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The Oxygen Tension of the Amniotic Fluid*
THE OXYGEN
TENSION
OF THE AMNIOTIC SVEN FRANCO
FLUID*
M.D., G~STA ROOTH, M.D., CALIGARA, PH.D., LUND, SWEDEN
SJ~STEDT,
(From the Departments of Obstetrics and Gynaecology and Internal tal, Lund, and the Wenner-Greta Cardiovascular Research Laboratory, holm, Sweden)
Medicine, Norrtuil
University Hospital,
AND
HospiStock-
T
HE possibility of studying the oxygen tension (~0~) of the human fetus before birth is very limited. The only available method of obtaining an intrauterine ~0, determination is to investigate the amniotic fluid. As the whole surface of the fetus is exposed to the amniotic fluid, the p0, of this fluid can be expected to bear an important relation to that of the fetus. In rabbits, the p0, of the amniotic fluid was measured by Campbell” but no analyses of the pop of the human amniotic fluicl seem to have been made.
Material The amniotic fluid from 45 patients has been analyzed. In 18 cases the amniotic fluid was taken at or near term and in 27 cases the fluid was taken from women undergoing legal abortion. In order to get another intra-abdominal p0, determination for comparison, the fluid from 10 benign ovarian cysts was taken. Cases 1 to 6 and 8 to 10 were follicle cysts and Case 7 a lutein cyst. They varied from the size of a walnut to that of a football. At or near term the uterus was punctured percutaneously (in 7 cases) or during cesarean section (in 11 cases) after the abdominal wall had been opened. Before percutaneous puncture it may be necessary to ascertain by x-ray where the placenta is situated. If it is on the ventral side of the uterus no puncture should be undertaken. Sometimes it was very difficult or impossible to obtain the fluid, especially if the fetus was small and the amount of amniotic fluid scant. If the fluid was viscous and contained many cells, it often could not be used for pOZ measurements with the dropping mercury electrode as the cellular agglomeration disturbed the regular flow of the mercury. Since we have the Clark electrode these cell-rich fluids also can easily be investigated. With one exception, none of the punctures resulted in complications. One woman in whom a percutaneous puncture had been made complained of pains in the upper abdomen, but within half an hour these ceased. Probably she had a minor intraperitoneal hemorrhage caused by the needle in the uterine wall. In the course of induced abortion, the uterus was either punctured after the opening of the abdominal wall, as in cesarean section, or the puncture was made through the anterior fornix of the vagina. The ovarian cysts were punctured in the course of abdominal operations. *This study has been supported by grants from the Association Children. New York. 1226
for the Aid of Crippled
\ oll nle
76
Y 11mher 0
OXYGEN
TENSION
OF
AMNIOTIC
FLUID
L227
Methods of Measuring the Oxygen Tension The oxygen tension was measured polarographically. The analyses were at. first done with the dropping mercury electrode (Methods I and II) by the standard technique for complete polarograms.” Later a Clark4 electrode (Method 111) was used at a fixed voltage. The polarograph is a LKB-Blomgren polarizer with a Leeds & Northrup Speedomax recorder. filethods I and U.-Because of the variability in the physical properties ot the amniotic fluid, the amount of dissolved oxygen, which is directly proport,ional to the PO,, cannot be calculated directly or from a calibration line of gtlncral validity. Instead calibration points nlust, bc maclc on each separate This was accomplished in two different ways: Siltl)lC’.
1. By equilibrating the fluid with gas mixtures (Jf known osygcn tensions. This was done in the first 15 cases. 2. By mixing the sample wilh 0.8 iX potassium chloride aqueous solution of known oxygen tension (internal stanclard technique). This was used in 16 ea,scsof amniotic fluid and in 8 of the cysts. Methods I and II are discussed in more detail in another work.c .Veth.od III.-The Clark electrode is very convenient for measurements of p0, in biological fluids. The calibration curve made on KC1 solution or water is also valid for this fluid. The sample to be measured is introduced into a “cell” containing 2 ml. of fluid. Before being filled with the amniotic fluid, t,hc ccl1 is washed with a gas mixture which has a p0, of about the same magnitude as is expected in the sample. Alternatively, the cell may be washed two or three times with the sample itself. Measurements tlonc without this washing will illvariably be too high. This method was used in 14 casesof amniotic fluid and in 3 of t,he cysts. With the Clark electrode it is possible to take a double reading of the p0, in the amniot,ic fluid in 5 minutes, whereas one single reading takes 60 minutes with ,\Tcthod I and 20 minutes with Method II. The accuracy of Method I is of the order k 4 mm.. of Method II t 2 mm.! and of M&hod III + 1.5 mnl. Table I shows the results of repeated measureIttents with ill&hod III. The maximum devia.tion is i 1.5 mm. but the mf’an deviation is only _+0.5 mm.
SJGSTEDT,
1228
ROTH,
AND CALIGAR,A
Am.J.Obrt.
& Gynec.
December.
1958
It is obvious that for this type of p0, measurement the Clark electrode has great advantages over the dropping mercury electrode. Results The p0, of the 45 specimens of amniotic fluids is shown in Table II. The p0, varies between 1 mm. and 31 mm. Hg but most of the values are between 6 and 14 mm. (28 cases). Because of the very low oxygen capacity of the amniotic fluid, small air bubbles make big errors and on the basis of our present experience we suspect that the high values are due to technical errors. TABLE
II.
CORRELATION
METHOD1 GESTATIONTIME ) IN WEEKS I Induced Abortion.10
PO2
OF THE OXYGEN TENSION IN AMNIOTIC FLUID WITH THE LENGTH OF GESTATION* -----~~__ -~~ METHOD11 METHOD111 ) GESTATIONTIME 1 t GESTATIONTIME t INWEEKS IN WEEKS I PO2 I
_)
14 :;
18 139
12 14 14 15
18 20 20
19
15 15
7
6 7
17 20 22
11 9
ifi
19 23 B
20 B
1: 15
36 $
25
13 4 13 13 31
18 20 20
18 B Cesarean
14 8 20 14
17 17
17 1
zi
8
11
Section.-
37 38 40 40 43
2 8 10 7 6
Percutaneous 40
10
40
14
3": 41 41
some
4 2 8
Puncture.-
7
20
35 40
40 40 *In WX!"t-&CY.
-.
cases
marked
with
? it was
not
possible
to establish
the
8 9 gestation
time
with
The p0, of the 10 ovarian cysts is given in Table III. The fluid of some of these cysts had a notable oxygen consumption and corrections have been made for this. In the amniotic fluid, the oxygen consumption over a period of 1 hour is negligible. TABLE
III.
THE
OXYGEN
TENSION
OF BENIQN
METHOD11
OVARIAN
CYSTS
METHOD
CASE
PO2
CASE
i
39 47
98
3
42
10
% 6 7
43 58 41 44
I
III
PO2 41 44 33
-
OXYGEN
TENSION
OF
AMNIOTIC
FLUID
1229
Comment The pOZ of the ovarian cysts can be compared to that in the nitrogen bubble of Campbell,2 who found a mean value of 40 to 50 mm. Hg intra-abdominally. Our values for the ovarian cysts are of the same magnitude and probably represent the intra-abdominal p0, in man. The p0, in the amniotic fluid is much lower and the mean value in our 44 cases is 11 mm. Hg. This value is very similar to that of Campbell,3 who measured the ~0, in the amniotic sac of rabbits. His values were between 3 and 33 mm. Hg with a mean value of 18 mm. Hg in 11 cases. Campbell made these analyses, too! with the nitrogen bubble technique. The relation between the p0, in the amniotic fluid and that of the fetus is interesting and important. In 1957 we6 reported experiments on the transportation of oxygen through the skin, using a modification of the Raumbcrgcr and Goodfriend’ method of analyzing the arterial p0, through t,he skin of a heat,ed finger. It was found that the arterial pOZ equilibrates through the skin into a, salt solution in which the finger is immersecl. We therefore have yeason to suppose t,hat the oxygen tension of the amniotic fluid and the oxygen lension of the skin of the fetus are in equilibriutn. Oxygen can enter or leave the amniotic fluid through either the placenta or the layers of the amniotic sac or through the skin of the fetus. Possibly some oxygen is also consumed by the cells in the amniotic fluid but, if so. this consumption is very small as we have found. It is not possible to estimat,c how t,he p02 in the amniotic fluid is balanced, but because of the large sursfacae of the fetus as compared with the other surfaces which are active in this respect.. it is reasonable to assume that the p0, of the amniotic fluid will resemblr the p0, of the tissues of the skin of the fetus. The adult arterial p02 is about 100 mm. Hg. The venous p0, is about 30 to 50 mm. and the p0, of the intra-abdominal or subcutaneous tissues between 30 and 50 mm. The arterial pO1 of the fetus is about 30 mm. and its venous p0, about, 10 mm. Hg. From this it may be guessed that the tissue p0, of the fetus is also about 10 mm. Hg. As the values observed in the amniotic fluid are of this magnitude, it seems probable that these values also indicate the ~0, in the skin of the fetus in utero. In 5 cases, the ~0, of the amniotic fluid was less than 5 mm. Hg. This is particularly interesting because these values suggest hypoxia of the fetus, but it is as yet too early to tell whether the measurements of the pOZ of the amniotit? fluid may br used to show intrauterine hyposia. Summary The mean pOZ of the amniotic fluid in 45 cases was found to be 11 mm. Hg ancl of 10 ovarian cysts 44.9 mm. Hg.
1230
SJbSTEDT,
ROOTH,
AND
CALlGAHA
.\m. J. Obst. & Gi~rcc. December. i’i
References 1. 2. 3. 4. 5.
Baumberger, J. P., and Goodfriend, R. B.: Federation Proc. 11: 11, 1954. Campbell, J. A.: J. Physiol. 59: 1, 1924-1925. Campbell, J. A.: J. Physiol. 87: 68p., 1936. Clark, L. C., Jr.: Am. Sot. Art. Int. Org. 2: 41, 1956. Kolthoff, I. M., and Lingane, J.: Polarography, New York, 1952, Interscience Publishers, Inc. 6. Rooth, G., Sjostedt, S., and Caligara, F.: Science Tools 4: 3, 1957. In Walker, J., and Turnbull,, A. C., editors: The 7. Rooth, G., SjSstedt, S., and Caligara, F.: London, Blackwell Scientific Publications. Oxygen Supply to the Human Fetus, (In press.)
TENSION
OF THE AMNIOTIC SVEN FRANCO
FLUID*
M.D., G~STA ROOTH, M.D., CALIGARA, PH.D., LUND, SWEDEN
SJ~STEDT,
(From the Departments of Obstetrics and Gynaecology and Internal tal, Lund, and the Wenner-Greta Cardiovascular Research Laboratory, holm, Sweden)
Medicine, Norrtuil
University Hospital,
AND
HospiStock-
T
HE possibility of studying the oxygen tension (~0~) of the human fetus before birth is very limited. The only available method of obtaining an intrauterine ~0, determination is to investigate the amniotic fluid. As the whole surface of the fetus is exposed to the amniotic fluid, the p0, of this fluid can be expected to bear an important relation to that of the fetus. In rabbits, the p0, of the amniotic fluid was measured by Campbell” but no analyses of the pop of the human amniotic fluicl seem to have been made.
Material The amniotic fluid from 45 patients has been analyzed. In 18 cases the amniotic fluid was taken at or near term and in 27 cases the fluid was taken from women undergoing legal abortion. In order to get another intra-abdominal p0, determination for comparison, the fluid from 10 benign ovarian cysts was taken. Cases 1 to 6 and 8 to 10 were follicle cysts and Case 7 a lutein cyst. They varied from the size of a walnut to that of a football. At or near term the uterus was punctured percutaneously (in 7 cases) or during cesarean section (in 11 cases) after the abdominal wall had been opened. Before percutaneous puncture it may be necessary to ascertain by x-ray where the placenta is situated. If it is on the ventral side of the uterus no puncture should be undertaken. Sometimes it was very difficult or impossible to obtain the fluid, especially if the fetus was small and the amount of amniotic fluid scant. If the fluid was viscous and contained many cells, it often could not be used for pOZ measurements with the dropping mercury electrode as the cellular agglomeration disturbed the regular flow of the mercury. Since we have the Clark electrode these cell-rich fluids also can easily be investigated. With one exception, none of the punctures resulted in complications. One woman in whom a percutaneous puncture had been made complained of pains in the upper abdomen, but within half an hour these ceased. Probably she had a minor intraperitoneal hemorrhage caused by the needle in the uterine wall. In the course of induced abortion, the uterus was either punctured after the opening of the abdominal wall, as in cesarean section, or the puncture was made through the anterior fornix of the vagina. The ovarian cysts were punctured in the course of abdominal operations. *This study has been supported by grants from the Association Children. New York. 1226
for the Aid of Crippled
\ oll nle
76
Y 11mher 0
OXYGEN
TENSION
OF
AMNIOTIC
FLUID
L227
Methods of Measuring the Oxygen Tension The oxygen tension was measured polarographically. The analyses were at. first done with the dropping mercury electrode (Methods I and II) by the standard technique for complete polarograms.” Later a Clark4 electrode (Method 111) was used at a fixed voltage. The polarograph is a LKB-Blomgren polarizer with a Leeds & Northrup Speedomax recorder. filethods I and U.-Because of the variability in the physical properties ot the amniotic fluid, the amount of dissolved oxygen, which is directly proport,ional to the PO,, cannot be calculated directly or from a calibration line of gtlncral validity. Instead calibration points nlust, bc maclc on each separate This was accomplished in two different ways: Siltl)lC’.
1. By equilibrating the fluid with gas mixtures (Jf known osygcn tensions. This was done in the first 15 cases. 2. By mixing the sample wilh 0.8 iX potassium chloride aqueous solution of known oxygen tension (internal stanclard technique). This was used in 16 ea,scsof amniotic fluid and in 8 of the cysts. Methods I and II are discussed in more detail in another work.c .Veth.od III.-The Clark electrode is very convenient for measurements of p0, in biological fluids. The calibration curve made on KC1 solution or water is also valid for this fluid. The sample to be measured is introduced into a “cell” containing 2 ml. of fluid. Before being filled with the amniotic fluid, t,hc ccl1 is washed with a gas mixture which has a p0, of about the same magnitude as is expected in the sample. Alternatively, the cell may be washed two or three times with the sample itself. Measurements tlonc without this washing will illvariably be too high. This method was used in 14 casesof amniotic fluid and in 3 of t,he cysts. With the Clark electrode it is possible to take a double reading of the p0, in the amniot,ic fluid in 5 minutes, whereas one single reading takes 60 minutes with ,\Tcthod I and 20 minutes with Method II. The accuracy of Method I is of the order k 4 mm.. of Method II t 2 mm.! and of M&hod III + 1.5 mnl. Table I shows the results of repeated measureIttents with ill&hod III. The maximum devia.tion is i 1.5 mm. but the mf’an deviation is only _+0.5 mm.
SJGSTEDT,
1228
ROTH,
AND CALIGAR,A
Am.J.Obrt.
& Gynec.
December.
1958
It is obvious that for this type of p0, measurement the Clark electrode has great advantages over the dropping mercury electrode. Results The p0, of the 45 specimens of amniotic fluids is shown in Table II. The p0, varies between 1 mm. and 31 mm. Hg but most of the values are between 6 and 14 mm. (28 cases). Because of the very low oxygen capacity of the amniotic fluid, small air bubbles make big errors and on the basis of our present experience we suspect that the high values are due to technical errors. TABLE
II.
CORRELATION
METHOD1 GESTATIONTIME ) IN WEEKS I Induced Abortion.10
PO2
OF THE OXYGEN TENSION IN AMNIOTIC FLUID WITH THE LENGTH OF GESTATION* -----~~__ -~~ METHOD11 METHOD111 ) GESTATIONTIME 1 t GESTATIONTIME t INWEEKS IN WEEKS I PO2 I
_)
14 :;
18 139
12 14 14 15
18 20 20
19
15 15
7
6 7
17 20 22
11 9
ifi
19 23 B
20 B
1: 15
36 $
25
13 4 13 13 31
18 20 20
18 B Cesarean
14 8 20 14
17 17
17 1
zi
8
11
Section.-
37 38 40 40 43
2 8 10 7 6
Percutaneous 40
10
40
14
3": 41 41
some
4 2 8
Puncture.-
7
20
35 40
40 40 *In WX!"t-&CY.
-.
cases
marked
with
? it was
not
possible
to establish
the
8 9 gestation
time
with
The p0, of the 10 ovarian cysts is given in Table III. The fluid of some of these cysts had a notable oxygen consumption and corrections have been made for this. In the amniotic fluid, the oxygen consumption over a period of 1 hour is negligible. TABLE
III.
THE
OXYGEN
TENSION
OF BENIQN
METHOD11
OVARIAN
CYSTS
METHOD
CASE
PO2
CASE
i
39 47
98
3
42
10
% 6 7
43 58 41 44
I
III
PO2 41 44 33
-
OXYGEN
TENSION
OF
AMNIOTIC
FLUID
1229
Comment The pOZ of the ovarian cysts can be compared to that in the nitrogen bubble of Campbell,2 who found a mean value of 40 to 50 mm. Hg intra-abdominally. Our values for the ovarian cysts are of the same magnitude and probably represent the intra-abdominal p0, in man. The p0, in the amniotic fluid is much lower and the mean value in our 44 cases is 11 mm. Hg. This value is very similar to that of Campbell,3 who measured the ~0, in the amniotic sac of rabbits. His values were between 3 and 33 mm. Hg with a mean value of 18 mm. Hg in 11 cases. Campbell made these analyses, too! with the nitrogen bubble technique. The relation between the p0, in the amniotic fluid and that of the fetus is interesting and important. In 1957 we6 reported experiments on the transportation of oxygen through the skin, using a modification of the Raumbcrgcr and Goodfriend’ method of analyzing the arterial p0, through t,he skin of a heat,ed finger. It was found that the arterial pOZ equilibrates through the skin into a, salt solution in which the finger is immersecl. We therefore have yeason to suppose t,hat the oxygen tension of the amniotic fluid and the oxygen lension of the skin of the fetus are in equilibriutn. Oxygen can enter or leave the amniotic fluid through either the placenta or the layers of the amniotic sac or through the skin of the fetus. Possibly some oxygen is also consumed by the cells in the amniotic fluid but, if so. this consumption is very small as we have found. It is not possible to estimat,c how t,he p02 in the amniotic fluid is balanced, but because of the large sursfacae of the fetus as compared with the other surfaces which are active in this respect.. it is reasonable to assume that the p0, of the amniotic fluid will resemblr the p0, of the tissues of the skin of the fetus. The adult arterial p02 is about 100 mm. Hg. The venous p0, is about 30 to 50 mm. and the p0, of the intra-abdominal or subcutaneous tissues between 30 and 50 mm. The arterial pO1 of the fetus is about 30 mm. and its venous p0, about, 10 mm. Hg. From this it may be guessed that the tissue p0, of the fetus is also about 10 mm. Hg. As the values observed in the amniotic fluid are of this magnitude, it seems probable that these values also indicate the ~0, in the skin of the fetus in utero. In 5 cases, the ~0, of the amniotic fluid was less than 5 mm. Hg. This is particularly interesting because these values suggest hypoxia of the fetus, but it is as yet too early to tell whether the measurements of the pOZ of the amniotit? fluid may br used to show intrauterine hyposia. Summary The mean pOZ of the amniotic fluid in 45 cases was found to be 11 mm. Hg ancl of 10 ovarian cysts 44.9 mm. Hg.
1230
SJbSTEDT,
ROOTH,
AND
CALlGAHA
.\m. J. Obst. & Gi~rcc. December. i’i
References 1. 2. 3. 4. 5.
Baumberger, J. P., and Goodfriend, R. B.: Federation Proc. 11: 11, 1954. Campbell, J. A.: J. Physiol. 59: 1, 1924-1925. Campbell, J. A.: J. Physiol. 87: 68p., 1936. Clark, L. C., Jr.: Am. Sot. Art. Int. Org. 2: 41, 1956. Kolthoff, I. M., and Lingane, J.: Polarography, New York, 1952, Interscience Publishers, Inc. 6. Rooth, G., Sjostedt, S., and Caligara, F.: Science Tools 4: 3, 1957. In Walker, J., and Turnbull,, A. C., editors: The 7. Rooth, G., SjSstedt, S., and Caligara, F.: London, Blackwell Scientific Publications. Oxygen Supply to the Human Fetus, (In press.)