Arcst. N.Z.J. Obstet. Gynaec. (1979) 19: 135

Fetal Heart Rate Monitoring During Ambulant Labour Using a Modified Adult Radiotelemetry System Alastair H. MacLennan' and Roslyn C . Green2 Department of Obstetrics and Gynaecology, University of Adelaide, and Queen Victoria Hospital, Adelaide

Summary: A commercially available adult radiotelemetry system has been adapted successfully to allow continuous fetal heart rate monitoring during labour in ambulant patients. The modifications necessary to the adult equipment and its routine use in a large maternity unit are described. High quality recordings were obtained from 90% of the patients studied, with minimal inconvenience to the patient. The telemetry system combined the benefits of intrapartum fetal heart rate monitoring with those of ambulation during labour, decreasing the patient anxiety often associated with visible fetal monitoring.

Intrapartum fetal heart rate monitoring appears to reduce perinatal mortality and morbidity in high risk cases (Renou et a]., 1976) and possibly also in low risk cases (Kubli, 1977; Beard et al., 1977). However, large randomised controlled trials have yet to prove the value of such monitoring in low risk pregnancy. It is necessary to show such an advantage, particularly with respect to low risk patients, in view of such disadvantages as cost, centralisation of care, immobilisation of the patient and increased apprehension to both patient and her partner engendered by visible electronic equipment (Starkman, 1977). Modern obstetrics has been associated with increasing intervention and mobilisation of the patient with intravenous drips, tubes and wires. Radiotelemetry allows ambulation and the removal of the monitor from the patient's environment, overcoming many of the disadvantages of conventional monitoring. 1 . Senior Lecturer. 2. Research Sister. Address correspondence: A. H. MacLennan, Department of Obstetrics and Gynaecology, Queen Victorja Hospital, 160 Fullarton Road, Rose Park, South Australia, 5067.

Small clinical trials with 5, 10 and 30 patients, respectively, were reported by Neuman et al. ( 1970), Walker et al. (1970) and Flynn and Kelly ( 1976) ; these showed that satisfactory fetal heart recordings could be obtained using radiotelemetry equipment, but experience of routine use of such equipment was not reported. Technical improvements in other fields of medicine and reasonably inexpensive adult cardiac radiotelemetry equipment is now commercially available (Hewlett-Packard Pty. Ltd.). This paper reports on the adaptation of this telemetry system and its application in the routine management of labour in an attempt to increase the acceptability of monitoring, but to decrease the amount of apparent interference in the labour process. METHODS AND PATIENTS

Equipment The equipment used was the Hewlett-Packard model 78100A transmitter and 78101A telemetry receiver (figure 1 ). Each transmitter operates at a slightly different frequency between 450 and 470 Megahertz and thus only the appropriate fetal heart is recorded by each receiver when more than one






patient is being monitored. The operating range is approximately 300 metres in our unit and good recordings were obtained even when the patient was several floors away from the receiver. No interference at the above frequencies has been experienced and the Postal and Telecommunications Department of the Commonwealth of Australia in Adelaide has approved this equipment and assigned the appropriate frequency for this use. The other technical details of the units described are as follows: modulation type, AM/FM; power, 0.002 Pm (Watts); and frequency tolerance, 3 kilohertz. Two warning signals are displayed on the receiver which flash when there is a loose electrode, the transmitter battery is failing, or when the patient has moved out of range. The receiver and monitor are continuously on view in the nursing station, but can be moved into the patient’s room if required.

Figure 1. The Hewlett-packard modified adult transmitter and receiver. The transmitter is attached bv extended leads to a conventional scalp clip and maternal skin earthing lead. The receiver shown is attached to a Sonicaid FM2 fetal heart monitor.

The modifications made to the adult telemetry equipment for use in fetal monitoring are shown schematically in figure 2 . The electrode impedence levels of the fetal scalp are usually much higher than those of adult skin and thus resistors R1 and R2 have been placed in the transmitter across the fetal leads to avoid the high inipedence sensing circuit in the transmitter from cutting out the transmission from the fetus. When a Sonicaid monitor is used, the output of the receiver has to be attenuated by resistors R:, and R., (which have a 1 O : l








Figure 2.

Diagram of necessary modifications to Hewlett-Packard adult telemetry system

78100A and 78101A for fetal heart monitoring. Resistors R , and R., are both 330,000 ohms

and have been placed in the transmitter ;icross the fetal leads. ResiQors K., and R, ;ire 10,000 ohms and 1,000 ohms, respectively.



Figure 3 . Fetal electrocardiograms from the same patient: tracing A was obtained by radiotelemetry and tracing B by conventional linkage to a Sonicaid monitor.

ratio). We used both Hewlett-Packard and Sonicaid monitors, the former giving fewer tracing artefacts. A standard fetal scalp electrode is applied after rupture of the membranes and the 2 wires from the scalp electrode are applied to the RA and L A terminals of the transmitter. The middle R L terminal is connected to a standard electrocardiogram stud electrode on the mother’s thigh and this serves as an earth lead. The transmitter and leads weigh 280 g and it measures 12.7 x 7.4 x 2.4 cm. It fits into a pocket on a belt that the patient comfortably wears above the fundus of the uterus. The connections between the scalp electrode wires and the cables from the transmitter are insulated from each other and from the mother, and are loosely secured to her in a comfortable position to allow ambulation. The above adaptations are now incorporated in the Hewlett-Packard 8020s Fetal Telemetry System, but if the cable to the monitor is modified to fit other makes of.feta1 monitors, resistors R:3 and Rq as described may have to be included in the new cable connection to the monitor.

Patients Patients were selected from those who wished to ambulate in labour and were not confined to bed by intravenous infusions, intrauterine pressure catheters, or epidural anaesthesia. In general, they were a “favourable” group, mostly in spontaneous labour, although some had undergone induced labour by either artificial rupture of the membranes or vaginal postaglandin FZa.When fetal distress was suggested by an abnormal tracing, the patient was connected conventionally to a fetal heart monitor with concomitant measurement of uterine contractions.


Three hundred patients have been monitored by intrapartum fetal cardiotelemetiy in the present study and 3 such telemetry units are now available in our delivery suite for routine fetal heart monitoring if desired by the obstetrician and the patient. Approximately 90% of the tracings were of high quality when the scalp clip and leads were correctly connected. These tracings were similar to those obtained via directly-attached leads (figure 3). In fact, in some instances the tracing obtained using radiotelemetry was purer because there was no interference from the mains electrical supply and the frequency-modulated system has an enhanced ability to reject interference. Satisfactory tracings were obtained whilst the patient was ambulant up to a distance of 300 metres. The average length of time that the patients were ambulant and monitored by radiotelemetry was just over 2 hours. The average length of labour was 5.5 hours; 76% of the patients had a spontaneous delivery and analgesic requirements were less than average for our population. Abnormal tracings by radiotelemetry were always confirmed by conventional linkage to a fetal heart monitor and n o babies were born with respiratory depression in the presence of a normal intrapartum tracing obtained by radiotelemetry. Poor tracings were generally associated with a loose scalp electrode, loss of contact of the mother’s earthing electrode, a failing battery, or unusually high fetal scalp impedence levels. Where those problems could be ruled out, remaining substandard tracings sometimes improved with descent of the head.




This form of monitoring was well accepted by the patients and nursing staff. I n particular, the patients appreciated the freedom to ambulate and the reassurance that the fetus was being monitored, without the anxiety of the presence of the monitor. DISCUSSION

Routine fetal monitoring by radiotelemetry and the encouragement of ambulation during as much of labour as reasonably possible has been introduced successfully into the management of parturition at our Hospital. Marked changes in delivery suite practices and sometimes, attitudes, have been necessary for many of the midwives and obstetricians involved. We have been impressed by the way the staff accepted these changes despite the fact that the delivery suite was not originally designed t o facilitate patient ambulation in labour. During the study, patients walked along corridors normally reserved for staff movement, as well as moving within the confines of their own rooms. Ideally; a patients' sitting room within the delivery suite, a garden or courtyard that is quiet and pleasant should be incorporated in the design of new delivery suites. Our own delivery suite is now being modified to accommodate this change. Intrapartum fetal monitoring by radiotelemetry rather than conventional monitoring appears to have several advantages. Firstly, it does not inhibit ambulation in labour. Flynn et al. (1978) in a randomised trial of labour in ambulant versus recumbent patients showed that ambulation was associated with significantly shorter labours, less analgesic requirement, less fetal distress, and less operative intervention at delivery. Our results support these findings, although our group in this feasibility study had no comparable control group of recumbent patients. A second advantage of radiotelemetry is that it is less likely to cause anxiety to either the patient or her partner, since the monitor is removed from their environment. In a study of the psychological consequences of fetal monitoring, Starkman ( 1977) found that the inability of the parents to fully under-

stand the monitor increased their apprehension concerning the health of the fetus. The cost of fetal monitoring could possibly be reduced in larger hospitals where several monitors are normally in use by incorporating the telemetry receivers into a single multichannel recorder. Although it may be possible to justify the cost of fetal heart rate monitoring in all patients, it is a minority of patients who require electronic monitoring of their contractions. We believe, therefore, that for most patients it would not be beneficial to record intrauterine pressure by radiotelemetry and indeed intrapartum monitoring would be less costly if monitors were available that simply recorded the fetal heart rate pattern. The few high risk patients could have the more costly conventional monitoring of intrauterine pressure, with continuous fetal pH measurement. Where induction of labour is necessary, vaginal prostaglandin F-, (MacLennan and Green, 1979) also allows the patient to ambulate during labour without the need for intravenous therapy in most cases. Thus, ambulation during labour is now possible, even when hormonal augmentation and fetal monitoring is desired. A cknowledgements We are grateful for the excellent cooperation and support of the visiting medical specialists and the nursing staff of the Queen Victoria Hospital, Adelaide, during the clinical trials. We are indebted to Mr. Michael Kelly of the Biomedical Engineering Department, Queen Elizabeth Hospital and Mr. Peter Strawbridge, Queen Victoria Hospital, Adelaide, for their electronics expertise. Our thanks to Miss Michele Fogarty for the preparation of the manuscript.

References Beard, R. W., Edington, P. T., and Sibanda, J. (1977), Coritrib. Gyriec. Obstet., 3: 14. Flynn, A., and Kelly, J . (1976), Brit. tried. J., 2: 842. Flynn, A,, and Kelly, J. (1978), Brit. rned. J . , 2 : 591. Kubli, F. (1977), Coritr. Gyriec. Obsiet., 3: 69. MacLennan, A. H., and Green, R. C. (1979), Laricer, 1: 17. Neurnan, M. R., Picconnatto, J., and Roux, J . F. (1970), Gyriec. liii.rst., 1: 92. Renou, P., et al. (1976), Anier. J . Obster. Gyriec., 125: 1976. Starkman, M. N . (1977), Obsret. w i d Gyriec., 50: 500. Walker, D., Grimwade. J.. and Wood, C . (1970). Med. J. A"., 2: 1078

Fetal heart rate monitoring during ambulant labour using a modified adult radiotelemetry system.

Arcst. N.Z.J. Obstet. Gynaec. (1979) 19: 135 Fetal Heart Rate Monitoring During Ambulant Labour Using a Modified Adult Radiotelemetry System Alastair...
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