Excerpted from OB GYN News April 1998

August 28th

Normal Baseline FHR
Doesn't Rule Out Hypoxia

Information on Electronic & Auscultative FETAL MONITORING

Excerpts from following article establish 4 major causes of intrapartum fetal death. This information give specific and straight-forward criteria for recognizing all four and acknowledges the ability of a trained practictioner to detect them using auscultation. This article also give other useful information in regard to defense in event of threatened litigation.

BY ERIK L. GOLDMAN, New York Bureau

Copenhagen - "A normal baseline fetal heart rate on admission cardiotocography (EFM tracing) is not a guarantee against fetal hypoxia", Dr. S. Arulkumaran said at the FIGO World Congress of Gynecology and Obstetrics

"You can have a normal baseline [heart rate] in a hypoxic baby," said Dr. Arulkumaran, professor of obstetrics and gynecology, National University Hospital, Singapore, "You want to see good accelerations and good baseline variability, showing that the autonomic functions are healthy"

In many ways, the pattern of change is more indicative of fetal health than the baseline heart rate itself. A healthy, reactive cardiotocogram (EFM) tracing will show patterns of alternating acceleration and good baseline variability, which indicate that the autonomic nervous system is well oxygenated.

In reviewing the findings of 1,067 admission 20-minutes CTC/EFM strips done at his institution, Dr. Arulkumaran recalled that it one case of intrapartum fetal death, the baseline heart rate was completely normal, and the only indication of hypoxia was a lack of normal variability and shallow decelerations -- a finding that is to overlook.

Essentially, babies die during labor in four ways

1). Acute hypoxia usually due to abruption or cord prolapse;

2). Subacute by hypoxia

3). Gradually developing hypoxia;

4). Pre-existing chronic hypoxia, which can have many causes.

Acute hypoxia is usually easy to identify since there will be obvious clinical signs of abruption or cord prolapse, The fetal heart monitor will typically show bradycardia (less than 80 beats per minute) and the blood pH falls quickly. In this situation a baby can die within 30 minutes.

In a subacute hypoxic there may be no overt signs, but the fetal heart monitor will show prolonged decelerations of greater than 90 seconds. The fetal heart rate spends very little time at baseline.

Gradually developing hypoxia is the most common pattern, and it is easy to detect. Early on in labor, the fetus will show good baseline variability, with clear accelerations. But with continued cord compression, the accelerations gradually disappear, indicating a cutoff of blood to the somatic nervous system.

This in turn is followed by a rise in heart rate, a compensatory mechanism in which the fetal heart attempts to counter hypoxia by raising cardiac output by increasing the pumping rate. A rapid rise in fetal heart rate, from approximately 150 bpm to 170 bpm, is a clear distress signal.

Preexisting hypoxia is easy to miss, because essentially the heart rate is steady, with little baseline variability. "If it is more than 90 minutes with this tracing, you must do something because babies do not sleep for more than 90 minutes," said Dr. Arulkumaran. A steady-state tracing of several hours’ duration definitely spells trouble, but it also may be due to drugs, infection, malformation or other causes.

He noted that acute, subacute and gradually developing hypoxia can be detected on auscultation by a skilled examiner. Pre-existing hypoxia, on the other hand, is virtually impossible to auscultate. "You'll listen to 140 [bpm] all the time, and finally, the baby will die."

In the Singapore study, 1,003 of the 1,067 admission CTGs/EFM tracing were reactive; the incidence of poor neonatal outcomes taken in aggregate was 1.4%.

Among the 53 cases with equivocal CTG tracings, the incidence of poor neonatal outcomes was 11.3%.

Among the 11 cases with "ominous" CTCs, the adverse outcome rate was 36.4 %. This included the one intrapartum death previously described and one neonatal death.

Addressing the broader question of the need for electronic fetal monitoring in normal" pregnancies, Dr. Arulkumaran said that while there are no definitive randomized trials to support widespread use of continuous monitoring in low-risk cases, it makes good clinical sense to do routine admission CTG, followed by intermittent auscultation.

Dr. Ingemar Ingemarsson, , professor of obstetrics and gynecology, University Hospital, Lund, Sweden, was enthusiastic about admission CTG itself, but was concerned about misinterpretation of CTG traces. "I have to say I am pessimistic regarding the ability of users to interpret the traces correctly, in Sweden, I see catastrophic cases after misinterpretation of' traces. If a doctor or midwife can't interpret the tracing, don't use the machine. In those cases it can do more harm than good," Dr. lngemarsson said.

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