Maternal hemodynamic measurements by electrical cardiometry in patients at risk for preeclampsia.
Abstract Number: S-24
Abstract Type: Original Research
Electrical cardiometry (EC) is a type of impedance cardiography which is easy to apply, well tolerated by patients and continuous in output. We report the use of EC to measure CO and SVR in 17 patients at risk for preeclampsia. The patients were evaluated at 22-25 weeks gestational age with Doppler ultrasonography to measure umbilical artery systolic/diastolic flow velocity ratio (S/D ratio) and uterine artery pulsatility index (PI). The Aesculon EC system was used to measure blood pressure (BP) and CO in the three patient positions adopted during sonography: SUP, supine; R DCUB, 45 degrees right decubitus; L DCUB, 45 degrees left decubitus.
Time spent in each position was approximately 5 minutes. BP was taken automatically by cuff on the patient’s left arm at least twice in each position and averaged. SVR was computed from the CO, BP and an assumed CVP = 6. Sampling time for each CO measurement was 10 seconds. All CO measurements were analyzed for signal quality index (SQI) and only measurements with SQI >70 were used.
Findings (Figure 1):
1) Supine systemic vascular resistance index (SVRI) and cardiac index (CI) are significantly correlated with S/D ratio, an index of fetoplacental resistance and overall placental health. This correlation is plausible since a diseased placenta may both offer increased resistance to the fetal circulation and release mediators which increase maternal SVR.
2) CI is higher and SVR is lower in the L DCUB position than in the other positions. This may be due to less aortocaval compression (ACC) in L DCUB, even at 22-25 weeks gestation. Unrecognized ACC might confound attempts to use SVR to predict or manage preeclampsia, since ACC may have the short term effect of increasing SVR by activating the sympathetic nervous system, independently from longer term effects of placenta-derived mediators on SVR.
These results are preliminary and our interpretations are speculative. No measurements were taken in the full right and left lateral decubitus positions and hence some degree of ACC may still have been present during all of the measurements. EC deserves further evaluation as an easy to use method of continuously measuring CO and SVR in pregnant patients.