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Evaluation of fetal blood pH as a reflection of fetal well-being
Evaluation of fetal blood pH as a reflection of fetal well-being JOHN Iowa
S. city,
MCDONALD,
M.D.
Iowa
The determination of fetal blood pH prior to delivery is an acceptable and useful technique for following those cases in which fetal distress has become evident. In certain instances, it can predict impending danger to the fetus who is incapable of adjusting to further stresses, and, in others, it can predict a successful outcome in spite of continued evidence of fetal distress. Therefore, it would appear one could institute more confident management in cafes presenting with fetal distress. Furthermore, future studies may reveal neonatal therapy is possible to correct for seuere acid-base deviations experienced during the process of labor and delivery.
CRITERIA
to what designates fetal distress have not been, and still are not, clear. The assessment of fetal well-being has centered primarily about the status of the fetal heart and the presence or absence of meconium staining of the amniotic fluid. Yet, there is a poorly defined zone between normalcy and periodic irregularities of the fetal heart which is of concern to the obstetrician who would like to know the true condition of the fetus. James and co-workers’ conducted studies on the acid-base status of the infant in the immediate postpartum period and concluded that often acidosis is found despite a vigorous infant. James2 suggested this may be a reflection of a degree of asphyxiation experienced in the delivery process. He further suggested that re-establishment of blood flow in ischemic areas and the unloading of acid products of metabolism, which had accumulated during periods of oxygen deprivation, contributed to this condition of acidosis.” Until now we have relied upon auscultation of the fetal heart tones and observation of the amniotic fluid to reveal situations in which the fetus is being subjected to unusual stresses. These serve as useful screening pro-
cedures, but the true condition of the fetus and his response to stress cannot be evaluated by these methods. Thus, it would appear there is need of a diagnostic method which would distinguish between those cases of distress in which the fetus had accommodated and was not in jeopardy, and those cases in which accommodation had not occurred. Because fetal stresses are associated with an increase in the acid products of metabolism, an investigation of the pH of the fetal blood may evaluate his well-being.4 Saling4 recommended the determination of pH prior to delivery by using small quantities of blood taken from the presenting part of the fetus to establish the diagnosis of fetal distress. He felt that blood samples taken from the fetus were representative enough to permit conclusions regarding the well-being on the fetus. His hospital experienced a reduction in the perinatal mortality rate from 4.83 to 3.31 per cent after introduction of this method. These findings aroused interest in this technique, and, in accordance, the aims of this research are outlined : ( 1) to determine if fetal blood obtained by dermapuncture is representative of the acid-base status of the fetus; (2) to determine if a correlation exists between fetal blood pH and the one minute Apgar score; (3) to determine if a correla-
From the Department of Obstetrics and Gynecology, University of Iowa Hospitals. 912
Fetal
tion exists between fetal blood pH and signs of clinical distress, and (4) to determine if the tcchni que of dcrmapuncture is feasible and accep table. Should each of the four aims be achieved, it would bf c possible to anticipate fetal distress and antici pate active corrective measures to
Fig. held
1. Dcrmapuncturc. with a hrmostat
Fig. 2. A capillary :rllowin,q the blood
blood
pH
as
of
fetal
well-being
Y13
restore acid-base balance to nom: Ml it mediately after delivery. In addition, allow us to select those cases in whicl 1 i ean section is indicated. or perhal, importantly it may allow us to avoid c delivery or difficult vaginal operatives ( in some instanms.
The fetal scalp is elevated with an Allis to prevent deep penetration of the tissues.
tube is filled by touching to be drawn in by capillary
indicator
the end action.
of
the
clamp
tube
and
to the
:I scalpel
drop
blade
of blood
is
anti
ini-
914
April 1, 1967
McDonald
Am.
Methods
Pregnant women at term with a fetus in either vertex or breech presentation were studied. The procedure was explained to the patient and her permission obtained. Patients of any parity were investigated with a special effort made to follow those in which there were signs of fetal distress. Likewise, patients of high-risk status, such as diabetic patients, patients with third trimester hemorrhage, postmaturity, pre-eclampsia, and those with Rh sensitization were included. A total of 64 infants were studied. After 4 cm. of cervical dilatation, the presenting part of the fetus was exposed with right angle retractors, sponged first with Frigiderm* and second with silicone.? Next, the skin of the fetus was tented up with a long Allis clamp and then, just prior to the onset of a contraction, a No. 11 Sterisharp scalpel blade was used to pierce the skin (Fig. 1) . During the contraction, blood from the puncture site formed a discrete drop which was transferred to the microhematocrit tube by capillary action (Fig. 2). This, in turn, was handed out of the sterile field and the pH value obtained. In addition, the umbilical cord was doubly clamped at the time of delivery and a section submitted for blood pH analysis so that a comparison might be obtained between fetal blood pH and the pH of blood from the umbilical artery and vein. pH determinations were made with the Radiometer pH meter. To minimize thermal instability and electrochemical hysteresis, it was left connected to a power source at all times. This was an ideal pH meter to use because it was reliable and had good stability. Transfer of the blood from the microhematocrit tube to the capillary electrode of the pH meter was simplified by the presence of a polyethylene capillary tip on the instrument. This tip could be inserted into the microhematocrit tube and the blood drawn into the ‘Frigiderm contains dichlorotetroffuoroethane which is Q skin-refrigerant anesthetic. It is used here to promote vasodilatation of a small area from which blood is to he taken. tSiliconc a discrete
defoamer is used to promote drop of blood on the skin.
the
Ionnation
of
J. Obst.
& Gynec.
electrode. The entire process including exposure, skin preparation, dermapuncture, and pH measurement occupied less than 3 minutes. Results
An illustration of the relationship between fetal blood pH and the pH values of blood from umbilical artery and vein is depicted in Fig. 3. These 15 cases were selected to illustrate the point that the fetal blood pH values were between those for the umbilical cord vessels over the entire range of observed values. In these cases, fetal blood pH in 7 instances approximated the value of the umbilical vein, in 5 instances fell halfway between, and in 3 others approximated the value recorded for the umbilical artery. In the total series of cases, 55 of the 64 fetal blood pH values fell somewhere between those of the umbilical artery and umbilical vein. However, there were 9 cases where the fetal blood pH actually was lower than that of the umbilical artery.
I
Fig. 3. The dermapuncture, artery over cases.
3
5 7 SELECTED CASE:
II
13
15
relationship of blood pH values from umbilical vein, and umbilical a wide range of pH in 15 selected
APGAA SCORE
Fig. 4. The
relationship of blood pH and Apgar score in 50 cases in which there was no evidence of clinical distress.
Fetal
Table
I. Values
in a total
of 64 cases. 50 with
blood
no fetal
pH as indicator
distress
and
of fetal
I4 with
well-being
115
ffatal
distress Blood Fetal
No
fetal
distress
‘.
skin
pH
Umbilical
Mean
Rang.5
7.30
7.09-7.45
Mean
cord Im
(Umbilical
Range
- --__---.. Menn
artery)
A P&W-
-. .~ Kangr*
7.3
1-S
7.0
54
7.00-7.45
7.27
( CJmbilical vein) 7.34 7.10-7.52
Yrtal
distress
7.26
7.09-7.38
(Umbilical (Umbilical
vein) 7.23-7.40
7.30
Values for fetal blood pH as related to Apgar scores are graphically illustrated in Fig. 4. All of these determinations were purposely made on cases in which there was no indication of fetal distress. There are a total of 50 cases. All but 5 had Apgar scores of 6 or more. These 5 exhibited a pH of less than 7.25. On the other hand, there are 8 cases of pH values of less than 7.25 which exhibit Apgar scores of 6 or more. A total of 37 cases showed pH values of 7.25 or greater and Apgar scores of 6 or more. Similar values are found in Fig. 5 but all ok these cases were diagnosed as having fetal distress either by an irregularity of the heartbeat. meconium staining of the amniotic flllid, or both. There are 14 cases in this series. There arc 2 cases with Apgar scores of less tha,n 6 and once again both have pH values of less than 7.25. However, there are 4 cases in which the pH is less than 7.25 but the Apgar score is 6 or greater. The remaining 8 cases all have pH values of 7.25 or greater and exhibit Apgar scores of 7 or greater. Comparison of the two groups studied and illustrated in Fig. 3 and Fig. 4 is not worthwhile since the latter group contains only 14 cases. However, some idea as to the average pH value of the two groups can be obtained by referring to Table I. It is evident from this table that the descending order of pH values is: umbilical vein, fetal skin, and umbilical artery. One-minute Apgar scores were recorded for all cases, and it is evident there
artery) 7.03-7.35
7.21
:. ... .: APGAR SCORE Fig. 5. The relationship of blood pII to ;\pzar score in 14 cases in which thrre WRY FVICICIII~~~ of clinical distress.
8LOOD pH VALUES BEFOREAND AFTER DELIVERY
Sekcbd cases
740r
720
.- t
-ALL.
*-my.
7o*-i-
Delivery
1 15’
’ 30’
.-.-. 5 45’ ---FL
2” -~I4”
Fig. 6. Ten caws selected to illustrate blood changes before, during, and after birth.
pH
916
McDonald
is no significant difference between the two groups in spite of the second group depicted in Fig. 5 containing cases of clinical fetal distress. Blood pH values before and after delivery at varying intervals are illustrated in Fig. 6. In every instance there is a gradual fall in the pH values after delivery, and in all but Cases 3, 7, and 9 this fall is in evidence within 15 minutes after delivery. After 4 hours, all cases a gradual except Nos. 7 and 10 exhibited rise in the pH approximating the values recorded just prior to delivery. Subsequently, No. 10 developed clinical signs of respiratory distress syndrome while No. 7 did well. Finally, one interesting aspect is a tendency for a small, but definite, fall in the pH as the fetus moves down the vaginal tube toward delivery. Comment Previous work has been done to show capillary blood obtained from a hyperemic area of skin is comparable to arterial blood and recent studies reveal bloods obtained from such areas approximate the pH values of arterial blood.6 Barcroft, Barr-on, and Cowier believed the umbilical vein represented the arterial status of the fetus since blood en route to the head and upper extremities contained more oxygen than that going to the lower extremities. However, Dawes, Mott, and Widdicombe’ believed the umbilical artery represented the arterial circuit of the fetus since blood supplying the brain contained only slightly more oxygen than that in the umbilical artery and since the latter represents the blood supplying the fetal tissues. Actually, fetal arterial blood is a mixture of oxygenated umbilical vein blood and systemic venous return to the right atrium. In the total series of 64 cases, 55 of the fetal blood pH values were between those of the umbilical artery and umbilical vein. Furthermore, Fig. 3 reveals the values for the dermapunctures were consistently between those for the umbilical artery and umbilical vein pH values. From these data, it appeared
Am.
Aplil 1, 1967 .I. Obst. & Gynec.
fetal blood from dermapuncture was representative of fetal arterial blood. Nevertheless, there were 9 instances in the entire series where the fetal blood pH was lower than that in the umbilical artery. Frigiderm was not used in 3, thus a lack of hyperemic effect may have provided a blood sample with elevated carbon dioxide concentration. In 3 others, there was a marked formation of caput, and probably a stasis tending to increase the local carbon dioxide concentration. However, no explanation can be offered for the remaining 3 cases. Thus, it would appear that fetal blood obtained by dermapuncture from an area of active hyperemia usually reveals the acid-base status of the fetus. In Fig. 4 there are 37 cases which exhibit pH of greater than 7.25 prior to delivery which have Apgar scores of 6 or greater, and there are 5 cases of pH values of less than 7.25 which have Apgar scores of less than 6. Therefore, it would appear a relationship does exist between fetal blood pH and the 1 minute Apgar score. However, there are 8 cases which exhibit pH values of less than 7.25 yet have Apgar scores of greater than 6. These must be viewed as failures of fetal blood pH to predict fetal well-being. Explanations for these failures may be that carbon dioxide was elevated in the areas of blood collection due to excessive caput formation, inadequate skin preparation, or pressure from retractors or the Allis clamp used to grasp the skin. In spite of these 8 cases, a correlation is apparent and as the pH value drops below 7.15 there are only 2 cases with Apgar scores of greater than 6. Saling mentioned that a faulty assessment of the fetus may occur in 1.1 per cent if only the pH value is relied upon for diagnosis. Therefore, though a fair correlation does exist between pH and Apgar score it is recommended that more than one determination be obtained to minimize random low pH values and to establish a trend, and that careful attention is paid to preparation of skin from which the sample is to be taken. There was an attempt to study as many
Fetal
casps of fetal distress as possible, but there were only 14 instances of clinically determined fetal distress during the period of investigation. The data presented in Fig. 5 were collected from cases in which a clinical diagnosis of fetal distress was made. Fair comparison exists between fetal blood pH and Apgar scores with 8 cases of values of 7.15 or more and Apgar scores of 6 or greater. Thrre patients had values of less than 7.2.5 and Apgar scores of 6 or less. H owevet-, ther-r were 3 cases of pH values below 7.25 but Apgar scores of greater than 6. Frorn the data collected, it appears a poor correlation exists between pH values and clinical signs of fetal distress. In addition, the Apgar score and the fetal blood pH findings both discredited the clinical diagnosis of fetal distress. Howc\,er. this group is too small for any conclusions. The, technique of dermapuncturc is both feasible and acceptable yet there are certain points to consider. The maintenance of such a technique poses some problems. The operator of the 1111 meter must know something about rlcctronic. irlstrurrlerltatiorl to assure stability and reliability anytime of the day or night. Thr operator must be on call and ready at a tlloment’s notice to make a determination. In addition, the instrument must he located in an area convenient to the labor and delivery suite. There were only 3 complications in tile Lotal 64 cases and all 3 of these were nlinor. One consisted of a snlall 4 mm. scalp laceration which was sululed and Lhe other two were small scalp hematotnas 1 cm. by 2 cm. in size which regressed spontaneously. Thus, there were no seriou\ complications as a result of the procedurca performed by the author in this series. There is a report, however, of an intrauterine exsanguination of the fetus associated with tllis Lechniquc- it1 thr literature.”
blood
pH
as
indicator
of
fetal
well-beinq
917
In the group with clinical frtal disiress, there was no instance of a steady declilre of the pH valur, but in the group of patients where clinical signs of fetal (iisLrc.ss were absent, there was one instances in w-hit-h the pH fell from 7.35 to 7.10 over a -1 tlorlr period. This was in a 31-year-aid primigravida with an infanL in breech presentation who was finally delivered by cesarrsn scctic:Il of a 4,100 gram infant with an Apxar WC):~
REFERENCES
1
James, L. S., Weisbrot, I. M., Prince, C. E., Holaday, D. A.. and Apgar V.: J. Pediat. 52: :ri9. 19.58.
2. James,
L. S.: Arta ppdiat. 41: 17. 122. ) 3. James, L. S.: In. May. C. D.. editor
t960.
(Suppi.
tlio-
918
McDonald
chemical Alterations Observed in The Neonate, Report of the Forty-First Ross Conference on Pediatric Research, Columbus, Ohio, 1962, Ross Laboratories, pp. 35-40. 4. Saling, E.: J. Internat. Fed. Gynec. & Obst. 3: 100, 1965. 5. Huntingford, Peter: Lancet 1: 95, 1964. 6. Sigaard-Andersen, O., Engel, K., Joergensen, K., and Astrup, P.: Scandinav. J. Clin. & Lab. Invest. 12: 172, 1960.
April 1, 1967 Am. J. Obst. & Gynec.
7. Barcroft, J., Barron, D. H., and Cowie, A.: J. Physiol. 97: 338, 1940. 8. Dawes, G. S., Mott, J. C., and Widdicombe, J. G.: J. Physiol. 126: 563, 1954. 9. Saling, E.: J. Internat. Fed. Gynec. & Obst. 3: 100, 1965. 10. James, L. S., Weisbrot, I. M., Prince, C. E., Holaday, D. A., and Apgar V.: J. Pediat. 52: 379, 1958.
S. city,
MCDONALD,
M.D.
Iowa
The determination of fetal blood pH prior to delivery is an acceptable and useful technique for following those cases in which fetal distress has become evident. In certain instances, it can predict impending danger to the fetus who is incapable of adjusting to further stresses, and, in others, it can predict a successful outcome in spite of continued evidence of fetal distress. Therefore, it would appear one could institute more confident management in cafes presenting with fetal distress. Furthermore, future studies may reveal neonatal therapy is possible to correct for seuere acid-base deviations experienced during the process of labor and delivery.
CRITERIA
to what designates fetal distress have not been, and still are not, clear. The assessment of fetal well-being has centered primarily about the status of the fetal heart and the presence or absence of meconium staining of the amniotic fluid. Yet, there is a poorly defined zone between normalcy and periodic irregularities of the fetal heart which is of concern to the obstetrician who would like to know the true condition of the fetus. James and co-workers’ conducted studies on the acid-base status of the infant in the immediate postpartum period and concluded that often acidosis is found despite a vigorous infant. James2 suggested this may be a reflection of a degree of asphyxiation experienced in the delivery process. He further suggested that re-establishment of blood flow in ischemic areas and the unloading of acid products of metabolism, which had accumulated during periods of oxygen deprivation, contributed to this condition of acidosis.” Until now we have relied upon auscultation of the fetal heart tones and observation of the amniotic fluid to reveal situations in which the fetus is being subjected to unusual stresses. These serve as useful screening pro-
cedures, but the true condition of the fetus and his response to stress cannot be evaluated by these methods. Thus, it would appear there is need of a diagnostic method which would distinguish between those cases of distress in which the fetus had accommodated and was not in jeopardy, and those cases in which accommodation had not occurred. Because fetal stresses are associated with an increase in the acid products of metabolism, an investigation of the pH of the fetal blood may evaluate his well-being.4 Saling4 recommended the determination of pH prior to delivery by using small quantities of blood taken from the presenting part of the fetus to establish the diagnosis of fetal distress. He felt that blood samples taken from the fetus were representative enough to permit conclusions regarding the well-being on the fetus. His hospital experienced a reduction in the perinatal mortality rate from 4.83 to 3.31 per cent after introduction of this method. These findings aroused interest in this technique, and, in accordance, the aims of this research are outlined : ( 1) to determine if fetal blood obtained by dermapuncture is representative of the acid-base status of the fetus; (2) to determine if a correlation exists between fetal blood pH and the one minute Apgar score; (3) to determine if a correla-
From the Department of Obstetrics and Gynecology, University of Iowa Hospitals. 912
Fetal
tion exists between fetal blood pH and signs of clinical distress, and (4) to determine if the tcchni que of dcrmapuncture is feasible and accep table. Should each of the four aims be achieved, it would bf c possible to anticipate fetal distress and antici pate active corrective measures to
Fig. held
1. Dcrmapuncturc. with a hrmostat
Fig. 2. A capillary :rllowin,q the blood
blood
pH
as
of
fetal
well-being
Y13
restore acid-base balance to nom: Ml it mediately after delivery. In addition, allow us to select those cases in whicl 1 i ean section is indicated. or perhal, importantly it may allow us to avoid c delivery or difficult vaginal operatives ( in some instanms.
The fetal scalp is elevated with an Allis to prevent deep penetration of the tissues.
tube is filled by touching to be drawn in by capillary
indicator
the end action.
of
the
clamp
tube
and
to the
:I scalpel
drop
blade
of blood
is
anti
ini-
914
April 1, 1967
McDonald
Am.
Methods
Pregnant women at term with a fetus in either vertex or breech presentation were studied. The procedure was explained to the patient and her permission obtained. Patients of any parity were investigated with a special effort made to follow those in which there were signs of fetal distress. Likewise, patients of high-risk status, such as diabetic patients, patients with third trimester hemorrhage, postmaturity, pre-eclampsia, and those with Rh sensitization were included. A total of 64 infants were studied. After 4 cm. of cervical dilatation, the presenting part of the fetus was exposed with right angle retractors, sponged first with Frigiderm* and second with silicone.? Next, the skin of the fetus was tented up with a long Allis clamp and then, just prior to the onset of a contraction, a No. 11 Sterisharp scalpel blade was used to pierce the skin (Fig. 1) . During the contraction, blood from the puncture site formed a discrete drop which was transferred to the microhematocrit tube by capillary action (Fig. 2). This, in turn, was handed out of the sterile field and the pH value obtained. In addition, the umbilical cord was doubly clamped at the time of delivery and a section submitted for blood pH analysis so that a comparison might be obtained between fetal blood pH and the pH of blood from the umbilical artery and vein. pH determinations were made with the Radiometer pH meter. To minimize thermal instability and electrochemical hysteresis, it was left connected to a power source at all times. This was an ideal pH meter to use because it was reliable and had good stability. Transfer of the blood from the microhematocrit tube to the capillary electrode of the pH meter was simplified by the presence of a polyethylene capillary tip on the instrument. This tip could be inserted into the microhematocrit tube and the blood drawn into the ‘Frigiderm contains dichlorotetroffuoroethane which is Q skin-refrigerant anesthetic. It is used here to promote vasodilatation of a small area from which blood is to he taken. tSiliconc a discrete
defoamer is used to promote drop of blood on the skin.
the
Ionnation
of
J. Obst.
& Gynec.
electrode. The entire process including exposure, skin preparation, dermapuncture, and pH measurement occupied less than 3 minutes. Results
An illustration of the relationship between fetal blood pH and the pH values of blood from umbilical artery and vein is depicted in Fig. 3. These 15 cases were selected to illustrate the point that the fetal blood pH values were between those for the umbilical cord vessels over the entire range of observed values. In these cases, fetal blood pH in 7 instances approximated the value of the umbilical vein, in 5 instances fell halfway between, and in 3 others approximated the value recorded for the umbilical artery. In the total series of cases, 55 of the 64 fetal blood pH values fell somewhere between those of the umbilical artery and umbilical vein. However, there were 9 cases where the fetal blood pH actually was lower than that of the umbilical artery.
I
Fig. 3. The dermapuncture, artery over cases.
3
5 7 SELECTED CASE:
II
13
15
relationship of blood pH values from umbilical vein, and umbilical a wide range of pH in 15 selected
APGAA SCORE
Fig. 4. The
relationship of blood pH and Apgar score in 50 cases in which there was no evidence of clinical distress.
Fetal
Table
I. Values
in a total
of 64 cases. 50 with
blood
no fetal
pH as indicator
distress
and
of fetal
I4 with
well-being
115
ffatal
distress Blood Fetal
No
fetal
distress
‘.
skin
pH
Umbilical
Mean
Rang.5
7.30
7.09-7.45
Mean
cord Im
(Umbilical
Range
- --__---.. Menn
artery)
A P&W-
-. .~ Kangr*
7.3
1-S
7.0
54
7.00-7.45
7.27
( CJmbilical vein) 7.34 7.10-7.52
Yrtal
distress
7.26
7.09-7.38
(Umbilical (Umbilical
vein) 7.23-7.40
7.30
Values for fetal blood pH as related to Apgar scores are graphically illustrated in Fig. 4. All of these determinations were purposely made on cases in which there was no indication of fetal distress. There are a total of 50 cases. All but 5 had Apgar scores of 6 or more. These 5 exhibited a pH of less than 7.25. On the other hand, there are 8 cases of pH values of less than 7.25 which exhibit Apgar scores of 6 or more. A total of 37 cases showed pH values of 7.25 or greater and Apgar scores of 6 or more. Similar values are found in Fig. 5 but all ok these cases were diagnosed as having fetal distress either by an irregularity of the heartbeat. meconium staining of the amniotic flllid, or both. There are 14 cases in this series. There arc 2 cases with Apgar scores of less tha,n 6 and once again both have pH values of less than 7.25. However, there are 4 cases in which the pH is less than 7.25 but the Apgar score is 6 or greater. The remaining 8 cases all have pH values of 7.25 or greater and exhibit Apgar scores of 7 or greater. Comparison of the two groups studied and illustrated in Fig. 3 and Fig. 4 is not worthwhile since the latter group contains only 14 cases. However, some idea as to the average pH value of the two groups can be obtained by referring to Table I. It is evident from this table that the descending order of pH values is: umbilical vein, fetal skin, and umbilical artery. One-minute Apgar scores were recorded for all cases, and it is evident there
artery) 7.03-7.35
7.21
:. ... .: APGAR SCORE Fig. 5. The relationship of blood pII to ;\pzar score in 14 cases in which thrre WRY FVICICIII~~~ of clinical distress.
8LOOD pH VALUES BEFOREAND AFTER DELIVERY
Sekcbd cases
740r
720
.- t
-ALL.
*-my.
7o*-i-
Delivery
1 15’
’ 30’
.-.-. 5 45’ ---FL
2” -~I4”
Fig. 6. Ten caws selected to illustrate blood changes before, during, and after birth.
pH
916
McDonald
is no significant difference between the two groups in spite of the second group depicted in Fig. 5 containing cases of clinical fetal distress. Blood pH values before and after delivery at varying intervals are illustrated in Fig. 6. In every instance there is a gradual fall in the pH values after delivery, and in all but Cases 3, 7, and 9 this fall is in evidence within 15 minutes after delivery. After 4 hours, all cases a gradual except Nos. 7 and 10 exhibited rise in the pH approximating the values recorded just prior to delivery. Subsequently, No. 10 developed clinical signs of respiratory distress syndrome while No. 7 did well. Finally, one interesting aspect is a tendency for a small, but definite, fall in the pH as the fetus moves down the vaginal tube toward delivery. Comment Previous work has been done to show capillary blood obtained from a hyperemic area of skin is comparable to arterial blood and recent studies reveal bloods obtained from such areas approximate the pH values of arterial blood.6 Barcroft, Barr-on, and Cowier believed the umbilical vein represented the arterial status of the fetus since blood en route to the head and upper extremities contained more oxygen than that going to the lower extremities. However, Dawes, Mott, and Widdicombe’ believed the umbilical artery represented the arterial circuit of the fetus since blood supplying the brain contained only slightly more oxygen than that in the umbilical artery and since the latter represents the blood supplying the fetal tissues. Actually, fetal arterial blood is a mixture of oxygenated umbilical vein blood and systemic venous return to the right atrium. In the total series of 64 cases, 55 of the fetal blood pH values were between those of the umbilical artery and umbilical vein. Furthermore, Fig. 3 reveals the values for the dermapunctures were consistently between those for the umbilical artery and umbilical vein pH values. From these data, it appeared
Am.
Aplil 1, 1967 .I. Obst. & Gynec.
fetal blood from dermapuncture was representative of fetal arterial blood. Nevertheless, there were 9 instances in the entire series where the fetal blood pH was lower than that in the umbilical artery. Frigiderm was not used in 3, thus a lack of hyperemic effect may have provided a blood sample with elevated carbon dioxide concentration. In 3 others, there was a marked formation of caput, and probably a stasis tending to increase the local carbon dioxide concentration. However, no explanation can be offered for the remaining 3 cases. Thus, it would appear that fetal blood obtained by dermapuncture from an area of active hyperemia usually reveals the acid-base status of the fetus. In Fig. 4 there are 37 cases which exhibit pH of greater than 7.25 prior to delivery which have Apgar scores of 6 or greater, and there are 5 cases of pH values of less than 7.25 which have Apgar scores of less than 6. Therefore, it would appear a relationship does exist between fetal blood pH and the 1 minute Apgar score. However, there are 8 cases which exhibit pH values of less than 7.25 yet have Apgar scores of greater than 6. These must be viewed as failures of fetal blood pH to predict fetal well-being. Explanations for these failures may be that carbon dioxide was elevated in the areas of blood collection due to excessive caput formation, inadequate skin preparation, or pressure from retractors or the Allis clamp used to grasp the skin. In spite of these 8 cases, a correlation is apparent and as the pH value drops below 7.15 there are only 2 cases with Apgar scores of greater than 6. Saling mentioned that a faulty assessment of the fetus may occur in 1.1 per cent if only the pH value is relied upon for diagnosis. Therefore, though a fair correlation does exist between pH and Apgar score it is recommended that more than one determination be obtained to minimize random low pH values and to establish a trend, and that careful attention is paid to preparation of skin from which the sample is to be taken. There was an attempt to study as many
Fetal
casps of fetal distress as possible, but there were only 14 instances of clinically determined fetal distress during the period of investigation. The data presented in Fig. 5 were collected from cases in which a clinical diagnosis of fetal distress was made. Fair comparison exists between fetal blood pH and Apgar scores with 8 cases of values of 7.15 or more and Apgar scores of 6 or greater. Thrre patients had values of less than 7.2.5 and Apgar scores of 6 or less. H owevet-, ther-r were 3 cases of pH values below 7.25 but Apgar scores of greater than 6. Frorn the data collected, it appears a poor correlation exists between pH values and clinical signs of fetal distress. In addition, the Apgar score and the fetal blood pH findings both discredited the clinical diagnosis of fetal distress. Howc\,er. this group is too small for any conclusions. The, technique of dermapuncturc is both feasible and acceptable yet there are certain points to consider. The maintenance of such a technique poses some problems. The operator of the 1111 meter must know something about rlcctronic. irlstrurrlerltatiorl to assure stability and reliability anytime of the day or night. Thr operator must be on call and ready at a tlloment’s notice to make a determination. In addition, the instrument must he located in an area convenient to the labor and delivery suite. There were only 3 complications in tile Lotal 64 cases and all 3 of these were nlinor. One consisted of a snlall 4 mm. scalp laceration which was sululed and Lhe other two were small scalp hematotnas 1 cm. by 2 cm. in size which regressed spontaneously. Thus, there were no seriou\ complications as a result of the procedurca performed by the author in this series. There is a report, however, of an intrauterine exsanguination of the fetus associated with tllis Lechniquc- it1 thr literature.”
blood
pH
as
indicator
of
fetal
well-beinq
917
In the group with clinical frtal disiress, there was no instance of a steady declilre of the pH valur, but in the group of patients where clinical signs of fetal (iisLrc.ss were absent, there was one instances in w-hit-h the pH fell from 7.35 to 7.10 over a -1 tlorlr period. This was in a 31-year-aid primigravida with an infanL in breech presentation who was finally delivered by cesarrsn scctic:Il of a 4,100 gram infant with an Apxar WC):~
REFERENCES
1
James, L. S., Weisbrot, I. M., Prince, C. E., Holaday, D. A.. and Apgar V.: J. Pediat. 52: :ri9. 19.58.
2. James,
L. S.: Arta ppdiat. 41: 17. 122. ) 3. James, L. S.: In. May. C. D.. editor
t960.
(Suppi.
tlio-
918
McDonald
chemical Alterations Observed in The Neonate, Report of the Forty-First Ross Conference on Pediatric Research, Columbus, Ohio, 1962, Ross Laboratories, pp. 35-40. 4. Saling, E.: J. Internat. Fed. Gynec. & Obst. 3: 100, 1965. 5. Huntingford, Peter: Lancet 1: 95, 1964. 6. Sigaard-Andersen, O., Engel, K., Joergensen, K., and Astrup, P.: Scandinav. J. Clin. & Lab. Invest. 12: 172, 1960.
April 1, 1967 Am. J. Obst. & Gynec.
7. Barcroft, J., Barron, D. H., and Cowie, A.: J. Physiol. 97: 338, 1940. 8. Dawes, G. S., Mott, J. C., and Widdicombe, J. G.: J. Physiol. 126: 563, 1954. 9. Saling, E.: J. Internat. Fed. Gynec. & Obst. 3: 100, 1965. 10. James, L. S., Weisbrot, I. M., Prince, C. E., Holaday, D. A., and Apgar V.: J. Pediat. 52: 379, 1958.