Scalp Lead Placement 

Updated: Jun 20, 2018
Author: Michael G Ross, MD, MPH; Chief Editor: Christine Isaacs, MD 

Overview

Background

Internal cardiac monitoring with a scalp lead is used to identify fetuses at risk for serious complications from hypoxia during labor. Labor represents a unique stress on the fetus in utero. Uterine contractions reduce the flow of maternal blood to the placenta, in some cases uncovering a deficit in placental capacity. In addition, labor and the associated rupture of the chorioamnion may be associated with various other pregnancy risks, including intrauterine bacterial infection, umbilical cord compression, and placental abruption.

Recording the fetal heart rate in labor was developed in the 1960s as a means of assessing fetal status and documenting fetal well-being. Currently, 2 technologies are commonly available: an “external” monitor that uses Doppler technology to identify fetal heart motion via a sensor applied to the maternal abdomen and an “internal” monitor that directly records the fetal ECG via a single electrode applied to the fetal scalp (a fetal scalp electrode). Inherent differences are observed between the signal recordings via these 2 methods. The fetal scalp electrode detects actual beat-to-beat electrical signals of the fetal heart, whereas the external monitor uses an "averaging algorithm" to smooth the signal generated from the Doppler.

Regardless of the technology, the result is a recorded fetal heart rate. The fetal heart rate pattern is interpreted according to a standard set of criteria[1] with the goal being to identify fetuses at risk for serious complications during labor. The system remains imperfect, as a large number of fetuses display patterns that are neither clearly normal (category 1) or clearly abnormal (category 3). However, the ability to perform continuous fetal heart monitoring in labor is part of the standard of care for an obstetric unit in the United States.

Indications

Fetal heart rate monitoring via a fetal scalp electrode is indicated whenever other monitoring modalities are unsatisfactory in a laboring patient with ruptured membranes. For a low-risk patient, intermittent auscultation of the fetal heart may provide acceptable monitoring. In many cases, however, a continuous record of the fetal heart rate is indicated or is preferred by the patient or her physician. When used for continuous monitoring in labor, an external monitor may not provide a continuous record. Studies confirm that external monitoring yields a more intermittent fetal heart record in labor, especially in the second stage.[2] In the patient with an at-risk fetus, this loss of signal may be unacceptable. In addition, fetal heart monitoring may be more difficult with an external monitor in some categories of patients, such as very obese mothers or those with fetal arrhythmias.

In the past, a fetal electrode was necessary to obtain a valid assessment of fetal heart rate beat-to-beat variability (an important component of the interpretation of the intrapartum fetal heart rate pattern). New criteria no longer include a specific assessment of beat-to-beat variability; rather, they incorporate a combined assessment of short-term and long-term variability. Further, current fetal monitors have improved computerized processing of the Doppler signal from the external monitor (“autocorrelation”), which permits more accurate assessment of the heart rate variability and reduces the need for internal heart rate monitoring.

The electrode is removed at the time of delivery. Earlier electrode removal may be performed prior to cesarean or vacuum delivery or if the electrode ceases to function.

Contraindications

Placement of a fetal electrode is relatively or absolutely contraindicated in the following circumstances:

  • The fetal membranes are intact.

  • Delivery is not planned. The patient is not in labor or labor is to be stopped if possible.

  • Any contraindication to cervical examination, such as placenta previa, is present.

  • The mother declines the procedure.

  • Infectious risks to the fetus (eg, HIV, active herpes) are recognized.

Of note, fetal electrodes may be applied to breech presentations.

 

Periprocedural Care

Equipment

The most common fetal scalp electrode consists of a single ECG electrode in the form of a spiral needle. This is attached to paired wires that extend out of the mother’s vagina and are inserted into a ground plate that is typically placed on the maternal thigh. A cable from the ground plate then transmits the ECG signal to the fetal monitor. For placement, the electrode is placed within an introducer, a tube that protects the mother’s vagina from the needle. A device is available that allows the operator to rotate the electrode from outside the vagina, penetrating the fetal scalp with the needle. See the image below.

Parts of a fetal scalp electrode (elements that re Parts of a fetal scalp electrode (elements that remain after introduction of the electrode are 2, 3 and 11, marked with a star (*) 1: Overall electrode with introducer 2: Electrode hub* 3: Spiral electrode* 4: Knob (used to turn the electrode assembly during application) 5: Sheath (transmits turning motion to the electrode hub) 6: Connection between sheath and hub 7: Tube (protects maternal tissues during electrode introduction) 8: Direction of motion of tube during introduction 9: Direction of rotation to set electrode 10: Direction of motion for removal of introducer after electrode is seated 11: Electrode wires*

Embedding the needle in the fetal scalp retains the electrode in place. Other models of scalp electrodes (eg, clip) have also been used.

Complications

Placement of a fetal spiral electrode rarely may be associated with complications in the mother, the fetus, or the medical practitioner.

Mother

The fetal electrode may lacerate the maternal vagina or cervix during placement or if inadvertently placed on the mother rather than the fetus. In experienced hands, this complication is rare.

The use of internal monitors may also increase the risk to the mother of chorioamnionitis or endometritis, although this is more likely to be associated with internal uterine pressure monitors. A special concern is when a fetal electrode is pulled from the vagina into the operative field at the time of cesarean delivery. Exposure of this type may be reduced by attention to removing the electrode at the time of incision, but some electrodes are difficult to remove; in an emergency, removal of the electrode prior to delivery may not be possible.

Estimating the magnitude of this risk is difficult because mothers undergoing fetal scalp monitoring have various risk factors for infection, especially when followed by cesarean delivery. The incremental risk is likely small. In general, patients delivering after internal monitoring are managed the same as other patients. Those delivering vaginally are observed, whereas prophylactic antibiotic administration is recommended for all patients who undergo cesarean delivery.

Fetus

The fetal electrode may lacerate the fetal scalp.[3] In addition, misplacement of the electrode has resulted in penetration of the fetal eye[4] and use of a fetal scalp electrode has been associated with a fetal cerebrospinal fluid (CSF) leak.[5] Finally, the needle electrode can break, with retention of a portion of the needle in the fetal scalp.[6] These complications are rare, and only case reports appear in the literature.

The placement of a fetal electrode is associated with an increased, although very low, risk of neonatal infection. Newborn scalp abscesses have been described due to Escherichia coli[7] and gonococcus,[8] as well as necrotizing fasciitis of the scalp due to group A streptococcus.[9]

In older literature, placement of a fetal electrode increased the risk of death from neonatal sepsis due to group B streptococcus (GBS); in a study performed before universal GBS screening, the risk was 8 times higher in the electrode group.[10] Placement of a fetal electrode has been associated with an increased risk of fetal transmission of maternal viral agents, including HIV[11] and active genital herpes,[12] and electrode use should be avoided if these infections are present.

Practitioner

The electrode tip may penetrate the glove, and even the hand, of the examiner either at the time of placement or if the electrode becomes dislodged, causing exposure to maternal body fluids. Attention to technique reduces the likelihood of injuries related to electrode placement. Dislodged electrodes should be completely removed if at all possible.

 

Technique

Approach Considerations

Significant debate surrounds the value of fetal heart rate recording in labor. A meta-analysis suggested that performance of continuous fetal heart rate monitoring in labor is associated with a decrease in neonatal seizures, but not a reduction in other newborn morbidities, including cerebral palsy or infant mortality.[13] However, fetal heart rate monitoring in labor is associated with an increased incidence of both cesarean and operative vaginal deliveries. Despite this lack of convincing evidence of efficacy, fetal heart rate monitoring in labor has become the standard of care in most parts of the United States. Efforts to improve efficacy have included establishment of standards for fetal heart rate tracing assessment and intervention.

Numerous refinements of the technique have been proposed in an attempt to improve the predictive power of the test. In the past, continuous fetal tissue pH and fetal O2 saturation have been used for the prediction of fetal status in labor, although neither of these is currently in use. A promising technology is computerized analysis of the fetal ECG waveform (S-T segment analysis).

Some reports suggest that S-T segment analysis is associated with better fetal outcome (less neonatal encephalopathy, fewer infants with severe metabolic acidosis), with a similar operative delivery rate when compared with conventional continuous monitoring in labor.[14, 15] Additionally, another product measures fetal heart ECG via electrode patches placed on the maternal abdomen with close correlation with the direct fetal ECG.[16]

Scalp Lead Placement

Placement of a fetal electrode requires that the fetal membranes are ruptured, and that the cervix is sufficiently dilated to allow insertion of the device. The fetal presentation should be known, and the mother should consent verbally to the procedure. Placement of the electrode is performed as follows (see the image below).

Application of the scalp electrode: after introduc Application of the scalp electrode: after introduction of the system into the maternal vagina, the introducer is placed against the fetal head, over the parietal or occipital bone (inset). Pressure is applied to the electrode, and a rotary motion is used to drive the needle electrode into the fetal scalp. The introducer is then removed, leaving the electrode in place.

See the list below:

  • Counsel the patient about the procedure.

  • Prepare supplies.

  • Apply the leg plate to the maternal thigh.

  • Prepare for sterile vaginal examination (eg, wash hands, don sterile gloves).

  • Insert fingers into the vagina and palpate the fetal scalp. Ensure membranes are ruptured. Some authors have reported using the scalp electrode to rupture the membranes, in cases in which the usual means for membrane rupture were unsuccessful.

  • Ensure fetal position. Choose a location over parietal or occipital bone, away from sutures and other fetal or maternal structures. Application to the fetal buttocks may also be considered if the patient is to attempt breech vaginal delivery.

  • Retract the electrode into the introducer until the needle is not exposed. Insert the introducer into the vagina up to the fetal scalp.

  • Maintaining pressure on the fetal scalp, turn the electrode assembly clockwise. Take care not to elevate the fetal head out of the pelvis (risk of cord prolapse).

  • Disengage the wires from the introducer and remove the introducer assembly. Insert wires into the leg plate.

  • Document procedure and result (fetal heart rate pattern).

  • Electrode removal requires that the electrode be rotated counterclockwise so as to safely detach the needle from the fetal scalp; this is accomplished by turning the wires in the desired direction.

At times, removing the electrode prior to delivery of the fetus is difficult to impossible; often this is due to tangling of the electrode in fetal hair. In these cases, the electrode wires may be cut off short and removal of the electrode left until after delivery.

Attempting to detach the electrode by pulling is not appropriate because this may lacerate the fetal scalp.