Leonard Indyk

Umbilical vein occlusion and transient acceleration of the fetal heart rate. Experimental observations in subhuman primates.

Transient acceleration of the fetal heart rate is commonly seen in the cardiotachometer tracing of the human fetus during labor. A likely cause appeared to be partial occlusion of the umbilical cord. On the basis of this hypothesis, fetal cardiovascular responses to partial occlusion of the umbilical cord or isolated intra-abdominal portion of umbilical vein were studied in near-term pregnant baboons and rhesus monkeys prior to and following sympathetic blockade with dibenzyline and propranolol. The responses were of two types. In the well-oxygenated fetus, partial occlusion resulted in transient acceleration of heart rate and a decrease in pulse pressure. This response was abolished with dibenzyline or propranolol. In the hypoxic fetus, partial occlusion resulted in either bradycardia and hypotension or hypotension with no alteration in heart rate. Thus, transient acceleration of the fetal heart rate can be explained on the basis of a sympathetic response to diminished venous return. It would appear to be an early sign of a potential cord complication. This response will not be seen if the fetus becomes asphyxiated and hypoxic.

Intermittent phototherapy in the treatment of jaundice in the premature infant

A controlled trial of the use of intermittent phototherapy for the treatment of hyperbilirubinemia in newborn infants is reported. Periods of illumination of (1) 15 minutes light on, 15 minutes light off, (2) 15 minutes on, 30 minutes off, and (3) 15 minutes on, 60 minutes off are as effective as is continuous illumination. A comparison with previous trials of intermittent phototherapy is made and differences in results are explained using as a model the action of light on bilirubin.

The relationship of fetal heart rate patterns to the fetal transcutaneous Po2

Continuous transcutaneous PO2 (tcPO2) monitoring of the human fetus was performed during 46 labors, 30 of which were complicated by abnormal fetal heart rate (FHR) patterns. FHR variability decreased with increases in the fetal tcPO2, and FHR variability increased with decreases in the fetal tcPO2. Analysis of the tcPO2 and FHR tracings provided an explanation for this apparent discrepancy. While rising fetal tcPO2 values were usually associated with decreased FHR variability, the pattern of late deceleration and decreased variability must still be considered an ominous pattern. The fetal tcPO2 declined during the deceleration and rose thereafter, with corresponding decreased FHR variability. Incomplete recovery of the fetal tcPO2 was associated with progressive acidosis. Repetitive and isolated late deceleration patterns showed markedly dissimilar fetal tcPO2 changes, suggesting different mechanisms may be involved in their production. Further studies are required before any definite conclusions can be drawn about the relationship of the FHR and the fetal tcPO2.

Safe and Effective Use of Transcutaneous Blood Gas Monitors

The Medical Devices Amendments of 1976 (PL 94–295) will compel users of transcutaneous monitors to comply with Class II, Performance Standards. These standards will have to provide reasonable assurance of the safety and effectiveness of the device. Similar standards are in preparation for other cardiac and respiratory monitors. Dangers of tcPo2 monitors include shock and burn, which requires attention to the insulation of the monitor from the power line and from recorders used to record the output. Optimal safe time vs. temperature limits have not yet been established, and these may vary with age, skin site, blood pressure and body and environmental temperature. The usefulness of alarms for Po2, sensor temperature and heating power, and their limits remain to be defined by extensive clinical use. Standards for drift, reproducibility, recalibration interval and accuracy will have to be set after more extensive clinical use especially by groups not involved in the initial prototype development and testing. In order to prove that these devices are also effective, physicians will have to document that care would have been different, and might have impaired patient safety, if the device had not been used.

149 CONTINUOUS MONITORING OF PO 2 FOLLOWING CAR DIAC SURGERY

The transcutaneous oxygen tension (PtcO2) was studied in 18 children (age - 6 mos. to 13 yrs; wt.-5 kg. to 54 kg.) following open heart surgery. Four of the operations were done under deep hypothermia (Tcore = 15-20°C), 11 under mild hypothermia (24-28°C) and 3 at normothermia(>34).The PtcO2 was recorded continuously for a period of several hours while an arterial catheter was in place, beginning within 8 hours after completion of surgery. Core temperature was at least 35°C in all patients at the start of recording. An electrode temperature of either 44°C or 45°C was utilized. PaO2 values from arterial blood samples were correlated with PtcO2. A plot of all paired values had a greater scatter than had been previously encountered with the use of the electrode in sick newborns (r=.53 vs r=.94). Virtually all of the PtcO2 values were lower than PaO2 with 20% of the PtcO2 values considered unacceptable on the basis of large discrepancies at the low range of PO2. Correlation at 45C electrode temperature was better than at 44C (r=.62 vs. r=.41). PtcO2 values taken beyond 8 hours post-surgery correlated significantly better than those taken earlier (r=.78 vs. r=.24). Despite differences in the individual quantitative correlations, abrupt changes in PO2 reflecting changes in respiratory status were consistently detected rapidly. These studies indicate that recording of the PtcO2 is potentially a valuable tool in the monitoring of post-operative cardiac patients.

126 TRANSCUTANOUS OXYGEN TENSION (PtcO2) IN NEONATES WITH CYANOTIC CONGENITAL HEART DEFECTS (CCHD) AND PULMONARY DISEASE (PD)

Previous studies in sick infants utilizing transcutaneous 02 sensors indicated significant fluctuations in resting Ptc02 and marked decreases in response to crying(Ped.Res. 10:422,1976). The purpose of this study was to determine the pattern of Ptc02 in babies with CCHD as compared to a matched group of neonates with PD. Continuous Ptc02 recordings were obtained in 18 newborns:8 with CCHD and 9 with PD. Observations were made during the resting state and 38 episodes of crying.Resting Ptc02 was 26±12 torr in the CCHD group and 66±torr in the babies with PD. Fluctuations were virtually absent in the patients with CCHD (average variability: CCHD=±0.5; PD=±4.0 torr). Ptc02 fall in response to crying was found to be significantly smaller in the CCHD group (6±4 torr) than in the PD patients (22±16 torr). An exception was an infant with pulmonary atresia after a Waterston shunt who had predominantly pulmonary manifestations, and displayed a significant fall in Ptc02 (12.5 torr) during crying.The data indicate that infants with intracardiac R→L shunts have a non-varying pattern of arterial 02 desaturation as compared with the more labile behavior of the PD group. The stability of Ptc02 in neonates with CCHD may have diagnostic usefulness, and supports the reliability of isolated arterial p02 determinations in babies with heart disease.

A NEW MECHANISM FOR LATE DECELERATION OF THE FETAL HEART RATE

Late deceleration of the fetal heart rate (FHR) is a sign of severe fetal asphyxia, but is also seen occasionally when the fetus is neither acidotic nor hypoxic. In a search for other possible causes we postulated that with partial occlusion of the umbilical cord during uterine contractions, the low pressure venous flow would be reduced before changes in arterial flow. This would result in the accumulation of fetal blood in the placenta. Release of the partial occlusion after the contraction would be followed by an increase in venous return and brodycardia from parasympathetic stimulation.Catheters & electrodes were inserted into 12 fetal baboons, mean gestational age 153 days & an occluding device was placed round the intra-abdominol portion of the UV. After 2 hours recovery (fetal pHa 7.36 ± 0.004 and SaO2 62 ± 2.3%) water was gradually injected into the cuff in a volume previously shown to partially occlude the UV. With partial occlusion, FHR rose from 189 to 203 beats/min. These changes in heart rate were significantly different from control (p<.001). The brodycardia was accompanied by a significant elevation of BP.These observations provide an alternative explanation for the pattern of late deceleration of the FHR & stress the importance of monitoring the fetal acid-base state for correct interpretation of fetal heart rate patterns.