Continuous Systolic Blood Pressure Monitoring By the Difference in Electrocardiogram and Pulse Oximetry in Near-Term, Exteriorized Goat Fetuses

Objective: Our purpose was to determine whether systolic arerial pressure, as predicted from the delay time from the electrocardiogram to pulse oximeter waveform, correlates with directly measured systolic blood pressure. Methods: Six Japanese Saanen goats at 120-125 days' gestation were used. Experiments were conducted in acutely operated animals under anesthesia. We placed catheters in the caroti artery and jugular vein, electrodes on the chest, and a pulse oximeter probe on the tongue. Systolic blood pressure (Psm), fetal heart rate (FHR), delay time (Td), and pulse oximeter waveform were monitored continuously, and the data were stored. Systolic blood pressure was estimated (Pse) by the simlpe linear equation of Td. Fetal blood pressure was decreased 10% by hydralazine and blood withdrawal. Correlation coefficients and the agreement between Psm and Pse were determined. Results: A significant correlation (P < .01) with good bias values (< 8 mmHg) and precision vlaues (< 5 mmHg) was obtanied between Psm and Pse in all animals. There was also a significant correlation between Psam and Pse with high coefficients for hydralazine (r2 = 0.82 ± 0.12) and for withdrawal (r2 = 0.85 ± 0.15). The correlations became slightly scattered in acidemia (pH < 7.25). Conclusion: This technique has the potential to provide information on fetal blood pressure during labor and delivery on a beat-by-beat basis, which will aid in the interpretation of electronic FHR recordings.