Penetration of the subarachnoid space by fetal scalp electrode

Fetal scalp electrodes of various designs are used widely for continuous intrapartum fetal heart rate monitoring. Minor lacerations of the scalp are common and 1.0 -4.5% of infants may develop scalp ulceration or abscess.' 'We describe two cases in which there was penetration of the subarachnoid space with leakage of cerebrospinal fluid associated with the use of a scalp electrode of the single helix type.

Case reports

Case 1-A 20-year-old primigravida was admitted in spontaneous labour at 38 weeks of gestation. A fetal scalp electrode was applied at 4 cm cervical dilatation with the fetal head in the left occipitoanterior position. Spontaneous vaginal delivery of a 'nature boy weighing 3130 g occurred four hours later. The baby was in good condition with Apgar scores of 9 and 10 at one and five minutes respectively. Three hours after delivery we noted leakage of clear cerebrospinal fluid from the scalp electrode site over the posterior fontanelle. Conservative treatment with a dry dressing, prophylactic antibiotics, and nursing of the baby in a sitting position resulted in resolution of the link within 48 hour without any apparent complications.

Case 2-A 20-year-old primigravida was admitted in spontaneous labour at 39 weeks. A fetal scalp electrode was applied at 3 cm cervical dilatation with the fetal head in the right occipitoanterior position. Spontaneous vaginal delivery of a mature girl weighing 3050 g occurred seven hours later. The baby was in good condition with Apgar scores of 9 and 10 at one and five minutes. Routine examination after birth disclosed leakage of dear fluid from

the electrode site over the right parietal bone, 2~5 cm behind the posterior edge of the anterior fontanelle. As in case I there was rapid resolution of the leak (in this case within 24 hours) without any neurological complications. The position of the injury suggested that there had been penetration or both bone and dura resulting in the leak.

Fetal scalp hair and tissue entrapped between electrode wire and plastic body of device.

Comment

Penetrating injuries of the skull may lead to infection and meningitis and to intracranial haemorrhage due to vascular injury. There may be a long-term risk of epilepsy due to cortical injury and scarring.

In each of these two cases the electrode was applied without difficulty by an experienced midwife. In one the application was unsatisfactory as it was over the posterior fontanelle, but in the other the application was in an ideal position over the parietal bone. Our staff have reported several instances of difficulty in removing these electrodes, and we think that the injuries were sustained during removal rather than application.

There are two important design features of the single helix electrode, which contribute to the difficulty of removal. Firstly, the attachment of the helical electrode wire close to the perimeter of the plastic body causes the axis of rotation of the electrode to be indeterminate and variable during both application and removal. Secondly, the narrow angle of insertion of the electrode wire into the plastic body creates a wedge within which fetal scalp hair and tissue may become entrapped (figure). The effect of these design features is such that any traction applied to the electrode during its removal may cause the wire to straighten and thereby increase its potential depth of penetration. Any oscillating rotation, which may be used to free the electrode, carries the risk of deeper penetration of the tip through the fetal scalp. We think that this is the most likely mechanism for the penetration of the parietal bone in case 2.

In view of these potentially serious injuries we believe that the use of the single helix scalp electrode should he abandoned in favour of either the double helix or Copeland pattern, whose design features prevent the type of injuries that we desaibe.3

1 Ashkenazi S, Metzker A, Merlob P, Ovadia 3, Reisner SH. Scalp changes after fetal monitoring. Arch Dis, Child 1985;80:267-9.

2 Okada DM, Chow AW. Neonatal scalp abscess following intra-partum fetal monitoring: prospective comparison of two spiral electrodes. Am 3 Obstet Gynecol 1977127 :S75-8.

3 Department of Health and Social Security. Helical foetal scalp electrodes. DHSS Safety I14ormation Bulletin 1985, No 21.

(Accepted 17thJnly 1985)

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Department of Obstetrics and Gynaecology, North Manchester General Hospital, Crumpsall, Manchester MS 6RB

D S SHARP, Ma, MRCOG, consultant obstetrician

J M COURIEL, Ma, MRCP, consultant paediatrician

Correspondence to: Mr Sharp.BMJ/ 1546/85/A

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