British Journal of Obstetrics and Gynaecology April, 1977. Vol84. pp 281-284
FETAL HEART RATE MONITORING DURING CAESAREAN SECTION BY
A. B. W. TAYLOR, Consultant Obstetrician Bowthorpe Maternity Hospital, Wisbech, Cambridgeshire Summary The fetal heart rate was monitored during 30 deliveries by Caesarean section. General anaesthesia, but not epidural analgesia, caused a loss of beat-to-beat variation, but appeared to have no other adverse effects on fetal heart rate. The loss of beat-to-beat variation occurred after intravenous thiopentone and was most marked when atropine was used as premedication.
TIME which elapses between induction of anaesthesia and delivery of the fetus by Caesarean section tends to be an uncharted area in fetal monitoring. A study was therefore undertaken of cardiotocographic recording during this interval. It was thought that the results would form a basis for opinions about techniques used before and during Caesarean section.
The FHR record extended from induction of anaesthesia through to delivery of the fetal head. The time of intravenous induction, intubation and the administration of any drugs was noted on the recordings and also the stages of Caesarean section from skin incision to opening the uterus and delivery of the fetal head. All patients who were delivered under general anaesthesia were premedicated with an intravenous injection of either atropine (0.6 mg) or hyoscine (0.4 mg) and were started on an intravenous infusion of 5 per cent dextrose. The patient was placed in the supine position with a 20 degree head-down tilt, and was asked to breathe pure oxygen for 5 minutes. She was then given an intravenous injection of thiopentone (250 to 300 mg) and succinylcholine (50 to 150 mg). Cricoid pressure was applied by an assistant and was maintained until the trachea had been intubated, after which the patient was maintained with nitrous oxide and oxygen. All patients who were delivered with epidural analgesia were given 25 to 30 ml of 0 . 5 per cent plain bupivicaine and no premedication. After the block was established, patients were placed in a right lateral tilt position. In two patients the abdomen was opened by a vertical subumbilical incision. In the remainder a transverse suprapubic skin incision was made using the technique described by Cohen (1972).
PATIENTS AND METHODS Thirty patients were studied: 22 operations were carried out under general anaesthesia and 8 under epidural analgesia. All but two patients were in labour. The indications for Caesarean section were failure to progress or cephalopelvic disproportion (12 patients), clinical signs of fetal distress or an abnormal fetal heart rate (FHR) trace (12 patients), complications associated with breech presentations (3 patients) and fulminating pre-eclampsia (3 patients). The birth weight of the infants was between 2.20 and 4.03 kg. A clip or Surgicraft Copeland electrode was attached to the presenting part of the fetus after rupturing the membranes and the FHR trace was recorded at a paper speed of 1 cm or 2 cm per minute with a Hewlett Packard 8020A fetal monitor. Contractions were recorded in 7 patients with an intrauterine catheter and in 17 with an external abdominal transducer. 281
The criteria for evaluating continuous records of the fetal heart were those of Huntingford and Pendleton (1969). Loss of beat-to-beat variation (or a silent pattern) was defined as a baseline fetal heart rate variation of less than five beats per minute, while a variation in the baseline heart rate of more than 25 beats in any minute was called a saltatory pattern (Hammacher ef al, 1968).
RESULTS The time intervals between induction of anaesthesia and delivery of the fetus ranged from 5 to 13 minutes. The basal FHR normally remained stable. If there had been previous decelerations during contractions, these decelerations tended to be less marked after the patient was anaesthetized. One patient, who still had some oxytocin in the drip chamber, was inadvertently given a bolus of oxytocin and this resulted in a tetanic contraction associated with a sustained deceleration of the fetal heart
rate. In the absence of fetal distress, there was normally a loss of beat-to-beat variation within two minutes of the intravenous injection of thiopentone (Fig. 1). This silent pattern was most marked if atropine had been given intravenously as premedication. There was no loss of beat-to-beat variation in the eight patients who had a Caesarean section under epidural block (Fig. 2). For some patients incision of the uterus was associated with a short acceleration or a saltatory fetal heart rate pattern and this was typically followed by deceleration of the fetal heart rate during delivery of the fetal head, in vertex presentations. This bradycardia was most marked in cases of delay due to difficulty during delivery of the fetal head. The Apgar score at one minute bore no apparent relation to the length of the interval between induction of anaesthesia and delivery (see Fig. 3). The patients who were delivered under an epidural block were not included in Figure 3. The Apgar score of those babies was invariably high.
FIG.1 Caesarean section under general anaesthesia. There is a loss of beat-to-beat variation following intravenous thiopentone (250 mg given 30 seconds before intubation) followed by excessive beat-to-beat variation with the uterine incision and a deceleration occurs with delivery of the fetal head. (Paper speed 2 crn/rninute.)
FETAL HEART RATE DURING CAESAREAN SECTION
m FIG.2 Caesarean section under epidural block only. Note no loss of beat-to-beat variation and acceleration of fetal heart rate with uterine incision. (Paper speed 1 cmlminute.)
O A 00
Relationship between Apgar score at one minute and interval between induction of anaesthesia and delivery of the baby. The shaded triangles show those patients in whom an abnormal FHR trace was the indication for Caesarean section.
DISCUSSION The loss of beat-to-beat variation following the intravenous injection of thiopentone was similar to that caused by diazepam (Scher et al, 1972); it occurred after a similar interval of time and probably indicated sedation of the fetus with inhibition of central cardiac reflexes. The view of Hammacher (1969) is that the'altered pattern indicates a reduction in the adaptive ability of the fetal heart. Atropine also causes loss of beat-to-beat variation (Hon and Sze-Ya, 1969). Although a silent pattern is often associated with intrapartum fetal hypoxia a less sinister significance is attributed to the same pattern when it is drug induced. The appearance of a saltatory pattern, which appeared when the uterus was incised, may represent a reaction to stress by the fetus. When this appears after a silent interval then it also shows that the autonomic innervation of the fetal heart is capable of reacting to the stress in spite of any residual effects of thiopentone. The bradycardia which occurs during delivery of the fetal head may be due to
head compression. In cases where there was difficulty, the bradycardia may have represented hypoxia due to changes in the feto-placental circulation. The stability of the FHR trace before the uterus is opened suggests that fetal welfare is maintained during anaesthesia, in particular as it has been shown in the conscious patient that an abnormal FHR trace usually precedes the development of fetal acidosis (Wood et al, 1969). Several studies have shown that an induction of anaesthesia to delivery interval of more than ten minutes does not depress the baby unduly (Crawford, 1956; Cohen, 1962). Crawford et al (1972) stressed the importance of lateral tilt to prevent caval compression at Caesarean section. Crawford et al(l976) noted that the time that elapsed between incision of the uterus and delivery of the baby was more closely related to depression of the newborn than the time that elapsed between induction of anaesthesia and incision of the uterus. It follows that there is no need for haste between induction of anaesthesia and incision of the uterus, particularly if the fetus is being monitored. However, once the uterus has been opened, delay in delivery of the baby would seem undesirable. Thus, skin preparation and draping procedures need not be carried out before induction of anaesthesia and in the absence of prolapse of the umbilical cord or severe maternal haemorrhage, no attempt need be made to save a few minutes by using a vertical, rather than a transverse skin incision.
ACKNOWLEDGEMENTS Part of this work was undertaken while I was Senior Registrar on rotation from the Hammersmith Hospital to the Northampton General Hospital and I thank Professor J. C. McClure Browne and Mr A. E. Alment for their advice and permission to work on their patients. REFERENCES Cohen, E. N. (1962): Anaesthesia and Analgesia, 41, 122. Cohen, S. J. (1972): Abdominal and Vaginal Hysterectomy. Heinemann, London, p 19. Crawford, J. S. (1956): British Journal of Anaesthesia, 28, 146. Crawford, J. S., Burton, M., and Davis, P. (1972): British Journal of Anaesthesia, 44, 477. Crawford, J. S., James, F. M., Davies, P., and Crawley, M. (1976): British Journal of Anaesthesia, 48, 661. Hammacher, K. (1969): First European Congress of Perinatal Medicine, Berlin. Edited by P. J. Huntingford, K. A. Huter and E. Saling, Academic Press, New York, p 80. Hammacher, K., Huter, K. A., Bokelmann, J., and Werners, P. H. (1968): Gynecologia, 166, 349. Hon, E. H., and Sze-Ya, Y. (1969): Medical Research Engineering, 8, 14. Huntingford, P. J., and Pendleton, H. J. (1969): Journal of Obstetrics and Gynaecology of the British Commonwealth, 76, 586. Scher, J., Hailey, D. M., and Beard, R. W. (1972): Journal of Obstetrics and Gynaecology of the British Commonwealth, 79, 635. Wood, C., Newman, W., Lumley, J., and Hammond, J. (1969): American Journal of Obstetrics and Gynecology, 105,942.