The effect of Fenoterol on maternal and fetal tcPO2 and heart rate

112

The effect of Fenoterol on maternal and fetal tcPOp and hear/t rate H. SCHNEIDER, F. STRANG, R. HUCH, A. HUCH

During the first stage of labor contractions were suppressed with fenoterol (PartusistenR) in 13 patients. In all cases labor had been completely uh- eventful before Start of fenoterol. After appropriate explanation maternal consent was obtained. The effect of fenoterol on the following Parameters was investigated: maternal transcutaneous P02, maternal thoracic impedance, maternal heart rate, intrauterine pressure, fetal transcutaneous ?$%> fetal heart rate.

The fetal tcP02 electrode was applied at a cervical dilatation of 4-6 cms using the method described by Huch, Huch, Schneider, Rooth (1). When a stable fetal "tcPOo was reached fenoterol was given to the mother by intra- venous infusion. fhe initial dose was 0.0011 mg/min. The dose was increased until contractions ceased or until a maternal tachycardia of >140 bpm was present. Maximum dose was 0.034 mg/min.

When contractions were suppressed the mother was instructed to breathe 100%

oxygen for 10 minutes. 4 different time periods were assessed:

1. A ten minute period just before fenoterol was given (prefenoterol) 2. a ten minute period when the patient received fenoterol before oxygen was given (fenoterol) 3. a stable 2-3 minute period when the patient re- ceived both fenoterol and oxygen (f + 02)· 4. a ten minute period after fenoterol was discontinued (after).

For each minute the fetal heart rate pattern was assessed using "a modified score (1). The lowest fetal heart rate score during the 10 minute period was taken for purposes of evaluation.

There were typical changes in fetal scalp tcP02 with contractions which consisted of an early rise and subsequent drop in tcP02 once the peak of a contraction was reached. The extent of the drop in tcPU2 showed a signi- ficant positive correlation with the intensity of the corresponding con- traction. In most instances this drop was less than 2 mm Hg and is explained äs an effect of the reduced intervillous space bloodflow during uterine

contractions.

During fenoterol administration contractions were significantly decreased (Table 1). When fenoterol was discontinued the contractions returned to their original level.

There was no significant difference between mean fetal tcPÜ2 before feno- terol and during suppression of contractions ( F i g . l ) .

With the mother breathing additional oxygen a rise in tcPU2 was seen in all cases ( F i g . l ) .

While maternal heart rate showed a significant rise during fenoterol infu- sion fetal heart rate remained unchanged (Table 1).

There i s some evidence from animal experiments (2) äs well äs measurements i n . h u m a n s . ( 3 ) that fenoterol induces an increase in uteroplacental blood flow. We have shown that at least in normal term labor suppression of uterine contractions does not result in a significant increase in fetal tcP02- This is clearly different in cases with mild preexisting fetal- hypo- xia where fenoterol infusion will together with the suppression of labor give a rise in fetal tcPÜ2 (4). The most effective improvement in the oxy- gen supply of a compromised fetus in labor will clearly be achieved with a combination of suppression of uterine contraction with fenoterol plus an elevation of the mother1s P02 by giving additional oxygen.

0300-5577/81/0091-0030 * 2.00 Copyright by Walter de Gruyter & Co.

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Blbliography

1. A. HUCH, R. HUCH, H. SCHNEIDER, G. ROOTH:

Continuous transcutaneous monitoring of fetal oxygen tension during labor Brit. J. Obstet. Gynec., Suppl. No l, 1977

2. S.C. Brennan, M.K. MC Laughlin, R.A. Chez:

Effects of prolonged Infusion of£-adrenergic agonists on uterine and umbilical blood flow in pregnant sheep

Am.J. Obstet. Gynec. 128 (1977) 709

3. T.H. Lippert, P.B. De Grandi, R. Fridrich:

Actions of the uterine relaxant, fenoterol, on uteroplacental hemody- namics in human subjects

Am. J. Obstet. Gynec. 125 (1976), 1093 4. B. Liedtke, H. Pendel und M. Janik

Kontinuierliche Sauerstoffmessung beim Feten sub partu unter tokolyti- scher Behandlung mit Fenoterol

In: Fenoterol bei der Behandlung in der Geburtshilfe und Perinatologie Ed. H. Jung und E. Friedrich, Thieme 1968, 215

Priv.-Doz.Dr.H.Schneider Dept·f.Frauenheilkunde Universität Zürich Frauenklinikstr.1O CH-8O91 Zürich/Swiss