICOM device consistently overestimated cardiac output when compared with 2-dimensional transthoracic echocardiography at all timepoints in the control group and in the first trimester and postpartum period for the cardiovascular disease group. The physiological changes of pregnancy, specifically the mean chest circumference and total body water, may alter the accuracy of the cardiac output measurement by the NICOM device as they are currently estimated. Although NICOM has been validated for use in the critical care setting, there is insufficient data to support its use in pregnancy.

Accuracy and trending ability of finger plethysmographic cardiac output monitoring in late pregnancy

PURPOSE

Individuals in late pregnancy are at risk of significant hemodynamic variations, especially during Cesarean delivery. Although non-invasive monitoring might enable the early detection of variations in cardiac output (CO), clinical validation is lacking.

METHODS

In a prospective, single-center study, we measured CO simultaneously with finger plethysmography and transthoracic echocardiography in 100 third-trimester pregnant individuals in the supine and left lateral decubitus (LLD) positions.

RESULTS

A Bland-Altman analysis revealed a mean (standard deviation) bias of 1.36 (1.04) L·min-1 in the supine position (95% limits of agreement, -0.68 to 3.4 L·min-1; percent error, 26.6%), indicating overestimation by finger plethysmography. The intra-class correlation coefficient was 0.43 (95% confidence interval [CI], 0.33 to 0.51). Regarding the changes in CO induced by the supine-to-LLD transition, the concordance rate in a four-quadrant plot was 98.3% (95% CI, 91.1 to 99.9%).

CONCLUSION

Our study showed a poor reliability of finger plethysmography for static measurement of CO. Nevertheless, finger plethysmography had a reasonably high concordance rate for the detection of CO changes secondary to positional changes in late-pregnant individuals. STUDY REGISTRATION DATE: www.

CLINICALTRIALS

gov (NCT03735043); registered 8 November 2018.

Clinical validation of bioreactance for the measurement of cardiac output in pregnancy

Maternal cardiac dysfunction is associated with pre-eclampsia, fetal growth restriction and haemodynamic instability during obstetric anaesthesia. There is growing interest in the use of non-invasive cardiac output monitoring to guide antihypertensive and fluid therapies in obstetrics. The aim of this study was to validate thoracic bioreactance using the NICOM® instrument against transthoracic echocardiography in pregnant women, and to assess the effects of maternal characteristics on the absolute difference of stroke volume, cardiac output and heart rate. We performed a prospective study involving women with singleton pregnancies in each trimester. We recruited 56 women who were between 11 and 14 weeks gestation, 57 between 20 and 23 weeks, and 53 between 35 and 37 weeks. Cardiac output was assessed repeatedly and simultaneously over 5 min in the left lateral position with NICOM and echocardiography. The performance of NICOM was assessed by calculating bias, 95% limits of agreement and mean percentage difference relative to echocardiography. Multivariate regression analysis evaluated the effect of maternal characteristics on the absolute difference between echocardiography and NICOM. The mean percentage difference of cardiac output measurements between the two methods was ±17%, with mean bias of -0.13 l.min^-1 and limits of agreement of -1.1 to 0.84; stroke volume measurements had a mean percentage difference of ±15%, with a mean bias of -0.8 ml (-10.9 to 12.6); and heart rate measurements had a mean percentage difference of ±6%, with a mean bias of -2.4 beats.min^-1 (-6.9 to 2.0). Similar results were found when the analyses were confined to each individual trimester. The absolute difference between NICOM and echocardiography was not affected by maternal age, weight, height, race, systolic or diastolic blood pressure. In conclusion, NICOM demonstrated good agreement with echocardiography, and can be used in pregnancy for the measurement of cardiac function.

Methods and considerations concerning cardiac output measurement in pregnant women: recommendations of the International Working Group on Maternal Hemodynamics

Cardiac output (CO), along with blood pressure and vascular resistance, is one of the most important parameters of maternal hemodynamic function. Substantial changes in CO occur in normal pregnancy and in most obstetric complications. With the development of several non-invasive techniques for the measurement of CO, there is a growing interest in the determination of this parameter in pregnancy. These techniques were initially developed for use in critical-care settings and were subsequently adopted in obstetrics, often without appropriate validation for use in pregnancy. In this article, methods and devices for the measurement of CO are described and compared, and recommendations are formulated for their use in pregnancy, with the aim of standardizing the assessment of CO and peripheral vascular resistance in clinical practice and research studies on maternal hemodynamics. Copyright © 2019 ISUOG. Published by John Wiley & Sons Ltd.

Hyperoxygenation in pregnancy exerts a more profound effect on cardiovascular hemodynamics than is observed in the nonpregnant state

BACKGROUND

Supplemental oxygen is administered to pregnant women in many different clinical scenarios in obstetric practice. Despite the accepted uses for maternal hyperoxygenation, the impact of hyperoxia on maternal hemodynamic indices has not been evaluated. As a result, there is a paucity of data in the literature in relation to the physiological changes to the maternal circulation in response to supplemental oxygen.

OBJECTIVE

The hemodynamic effects of oxygen therapy are under-recognized and the impact of hyperoxygenation on maternal hemodynamics is currently unknown. Using noninvasive cardiac output monitoring which employs transthoracic bioreactance, we examined the effect of brief hyperoxygenation on cardiac index, systemic vascular resistance, blood pressure, stroke volume, and heart rate in pregnant mothers during the third trimester, compared with those effects observed in a nonpregnant population subjected to the same period of hyperoxygenation.

STUDY DESIGN

Hemodynamic monitoring was performed in a continuous manner over a 30-minute period using noninvasive cardiac output monitoring. Hyperoxygenation (O₂ 100% v/v inhalational gas) was carried out at a rate of 12 L/min via a partial non-rebreather mask for 10-minutes. Cardiac index, systemic vascular resistance, stroke volume, heart rate, and blood pressure were recorded before hyperoxygenation, at completion of hyperoxygenation, and 10 minutes after the cessation of hyperoxygenation. Two-way analysis of variance with repeated measures was used to assess the change in hemodynamic indices over time and the differences between the 2 groups.

RESULTS

Forty-six pregnant and 20 nonpregnant women with a median age of 33 years (interquartile range, 26-38 years) and 32 years (interquartile range, 28-37 years) were recruited prospectively, respectively (P=.82). The median gestational age was 35 weeks (33-37 weeks). In the pregnant group, there was a fall in cardiac index during the hyperoxygenation exposure period (P=.009) coupled with a rise in systemic vascular resistance with no recovery at 10 minutes after cessation of hyperoxygenation (P=.02). Heart rate decreased after hyperoxygenation exposure and returned to baseline by 10 minutes after cessation of therapy. There was a decrease in stroke volume over the exposure period, with no change in systolic or diastolic blood pressure. In the nonpregnant group, there was no significant change in the cardiac index, systemic vascular resistance, stroke volume, heart rate, or systolic or diastolic blood pressure during the course of exposure to hyperoxygenation.

CONCLUSION

Hyperoxygenation during the third trimester is associated with a fall in maternal cardiac index and a rise in systemic vascular resistance without recovery to baseline levels at 10 minutes after cessation of hyperoxygenation. The hemodynamic changes that were observed in this study in response to hyperoxygenation therapy during pregnancy could counteract any intended increase in oxygen delivery. The observed maternal effects of hyperoxygenation call for a reevaluation of the role of hyperoxygenation treatment in the nonhypoxemic pregnant patient.

Phenotypes of Pregnant Women Who Subsequently Develop Hypertension in Pregnancy

BACKGROUND

Hypertensive disorders complicating pregnancy are a major cause of maternal death. Our objective was to evaluate maternal clinical, hemodynamic, and placental prognostic indicators in a consolidated manner to identify women who develop hypertension in pregnancy.

METHODS AND RESULTS

Twenty-six normotensive pregnant women from a specialized Placenta Clinic at increased risk of developing de novo hypertension and 20 normotensive healthy pregnant controls were recruited at 22 to 26 weeks' gestation. Fourteen maternal clinical, hemodynamic, and placental characteristics were assessed in the second trimester and aggregated. Principal component analysis of this combined data set determined that 3 dimensions accounted for 56% of the cohort variability. The first dimension accounted for 31% of the cohort variability, with significant contributions from total peripheral resistance, endoglin, and cardiac output. The second dimension was predominantly influenced by body mass index and mean arterial pressure, while uric acid and myeloperoxidase mainly contributed to the third dimension. Unsupervised clustering identified 3 groups within this combined data set. Total peripheral resistance was the most significant distinguishing parameter between these groups (P<0.0001), followed by placental growth factor, endoglin, and cardiac output (P<0.0001). Using these 4 parameters, a receiver operating curve was constructed with an area under the curve of 0.975 (95% confidence interval 0.93-1) for the prediction of developing hypertension in pregnancy.

CONCLUSIONS

Consolidated assessment of prognostic indicators in the second trimester of pregnancy may be useful to characterize and distinguish pathways by which women may develop hypertension in pregnancy. This approach could contribute to the development of pathway-specific preventative and antihypertensive treatment strategies.

Mechanisms and Clinical Significance of Endothelial Dysfunction in High-Risk Pregnancies

The maternal cardiovascular system undergoes critical anatomic and functional adaptations to achieve a successful pregnancy outcome which, if disrupted, can result in complications that significantly affect maternal and fetal health. Complications that involve the maternal cardiovascular system are among the most common disorders of pregnancy, including gestational hypertension, preeclampsia, gestational diabetes, and impaired fetal growth. As a central feature, maternal endothelial dysfunction is hypothesized to play a predominant role in mediating the pathogenesis of these high-risk pregnancies, and as such, might proceed and precipitate the clinical presentation of these pregnancy disorders. Improving or normalizing maternal endothelial function in high-risk pregnancies might be an effective therapeutic strategy to ameliorate maternal and fetal clinical outcomes.