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Simultaneous measurement of fetal tissue pH and transcutaneous pO2 during labor
Europ. J. Ohsrer. Gynec. reprod. Biol., 17 (1984) 69-76 Elsevier
69
UO ooo89
Simultaneous measurement of fetal tissue pH and transcutaneous p 0, during labor Clarel Antoine,
Bruce K. Young and Frank Silverman
The Diwaon o/Maternal- Feral Uedrcine, Departmen! of Obsrerrics and Gynecolog): New York tinroersrr~ School of Medicine and Bellevue Hospital, New York. NY. U.S. A.
ANTOINE, C.. YOUNG, B.K. and SILVERMAN, F. (1984): Simultaneous measurement of fetal tissue pH and transcutaneous ~0, during labor. Europ. J. Obsrer. Gynec. reprod Biol., 17/2.3. 69-76. Simultaneous measurement of fetal heart rate (FHR). uterine contractions (UC), continuous fetal tissue pH (TpH) and transcutaneous p0, (tcp0,) was attempted in 40 high-risk parturients monitored for an average duration of 117+ 74 min. There were only two failures (9%) in the last 23 cases, with satisfactory recording of all parameters in 78% of the total. At present, the feasibility of simultaneous biochemical monitoring is limited to the active phase of labor. Fetal scalp and umbilical arterial blood pH and ~0, were obtained as well. The biochemical data showed a good correlation between tcp0,. scalp capillary pG, and umbilical artery ~0, (P < 0.02). The correlation was not significant between similar pH comparisons, although an average difference of 0.04 pH units was observed between the final TpH and umbilical artery pH. Both fetal TpH and tcp0, fell progressively during labor. Preliminary findings comparing TpH. tcp0, and FHR suggest that changes in tcp0, rapidly reflect changing maternal and fetal conditions, while TpH responds more slowly and less sensitively. fetal heart rate; acid-base
balance;
labor
Introduction
Abnormal fetal heart rate (FHR) patterns during labor are thought to be associated with fetal acidosis and hypoxia. However, the specific relationships remain ill-defined despite extensive research. Intermittent fetal scalp capillary blood sampling (FSB) is now accepted in the evaluation of a compromised fetus. One of the major drawbacks of FSH is that the information derived describes the status of the fetus at that time. The procedure must be repeated for continued assessment of the fetus, usually two or three times during the course of labor. The miniature electrodes developed by Stamm et al. (1976) for pH and Huch et al. (1969) for ~0, were adapted to continuous evaluation of the fetus in labor. Continuous monitoring of tissue pH (TpH) and transcutaneous p02 (tcp0,) have been used independently to assess the high-risk human fetus (Huch et al., 1977; Sturbois et al., 1977). Attempts to study simultaneously both TpH and tcp0, in the same human fetus may elucidate the applicability of each technique, and may clarify the relationship of OO28-2243/84/$03.00
d: 1984 Elsevier Science Publishers
B.V.
70
these parameters to FSB, FHR patterns, neonatal outcome, and to each other (Kaneoka et al., 1979; Weber and Secher, 1981). The present study was initiated to examine continuous monitoring of fetal TpH and tcp0, simultaneously in the same fetus. Materials and methods Forty parturients at Bellevue Hospital had electrodes attached to the fetal scalp for simultaneous continuous biochemical monitoring. All of the subjects were at term with a cephalic presentation. They also had one or more high-risk criteria before labor or developed an abnormal fetal monitoring record during labor. Informed consent was obtained from every patient. The pH and ~0, electrodes and monitors were supplied by Roche Medical Electronics (Roche-Kontron, Cranbury, NJ). Before the experiment, the TpH microelectrode was sterilized, prepared and calibrated with standard buffers of 7.00 and 7.40 at 38’C. Similarly, the fetal ~0, sensor was prepared and calibrated to the ~0, of the humidified ambient air, and to zero using 100% nitrogen. In general, at least 1 h of stabilization elapsed between calibrations and placement of the electrodes. The patient was placed in a dorsolithotomy position. The cervix was at least 4 cm dilated, membranes were ruptured, and the vertex was engaged for the application of either electrode alone. A modified amnioscope and special tools were used to insert the pH electrode through the center of a button electrode into the fetal scalp. This system, connected to a fetal monitor, provides continuous FHR and TpH measurements every 15 s, as described previously (Young et al., 1978; Lauersen et al., 1979). Half an hour was allowed for stabilization of the TpH electrode in vivo. At 7 cm or more of cervical dilatation, after application of the pH electrode, the membrane-covered ~0, sensor was fixed to the unshaven fetal scalp using a tissue glue. This sensor is identical to the neonatal version (Roche Oxymonitor, Kontron-Roche Medical Electronics, Cranbury, NJ) in current clinical use, except for the means of fixation and the right-angle attachment of the electronic cable to the electrode. In an effort to improve attachment and avoid shaving the fetal scalp, the ~0, sensor was fitted with a plastic ring containing a circumferential well in which the tissue glue was placed. This modification permitted an airtight attachment of the electrode without shaving the fetal scalp, except for the hairiest babies. Most studies have shaven the fetal scalp, but others have successfully avoided this manipulation (Lofgren and Jacobson, 1977; Weber and Secher, 1979; Lofgren, 1981). The ~0, electrode contains a heating system and two thermistors which regulate and maintain the skin temperature at 43-44’C, and was stabilized over 15-40 min after application, in order to obtain the maximum vasodilation necessary to its proper reading. All parameters were recorded on a special monitor (Fig. 1). Simultaneous monitoring of TpH and tcp0, was carried out in all cases as close to delivery as possible, as well as into neonatal life in 7 instances. The electrodes were calibrated both at the start and at the end of each experiment to evaluate for drift. Apgar score was assigned by a pediatrician. The infant scalp routinely was examined at birth and cleansed with a Povidone iodine solution. This was repeated daily in the nursery.
Fig. 1. Schematic drawing of a spiral ECG electrode, TpH, and tcp0, are connected through separate cables to their respective modules. recorded on a multichannel monitor.
electrodes on the fetal scalp. These Fetal and maternal parameters are
Simultaneous fetal capillary scalp and maternal venous samples were obtained shortly before placement of each electrode. These were repeated as often as clinically indicated and immediately analyzed for pH and ~0, by means of a microanalyzer (Corning 165, Corning, KY). Umbilical arterial blood was collected at birth for similar studies. Fetal scalp capillary and umbilical blood gases were compared with the continuous data. Because of the rapid variation in tcpO,, these data were selected at a stable area in the continuous recording, taking the tcp0, averaged over 5 min of continuous readings before the scalp blood sample. This was necessary due to the rapid fluctuation of the tcp02 and the effect of the sampling procedure. Since the TpH fluctuates over several minutes, and not as rapidly as the tcpO,, the last TpH reading before the blood sample was utilized for comparison. The continuous values immediately before sampling thus were chosen primarily because of the effect of the sampling procedure itself on the continuous tcp0, and TpH readings. Statistical analysis was done by computing the mean, standard deviation and correlation coefficient. A P value less than 0.05 was considered significant. Results
Forty high-risk patients underwent application of the electrodes for continuous fetal TpH and tcp0, monitoring. Thirty-one of these patients (78%) were success-
12
fully monitored for a duration of 30 to 220 min. The average length of monitoring was 117 k 74 min. The 9 failed attempts (22%) were the result of displacement or dislodgement of the pH electrode during the application of the p0, electrodes (3 cases), hairy fetal scalp, and/or insufficient tissue glue with air contamination of the p0, sensor (6 cases). Most of the 9 failures were attributed to inexperience as there were only 2 failures (9%) in the last 23 cases. Values of TpH between 7.10 and 7.38, and of tcp0, between 8 and 30 mmHg at initial reading after stabilization were considered evidence of good application. In 25 experiments, the electrodes remained attached to the fetal scalp until at least 30 min before delivery. Most of these cases demonstrated periods of poor recording during parts of the second stage of labor. Despite this, seven of these cases were monitored successfully with one of the two electrodes beyond the second stage for 5 to 30 min after birth. These latter cases verified continued normal functioning of the electrodes in the newborn. The effect of mechanical displacement during labor was noted as an abrupt increase of TpH, and was usually observed during crowning of the fetal head or within 1 min of delivery. Similarly, in one of the successfully monitored neonatal tcp0, cases, the scalp tcp0, increased from 8 mmHg at birth to 20 mmHg within 1 min. reaching 72 mmHg at 20 min of life. A neonatal p0, sensor which had been placed on the chest at birth read 88 mmHg at this time. Six of the successful applications were interrupted at various times before delivery because one or both electrodes were dislodged during pelvic examinations, fetal head rotation, in preparation for abdominal delivery, or other necessary manipulations in the clinical care of the patient. Drift for the TpH ranged between 0.01 and 0.03 pH units per hour. The tcp0, drift was difficult to determine in most cases due to the poor condition of the electrode when detached from the fetal or neonatal scalp. However, despite attached fetal hair and glue, drift was l-2 mmHg per hour in the cases where end calibration was obtained. Thus, both TpH and tcp0, showed a downward drift during use. Nevertheless, the degree of drift was not physiologically significant for both pH and PO,. In all but 4 of the cases, the tcp0, was at a physiological level within 5 min while the electrode was held against the fetal scalp to permit the glue to adhere. As pressure is released, a transient rise of tcp0, is seen, usually followed by a rapid reequilibration and stabilization at a physiological value over the next 15-20 min (Fig. 2). Subsequently, the readings obtained were used for’ comparison with the blood values. A decline in fetal cutaneous p0, corresponding to the onset of uterine contractions most likely represents a localized blood flow phenomenon. This is observed in 37% of the cases (Fig. 3). The TpH remained unchanged during uterine contractions which were not associated with FHR changes. Thus, tcp0, sometimes fell in response to uterine contractions, while TpH did not. The biochemical data collected from 20 cases are summarized in Table I. The mean fetal scalp pH before the application of the p0, electrode was 7.31 with a corresponding mean TpH of 7.23. The mean final tissue pH was 7.22, 0.04 pH units lower than the pH of the umbilical artery blood, 7.26. This corresponds with our previous observations, in which TpH averages 0.04 units lower than blood pH (Young et al., 1978). The TpH and blood pH were poorly correlated. The average tcp0, of 20.7 mmHg correlated with the FSB p0, of 21.3. r = 0.69. P < 0.01. The
Fig. 2. Application of fetal transcutaneous ~0, (FCpO,) electrode. Note that the gradual decline of FCpO, during the application is followed by a temporary rise (arrow). Prompt return and stabilization to physiological values follow. The disturbances in fetal heart rate (FHR) and tissue pH (pH) readings during FCpO, application are only transient. Note that pH readings represented by vertical bars every 15 s are superimposed on uterine contractions (UC). The paper speed is 4 cm/mm. The scale is expanded to show the range of tcp0, in maternal measurements as well as fetal.
umbilical artery ~0, of 16.6 correlated with the final tcp0, mean of 15.0 mmHg, r = 0.55, P < 0.02. The 1-min Apgar score was less than 7 in five of the 40 neonates. The 5-min score was at least 8 in all but two. Eight infants were born by cesarean section. There was no maternal morbidity related to the monitoring. A fetal scalp laceration occurred during the first few trials as a result of an overzealous attempt to replace the pH electrode. This infant was discharged in good condition on the 7th day of life.
Fig. 3. Falling FCpO, with UC, with no relationship configuration. From top to bottom are the FCpOa, on fetal TpH readings. The latter are represented cm/min.
to FHR. The decline in fetal tcp0, parallels the UC the FHR and the uterine contractions superimposed by vertical bars every 15 s. The paper speed is 4
TABLE I Comparison of TpH, tcpOz with scalp capillary and umbilical artery gases Initial
Mean S.D.
FSB pH
TPH
TPH
UA
7.31 *0.05
7.23 f 0.05
7.22 f 0.06
1.26 f 0.06
0.24 NS
;
Mean S.D. rp
Final
0.36 NS
FSB ~0,
tcIJo2
tcpo,
UA
21.3 * 5.1
20.7 k4.8
15 55.6
16.6 + 5.9
0.69 < 0.01
0.55 0.02 > P > 0.01
Discussion We have been able to monitor continuous fetal pH and ~0, simultaneously during the active phase of labor, An improved success rate was obtained with experience, as there were only two failures in the last 23 cases. An attempt to pursue the continuous monitoring of both pH and ~0, into neonatal life was partially successful in seven cases, as only one of the two electrodes remained functioning. These cases demonstrated the effect of mechanical factors on TpH and tcpOz recordings, as an abrupt increase was observed when these electrodes were no longer compressed by changes in fetal position. These factors reduce the validity of the electrodes when compared to scalp capillary and umbilical artery data. Moreover, the lack of correlation between blood and TpH in these data make the absolute pH values less reliable. Despite this, the TpH and blood pH changes were in the same direction, showing a parallel decline through labor even when the values did not correspond. A recent study from our laboratory has confirmed the comparative performance of the TpH electrode versus a standard pH analyzer in vitro (Antoine et al., 1981). The observations in the present study show that discrepancies among different investigators most likely reflect mechanical difficulties with stabilization and fixation of the pH electrode, as well as differences between blood and tissue fluid. In this study, the poor correlation between scalp capillary pH and TpH reflect the mechanical problems of fixation of the TpH electrode, the wide variation in both FSB and TpH values, and the effects of head compression (O’Connor et al., 1979) in a small sample for statistical evaluation. An average difference of 0.04 units was observed between the final TpH and the pH of the umbilical artery, in agreement with previously published data (Young et al., 1978). The TpH fluctuates about 0.01 pH units over the interval from one contraction to the next. It does not vary or goes up about 0.01 pH units with contractions in the absence of FHR changes. It may be
75
useful in assessing the trend of pH changes in the patients studied. While the fetal ~0, response may be closely dependent on the maternal state of oxygenation, uterine contractions and FHR changes may be important influences. The present study shows that a fall in fetal tcp0, is frequently seen in response to uterine contractions, though not always. This may represent fetal hypoxemia or a localized blood flow phenomenon. Effects of head compression on fetal scalp blood flow (O’Connor and Hytten, 1979) may alter the tcp0, by changing the blood flow under the electrode. The importance of local blood flow under these electrodes has been emphasized by recent work from our own laboratory in studies on rabbits (Silverman and Young, 1983). In addition, fetal stress and catecholamine release may further affect local blood flow, reducing tcp0, measurements unrelated to the blood ~0, level (Jensen et al., 1982). Despite these caveats. good correlation was found between tcpOz and scalp capillary ~0, (r = 0.69. P -c0.01). and umbilical artery ~0, (r = 0.55, P < 0.02). Both the fetal TpH and tcp0, fall progressively during labor. The tcp0, changes rapidly in response to various maternal and fetal conditions, while TpH responds more slowly and less sensitively. TpH most likely is a reflection of the overall acid-base status of the fetus rather than its oxygenation, while tcp0, reflects both blood flow and ~0, under the electrode. Thus, the two measurements are assessing different phenomena when functioning optimally. Both continuous TpH and tcp0, will reflect the pathophysiology of FHR patterns as well (Huch et al., 1977: Kaneoka et al., 1979; Young et al., 1979). However, these effects must be gauged against the background of the alterations of tcp0, and TpH caused by other factors. The results of this study demonstrate that it is technically possible to monitor simultaneously TpH, tcpO,, FHR and uterine contractions. Further refinement of both biochemical electrodes might lead to better knowledge of fetal physiology. At present, the vagaries of the clinical situation may alter the data generated by the electrodes too much to make them reliable indicators of fetal distress. Further studies are necessary to assess the influence of maternal and mechanical factors in the interpretation of these data, in order to describe accurately the significance of pH and ~0, changes in the fetus. References Antoine.
C., Silverman,
F. and Young,
B.K.
(1981):
A comparison
of tissue pH
monitoring
with
a
standard blood pH analyzer. Clin. Chem., 27, 2070-2071. Huch.
A., Huch,
R. and Lubbers,
auf der Kopfhaut
D.W.
des Neugeborenen
on the scalp of the newborn).
(1969):
Quantitative
(Quantitative
Arch. Gynak.,
Continuous
oxygen tension during labour. Brit. 1. Obstet. Gynaec., W. and Kastendieck,
E. (1982):
ments in the sheep fetus and catecholamine Annual Kaneoka,
Meeting.
February
N.H..
Miller,
of the oxygen pressure
transcutaneous
monitoring
Shock indication
1982, p. 31. San Antonio. K. (1979):
of fetal
Suppl. No. 1, 84. l-39. by transcutaneous
release. Society of Perinatal Obstetricians,
T.. Aso. M., Qzono, H. and Shirakawa,
pregnancies. J. perinat. Lauersen,
4-7,
Sauerstoffdtuckmessung
measurement
207, 443-451.
Huch, A., Huch, R., Schneider, H. and Rooth, G. (1977): Jensen, A., Kunzel,
polarographische
polarographic
p0,
measure-
Abstract
Book,
Texas. Multiphasic
fetal monitoring
in the high-risk
Med., 7, 291-301.
F.C. and Paul, R.H.
pH. Amer. J. Obstet. Gynec..
133. 44-50.
(1979):
Continuous
intrapartum
monitoring
of fetal scalp
Lofgren, 0. and Jacobson, L. (1977): Monitoring of transcutaneous pOr in the fetus and mother during normal labor. J. perinat. Med., 5, 252-259. Lofgren, 0. (1981): Continuous transcutaneous oxygen monitoring in fetal surveillance during labor. Amer. J. Obstet. Gynec., 141, 729-735. O’Connor, M.C. and Hytten, F.E. (1979): Measurement of fetal transcutaneous oxygen tension. Problems and potential. Brit. J. Obstet. Gynaec., 86, 948-953. O’Connor, MC., Hytten, F.E. and Zanelli, G.D. (1979): Is the fetus ‘scalped’ in labor? Lancet, ii, 947-948. Silverman, F. and Young, B.K. (1983). Effects of temperature on arterial and cutaneousp0, in the rabbit. Gynecol obstet. Invest., 15, 283-290. Stamm, 0.. Latscha, U., Janecek, P. and Campana, A. (1976): Development of a special electrode for continuous subcutaneous pH measurement in the infant scalp. Amer. J. Obstet. Gynec., 124,193-195. Sturbois, G., Uzan, S., Rotten, D., Breart, G. and Sureau, C. (1977): Continuous subcutaneous pH measurement in human fetuses. Correlations with scalp and umbilical blood pH. Amer. J. Obstet. Gynec., 128, 901-903. Weber, T. and Secher, N.J. (1979): Continuous measurement of transcutaneous fetal oxygen tension during labour. Brit. J. Obstet. Gynaec., 86, 954-958. Weber, T. and Secher, N.J. (1981): Continuous monitoring fetal scalp p0, and pH during labor. In: Clinical Perinatal Biochemical Monitoring. Editors: N.H. Lauersen and H.M. Hochberg. Williams St Wilkins, Baltimore/London. Young, B.K., Noumoff, J., Klein, S.A. and Katz, M. (1978): Continuous fetal tissue pH measurement in labor. Obstet. and Gynec., 52, 533-538. Young, B.K., Katz, M. and Klein, S.A. (1979): The relationship of heart rate patterns and tissue pH in the human fetus. Amer. J. Obstet. Gyneoc., 134, 685-690.
69
UO ooo89
Simultaneous measurement of fetal tissue pH and transcutaneous p 0, during labor Clarel Antoine,
Bruce K. Young and Frank Silverman
The Diwaon o/Maternal- Feral Uedrcine, Departmen! of Obsrerrics and Gynecolog): New York tinroersrr~ School of Medicine and Bellevue Hospital, New York. NY. U.S. A.
ANTOINE, C.. YOUNG, B.K. and SILVERMAN, F. (1984): Simultaneous measurement of fetal tissue pH and transcutaneous ~0, during labor. Europ. J. Obsrer. Gynec. reprod Biol., 17/2.3. 69-76. Simultaneous measurement of fetal heart rate (FHR). uterine contractions (UC), continuous fetal tissue pH (TpH) and transcutaneous p0, (tcp0,) was attempted in 40 high-risk parturients monitored for an average duration of 117+ 74 min. There were only two failures (9%) in the last 23 cases, with satisfactory recording of all parameters in 78% of the total. At present, the feasibility of simultaneous biochemical monitoring is limited to the active phase of labor. Fetal scalp and umbilical arterial blood pH and ~0, were obtained as well. The biochemical data showed a good correlation between tcp0,. scalp capillary pG, and umbilical artery ~0, (P < 0.02). The correlation was not significant between similar pH comparisons, although an average difference of 0.04 pH units was observed between the final TpH and umbilical artery pH. Both fetal TpH and tcp0, fell progressively during labor. Preliminary findings comparing TpH. tcp0, and FHR suggest that changes in tcp0, rapidly reflect changing maternal and fetal conditions, while TpH responds more slowly and less sensitively. fetal heart rate; acid-base
balance;
labor
Introduction
Abnormal fetal heart rate (FHR) patterns during labor are thought to be associated with fetal acidosis and hypoxia. However, the specific relationships remain ill-defined despite extensive research. Intermittent fetal scalp capillary blood sampling (FSB) is now accepted in the evaluation of a compromised fetus. One of the major drawbacks of FSH is that the information derived describes the status of the fetus at that time. The procedure must be repeated for continued assessment of the fetus, usually two or three times during the course of labor. The miniature electrodes developed by Stamm et al. (1976) for pH and Huch et al. (1969) for ~0, were adapted to continuous evaluation of the fetus in labor. Continuous monitoring of tissue pH (TpH) and transcutaneous p02 (tcp0,) have been used independently to assess the high-risk human fetus (Huch et al., 1977; Sturbois et al., 1977). Attempts to study simultaneously both TpH and tcp0, in the same human fetus may elucidate the applicability of each technique, and may clarify the relationship of OO28-2243/84/$03.00
d: 1984 Elsevier Science Publishers
B.V.
70
these parameters to FSB, FHR patterns, neonatal outcome, and to each other (Kaneoka et al., 1979; Weber and Secher, 1981). The present study was initiated to examine continuous monitoring of fetal TpH and tcp0, simultaneously in the same fetus. Materials and methods Forty parturients at Bellevue Hospital had electrodes attached to the fetal scalp for simultaneous continuous biochemical monitoring. All of the subjects were at term with a cephalic presentation. They also had one or more high-risk criteria before labor or developed an abnormal fetal monitoring record during labor. Informed consent was obtained from every patient. The pH and ~0, electrodes and monitors were supplied by Roche Medical Electronics (Roche-Kontron, Cranbury, NJ). Before the experiment, the TpH microelectrode was sterilized, prepared and calibrated with standard buffers of 7.00 and 7.40 at 38’C. Similarly, the fetal ~0, sensor was prepared and calibrated to the ~0, of the humidified ambient air, and to zero using 100% nitrogen. In general, at least 1 h of stabilization elapsed between calibrations and placement of the electrodes. The patient was placed in a dorsolithotomy position. The cervix was at least 4 cm dilated, membranes were ruptured, and the vertex was engaged for the application of either electrode alone. A modified amnioscope and special tools were used to insert the pH electrode through the center of a button electrode into the fetal scalp. This system, connected to a fetal monitor, provides continuous FHR and TpH measurements every 15 s, as described previously (Young et al., 1978; Lauersen et al., 1979). Half an hour was allowed for stabilization of the TpH electrode in vivo. At 7 cm or more of cervical dilatation, after application of the pH electrode, the membrane-covered ~0, sensor was fixed to the unshaven fetal scalp using a tissue glue. This sensor is identical to the neonatal version (Roche Oxymonitor, Kontron-Roche Medical Electronics, Cranbury, NJ) in current clinical use, except for the means of fixation and the right-angle attachment of the electronic cable to the electrode. In an effort to improve attachment and avoid shaving the fetal scalp, the ~0, sensor was fitted with a plastic ring containing a circumferential well in which the tissue glue was placed. This modification permitted an airtight attachment of the electrode without shaving the fetal scalp, except for the hairiest babies. Most studies have shaven the fetal scalp, but others have successfully avoided this manipulation (Lofgren and Jacobson, 1977; Weber and Secher, 1979; Lofgren, 1981). The ~0, electrode contains a heating system and two thermistors which regulate and maintain the skin temperature at 43-44’C, and was stabilized over 15-40 min after application, in order to obtain the maximum vasodilation necessary to its proper reading. All parameters were recorded on a special monitor (Fig. 1). Simultaneous monitoring of TpH and tcp0, was carried out in all cases as close to delivery as possible, as well as into neonatal life in 7 instances. The electrodes were calibrated both at the start and at the end of each experiment to evaluate for drift. Apgar score was assigned by a pediatrician. The infant scalp routinely was examined at birth and cleansed with a Povidone iodine solution. This was repeated daily in the nursery.
Fig. 1. Schematic drawing of a spiral ECG electrode, TpH, and tcp0, are connected through separate cables to their respective modules. recorded on a multichannel monitor.
electrodes on the fetal scalp. These Fetal and maternal parameters are
Simultaneous fetal capillary scalp and maternal venous samples were obtained shortly before placement of each electrode. These were repeated as often as clinically indicated and immediately analyzed for pH and ~0, by means of a microanalyzer (Corning 165, Corning, KY). Umbilical arterial blood was collected at birth for similar studies. Fetal scalp capillary and umbilical blood gases were compared with the continuous data. Because of the rapid variation in tcpO,, these data were selected at a stable area in the continuous recording, taking the tcp0, averaged over 5 min of continuous readings before the scalp blood sample. This was necessary due to the rapid fluctuation of the tcp02 and the effect of the sampling procedure. Since the TpH fluctuates over several minutes, and not as rapidly as the tcpO,, the last TpH reading before the blood sample was utilized for comparison. The continuous values immediately before sampling thus were chosen primarily because of the effect of the sampling procedure itself on the continuous tcp0, and TpH readings. Statistical analysis was done by computing the mean, standard deviation and correlation coefficient. A P value less than 0.05 was considered significant. Results
Forty high-risk patients underwent application of the electrodes for continuous fetal TpH and tcp0, monitoring. Thirty-one of these patients (78%) were success-
12
fully monitored for a duration of 30 to 220 min. The average length of monitoring was 117 k 74 min. The 9 failed attempts (22%) were the result of displacement or dislodgement of the pH electrode during the application of the p0, electrodes (3 cases), hairy fetal scalp, and/or insufficient tissue glue with air contamination of the p0, sensor (6 cases). Most of the 9 failures were attributed to inexperience as there were only 2 failures (9%) in the last 23 cases. Values of TpH between 7.10 and 7.38, and of tcp0, between 8 and 30 mmHg at initial reading after stabilization were considered evidence of good application. In 25 experiments, the electrodes remained attached to the fetal scalp until at least 30 min before delivery. Most of these cases demonstrated periods of poor recording during parts of the second stage of labor. Despite this, seven of these cases were monitored successfully with one of the two electrodes beyond the second stage for 5 to 30 min after birth. These latter cases verified continued normal functioning of the electrodes in the newborn. The effect of mechanical displacement during labor was noted as an abrupt increase of TpH, and was usually observed during crowning of the fetal head or within 1 min of delivery. Similarly, in one of the successfully monitored neonatal tcp0, cases, the scalp tcp0, increased from 8 mmHg at birth to 20 mmHg within 1 min. reaching 72 mmHg at 20 min of life. A neonatal p0, sensor which had been placed on the chest at birth read 88 mmHg at this time. Six of the successful applications were interrupted at various times before delivery because one or both electrodes were dislodged during pelvic examinations, fetal head rotation, in preparation for abdominal delivery, or other necessary manipulations in the clinical care of the patient. Drift for the TpH ranged between 0.01 and 0.03 pH units per hour. The tcp0, drift was difficult to determine in most cases due to the poor condition of the electrode when detached from the fetal or neonatal scalp. However, despite attached fetal hair and glue, drift was l-2 mmHg per hour in the cases where end calibration was obtained. Thus, both TpH and tcp0, showed a downward drift during use. Nevertheless, the degree of drift was not physiologically significant for both pH and PO,. In all but 4 of the cases, the tcp0, was at a physiological level within 5 min while the electrode was held against the fetal scalp to permit the glue to adhere. As pressure is released, a transient rise of tcp0, is seen, usually followed by a rapid reequilibration and stabilization at a physiological value over the next 15-20 min (Fig. 2). Subsequently, the readings obtained were used for’ comparison with the blood values. A decline in fetal cutaneous p0, corresponding to the onset of uterine contractions most likely represents a localized blood flow phenomenon. This is observed in 37% of the cases (Fig. 3). The TpH remained unchanged during uterine contractions which were not associated with FHR changes. Thus, tcp0, sometimes fell in response to uterine contractions, while TpH did not. The biochemical data collected from 20 cases are summarized in Table I. The mean fetal scalp pH before the application of the p0, electrode was 7.31 with a corresponding mean TpH of 7.23. The mean final tissue pH was 7.22, 0.04 pH units lower than the pH of the umbilical artery blood, 7.26. This corresponds with our previous observations, in which TpH averages 0.04 units lower than blood pH (Young et al., 1978). The TpH and blood pH were poorly correlated. The average tcp0, of 20.7 mmHg correlated with the FSB p0, of 21.3. r = 0.69. P < 0.01. The
Fig. 2. Application of fetal transcutaneous ~0, (FCpO,) electrode. Note that the gradual decline of FCpO, during the application is followed by a temporary rise (arrow). Prompt return and stabilization to physiological values follow. The disturbances in fetal heart rate (FHR) and tissue pH (pH) readings during FCpO, application are only transient. Note that pH readings represented by vertical bars every 15 s are superimposed on uterine contractions (UC). The paper speed is 4 cm/mm. The scale is expanded to show the range of tcp0, in maternal measurements as well as fetal.
umbilical artery ~0, of 16.6 correlated with the final tcp0, mean of 15.0 mmHg, r = 0.55, P < 0.02. The 1-min Apgar score was less than 7 in five of the 40 neonates. The 5-min score was at least 8 in all but two. Eight infants were born by cesarean section. There was no maternal morbidity related to the monitoring. A fetal scalp laceration occurred during the first few trials as a result of an overzealous attempt to replace the pH electrode. This infant was discharged in good condition on the 7th day of life.
Fig. 3. Falling FCpO, with UC, with no relationship configuration. From top to bottom are the FCpOa, on fetal TpH readings. The latter are represented cm/min.
to FHR. The decline in fetal tcp0, parallels the UC the FHR and the uterine contractions superimposed by vertical bars every 15 s. The paper speed is 4
TABLE I Comparison of TpH, tcpOz with scalp capillary and umbilical artery gases Initial
Mean S.D.
FSB pH
TPH
TPH
UA
7.31 *0.05
7.23 f 0.05
7.22 f 0.06
1.26 f 0.06
0.24 NS
;
Mean S.D. rp
Final
0.36 NS
FSB ~0,
tcIJo2
tcpo,
UA
21.3 * 5.1
20.7 k4.8
15 55.6
16.6 + 5.9
0.69 < 0.01
0.55 0.02 > P > 0.01
Discussion We have been able to monitor continuous fetal pH and ~0, simultaneously during the active phase of labor, An improved success rate was obtained with experience, as there were only two failures in the last 23 cases. An attempt to pursue the continuous monitoring of both pH and ~0, into neonatal life was partially successful in seven cases, as only one of the two electrodes remained functioning. These cases demonstrated the effect of mechanical factors on TpH and tcpOz recordings, as an abrupt increase was observed when these electrodes were no longer compressed by changes in fetal position. These factors reduce the validity of the electrodes when compared to scalp capillary and umbilical artery data. Moreover, the lack of correlation between blood and TpH in these data make the absolute pH values less reliable. Despite this, the TpH and blood pH changes were in the same direction, showing a parallel decline through labor even when the values did not correspond. A recent study from our laboratory has confirmed the comparative performance of the TpH electrode versus a standard pH analyzer in vitro (Antoine et al., 1981). The observations in the present study show that discrepancies among different investigators most likely reflect mechanical difficulties with stabilization and fixation of the pH electrode, as well as differences between blood and tissue fluid. In this study, the poor correlation between scalp capillary pH and TpH reflect the mechanical problems of fixation of the TpH electrode, the wide variation in both FSB and TpH values, and the effects of head compression (O’Connor et al., 1979) in a small sample for statistical evaluation. An average difference of 0.04 units was observed between the final TpH and the pH of the umbilical artery, in agreement with previously published data (Young et al., 1978). The TpH fluctuates about 0.01 pH units over the interval from one contraction to the next. It does not vary or goes up about 0.01 pH units with contractions in the absence of FHR changes. It may be
75
useful in assessing the trend of pH changes in the patients studied. While the fetal ~0, response may be closely dependent on the maternal state of oxygenation, uterine contractions and FHR changes may be important influences. The present study shows that a fall in fetal tcp0, is frequently seen in response to uterine contractions, though not always. This may represent fetal hypoxemia or a localized blood flow phenomenon. Effects of head compression on fetal scalp blood flow (O’Connor and Hytten, 1979) may alter the tcp0, by changing the blood flow under the electrode. The importance of local blood flow under these electrodes has been emphasized by recent work from our own laboratory in studies on rabbits (Silverman and Young, 1983). In addition, fetal stress and catecholamine release may further affect local blood flow, reducing tcp0, measurements unrelated to the blood ~0, level (Jensen et al., 1982). Despite these caveats. good correlation was found between tcpOz and scalp capillary ~0, (r = 0.69. P -c0.01). and umbilical artery ~0, (r = 0.55, P < 0.02). Both the fetal TpH and tcp0, fall progressively during labor. The tcp0, changes rapidly in response to various maternal and fetal conditions, while TpH responds more slowly and less sensitively. TpH most likely is a reflection of the overall acid-base status of the fetus rather than its oxygenation, while tcp0, reflects both blood flow and ~0, under the electrode. Thus, the two measurements are assessing different phenomena when functioning optimally. Both continuous TpH and tcp0, will reflect the pathophysiology of FHR patterns as well (Huch et al., 1977: Kaneoka et al., 1979; Young et al., 1979). However, these effects must be gauged against the background of the alterations of tcp0, and TpH caused by other factors. The results of this study demonstrate that it is technically possible to monitor simultaneously TpH, tcpO,, FHR and uterine contractions. Further refinement of both biochemical electrodes might lead to better knowledge of fetal physiology. At present, the vagaries of the clinical situation may alter the data generated by the electrodes too much to make them reliable indicators of fetal distress. Further studies are necessary to assess the influence of maternal and mechanical factors in the interpretation of these data, in order to describe accurately the significance of pH and ~0, changes in the fetus. References Antoine.
C., Silverman,
F. and Young,
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(1981):
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standard blood pH analyzer. Clin. Chem., 27, 2070-2071. Huch.
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Huch, A., Huch, R., Schneider, H. and Rooth, G. (1977): Jensen, A., Kunzel,
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Lofgren, 0. and Jacobson, L. (1977): Monitoring of transcutaneous pOr in the fetus and mother during normal labor. J. perinat. Med., 5, 252-259. Lofgren, 0. (1981): Continuous transcutaneous oxygen monitoring in fetal surveillance during labor. Amer. J. Obstet. Gynec., 141, 729-735. O’Connor, M.C. and Hytten, F.E. (1979): Measurement of fetal transcutaneous oxygen tension. Problems and potential. Brit. J. Obstet. Gynaec., 86, 948-953. O’Connor, MC., Hytten, F.E. and Zanelli, G.D. (1979): Is the fetus ‘scalped’ in labor? Lancet, ii, 947-948. Silverman, F. and Young, B.K. (1983). Effects of temperature on arterial and cutaneousp0, in the rabbit. Gynecol obstet. Invest., 15, 283-290. Stamm, 0.. Latscha, U., Janecek, P. and Campana, A. (1976): Development of a special electrode for continuous subcutaneous pH measurement in the infant scalp. Amer. J. Obstet. Gynec., 124,193-195. Sturbois, G., Uzan, S., Rotten, D., Breart, G. and Sureau, C. (1977): Continuous subcutaneous pH measurement in human fetuses. Correlations with scalp and umbilical blood pH. Amer. J. Obstet. Gynec., 128, 901-903. Weber, T. and Secher, N.J. (1979): Continuous measurement of transcutaneous fetal oxygen tension during labour. Brit. J. Obstet. Gynaec., 86, 954-958. Weber, T. and Secher, N.J. (1981): Continuous monitoring fetal scalp p0, and pH during labor. In: Clinical Perinatal Biochemical Monitoring. Editors: N.H. Lauersen and H.M. Hochberg. Williams St Wilkins, Baltimore/London. Young, B.K., Noumoff, J., Klein, S.A. and Katz, M. (1978): Continuous fetal tissue pH measurement in labor. Obstet. and Gynec., 52, 533-538. Young, B.K., Katz, M. and Klein, S.A. (1979): The relationship of heart rate patterns and tissue pH in the human fetus. Amer. J. Obstet. Gyneoc., 134, 685-690.