Continuous intrapartum monitoring of fetal scalp pH NIELS
H.
FRANK
LAUERSEN,
C.
M.D.
MILLER,
M.D.
RICHARD
H.
M.D.
Los Angeles,
Ca I{fornici
PAUL,
Forty patients were monitored intrapartum with a continuous fetal scalp tissue pH electrode in the mean time of 2.39 hours. The monitoring records were considered “accurate” with good correlation to the intermittent fetal scalp capillary pH values in 76.9 per cent. The correlation coefficient was 0.74. The “accuracy” improved in the latter 23 cases to 87 per cent with a correlation coefficient of 0.82. This improvement was probably due to modification of the application technique, as well as to a new calibration method at 37 degrees. Continuous fetal scalp pH monitoring was clinically useful in 65 per cent, it was partially useful in 20 per cent, but of no value in 15 per cent of the patients studied. There were no apparent maternal complications with the use of this technique and 38 of the infants had no sequelae. Two infants had complications: one developed inflammation of the electrode site. This was treated with antibiotics. One electrode broke during the application and a fragment of the electrode tip remained in the fetal scalp. All the infants were grossly normal and there was a good correlation between the continuous pH readings and the immediate neonatal outcome. (AM. J. OBSTET. GYNECOL. 133:44, 1979.)
IN THE PAST two decades there has been a sharp decline in the perinatal mortality rate. This is partially due to the increased use of electronic fetal heart rate (FHR) monitoring. One of the first reported successful uses of continuous biophysical monitoring of the fetal heart rate was reported in 1957 by Hon.’ The same year Southern’ demonstrated some correlation between fetal anoxia and changes in the fetal electrocardiogram (ECG). Subsequently, Hon3 described the use of electronic fetal heart patterns as a method of diagnosing fetal distress. The sophistication of electronic FHR monitoring has reached such a level that today it has become an extremely important tool in detecting fetal distress. It was realized that the FHR was not always able to accurately indicate the intrauterine condition of the fetus. Saling4 claimed in 1962 that reliable information of fetal physiology could be acquired by obtaining intermittent capillary blood samples from rhe From the Division q/ Matenaal-Fetal Medicine, Department of Obstetrics and Gynecologyl, Los 14ngele.c County-University of Southern Californuz Medical Center. Received
jar
publication
Reutied
April
17,
.4ccepted
.4pril
Reprint requests: Hospital-Cornell New York, New
44
March
13, 1978.
1978.
19,
1978. Dr.
NieO
Medical York
10021.
H. Lauerxen, Center, 1300
New York York Ave.,
presenting part of the fetus. He found that severe disturbances affecting the fetus were associated with low pH values, presumably as a result of fetal hypoxia with subsequent anaerobic metabolism producing lactic acidosis. These observations were supported by Beard and Morris.” Bretscher and Saling’ have reported normal fetal scalp pH values to be above 7.25. Biochemical fetal monitoring during labor has become an integrated part of evaluation of the intrauterine environment. Quilligan and co-workers’-” have correlated normal and abnormal FHR patterns during labor with umbilical cord blood gases obtained immediately post partum. Kubli and associates’” have conducted an extensive investigation of the correlation between various FHR patterns and pH scalp samplings during labor. These investigators found good correlation between severe FHR decelerations and fetal blood pH samples. A major disadvantage with fetal scalp evaluations is that intermittent scalp capillary samples are indicated in order to correctly manage a patient. Saling” believed that at least two samples were needed in order to correctly evaluate the fetal environment. The development of a continuous pH electrode offers the advantage that it will provide the physician with continuous acid-base information. Stamm’2 reported a significant correlation between tissue pH and intermittent capillary blood pH on ten newborn babies monitored with a continuous subcutaneous pH elec-
OOO’L-9978/79/0100~~+07$00.7010
0
1979
‘T-he (:. V. Mosb\
Co.
Volume Number
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trode. This same type of electrode was subsequently tested in animal models at Cornell Medical Center (Lauersen, Hochberg, and George, unpublished data). The initial results with this electrode demonstrated poor correlations to blood pH and thus the system was modified at the laboratory of Roche Medical Electronics Inc., New Jersey. The new pH system demonstrated a correlation coefficient of 0.85 between the continuous tissue pH electrode and blood pH.13 The potential use of this electrode for fetal scalp ussue pH measurements appeared promising but application to the fetal scalp required technical improvements. When these adaptations were carried out a study was undertaken to evaluate the clinical usefulness of this electrode during labor and compare the tissue pH and intermittent fetal scalp blood pH determinations.
Materials and methods Continuous fetal scalp pH monitoring was performed during active labor in 40 patients at the Women’s Hospital, Los Angeles County-University of Southern California Medical Center. The patient population included 29 primiparous and 11 parous patients. The mean age was 24% years and the gestational ages ranged from 36 to 45 weeks’ with a mean of 40% weeks. Thirty-six of the 40 patients undergoing intrapartum monitoring had a number of risk factors as indicated in Table I. In the four patients with no obvious maternal risk factors, the indication for FHR monitoring was the presence of fetal risk factors. All patients were monitored with direct FHR methods in the fetal intensive care unit. Fetal scalp blood sampling was performed only when it was felt this was indicated by the presence of late decelerations, variable decelerations, or other FHR abnormalities. An informed consent was obtained in all patients regarding the use of the continuous pH electrode. The patient was then placed in the stirrups of the labor bed and an amnioscope was inserted into the vagina. Once the fetal scalp was visualized, the indicated fetal scalp blood sample was obtained in a routine manner. A double helix spiral electrode designed to obtain the fetal ECG signal, provide readings, and to hold the fetal scalp pH electrode in the subcutaneous tissue was then applied (Fig. 1). After the spiral electrode was placed, a small incision with a scalp blade was made in the fetal scalp through a central opening in the spiral electrode. The tissue pH electrode, with the aid of a special tool, was passed through the center of the spiral electrode and the electrode tip was inserted into the small scalp incision to a depth of approximately 2 mm. The insulated
Continuous
monitoring
of fetal scalp
pH
45
REFERENCE DOUBLE SPIRAL ELECTRODE
SKIN SURFACE
PM SENSITIVE
SURFACE
-
SUBCUTANEOUS
TISSUE
Fig. 1. Illustration of the location of the fetal scalp electrode. The electrode is located in the center of a double spiral electrode. The tip of the glass electrode is the pH-sensitive part. The tip is seen located in the subcutaneous tissue. Table
I Risk factors
I
No.
Maternal
Pre-eclampsia Post dates Post maturity Chronic hypertension Rh immunization Falling estriols Intrauterine growth retardation Amniotitis None Total
I4 x 2 1 3 2 : 40
Fetal
Later decelerations Variable decelerations Bradycardia Loss of variability Meconium Total
7 14 3 IO 6 40
cables from both the spiral electrode and the tissue pH electrode were then attached to a fetal pH and heart rate monitor.* The fetal ECG signals and the uterine contractions were displayed in the usual fashion, on stripchart paper. The continuous fetal scalp pH was recorded on the same paper as a vertical bar printed every 15 seconds. The top of this bar indicates the tissue pH. There was, furthermore, a digital CRT display of the tissue pH. Intermittent fetal scalp capillary blood pH was subsequently obtained approximately every hour throughout the monitoring period. Umbilical venous and arterial cord blood samples were obtained at delivery and immediately sent for pH analysis. Inter*Roche Model 2 110 Tissue pH Monitor attached to a Roche Fetasonde Fetal Monitor 2106. Roche Medical Electronics Inc., Cranbury. New Jersey.
46
Lauersen,
Tissue
Miller,
and Paul
pti
7.1
7.2
Scalp Capillary
7.3 Blood
7.4
pH
Fig. 2. Scattergram showing the r-eIationship between continuous fetal scalp tissue pH and intermittent scalp capillary blood pH values. Table
II.
Accuracy
of
the
co11tinuous
fetal scalp tissue pH electrode
RWWd c~lassificnlion Acctlt-dtc
Marginal Poor Llnobtainable ‘lotal
mittent scalp pH determinations were compared with the continuous pH values. Only samples obtained within 20 minutes prior to the initial application of the continuous electrode or simultaneously during the monitoring were used. The final c-ontinuous pH value obtained prior to the removal of the electrode was (ompared to the umbilical
cord blood pH values only when no more than 20 minutes had elapsed prior to delivery. The continuous pH record was defined as “accurate” if the values were within 0.05 pH units of the intermittent pH values. It was considered “marginal” if the values were between 0.05 pH units and 0.10 pH units of the fetal scalp blood pH values. It was “poor” if the
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Continuous
monitoring
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scalp
pH
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Table III. Clinical
usefulness of the continuous fetal scalp tissue pH electrode
Fig. 3. Continuous pH monitor. The pH monitoring
unit is on the top of the right. The calibration unit with a 37 degree heating block is on top left. The pH electrode is placed in the calibration chamber. The Roche Fetasonde 2106 fetal ECG monitor is seen below. The continuous pH values are recorded simultaneously with the fetal ECG and uterine contractions on the stripchart. values deviated by more than 0.10 pH units. The continuous pH records were defined as “clinically useful” if accurate readings could be maintained throughout the monitoring period. The records were defined as partially useful if they only provided information during a part of the study or if the tissue pH drifted to very low values. Failure was defined when information could only be obtained for less than ten minutes. The infants’ Apgar scores were evaluated at the time of delivery and their scalps examined for possible lacerations or other injury. The electrode site was inspected daily to identify potential complications, such as infection.
Results Forty patients were monitored continuously with the fetal scalp pH electrode. The mean length of monitoring was 2.39 hours, ranging from 0.10 to 6.12 hours. In
Usefulness
No. of patients
Per cent
Clinically useful Partially useful Not useful Total
26 8 - 6 40
65 20 15
76.9 per cent of the patients, the results were classified as “accurate,” demonstrating a good correlation with the intermittent fetal scalp pH samplings throughout labor. There were “marginal” correlations in 10.3 per cent of the cases and “poor” correlations in the remaining 12.8 per cent of the patients studied (Table II). The correlation coefficient was 0.74 with a highly significant p value (Fig. 2). Some of the patients had an initial good correlation between the continuous pH values and the intermittent blood samplings, but the electrode loosened, with resulting low pH readings. This occurred more frequently in the early phase of the study, but as the technical skills of the operators improved, better applications were achieved. The “accuracy” of the continuous pH readings, which was 62.5 per cent in the first 17 cases, improved considerably in the latter 23 patients to 87 per cent with a correlation coefficient of 0.82. The improved results with the continuous scalp tissue pH electrode occurred simultaneously with the development of an improved calibration technique at 37 degrees rather than room temperature (Fig. 3). The application of the continuous pH electrode gave most reliable results when the electrode was applied to a thicker scalp area so that the electrode could be placed firmly perpendicular to the scalp. In the cases where the electrode was well applied, reliable pH values could be achieved even throughout the second stage of labor. The electrode was removed immediately before delivery without difficulty in most of the patients. In eight cases, the electrode was left attached to the fetal scalp throughout delivery, providing continuous pH readings for several minutes postpartum with good correlation to the neonatal state as judged by Apgar scores. One baby was monitored continuously for 45 minutes postnatally. Continuous fetal scalp pH monitoring was considered clinically useful in 65 per cent of the cases studied. It was partially useful in 20 per cent and of no value in 15 per cent (Table III). Thirty-five patients delivered vaginally, 24 deliveries were spontaneous, four were low forceps, and seven were delivered by vacuum extraction. Five of the patients were delivered by cesarean section for failure to
48
Lauersen, Miller, and Paul
Fig. 4. Illustration of a typical simultaneous recording of fetal scalp tissue pH, fetal heart rate, and uterine contractions. The upper tracing indicates the FHR; the lower tracing displays uterine contractions recorded in the usual fashion. The continuous scalp pH is recorded by a vertical bar appearmg every 15 seconds. The top of this bar indicates pH value. The paper speed is 3 cm. petminute. There was a good correlation between the intermittent fetal scalp pH values and the cotstinuous pH measurements. Note the relatively slow drop in the continuous pH values in spite of the increased severity of the variable decelerations. A 2,200 Cm. female infant, Apgar score 7 at one minute, 9 at five minutes, with signs of IUGR was delivered 15 minutes after this recording. The decrease in the tissue pH on the upper tracing was due to dislodgement of the electrode during scalp sampling. The comparisons were done one minute before the samplings because of the possibility of dislodgement during the vaginal manipulation. progress and suspected CPD. All the infants were grossly normal and there was a good correlation between the final continuous pH reading and immediate neonatal outcome. Six infants had a one-minute Apgar score of 6 or less, and 34 babies were born with a one-minute Apgar score of 7 or higher. All infants had an Apgar score of 7 or higher at five minutes.
Complications There wet-e no apparent maternal complications with the use of this technique. The majority of the infants, 38, had no more scalp trauma from the continuous pH electrode than from the intermittent scalp blood sampling incisions. As a matter of fact, the multiple intermittent incision marks were often much more
Continuous monitoring of fetal scalp pl-l 49
evident than the pH electrode application sites. In one patient in whom amnionitis existed during labor, the electrode site as well as the intermittent scalp sampling sites became indurated with signs of inflammation. This neonate was on prophylactic antibiotics, the inflammation improved, and the baby was discharged without sequelae. The electrode tip broke during application in one patient. The tip was subsequently, on x-ray, localized in the subcutaneous tissue but it was not removed, since there were no signs of irritation from the small glass fragment and it was judged difficult to retrieve it without possible injury to the infant.
Comment The clinical benefit of continuous monitoring of fetal scalp tissue pH lies in its potential to provide a more concise evaluation of the status of the fetus during labor. We found that the application of the continuous fetal scalp pH electrode required some skill, but with experience, an improved technique of application and calibration at 37 degrees, a correlation coefficient between the continuous pH readings, and the intermittent fetal scalp pH values of 0.82 was obtained. This substantiates the findings of Stamm and co-workers’2 in newborn infants as well as resultsI in the animal model. Our findings also correlated with the results reported by Sturbois and associates’4 in their study of 42 patients during labor. However, Sturbois’ group was only able to apply the electrode in 60 per cent of the patients, while in this study, using new techniques, the electrode was applied to all patients, although successful readings were not always obtained. The presently used technique of measuring intermittent fetal scalp blood pH has several limitations and disadvantages. The method is somewhat difficult and a small incision in the fetal scalp has to be made in order to obtain enough blood to carry out the pH measurements.‘“. lr,. “These values can be incorrect if there
REFERENCES
1. Hon, E. H.: Instrumentation of fetal electrocardiography, Science 125: 553, 1957. 2. Southern, E. M.: Fetal anoxia and its possible relation to changes in the prenatal fetal electrocardiograms, A~I. 1. OBSTiT.GyNE&L.
73: 233,
1957.
-
3. Hon. E. H.: The electronic evaluation of the fetal heart rate, AM. J. OBSTET. GYNECOL. 75: 1215, 1958. 4. Saling, E.: A new method for examination of the child during labor. Introduction, technique and principles, Arch. Gynaekol. 197: 108, 1962. 5. Beard, R. W., and Morris, E. D.: Foetal and maternal acid-base balance during normal labour, Br. J. Obstet. Gvnaecol. 72: 496, 1965. 6. Bietscher, J., and Saling, E.: pH values in the human fetus during labor, AM. J. OBSTET. CYNECOL. 97: 906, 1967.
are any air bubbles in the capillary tubes or if the measurements are not carried out immediately.17 It is furthermore necessary to obtain several fetal capillary samples in order to correctly manage a patient.“. lx The validity of the scalp blood sample analysis depends on the laboratory in which the analysis is being performed and the pH values can vary between 0.02 and 0.06 pH units in serially obtained capillary blood samplings. “9 I9 The average capillary blood pH value in this study was 0.026 pH units higher than the average tissue pH (Fig. 2). which is clinically quite acceptable. Continuous fetal scalp tissue pH monitoring was a useful clinical adjunct to fetal heart rate monitoring in several instances in which severe decelerations occurred. The continuous pH indicated that the infant was not in distress and there appeared to be no need for emergency delivery (Fig. 4). The continuous pH monitoring was even beneficial as an indicator of the trend in the changes of fetal pH in a few cases where the accuracy was only marginal. Continuous pH monitoring was often useful during the second stage of labor when a normal pH value could forestall an operative delivery for suspected fetal distress as-judged by abnormal FHR tracing. Although, in the last 23 patients, we found a high level of accuracy and technically acceptable records in 90 per cent of the patients, the practical application of the continuous fetal scalp pH still demands technical skill in order to obtain uniform and clinically valid results. Several improvements in calibration and simplification of application techniques are presently being undertaken. These modifications may, in the future, promise to make continuous fetal scalp monitoring an integrated part of modern high-risk monitoring. We wish to extend our gratitude to the nursing staff at the Fetal Intensive Care Unit as well as the interns and residents who assisted us during this investigation.
7. Quilligan, E. J., Katigbak, E., Nowacek, C., and Czarrecki, N.: Correlation of fetal heart rate patterns and blood gas values. I. Normal heart rate values, AM. J. OBSTET. GYNECOL. 90: 1343, 1964. 8. Quilligan, E. J., Katigbak, E., and Hofschild, J.: Correlation of fetal heart rate patterns and blood gas values. Il. Bradycardia, AM. J. OBSTET. GYNECOL. 91: 1123, 1965. 9. Quilligan, E. J., and Katigbak, E.: Correlation of fetal heart rate and acid-base balance at birth. Ill. Tachycardia, Obstet. Gynecol. 25: 371, 1965. 10. Kubli, F. W., Hon, E. H., Khazin, A. F., and Takemura, H.: Observations on heart rate and pH in the human fetus during labor, AM. J. OBSTET. GYNECOL. 104: 1190, 1969. 11.
Saling, E.: Fetal and neonatal hypoxia, London, Edward Arnold (Publishers) Ltd.
12. Stamm,
O., Latscha,
U., Janecek,
P.. and
Campana,
1968, A.:
50
13.
14.
15. 16.
Lauersen,
Miller,
Development cutaneous
pH
and Paul
of a special electrode for continuous submeasurement in the infant scalp, AM. J. OBSTET. G~NECOL. 124: 193, 1976. Hochberg, H. M., Lauersen, N. H., George, M. E. D., and Van Poznak, A.: Evalu%ion of continuous monitoring of tissue pH in cats, AM. J. OBSTET. GYNECOL. 131: 770. 1978. Sturbois. G., Uzan. S.. Ratten, D., Breart, G., and Sureau. C.: Continuous subcutaneous pH measurement in human fetuses, AM. J. OBSTET. GYNECOL. 128: 901, 1977. Kubli, F.: Influence of abor on fetal acid-base balance, Clin. Obstet. Gynecol. I \l: 168, 1968. Galloway, R. K.: Clinical experience with fetal blood pH
Information Most of
for
measurement in fetal distress, Br. J. Obstet. Gynawol. 77: 587, 1970. 17. Zemickow, K.: Der Luftkontakte influss auf Mikroblutproben des Feten (Effect of air contact on microscopic blood specimens of the fetus), Gynaecologia 161: 277, 1968. 18. Lumley, J., Potter, M.. Newman, W., Talbot, J.. Wakefield. E., and Wood, C.: The unreliability of a single estimation of fetal scalp blood pH, J. Lab. Chn. Med. 77: 535, 1971. 19. Lumley. J., McKinnon, L., and Wood. C.: Lack of agreement on normal values for fetal scalp blood. Br. J. Obstet. Gynaecol. 78: 13, 1971.
authors
the provisions of the Copyright Act of 1976 became effective on Januaq 1, 1978. Therefore, all manuscripts must be accompanied by the following written statement, signed by one author: “The undersigned author transfers all copyright ownership of the manuscript (title of article) to The C. V. Mosby Company in the event the work is published. The undersigned author warrants that the article is original, is not under consideration by another journal, and has not been previously published. I sign for and accept responsibility for releasing this material on behalf of any and all co-authors.” Authors will be consulted, when possible, regarding republication of their material.