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Maternal and fetal effects of exchange transfusion with a red blood cell substitute
Maternal and fetal effects of exchange transfusion with a red blood cell substitute Robert C. Cefalo, M.D., Ph.D., John W. Seeds, M.D., Herbert J. Proctor, M.D., and Vicki V. Baker, M.D. Chapel Hill, North Carolina Recent reports have demonstrated the efficacy of Fluosol-DA (20%) as a temporary erythrocyte substitute. We investigated two groups of pregnant ewes that underwent exchange transfusion. In group 1, the animals underwent a nearly total isovolemic exchange of Fluosol-DA (20%) for maternal whole blood; in group 2, the red blood cells were removed and the plasma along with Ringer's lactate was replaced isovolumetrically. Although group 1 animals received 100% oxygen and Fluosol-DA (20%), the maternal arterial P02 increased to 350 to 400 torr. However, the maternal blood oxygen content decreased during the exchange, with no change in fetal pH, Pco 2 , or hematocrit. Maternal blood pressure remained stable and there was a 40% to 50% increase in cardiac output and mean pulmonary arterial pressure. During the exchange, the maternal hematocrit decreased from a mean of 32% to 5.5%; the maternal fluorocrit at the end of the exchange was 9%. Throughout the Fluosol-DA (20%) exchange, the proportion of fetal brain oxyhemoglobin as estimated from infrared transcranial transmittance increased, as did the fetal blood P0 2 and oxygen content. In group 2, the maternal mean blood pressure decreased, and the hematocrit decreased from a mean of 32% to 8%. Despite an increase in the maternal P0 2 to 250 torr, the fetal P0 2 and oxygen content decreased in group 2. This investigation demonstrated that Fluosol-DA (20%) exchange of the mother does not impair delivery of oxygen to the fetus under the conditions of the study. (AM.
J.
OBSTET. GVNECOL. 148:859, 1984.)
Studies in both nonpregnant laboratory animals and nonpregnant humans have demonstrated the safety and efficacy of perfluorochemicals in both improving oxygen delivery and maintaining circulation during conditions of acute loss of blood. I - 5 Fluosol-DA (20%) is the trade name of an isotonic and isooncotic milky white synthetic erythrocyte emulsion that consists of electrolytes, starch, and the emulsified perfluorochemicals of perfluorodecalin and perfluorotripropylamine. Clinically, Fluosol-DA (20%) has been used in the severely anemic or hypovolemic nonpregnant adult who refuses blood. I, 2, 4, 5 This report presents the results of preliminary studies of the maternal and fetal cardiorespiratory effects of an isovolemic exchange transfusion of the near-term pregnant ewe with Fluosol-DA (20%). Methods and material
Two groups of mixed-breed ewes between 135 and 142 days' gestation were premedicated with 1 mg/kg of intramuscular ketamine hydrochloride and anesthetized with ketamine by continuous intravenous drip at
From the Departments of Obstetrics and Gynecology and Surgery, School of Medicine, University of North Carolina at Chapel Hill. Presented by invitation at the Second Annual Meeting of the American Gynecological and Obstetrical Society, Phoenix, Arizona, September 7-10, 1983. Reprint requests: Dr. Robert C. Cefalo, Department of Obstetrics and Gynecology, University of North Carolina School of Medicine, 214 MacNider Bldg., 202-H, Chapel Hill, North Carolina 27514.
7 to 9 mg/min via the external jugular vein. After intubation, the ewe's respiration was assisted by a respirator pump (Emerson volume-controlled ventilator, Model 3-PV) with room air initially, and then 100% oxygen. The maternal pulmonary artery was catheterized with a Swan-Ganz, flow-directed, thermal dilution catheter (Model 93A-131-7F). The catheter was floated into the pulmonary artery, with use of the characteristic pressure wave form to track its location. The maternal femoral artery was cannulated. Systemic and pulmonary arterial pressures were measured with pressure transducers (Hewlett-Packard Model 1280) and recorded on a multichannel recorder (Hewlett-Packard Model 7788A). Via laparotomy and hysterotomy incisions, the fetal head was exteriorized, with the amnion intact. Samples of fetal blood (1.0 ml) were obtained from an indwelling catheter placed in the jugular vein and advanced 8 to 10 em. The fetal head was stabilized within a modified Balfour retractor and fitted with a fiber-optic bundle and photomultiplier tube light detector for assessing continuous fetal cerebral oxygenation on the basis of the transcranial infrared spectrophotometric methodology of Seeds and associates. 6 The photomultiplier tube was positioned at 60 to 90 degrees to the incident light on the opposite side of the parietal fetal skull. The wave lengths of light at 770, 813, and 905 nm were presented to the fetal head, and changes in voltage at the photomultiplier tube were recorded continuously, as described by Jobsis. 7
859
860
Cefalo et al.
April 1. 1984 Am. J. Obstet. Gynecol.
Table I. Fluosol-DA (20%) emulsion composition after reconstitution Quantity Ingredient
(gm/dl)
Perftuorodecalin Perftuorotripropylamine Hydroxyethyl starch Pluoronic F-68 Glycerol Sodium chloride Egg yolk phospholypids Sodium bicarbonate Glucose Oleic acid Potassium chloride Calcium chloride Magnesium chloride Water for injection
14.0 6.0 3.0
2.7 0.8 0.6 0.4
0.21 0.18 0.04 0.03 0.02 0.02 Sufficient quantity
The sheep were divided into two groups. In group 1 (N = 4), the baseline period was followed by a period of maternal isovolemic exchange of Fluosol-DA (20%) for whole blood via a maternal femoral artery and vein with an IBM-2997 continuous-flow cell separator (IBM, Research Triangle Park, North Carolina). In group 2 (N = 4), the continuous-flow cell separator was used to remove maternal red blood cells and return the plasma supplemented with Ringer's lactate. Exchange transfusion in both groups was accomplished within 60 to 75 minutes. In group 1, the infusion rate of Fluosol-DA (20%) was approximately 80 ml/min, and each ewe had approximately 4,500 to 4,700 ml of whole blood exchanged with 5,000 ml of Fluosol-DA (20%). In group 2, approximately 1,400 to 1,600 ml of red blood cells was removed, and approximately 1,500 to 1,700 ml of plasma and 1,500 to 1,700 of Ringer's lactate was returned to the ewe. As described by Jobsis 7 and Seeds and associates,6 the known tissue transparency to infrared light and the known absorption peaks of reduced and oxygenated hemoglobin were used, processed electronically as voltage potentials at the photomultiplier tube, and recorded continuously. After the fetal hemoglobin voltage channels on the recorder had stabilized, they were zeroed with the mother breathing room air and again after the ewe was ventilated with 100% oxygen. Each ewe was killed at the conclusion of the experiment by ventilation with 100% nitrogen. Serial duplicate maternal and fetal hematocrits (hct) and fluorocrits (fct) (the volume percentage of the white bottom layer of perfluorochemicals centrifuged from blood) were determined in capillary tubes that were centrifuged for 10 minutes at 10,000 rpm. Data collected included continuous maternal femoral and pulmonary arterial pressure, intermittent (every 15 minutes) maternal cardiac output in duplicate by the
thermal dilution technique (Edward's Laboratory cardiac output model 9520A), and maternal arterial and mixed venous and fetal blood gases and pH. All maternal and fetal samples of blood for analysis of gas were obtained simultaneously and drawn anaerobically. The oxygen and carbon dioxide tensions and pH were measured with an Instrument Laboratory No. 113 gas analyzer at 38° C temperature. The pre-Fluosol-DA (20%) exchange oxygen (0 2) content of maternal arterial whole blood, M[02]~B' and mixed venous blood, M[02]~B' was calculated from the sum of the oxygen chemically combined with hemoglobin and physically dissolved oxygen as described by M[02]WB = [02]rbc + [02]dISS. in ml/0 2 /dl. 8 The [02]rbc was calculated from the product of the hemoglobin concentration, the derived percentage of oxygen saturation from the sheep blood oxygen dissociation curve, and the Hufner coefficient (1.34 ml of oxygen per gram of hemoglobin per 100 ml of blood at standard temperature and pressure).9 [02]dISS. was calculated as the product of the blood P02 and solubility coefficient of· oxygen in plasma. When Fluosol-DA (20%) is administered, oxygen is carried by hemoglobin and in physical solution by the perfluorochemical (pfc) and aqueous (aqu) phases. Rosen and associates8 described the calculations of whole blood-perfluorochemical emulsion mixture oxygen content with the use of Henry's law applied to the perfluorochemical and aqueous phases of whole blood mixture. The oxygen dissolved in the maternal perfluorochemical phase per deciliter of whole blood emulsion mixture in group 1 was determined by the formula [02]diSS. = [02]pfc + [02]aQu' The [02]pfc was determined by the formula [02]pfc
= apfc X ~~~ x
fct
=
0.000318 X P02 X fct, and the [02]aQU was determined Po by the formula [02]aQU = aaqu X 76~ X (l00 - fct) = 0.0000316 X P0 2 X (l00 - fct). The fetal blood content, f[02]wB, in milliliters of oxygen per deciliter of whole blood, was calculated from the product of the hemoglobin concentration, the Hufner solubility coefficient, the derived percentage oxyhemoglobin saturation from the fetal sheep blood oxygen dissociation curves, and fetal blood oxygen tension. 9 The amount of dissolved oxygen content in the fetal blood, f[02]~~' was calculated by the product of the Bunsen solubility coefficient and oxygen tension (0.0000316 X P0 2 X 100). Fluosol-DA (20%) was supplied by Alpha Therapeutic Corporation, Los Angeles, California, as manufactured by Green Cross Corporation, Osaka, Japan. Fluosol-DA (20%) is supplied in three parts which must be reconstituted before intravenous administration. The final perfluorochemical emulsion as listed in Table I has the appearance and consistency of skim milk, a
Exchange transfusion with red blood cell substitute 861
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EXP.3F
JANUARY IS,
CONTROL (100 %OXYGEN)
FLUOSOL EXCHANGE
MATERNAL NITROGEN
I
R~~::d L~___. -, - j ~/'-,_ - . - , - l l : , _ ~ ..:...~
Hemoglobm[
(=)~
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-.03
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(Torr)
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~~~~ooJ200._____io-.. ........ ___ la.lt. .N.iii. . . . . . . . . . . . Lot •• (Torr)
00
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.19 .04 03 .04
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loII,a.......-""rJIIIIII··.·..,'
- i
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Fig. 1. Example of ewe undergoing Fluosol-DA (20%) isovolemic exchange.
pH of 7.40, an osmolarity of 410 mOsm, oncotic pressure of 380 to 395 mm H 2 0, and an average particle size distribution of the perfluorochemical compound of 0.211-. The experimental protocol consisted of: (I) a postoperative baseline period of 20 to 30 minutes during which maternal arterial pressures were recorded continuously, with intermittent determinations of maternal and fetal blood gases and pH and maternal cardiac output, while the ewe breathed room air and after ventilation with 100% oxygen; (2) Fluosol-DA (20%) exchange transfusion period in which whole blood was removed at 70 to 80 mllmin in group 1 and the Fluosol-DA (20%) was infused at approximately 80 mllmin, and in group 2 the red blood cells were removed and the plasma and Ringer's lactate was coincidentally reinfused at approximately 80 mllmin; (3) a 15- to 20-minute period in which the ewe breathed 100% nitrogen to induce maternal and fetal hypoxia; (4) continuous recording of maternal blood and pulmonary arterial pressures and the infrared light transmittance as a reflection of the quantity of oxidized and reduced hemoglobin within the transilluminated cerebral field; and (5) intermittent (l5-minute) determinations of maternal and fetal blood gases and pH and maternal cardiac output.
Results Tables II and III list the relevant cardiorespiratory data. The weight of group 1 animals averaged 57 kg. Data from Kirschbaum and associates lO suggested an average maternal blood volume of 5.5 L, and, therefore, each ewe in group 1 had a nearly 95% exchange of whole blood with Fluosol-DA (20%) over a period of 60 to 75 minutes. The mean maternal baseline hematocrit in group 1 was 30.2%. At the end of the Fluosol
exchange, the mean hematocrit was S.5% and the mean fluorocrit was 9.0%. In group 2, the average weight of the animals was 55 kg, with an estimated blood volume of 5 L. The average amount of red blood cells removed over a period of approximately 60 minutes was 1,500 ml, and the returned plasma and Ringer's lactate each averaged 1,700 m!. The mean maternal baseline hematocrit was 32.8%. The mean hematocrit at the end of the 60minute period was 8%. In both groups 1 and 2, the fetal hematocrit remained stable, with means of 40.1 % and 39.2%, respectively. Cardiovascular. In group 1 animals, the mean blood pressure did not change appreciably during the Fluosol-DA (20%) exchange from the baseline values (Fig. 1). However, the mean cardiac output and the mean pulmonary arterial pressure increased approximately 40% and 50%, respectively, during the Fluosol-DA (20%) exchange. The pulmonary arterial pressure increased within a few minutes of starting the Fluosol-DA (20%) exchange (Fig. 1). In group 2 animals, the mean blood pressure decreased by 36% starting after approximately 30 minutes of exchange and by 47% by the end of the exchange, but the cardiac output and mean pulmonary arterial pressure did not change appreciably from baseline values. Respiratory. The maternal arterial P02 increased from the baseline values with the administration of 100% oxygen in both groups of animals. During the exchange with Fluosol-DA (20%) in group 1 animals, there was a further increase in the maternal arterial P02 of over 100%, as opposed to a further increase in the maternal arterial P0 2 of only 20% in the group 2 animals. During the exchange in group 1, the fetal blood P0 2 increased approximately 60% from 20.9 ± 3.8 torr to 35.2 ± 5.7 torr. During the exchange in group 2, the
862
Cefalo et al.
April 1, 1984 Am. J. Obstet. Gynecol.
Table II. Group 1; cardiorespiratory effects of exchange transfusion with Fluosol-DA (20%)
Maternal
Baseline 100% Oxygen IS min 30 min 45 min 60 min End + 10 min
Fluorocrit (%)
Hematocrit (%)
30.2 30.0 19.5 15.8 . 10.2 7.5 5.5
± ± ± ± ± ±
3.4 3.5 3.3 1.6 0.9 1.0 ± 0.6
3.5 5.5 10.2 8.0 9.0
± ± ± ± ±
Mean pulmonary arterial pressure (torr)
Mean* arterial pressure (torr)
91.67 93.33 91.33 90.83 90.00 90.83 86.70
0.5 0.5 0.9 0.4 0.1
± ± ± ± ± ± ±
2.2 1.40 7.47 6.86 5.77 6.86 7.64
17.08 16.25 27.50 29.58 31.25 32.50 30.00
± ± ± ± ± ± ±
Cardiac output (Umin)
1.42 1.42 2.05 3.75 4.38 3.16 6.67
3.73 2.73 3.55 5.80 7.08 6.75 5.90
± ± ± ± ± ± ±
0.85 0.52 0.84 1.48 1.48 1.65 1.70
Maternal arterial Po, (torr)
59.0 161.8 248.0 345.0 408.8 447.5 337.5
M[O,j:;"Rt
13.76 18.45 14.17 10.58 7.45 6.26 5.29
± ± ± ±
4.45 48.2 51.3 16.7 ± 36.7 ± 16.0 ± 84.2
± ± ± ±
1.00 1.87 1.73 0.82 ± 0.69 ± 0.68 ± 0.58
*Mean arterial pressure = pulse pressure/3 + diastolic. tMilliliters of oxygen per deciliter, oxygen content of maternal arterial whole blood, mixed venous whole blood. *Milliliters of oxygen per deciliter, oxygen content of maternal whole blood, perfluorochemical blood mixture. §Milliliters of oxygen per deciliter, oxygen content of fetal whole blood. II Milliliters of oxygen per deciliter, oxygen content dissolved in aqueous phase of fetal blood.
Table III. Group 2; cardiorespiratory effects of exchange transfusion with plasma and Ringer's lactate
Maternal
Baseline 100% Oxygen IS min 30 min 45 min 60 min End + 10 min
Hematocrit (%)
Mean* arterial pressure (torr)
32.8 29.4 23.5 19.2 13.6 10.3 10.0
104.50 90.0 83.34 69.17 62.50 51.10 53.34
± ± ± ± ± ± ±
2.8 3.0 2.5 2.8 0.9 1.2 1.0
± ± ± ± ± ± ±
5.53 7.58 7.04 6.29 5.34 4.44 6.67
Mean pulmonary arterial pressure (torr)
17.5 16.25 17.33 15.42 14.45 13.33 12.50
± ± ± ± ±
0.48 1.72 2.52 1.42 1.47 ± 2.89 ± 4.17
Cardiac output (Umin)
5.20 5.00 5.73 6.58 6.10 5.63 6.40
± ± ± ± ± ± ±
0.64 0.40 0.83 0.86 1.10 1.36 0.40
Arterial Po, (torr)
74.2 252.2 266.0 253.4 295.4 305.0 300.0
± ± ± ± ± ± ±
10.1 42.2 44.0 31.3 28.5 30.8 35.4
M[O,j~'Bt
18.73 20.00 16.88 13.69 10.03 7.66 6.19
± ± ± ±
1.32 0.9 1.57 1.98 ± 0.58 ± 0.74 ± 0.20
*Mean blood pressure = pulse pressure/3 + diastolic. tMilliliters of oxygen per deciliter, oxygen content of maternal whole blood. *Milliliters of oxygen per deciliter, oxygen content of maternal mixed venous blood. §Milliliters of oxygen per deciliter, oxygen content of fetal whole blood. II Milliliters of oxygen per deciliter, oxygen content dissolved in aqueous phase of fetal blood.
fetal blood P0 2 decreased approximately 36% from 25.5 ± 1.6 torr to 16.1 ± 3.8 torr despite maternal hyperoxia. After an initial increase in both the maternal arterial and mixed venous oxygen content during the baseline period of maternal hyperoxia, there was a marked decrease in the blood oxygen content in both groups during the exchange period. In group 1, whole blood-perfluorochemical mixture oxygen content, M[02]~~ increased at each interval of time, along with the fluorocrit. During the Fluosol-DA (20%) exchange period, the fetal blood oxygen content in the aqueous and whole blood phases increased by 47% and 65%, respectively, from the pre-exchanged baseline fetal blood content value (Figs. 2 and 3). However, in group 2 fetuses, there was a progressive decline in fetal blood oxygen content in both the aqueous and whole blood phases despite a high maternal blood oxygen tension (Figs. 2 and 3). Maternal arterial and venous blood pH
and PC02 levels did not change in either group of animals. Fetal pH and Pco2 levels did not change in group 1 animals; however, there was a marked decrease in fetal blood pH and increase in Pco2, along with a fall in fetal P0 2 and oxygen content in group 2 animals. Fetal brain oxygenation. In both groups, there was an increase in the proportion of oxygenated hemoglobin as measured optically in the fetus when the ewe received 100% oxygen prior to the exchange. During this time, the light transmission correlated with the increased fetal blood P02 and oxygen content. As noted in Fig. 1, which is representative of all four animals in group 1, there was a progressive increase in the proportion of oxygenated hemoglobin and a progressive decrease in reduced hemoglobin during the Fluosol exchange in the maternal ewe. This clear trend in group 1 fetuses was not consistently seen in group 2 fetuses. Each animal in the two groups reacted to the
Exchange transfusion with red blood cell substitute
Volume 148 Number 7
Fetal venous Po, (torr)
Hematocrit
M[O']:;"Bf 9.17 12.37 8.33 7.01 5.26 4.73 4.49
± ± ± ± ± ± ±
0.67 1.51 1.40 0.42 0.39 0.51 0.35
M[O,]~~'t
0.75 1.0 1.2 1.3 1.4
± ± ± ± ±
0.05 0.09 0.04 0.01 0.03
Fetal
(%)
39.8 40.6 40.6 40.4 40.8 40.6 40.4
Baseline 100% Oxygen 15 min 30 min 45 min 60 min End + 10 min
Hematocrit
M[0.J:;"Bt 9.69 14.19 8.84 5.57 2.96 2.20 1.81
± ± ± ± ± ± ±
0.81 2.59 1.90 1.25 0.74 0.26 0.49
Fetal
Baseline 100% Oxygen 15 min 30 min 45 min 60 min End + IO min
(%)
37.8 38.5 37.9 38.1 37.4 36.5 39.0
± ± ± ± ± ± ±
4.7 3.6 3.3 3.8 3.8 l.l
administration of 100% nitrogen as displayed in Fig. 1, which shows a sharp and immediate decrease in the quantity of oxygenated hemoglobin and an increase in the quantity of reduced hemoglobin. The fetal hematocrits did not reveal any gross evidence of perAuorochemicals. Chemical analysis by gas chromatography of fetal blood from group 1 animals did not reveal any evidence of placental transmission of the perAuorochemicals during the period of the study. Comment
In 1979, after studies on decerebrate human subjects, adult volunteers were given Fluosol-DA (20%).1 Since then, the clinical use of a perAuorochemical emulsion as an erythrocyte substitute has been shown to directly increase the delivery of oxygen to tissues by maintaining perfusion and transporting oxygen. Presently, in the United States, hemorrhaging or anemic patients who refuse blood and blood products are given Fluosol-DA (20%) in emergency situations under the protocol of a multi centered randomized control study approved by the Food and Drug Administration. Fluosol-DA (20%) is a balanced salt, glycerol, yolk
± ± ± ± ± ± ±
2.3 1.5 1.0 1.5 1.7 1.6 1.7
15.6 20.9 26.1 32.1 33.4 35.2 33.2
Venous Po, (torr)
19.1 25.5 24.8 19.61 19.4 16.1 13.8
± ± ± ± ± ± ±
2.2 1.6 1.5 2.7 2.3 2.7 2.5
± ± ± ± ± ± ±
j[O'/WB§ 4.96 7.75 8.92 10.99 11.69 12.35 12.55
0.09 3.8 6.3 7.2 7.0 5.7 4.1
± ± ± ± ± ± ±
f[O'/WB§ 6.10 9.65 8.87 7.03 5.89 3.65 3.35
± ± ± ± ± ± ±
1.39 0.82 0.36 0.07 0.75 0.214 0.61
0.47 2.09 2.22.59 2.24 2.11 2.11
863
f[O'/'"1"1I 0.043 0.060 0.069 0.081 0.084 0.088 0.084
± ± ± ± ± ± ±
0.004 0.009 0.016 0.019 0.018 0.0 I 7 0.014
f[O,]",!"" 0.054 0.078 0.074 0.061 0.055 0.041 0.040
± ± ± ± ± ± ±
0.009 0.007 0.005 0.006 0.006 0.003 0.003
phospholipid, and starch solution which contains 20 gmllOO ml of total solution of a fine particulate emulsion of perAuorodecalin and perAuorotripropylamine (Table I). Pluoronic F-68 is a nonionic surfactant and the major emulsifier that allows for the perftuorochemicals to mix with the blood. Fluosol-DA (20%) transports oxygen by direct solubility, and the volume of oxygen dissolved changes linearly with the P02 according to Henry's law. At room air, a 30% to 40% solution of the perAuorochemicals would carry as much oxygen as whole blood. However, this concentration is diffi.~lt to emulsify. In the presence of the emulsifier,a concentration of the perAuorochemicals has a p\1Ysiologic pH, oncotic and osmotic pressure, and mixes with whole blood (Table I). At room air, oxygen tension Fluosol-DA (20%) has only a small capacity to carry oxygen, and the emulsion acts primarily as a volume expander, because of the presence of Pluoronic F-68, which produces the oncotic pressure. With administration of 100% oxygen, Fluosol-DA (20%) has an oxygen-carrying capacity of 5.6 mlldl, which is approximately one third of that of whole blood.s In addition to the partial pressure of oxygen, the quantity of physi-
'2P.%
864 Cefalo et al.
April 1, 1984 Am. J. Obstet. Gynecol.
16.0 14.0
~ .... 12.0
E
~
10.0
IZ
~ 8.0
isu
6.0
In ~
[j 4.0 2.0
30
Room 100%
Air
~
45
60
TIME (Minutes)
70
IOO%Nz
90
Fig. 2. Oxygen content offetal whole blood in group 1 (±SEM), Fluosol-DA (20%) exchanged maternal ewes (0-0-0) and group 2 plasma and Ringer's lactate exchanged maternal ewes (-----).
.12 '0
......
E I-
z
w I-
z
.10 .08 .06
0
U ::0
.04
0
N
~ .02 Room 100"10 Air ~
15
30
45
TIME (Minutes)
60
70
90
IOO"loNz
Fig. 3. Oxygen content dissolved in aqueous phase fetal blood in group 1 (±SEM) Fluosol-DA (20%) exchanged maternal ewes (0-0--0) and group 2 plasma and Ringer's lactate exchanged maternal ewes (____ ).
cally dissolved oxygen carried by Fluosol-DA (20%) is related to the fluorocarbon concentration or fluorocrit. In the presence of a whole blood/Fluosol-DA (20%) mixture, oxygen will be carried (1) chemically combined with hemoglobin, (2) dissolved in the perfluorochemical emulsion, and (3) dissolved in the plasma. A recent clinical study reported that, in the presence of a fluorocrit of 3% and a high arterial Po2 , the arterial and mixed venous hemoglobin saturation studies reflected that the tissues will obtain most of their oxygen from dissolved oxygen prior to any significant oxygen obtained from hemoglobin. 4 The efficiency of the delivery of oxygen to the tissues by Fluosol-DA (20%) may be related to the low viscosity of the emulsion and the particulate size of 0.2 M which both support flow through small or constricted vessels and, thus, improve collateral and capillary circulation. Studies in animals
have shown a decrease in damage secondary to myocardial and cerebral ischemia when the animals received perfluorochemical emulsions and 95% to 100% oxygenY' 12 The use of Fluosol-DA (20%) during an isovolemic exchange in our preparation confirmed the efficacy of perfluorochemical as both a volume expander and an oxygen transport medium, since blood pressure was maintained and delivery of oxygen occurred across the placenta. The increase in pulmonary arterial pressure has been repeatedly reported in animal and human studies. 2 - 4 The increase in pulmonary arterial pressure is probably secondary to the volume-expanding properties of the emulsion. Vercelotti and associates l3 proposed an activation of the complement system as a mechanism of the increased pulmonary arterial pressure. Their studies in rabbits revealed an activation of the complement system after administration of Fluosol-DA (20%).13 In the same report, both the activation of complement and the increase in pulmonary arterial pressure were avoided in a human subject by prior administration of a corticosteroid. 13 The increased cardiac output reported in our group 1 animals may have been secondary to acute volume expansion or an adrenergic response to acute hemorrhage or to the surgical procedure. In group 2 animals, the blood pressure was not maintained despite a near isovolemic replacement with plasma and Ringer's lactate. Despite maternal hyperoxia, fetal P02 and oxygen content decreased, which may have been secondary to a decreased uteroplacental circulation. The findings in our studies are consistent with those in other investigations of maternal and fetal circulation and oxygen transfer in pregnant sheep subjected to acute hemorrhage. 14 These hypovolemic studies have demonstrated a decrease in uteroplacental circulation and fetal hypoxemia whether maternal blood pressure is normal or decreased and in the presence of normal maternal oxygen tension. 14 The transfer of oxygen across the placenta is a function of many factors, including differences in maternal and fetal Po 2 , maternal and fetal intervillous blood flow, the oxygen affinity and hemoglobin concentration of maternal and fetal blood, placental permeability, and differences in maternal and fetal PC02 • 15 • 16 Fetal oxygen uptake is favored by a high concentration of hemoglobin and a greater affinity for oxygen. The transfer of oxygen under normal conditions is not thought to be limited by resistance to diffusion of the placental membrane, but is flow-limited. The driving force across the placental membrane is the difference in the partial pressure of the physically dissolved gas in the maternal and fetal blood. Under normal conditions, 0.3 ml of oxygen/ 100 ml is physically dissolved in
Volume 148 Number 7
the plasma and approximately 15 to 17 ml of oxygen/ 100 ml is bound to hemoglobin. As the physically dissolved oxygen diffuses across the placenta, additional oxygen is released from the maternal hemoglobin. In our Fluosol-DA (20%) preparations, there was ready delivery of oxygen across the placenta in the presence of an increasing content of dissolved oxygen in the perfluorochemicallmaternal blood emulsion mixture and a decreasing maternal whole blood oxygen content. In addition, cardiac output was increased and mean blood pressure did not change. Under the conditions of our study of isovolemic exchange and maternal hyperoxia, the Fluosol-DA (20%)treated and the untreated groups of animals had a decrease in both maternal hematocrits and oxygen content of arterial and mixed venous blood. However, in the Fluosol-DA (20%) group, the fetal blood oxygen tension and oxygen content increased. The increase in blood oxygen content and oxygen tension in the fetus was reflected as a decrease in the proportion of reduced hemoglobin perfusing the brain, as determined by the infrared spectrophotometric method. It appears that, if blood pressure is maintained and cardiac output and maternal hyperoxia are increased, oxygen is readily released and transferred across the placenta in the presence of a perfluorochemical maternal blood mixture. The oxygen uptake and delivery properties of Fluosol-DA (20%) are rapid (almost twice that of hemoglobin), reversible, and temporary. The emulsion is taken up by the reticuloendothelial system of the liver and spleen and is excreted mainly by the lungs and skin without any catabolism. The emulsion is not metabolized in vivo, has a blood half-life of approximately 12 to 18 hours, and a body half-life of 7 to 8 days. Under conditions of acute hypovolemia secondary to loss of blood, in a patient who refuses blood, the administration of FluosoI-DA (20%) may allow for maternal resuscitation and stabilization and in utero resuscitation prior to delivery. In addition, other candidates for the use of erythrocyte substitutes in pregnancy may include patients whose pregnancies are complicated by carbon monoxide poisoning, sickle cell crisis, or drug overdose, in which situations an emergency exchange transfusion might be lifesaving for both mother and fetus. Further studies are necessary to test Fluosol-DA (20%) and its component parts as oxygen carriers and volume expanders in acute hypovolemic animal models. In addition, uteroplacental circulation, metabolic, and coagulation studies are necessary prior to clinical use of Fluosol-DA (20%) in the acute hypovolemic pregnant patient who refuses blood or blood products. These preliminary studies do seem to demonstrate that Fluosol-DA (20%) is effective in maintaining maternal
Exchange transfusion with red blood cell substitute
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cardiodynamic function, and that fetal oxygenation appears to increase despite a decrease in maternal blood oxygen content under the conditions of our study. We wish to thank Mr. Patrick Nash and Mr. William Palladino for their invaluable assistance with the research. REFERENCES I. Ohyanagi, H., Toshima, K., Sekita, M., Okamoto, M., Itah, T., Mitsuno, T., Naito, R., Suyama, T., and Yokoyama, K.: Clinical studies of perfluorochemical whole blood substitutes: Safety of Fluosol-DA (20%) in normal human volunteers, Clin. Ther. 2:306, 1979. 2. Tremper, K. K., Papin, R., Levine, E., Friedman, A., and Shoemaker, W. C.: Hemodynamic and oxygen transport effects of perfluorochemical blood substitute, Fluosol DA (20%), Crit. Care Med. 8:738, 1980. 3. Gould, S. A., Rosen, A. L., Sehgal, L. R., Sehgal, H. L., Rice, C. L., and Moss, G. S.: How good are fluorocarbon emulsions as O 2 carriers? Surg. Forum 32:299, 1981. 4. Tremper, K. K., Friedman, A. E., Levine, E. M., Lapin, R., and Camarillo, D.: The preoperative treatment of severely anemic patients with a perfluorochemical oxygentransport fluid, Fluosol-DA, N. Eng!. J. Med. 307:277, 1982. 5. Mitsuno, T., Ohyanagi, H., and Naito, R.: Clinical studies of a perfluorochemical whole blood substitute (FluosolDA), Ann. Surg. 195:60, 1982. 6. Seeds, J. W., Cefalo, R. C., Proctor, H. J., and Jobsis, F.: Near infrared spectrophotometry: A new technique for assessing fetal hypoxia, presented at the Thirtieth Annual Meeting of the Society for Gynecologic Investigation, Washington, D. C., March 17-20, 1983. (Abst. 543.) 7. Jobsis, F. F.: Non-invasive infrared monitoring of cerebral and myocardial oxygen sufficiency and circulatory parameters, Science 198:1264, 1977. 8. Rosen, A. L., Sehgal, L. R., Gould, S. A., Dalton, L., Rice, C. L., and Moss, G. S.: Fluorocarbon emulsions methodology to assess efficacy, Crit. Care Med. 10:149, 1982. 9. Bartels, H. P., Heinz, A., Hilpert, P., and Riegel, K.: In: Ditmer, D. S., editor: Blood and Other Body Fluids, Federation of the American Society of Experimental Biology, pp. 155, 159. ro. Kirschbaum, T. H., Brinkman, C. R., and Assali, N. S.: Effects of maternal-fetal blood exchange transfusion in fetal lambs, AM. J. OBSTET. GYNECOL. 110: 190, 1971. II. Glogar, D. H., Kloner, R. A., Muller,J., De Boer, L. W. V., Braunwald, E., and Clark, L. C., Jr.: Fluorocarbons reduce myocardial ischemic damage after coronary occlusion, Science 211:1439,1981. 12. Peerless, S. J., Ishikawa, R., Hunter, I. G., and Peerless, M. J.: Protective effects of Fluosol-DA in acute cerebral ischemia, Stroke 12:548, 1981. 13. Vercelotti, G., Hammerschmidt, D., Craddock, P., and Jacob, H.: Activation of plasma complement by per f1uorocarbon artificial blood: Probable mechanism of adverse pulmonary reaction in treated patients and rationale for corticosteroid prophylaxis, Blood 56: 1299, 1982. 14. Nuwayhid, B., Vaughn, D., Brinkman, C. R., III, and Assali, N. S.: Circulatory shock in pregnant sheep, AM. J. OBSTET. GYNECOL. 132:658, 1978. 15. Longo, L. D., Hill, E. P., Power, G. G.: Factors affecting placental oxygen transfer, in Longo, L. D., and Bartels, H., editors: Respiratory Gas Exchange and Blood Flow in the Placenta, DHEW Publication No. 73-361:345, Bethesda, Maryland, 1972. 16. Meschia, G.: Evolution of thinking in fetal respiratory physiology, AM. J. OBSTET. GYNECOL. 132:807, 1978.
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Discussion DR. Roy M. PITKIN, Iowa City, Iowa. Perftuorochemicals, organic compounds in which hydrogen atoms have been replaced by fluorine, bind with oxygen, and emulsified forms have been tested as a substitute for the oxygen-carrying role of blood. The first perfluorochemical produced for this purpose, Fluosol-DA (20%), has been widely publicized in the laypress, where it has been referred to, dramatically but inaccurately, as "artificial blood." The agent is currently being tested in humans under Investigational New Drug protocols in a few United States centers. To date, it has been used only in patients whose religious beliefs lead them to refuse blood transfusions under any circumstances. One such case was an obstetric patient, and I am indebted to Dr. Dwight P. Cruikshank, of the Medical College of Virginia, for providing me with the details of her course, so that I may relate them to you. She was a 34-year-old woman who experienced massive postpartum hemorrhage, probably from a low-lying placenta, immediately after vaginal delivery of twins. The use of ecbolic agents and bilateral hypogastric artery ligation was unsuccessful, and total hysterectomy was necessary for hemostasis. Extensive volume replacement with crystalloid solutions was given, and the postoperative hemoglobin and hematocrit values were 2.3 gm/dl and 7%, respectively. The patient was transferred by jet aircraft to Chicago and to Michael Reese Hospital, where she was given two units of Fluosol-DA (20%). This stabilized her hemodynamically, and she made a fairly uneventful, albeit prolonged, recovery. The potential for this exciting new approach is enormous, particularly in the practice of obstetrics, where the threat of hemorrhage is always present. Much more work needs to be done to investigate both safety and efficacy, but this preliminary study by Dr. Cefalo and his colleagues is encouraging. In acute experiments in sheep, induction of severe anemia by isovolemic replacement of the maternal volume with Fluosol-DA (20%) maintained maternal blood pressure and arterial oxygen content. More importantly, because it has not previously been demonstrated, fetal oxygenation was maintained as well. Thus, it seems to be clear that Fluosol-DA (20%) is capable of delivering oxygen effectively to the placenta and thence to the fetus. Moreover, Fluosol-DA (20%) itself was found not to cross the placenta. This study represents an important step in the evaluation of a new and potentially valuable therapeutic weapon. The project was well conceived and executed. The results are clearly described and interpreted. I have only two questions for Dr. Cefalo. The first is to ask him to speculate on any physiologic implications of his findings, with particular reference to the mechanism(s) of maternal-fetal oxygen transport. Fetal blood binds oxygen more avidly than does adult blood, presumably because of the differential binding characteristics of hemoglobin A and hemoglobin F to 2,3diphosphoglycerate. An increased oxygen affinity of
April 1, 1984 Am. J. Obstet. Gynecol.
fetal over adult erythrocytes is regarded as the principal mechanism that favors the transfer of oxygen from mother to fetus. What-if anything-does the finding that oxygen transfer to the fetus also occurs from a perfluorochemical on the maternal side of the placenta mean in this regard? Second, perhaps Dr. Cefalo would comment on any potential clinical significance involved in the remarkable degree of pulmonary hypertension observed with Fluosol-DA (20%) treatment. DR. CHARLES BRINKMAN, Los Angeles, California. I am also curious about the increase in both pulmonary arterial and systemic arterial pressures. You mentioned that you hypothesize that the intravascular volume had increased, probably secondary to the increased oncotic pressure. I wonder whether you have looked at either intravascular volumes or, with your Swan-Ganz catheter, pulmonary capillary wedge pressure which might give you some idea of what was going on the other side of the vascular tree. DR. THOMAS H. KIRSCHBAUM, East Lansing, Michigan. Several years ago, I experimented with a mathematical model of the sheep placental oxygen transfer system and demonstrated an argument that it is the nonlinear shape of the oxyhemoglobin dissociation curves of mother and fetus that limits oxygen transfer! and predicted that, to the extent that one could replace those dissociation curves with linear functions of P0 2 , a barrier to diffusibility across the placenta would diminish proportionally. Your work supports that argument, of course, just as did the work which my associates and F did with hyperbaric oxygenation of pregnant ewes. I wonder whether you have replaced fetal blood with Fluosol-DA, since we would predict the same facilitative effects on oxygen transfer across the placenta there. REFERENCES 1. Kirschbaum, T. H., and Shapiro, N. Z.: A mathematical model of placental oxygen transfer, J. Theoret. BioI. 25:380, 1969. 2. Kirschbaum, T. H., Dilts, P. V., Jr., and Assali, N. S.: Placental oxygen transfer in pregnant ewes during hyperbaric oxygenation, Pediatr. Res. 3:398, 1969.
DR. RICHARD P. PERKINS, Albuquerque, New Mexico. We had a patient of similar religious preference who had severe Rh isoimmunization, and the question came up about whether this product might serve some useful purpose in replacing fetal blood or being used in place of fetal transfusion. Thanks to the people at North Carolina, we were put in touch with the distributors of the product in this country and discussed with them the possibility of its use. We were told that an Act of Congress would constitute the initial step in getting this product for use in the fetus and children under 18 years of age. It appears that the oxygen affinity of this particular product is relatively low, in that it does take up oxygen readily when exposed to high concentrations and releases it readily. However, for use in the fetus, where P0 2
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availability at the placental level would be limited, it would seem, even if it does become approved, that it will not solve our problems of treating the affected fetus of the woman with this particular religious belief. DR. CEFALO (Closing). The questions asked by Dr. Pitkin are most appropriate. We must consider that Fluosol-DA 20% solution is very different from blood in that it carries a high partial pressure of oxygen in a biologic fluid with a high and useful concentration of dissolved oxygen. When we think about maternal-fetal transport of oxygen, we think about the mechanism of diffusion, and we must consider the role of partial pressure. The interesting thing with Fluosol is that the increase in the blood P0 2 that one sees with a blood/Fluosol mixture with high oxygen tension or high Flo" is greater than that which would be expected from the Flo, alone. This may be related to the fact that there are decreased pulmonary shunts secondary to the Fluosol with subsequent improved microcirculation of the pulmonary circulation, which may allow for a partial pressure of oxygen greater than expected from the Flo" level. This greater partial pressure allows for a higher gradient for transfer of oxygen from mother to fetus. The second factor that contributes to the increased partial pressure of oxygen is that the amount of oxygen dissolved in the Fluosol is greater than that of plasma and the amount that is released is faster. With an increased amount of dissolved oxygen, there is less oxygen released from the hemoglobin. This is very important because it allows for a higher venous blood oxygen saturation. Previously published work has indicated that the fetal blood oxygenation depends, in part, upon the venous oxygen saturation leaving the placental uterine veins. If a significant amount of oxygen transferring across the placenta is coming from the dissolved oxygen and if the venous oxygen saturation remains high, which our studies demonstrate, then that would allow for a better transfer of oxygen to the fetus. More important, we must think of the Fluosol as an acellular colloidal suspension and, as such, it is not flow limited. Therefore, we are thinking about an oxygen transfer medium that is not flow limited, which is unique. In fact, in a bloodlFluosol mixture, with its low shear rates, there is less increase in viscosity than with whole blood alone. This, combined with the fact that perfluorochemical tends to flow in low-flow areas
Exchange transfusion with red blood cell substitute 867
rather than high-flow areas where red blood cells are prone to travel, could allow oxygen transfer in vasoconstricted areas, which would also enhance maternalfetal oxygen transfer. In fact, ischemic cerebral and myocardium studies of various animals, together with Fluosol administration, has decreased the amount of damage secondary to the ischemia. The surface area is another factor in oxygen transfer. The surface area with the perfluorochemical particles is greater than that associated with red blood cells in an equal quantity of blood, again allowing for greater increase in oxygen transfer. Also in favor of oxygen transfer is the fact that the release of oxygen from Fluosol is twice as fast as that from hemoglobin. The increased pulmonary artery pressure has been very consistently demonstrated in animals and humans. In humans, even with a test dose of 0.5 ml of Fluosol, an increase in the pulmonary artery pressure has been noted. This sustained response is transitory, lasting only 60 to 75 minutes. When wedge pressures have been measured, they have been in the range of 18 to 20 torr. The immediate increase in the pulmonary artery pressure is much like we see with an intravenous bolus of E. coli endotoxin in the sheep, which has been related to prostaglandin production and release. With Fluosol administration there may be pulmonary vascular damage secondary to a leukostasis within the vasculature, a margination of the granulocytes and platelets which may be associated with pulmonary vasculature damage with release of vasoactive substances. Probably the vasoactive substances are prostaglandins, e.g., prostaglandin F2a. The other possible mechanism is that there is an increase in complement C5A upon administration of the Fluosol and that this complement may be activated because of the Pluronic F -68, the emulsifying agent. This activation has been averted by the use of a glucocorticoid prior to the administration of Fluosol. As far as exchange transfusion in the fetus with Fluosol, as questioned by Drs. Kirschbaum and Perkins, we are about to engage in a protocol to study exchange transfusion of the fetus with Fluosol. I believe that Dr. Perkins' comment is pertinent in that it takes a high P0 2 in adult blood, as far as we know, to increase the oxygen capacity of Fluosol. However, we do not know what is going to happen when we use it with fetal blood.
J.
OBSTET. GVNECOL. 148:859, 1984.)
Studies in both nonpregnant laboratory animals and nonpregnant humans have demonstrated the safety and efficacy of perfluorochemicals in both improving oxygen delivery and maintaining circulation during conditions of acute loss of blood. I - 5 Fluosol-DA (20%) is the trade name of an isotonic and isooncotic milky white synthetic erythrocyte emulsion that consists of electrolytes, starch, and the emulsified perfluorochemicals of perfluorodecalin and perfluorotripropylamine. Clinically, Fluosol-DA (20%) has been used in the severely anemic or hypovolemic nonpregnant adult who refuses blood. I, 2, 4, 5 This report presents the results of preliminary studies of the maternal and fetal cardiorespiratory effects of an isovolemic exchange transfusion of the near-term pregnant ewe with Fluosol-DA (20%). Methods and material
Two groups of mixed-breed ewes between 135 and 142 days' gestation were premedicated with 1 mg/kg of intramuscular ketamine hydrochloride and anesthetized with ketamine by continuous intravenous drip at
From the Departments of Obstetrics and Gynecology and Surgery, School of Medicine, University of North Carolina at Chapel Hill. Presented by invitation at the Second Annual Meeting of the American Gynecological and Obstetrical Society, Phoenix, Arizona, September 7-10, 1983. Reprint requests: Dr. Robert C. Cefalo, Department of Obstetrics and Gynecology, University of North Carolina School of Medicine, 214 MacNider Bldg., 202-H, Chapel Hill, North Carolina 27514.
7 to 9 mg/min via the external jugular vein. After intubation, the ewe's respiration was assisted by a respirator pump (Emerson volume-controlled ventilator, Model 3-PV) with room air initially, and then 100% oxygen. The maternal pulmonary artery was catheterized with a Swan-Ganz, flow-directed, thermal dilution catheter (Model 93A-131-7F). The catheter was floated into the pulmonary artery, with use of the characteristic pressure wave form to track its location. The maternal femoral artery was cannulated. Systemic and pulmonary arterial pressures were measured with pressure transducers (Hewlett-Packard Model 1280) and recorded on a multichannel recorder (Hewlett-Packard Model 7788A). Via laparotomy and hysterotomy incisions, the fetal head was exteriorized, with the amnion intact. Samples of fetal blood (1.0 ml) were obtained from an indwelling catheter placed in the jugular vein and advanced 8 to 10 em. The fetal head was stabilized within a modified Balfour retractor and fitted with a fiber-optic bundle and photomultiplier tube light detector for assessing continuous fetal cerebral oxygenation on the basis of the transcranial infrared spectrophotometric methodology of Seeds and associates. 6 The photomultiplier tube was positioned at 60 to 90 degrees to the incident light on the opposite side of the parietal fetal skull. The wave lengths of light at 770, 813, and 905 nm were presented to the fetal head, and changes in voltage at the photomultiplier tube were recorded continuously, as described by Jobsis. 7
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April 1. 1984 Am. J. Obstet. Gynecol.
Table I. Fluosol-DA (20%) emulsion composition after reconstitution Quantity Ingredient
(gm/dl)
Perftuorodecalin Perftuorotripropylamine Hydroxyethyl starch Pluoronic F-68 Glycerol Sodium chloride Egg yolk phospholypids Sodium bicarbonate Glucose Oleic acid Potassium chloride Calcium chloride Magnesium chloride Water for injection
14.0 6.0 3.0
2.7 0.8 0.6 0.4
0.21 0.18 0.04 0.03 0.02 0.02 Sufficient quantity
The sheep were divided into two groups. In group 1 (N = 4), the baseline period was followed by a period of maternal isovolemic exchange of Fluosol-DA (20%) for whole blood via a maternal femoral artery and vein with an IBM-2997 continuous-flow cell separator (IBM, Research Triangle Park, North Carolina). In group 2 (N = 4), the continuous-flow cell separator was used to remove maternal red blood cells and return the plasma supplemented with Ringer's lactate. Exchange transfusion in both groups was accomplished within 60 to 75 minutes. In group 1, the infusion rate of Fluosol-DA (20%) was approximately 80 ml/min, and each ewe had approximately 4,500 to 4,700 ml of whole blood exchanged with 5,000 ml of Fluosol-DA (20%). In group 2, approximately 1,400 to 1,600 ml of red blood cells was removed, and approximately 1,500 to 1,700 ml of plasma and 1,500 to 1,700 of Ringer's lactate was returned to the ewe. As described by Jobsis 7 and Seeds and associates,6 the known tissue transparency to infrared light and the known absorption peaks of reduced and oxygenated hemoglobin were used, processed electronically as voltage potentials at the photomultiplier tube, and recorded continuously. After the fetal hemoglobin voltage channels on the recorder had stabilized, they were zeroed with the mother breathing room air and again after the ewe was ventilated with 100% oxygen. Each ewe was killed at the conclusion of the experiment by ventilation with 100% nitrogen. Serial duplicate maternal and fetal hematocrits (hct) and fluorocrits (fct) (the volume percentage of the white bottom layer of perfluorochemicals centrifuged from blood) were determined in capillary tubes that were centrifuged for 10 minutes at 10,000 rpm. Data collected included continuous maternal femoral and pulmonary arterial pressure, intermittent (every 15 minutes) maternal cardiac output in duplicate by the
thermal dilution technique (Edward's Laboratory cardiac output model 9520A), and maternal arterial and mixed venous and fetal blood gases and pH. All maternal and fetal samples of blood for analysis of gas were obtained simultaneously and drawn anaerobically. The oxygen and carbon dioxide tensions and pH were measured with an Instrument Laboratory No. 113 gas analyzer at 38° C temperature. The pre-Fluosol-DA (20%) exchange oxygen (0 2) content of maternal arterial whole blood, M[02]~B' and mixed venous blood, M[02]~B' was calculated from the sum of the oxygen chemically combined with hemoglobin and physically dissolved oxygen as described by M[02]WB = [02]rbc + [02]dISS. in ml/0 2 /dl. 8 The [02]rbc was calculated from the product of the hemoglobin concentration, the derived percentage of oxygen saturation from the sheep blood oxygen dissociation curve, and the Hufner coefficient (1.34 ml of oxygen per gram of hemoglobin per 100 ml of blood at standard temperature and pressure).9 [02]dISS. was calculated as the product of the blood P02 and solubility coefficient of· oxygen in plasma. When Fluosol-DA (20%) is administered, oxygen is carried by hemoglobin and in physical solution by the perfluorochemical (pfc) and aqueous (aqu) phases. Rosen and associates8 described the calculations of whole blood-perfluorochemical emulsion mixture oxygen content with the use of Henry's law applied to the perfluorochemical and aqueous phases of whole blood mixture. The oxygen dissolved in the maternal perfluorochemical phase per deciliter of whole blood emulsion mixture in group 1 was determined by the formula [02]diSS. = [02]pfc + [02]aQu' The [02]pfc was determined by the formula [02]pfc
= apfc X ~~~ x
fct
=
0.000318 X P02 X fct, and the [02]aQU was determined Po by the formula [02]aQU = aaqu X 76~ X (l00 - fct) = 0.0000316 X P0 2 X (l00 - fct). The fetal blood content, f[02]wB, in milliliters of oxygen per deciliter of whole blood, was calculated from the product of the hemoglobin concentration, the Hufner solubility coefficient, the derived percentage oxyhemoglobin saturation from the fetal sheep blood oxygen dissociation curves, and fetal blood oxygen tension. 9 The amount of dissolved oxygen content in the fetal blood, f[02]~~' was calculated by the product of the Bunsen solubility coefficient and oxygen tension (0.0000316 X P0 2 X 100). Fluosol-DA (20%) was supplied by Alpha Therapeutic Corporation, Los Angeles, California, as manufactured by Green Cross Corporation, Osaka, Japan. Fluosol-DA (20%) is supplied in three parts which must be reconstituted before intravenous administration. The final perfluorochemical emulsion as listed in Table I has the appearance and consistency of skim milk, a
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Volume 148 Number 7
EXP.3F
JANUARY IS,
CONTROL (100 %OXYGEN)
FLUOSOL EXCHANGE
MATERNAL NITROGEN
I
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(Torr)
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~~~~ooJ200._____io-.. ........ ___ la.lt. .N.iii. . . . . . . . . . . . Lot •• (Torr)
00
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Fig. 1. Example of ewe undergoing Fluosol-DA (20%) isovolemic exchange.
pH of 7.40, an osmolarity of 410 mOsm, oncotic pressure of 380 to 395 mm H 2 0, and an average particle size distribution of the perfluorochemical compound of 0.211-. The experimental protocol consisted of: (I) a postoperative baseline period of 20 to 30 minutes during which maternal arterial pressures were recorded continuously, with intermittent determinations of maternal and fetal blood gases and pH and maternal cardiac output, while the ewe breathed room air and after ventilation with 100% oxygen; (2) Fluosol-DA (20%) exchange transfusion period in which whole blood was removed at 70 to 80 mllmin in group 1 and the Fluosol-DA (20%) was infused at approximately 80 mllmin, and in group 2 the red blood cells were removed and the plasma and Ringer's lactate was coincidentally reinfused at approximately 80 mllmin; (3) a 15- to 20-minute period in which the ewe breathed 100% nitrogen to induce maternal and fetal hypoxia; (4) continuous recording of maternal blood and pulmonary arterial pressures and the infrared light transmittance as a reflection of the quantity of oxidized and reduced hemoglobin within the transilluminated cerebral field; and (5) intermittent (l5-minute) determinations of maternal and fetal blood gases and pH and maternal cardiac output.
Results Tables II and III list the relevant cardiorespiratory data. The weight of group 1 animals averaged 57 kg. Data from Kirschbaum and associates lO suggested an average maternal blood volume of 5.5 L, and, therefore, each ewe in group 1 had a nearly 95% exchange of whole blood with Fluosol-DA (20%) over a period of 60 to 75 minutes. The mean maternal baseline hematocrit in group 1 was 30.2%. At the end of the Fluosol
exchange, the mean hematocrit was S.5% and the mean fluorocrit was 9.0%. In group 2, the average weight of the animals was 55 kg, with an estimated blood volume of 5 L. The average amount of red blood cells removed over a period of approximately 60 minutes was 1,500 ml, and the returned plasma and Ringer's lactate each averaged 1,700 m!. The mean maternal baseline hematocrit was 32.8%. The mean hematocrit at the end of the 60minute period was 8%. In both groups 1 and 2, the fetal hematocrit remained stable, with means of 40.1 % and 39.2%, respectively. Cardiovascular. In group 1 animals, the mean blood pressure did not change appreciably during the Fluosol-DA (20%) exchange from the baseline values (Fig. 1). However, the mean cardiac output and the mean pulmonary arterial pressure increased approximately 40% and 50%, respectively, during the Fluosol-DA (20%) exchange. The pulmonary arterial pressure increased within a few minutes of starting the Fluosol-DA (20%) exchange (Fig. 1). In group 2 animals, the mean blood pressure decreased by 36% starting after approximately 30 minutes of exchange and by 47% by the end of the exchange, but the cardiac output and mean pulmonary arterial pressure did not change appreciably from baseline values. Respiratory. The maternal arterial P02 increased from the baseline values with the administration of 100% oxygen in both groups of animals. During the exchange with Fluosol-DA (20%) in group 1 animals, there was a further increase in the maternal arterial P02 of over 100%, as opposed to a further increase in the maternal arterial P0 2 of only 20% in the group 2 animals. During the exchange in group 1, the fetal blood P0 2 increased approximately 60% from 20.9 ± 3.8 torr to 35.2 ± 5.7 torr. During the exchange in group 2, the
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April 1, 1984 Am. J. Obstet. Gynecol.
Table II. Group 1; cardiorespiratory effects of exchange transfusion with Fluosol-DA (20%)
Maternal
Baseline 100% Oxygen IS min 30 min 45 min 60 min End + 10 min
Fluorocrit (%)
Hematocrit (%)
30.2 30.0 19.5 15.8 . 10.2 7.5 5.5
± ± ± ± ± ±
3.4 3.5 3.3 1.6 0.9 1.0 ± 0.6
3.5 5.5 10.2 8.0 9.0
± ± ± ± ±
Mean pulmonary arterial pressure (torr)
Mean* arterial pressure (torr)
91.67 93.33 91.33 90.83 90.00 90.83 86.70
0.5 0.5 0.9 0.4 0.1
± ± ± ± ± ± ±
2.2 1.40 7.47 6.86 5.77 6.86 7.64
17.08 16.25 27.50 29.58 31.25 32.50 30.00
± ± ± ± ± ± ±
Cardiac output (Umin)
1.42 1.42 2.05 3.75 4.38 3.16 6.67
3.73 2.73 3.55 5.80 7.08 6.75 5.90
± ± ± ± ± ± ±
0.85 0.52 0.84 1.48 1.48 1.65 1.70
Maternal arterial Po, (torr)
59.0 161.8 248.0 345.0 408.8 447.5 337.5
M[O,j:;"Rt
13.76 18.45 14.17 10.58 7.45 6.26 5.29
± ± ± ±
4.45 48.2 51.3 16.7 ± 36.7 ± 16.0 ± 84.2
± ± ± ±
1.00 1.87 1.73 0.82 ± 0.69 ± 0.68 ± 0.58
*Mean arterial pressure = pulse pressure/3 + diastolic. tMilliliters of oxygen per deciliter, oxygen content of maternal arterial whole blood, mixed venous whole blood. *Milliliters of oxygen per deciliter, oxygen content of maternal whole blood, perfluorochemical blood mixture. §Milliliters of oxygen per deciliter, oxygen content of fetal whole blood. II Milliliters of oxygen per deciliter, oxygen content dissolved in aqueous phase of fetal blood.
Table III. Group 2; cardiorespiratory effects of exchange transfusion with plasma and Ringer's lactate
Maternal
Baseline 100% Oxygen IS min 30 min 45 min 60 min End + 10 min
Hematocrit (%)
Mean* arterial pressure (torr)
32.8 29.4 23.5 19.2 13.6 10.3 10.0
104.50 90.0 83.34 69.17 62.50 51.10 53.34
± ± ± ± ± ± ±
2.8 3.0 2.5 2.8 0.9 1.2 1.0
± ± ± ± ± ± ±
5.53 7.58 7.04 6.29 5.34 4.44 6.67
Mean pulmonary arterial pressure (torr)
17.5 16.25 17.33 15.42 14.45 13.33 12.50
± ± ± ± ±
0.48 1.72 2.52 1.42 1.47 ± 2.89 ± 4.17
Cardiac output (Umin)
5.20 5.00 5.73 6.58 6.10 5.63 6.40
± ± ± ± ± ± ±
0.64 0.40 0.83 0.86 1.10 1.36 0.40
Arterial Po, (torr)
74.2 252.2 266.0 253.4 295.4 305.0 300.0
± ± ± ± ± ± ±
10.1 42.2 44.0 31.3 28.5 30.8 35.4
M[O,j~'Bt
18.73 20.00 16.88 13.69 10.03 7.66 6.19
± ± ± ±
1.32 0.9 1.57 1.98 ± 0.58 ± 0.74 ± 0.20
*Mean blood pressure = pulse pressure/3 + diastolic. tMilliliters of oxygen per deciliter, oxygen content of maternal whole blood. *Milliliters of oxygen per deciliter, oxygen content of maternal mixed venous blood. §Milliliters of oxygen per deciliter, oxygen content of fetal whole blood. II Milliliters of oxygen per deciliter, oxygen content dissolved in aqueous phase of fetal blood.
fetal blood P0 2 decreased approximately 36% from 25.5 ± 1.6 torr to 16.1 ± 3.8 torr despite maternal hyperoxia. After an initial increase in both the maternal arterial and mixed venous oxygen content during the baseline period of maternal hyperoxia, there was a marked decrease in the blood oxygen content in both groups during the exchange period. In group 1, whole blood-perfluorochemical mixture oxygen content, M[02]~~ increased at each interval of time, along with the fluorocrit. During the Fluosol-DA (20%) exchange period, the fetal blood oxygen content in the aqueous and whole blood phases increased by 47% and 65%, respectively, from the pre-exchanged baseline fetal blood content value (Figs. 2 and 3). However, in group 2 fetuses, there was a progressive decline in fetal blood oxygen content in both the aqueous and whole blood phases despite a high maternal blood oxygen tension (Figs. 2 and 3). Maternal arterial and venous blood pH
and PC02 levels did not change in either group of animals. Fetal pH and Pco2 levels did not change in group 1 animals; however, there was a marked decrease in fetal blood pH and increase in Pco2, along with a fall in fetal P0 2 and oxygen content in group 2 animals. Fetal brain oxygenation. In both groups, there was an increase in the proportion of oxygenated hemoglobin as measured optically in the fetus when the ewe received 100% oxygen prior to the exchange. During this time, the light transmission correlated with the increased fetal blood P02 and oxygen content. As noted in Fig. 1, which is representative of all four animals in group 1, there was a progressive increase in the proportion of oxygenated hemoglobin and a progressive decrease in reduced hemoglobin during the Fluosol exchange in the maternal ewe. This clear trend in group 1 fetuses was not consistently seen in group 2 fetuses. Each animal in the two groups reacted to the
Exchange transfusion with red blood cell substitute
Volume 148 Number 7
Fetal venous Po, (torr)
Hematocrit
M[O']:;"Bf 9.17 12.37 8.33 7.01 5.26 4.73 4.49
± ± ± ± ± ± ±
0.67 1.51 1.40 0.42 0.39 0.51 0.35
M[O,]~~'t
0.75 1.0 1.2 1.3 1.4
± ± ± ± ±
0.05 0.09 0.04 0.01 0.03
Fetal
(%)
39.8 40.6 40.6 40.4 40.8 40.6 40.4
Baseline 100% Oxygen 15 min 30 min 45 min 60 min End + 10 min
Hematocrit
M[0.J:;"Bt 9.69 14.19 8.84 5.57 2.96 2.20 1.81
± ± ± ± ± ± ±
0.81 2.59 1.90 1.25 0.74 0.26 0.49
Fetal
Baseline 100% Oxygen 15 min 30 min 45 min 60 min End + IO min
(%)
37.8 38.5 37.9 38.1 37.4 36.5 39.0
± ± ± ± ± ± ±
4.7 3.6 3.3 3.8 3.8 l.l
administration of 100% nitrogen as displayed in Fig. 1, which shows a sharp and immediate decrease in the quantity of oxygenated hemoglobin and an increase in the quantity of reduced hemoglobin. The fetal hematocrits did not reveal any gross evidence of perAuorochemicals. Chemical analysis by gas chromatography of fetal blood from group 1 animals did not reveal any evidence of placental transmission of the perAuorochemicals during the period of the study. Comment
In 1979, after studies on decerebrate human subjects, adult volunteers were given Fluosol-DA (20%).1 Since then, the clinical use of a perAuorochemical emulsion as an erythrocyte substitute has been shown to directly increase the delivery of oxygen to tissues by maintaining perfusion and transporting oxygen. Presently, in the United States, hemorrhaging or anemic patients who refuse blood and blood products are given Fluosol-DA (20%) in emergency situations under the protocol of a multi centered randomized control study approved by the Food and Drug Administration. Fluosol-DA (20%) is a balanced salt, glycerol, yolk
± ± ± ± ± ± ±
2.3 1.5 1.0 1.5 1.7 1.6 1.7
15.6 20.9 26.1 32.1 33.4 35.2 33.2
Venous Po, (torr)
19.1 25.5 24.8 19.61 19.4 16.1 13.8
± ± ± ± ± ± ±
2.2 1.6 1.5 2.7 2.3 2.7 2.5
± ± ± ± ± ± ±
j[O'/WB§ 4.96 7.75 8.92 10.99 11.69 12.35 12.55
0.09 3.8 6.3 7.2 7.0 5.7 4.1
± ± ± ± ± ± ±
f[O'/WB§ 6.10 9.65 8.87 7.03 5.89 3.65 3.35
± ± ± ± ± ± ±
1.39 0.82 0.36 0.07 0.75 0.214 0.61
0.47 2.09 2.22.59 2.24 2.11 2.11
863
f[O'/'"1"1I 0.043 0.060 0.069 0.081 0.084 0.088 0.084
± ± ± ± ± ± ±
0.004 0.009 0.016 0.019 0.018 0.0 I 7 0.014
f[O,]",!"" 0.054 0.078 0.074 0.061 0.055 0.041 0.040
± ± ± ± ± ± ±
0.009 0.007 0.005 0.006 0.006 0.003 0.003
phospholipid, and starch solution which contains 20 gmllOO ml of total solution of a fine particulate emulsion of perAuorodecalin and perAuorotripropylamine (Table I). Pluoronic F-68 is a nonionic surfactant and the major emulsifier that allows for the perftuorochemicals to mix with the blood. Fluosol-DA (20%) transports oxygen by direct solubility, and the volume of oxygen dissolved changes linearly with the P02 according to Henry's law. At room air, a 30% to 40% solution of the perAuorochemicals would carry as much oxygen as whole blood. However, this concentration is diffi.~lt to emulsify. In the presence of the emulsifier,a concentration of the perAuorochemicals has a p\1Ysiologic pH, oncotic and osmotic pressure, and mixes with whole blood (Table I). At room air, oxygen tension Fluosol-DA (20%) has only a small capacity to carry oxygen, and the emulsion acts primarily as a volume expander, because of the presence of Pluoronic F-68, which produces the oncotic pressure. With administration of 100% oxygen, Fluosol-DA (20%) has an oxygen-carrying capacity of 5.6 mlldl, which is approximately one third of that of whole blood.s In addition to the partial pressure of oxygen, the quantity of physi-
'2P.%
864 Cefalo et al.
April 1, 1984 Am. J. Obstet. Gynecol.
16.0 14.0
~ .... 12.0
E
~
10.0
IZ
~ 8.0
isu
6.0
In ~
[j 4.0 2.0
30
Room 100%
Air
~
45
60
TIME (Minutes)
70
IOO%Nz
90
Fig. 2. Oxygen content offetal whole blood in group 1 (±SEM), Fluosol-DA (20%) exchanged maternal ewes (0-0-0) and group 2 plasma and Ringer's lactate exchanged maternal ewes (-----).
.12 '0
......
E I-
z
w I-
z
.10 .08 .06
0
U ::0
.04
0
N
~ .02 Room 100"10 Air ~
15
30
45
TIME (Minutes)
60
70
90
IOO"loNz
Fig. 3. Oxygen content dissolved in aqueous phase fetal blood in group 1 (±SEM) Fluosol-DA (20%) exchanged maternal ewes (0-0--0) and group 2 plasma and Ringer's lactate exchanged maternal ewes (____ ).
cally dissolved oxygen carried by Fluosol-DA (20%) is related to the fluorocarbon concentration or fluorocrit. In the presence of a whole blood/Fluosol-DA (20%) mixture, oxygen will be carried (1) chemically combined with hemoglobin, (2) dissolved in the perfluorochemical emulsion, and (3) dissolved in the plasma. A recent clinical study reported that, in the presence of a fluorocrit of 3% and a high arterial Po2 , the arterial and mixed venous hemoglobin saturation studies reflected that the tissues will obtain most of their oxygen from dissolved oxygen prior to any significant oxygen obtained from hemoglobin. 4 The efficiency of the delivery of oxygen to the tissues by Fluosol-DA (20%) may be related to the low viscosity of the emulsion and the particulate size of 0.2 M which both support flow through small or constricted vessels and, thus, improve collateral and capillary circulation. Studies in animals
have shown a decrease in damage secondary to myocardial and cerebral ischemia when the animals received perfluorochemical emulsions and 95% to 100% oxygenY' 12 The use of Fluosol-DA (20%) during an isovolemic exchange in our preparation confirmed the efficacy of perfluorochemical as both a volume expander and an oxygen transport medium, since blood pressure was maintained and delivery of oxygen occurred across the placenta. The increase in pulmonary arterial pressure has been repeatedly reported in animal and human studies. 2 - 4 The increase in pulmonary arterial pressure is probably secondary to the volume-expanding properties of the emulsion. Vercelotti and associates l3 proposed an activation of the complement system as a mechanism of the increased pulmonary arterial pressure. Their studies in rabbits revealed an activation of the complement system after administration of Fluosol-DA (20%).13 In the same report, both the activation of complement and the increase in pulmonary arterial pressure were avoided in a human subject by prior administration of a corticosteroid. 13 The increased cardiac output reported in our group 1 animals may have been secondary to acute volume expansion or an adrenergic response to acute hemorrhage or to the surgical procedure. In group 2 animals, the blood pressure was not maintained despite a near isovolemic replacement with plasma and Ringer's lactate. Despite maternal hyperoxia, fetal P02 and oxygen content decreased, which may have been secondary to a decreased uteroplacental circulation. The findings in our studies are consistent with those in other investigations of maternal and fetal circulation and oxygen transfer in pregnant sheep subjected to acute hemorrhage. 14 These hypovolemic studies have demonstrated a decrease in uteroplacental circulation and fetal hypoxemia whether maternal blood pressure is normal or decreased and in the presence of normal maternal oxygen tension. 14 The transfer of oxygen across the placenta is a function of many factors, including differences in maternal and fetal Po 2 , maternal and fetal intervillous blood flow, the oxygen affinity and hemoglobin concentration of maternal and fetal blood, placental permeability, and differences in maternal and fetal PC02 • 15 • 16 Fetal oxygen uptake is favored by a high concentration of hemoglobin and a greater affinity for oxygen. The transfer of oxygen under normal conditions is not thought to be limited by resistance to diffusion of the placental membrane, but is flow-limited. The driving force across the placental membrane is the difference in the partial pressure of the physically dissolved gas in the maternal and fetal blood. Under normal conditions, 0.3 ml of oxygen/ 100 ml is physically dissolved in
Volume 148 Number 7
the plasma and approximately 15 to 17 ml of oxygen/ 100 ml is bound to hemoglobin. As the physically dissolved oxygen diffuses across the placenta, additional oxygen is released from the maternal hemoglobin. In our Fluosol-DA (20%) preparations, there was ready delivery of oxygen across the placenta in the presence of an increasing content of dissolved oxygen in the perfluorochemicallmaternal blood emulsion mixture and a decreasing maternal whole blood oxygen content. In addition, cardiac output was increased and mean blood pressure did not change. Under the conditions of our study of isovolemic exchange and maternal hyperoxia, the Fluosol-DA (20%)treated and the untreated groups of animals had a decrease in both maternal hematocrits and oxygen content of arterial and mixed venous blood. However, in the Fluosol-DA (20%) group, the fetal blood oxygen tension and oxygen content increased. The increase in blood oxygen content and oxygen tension in the fetus was reflected as a decrease in the proportion of reduced hemoglobin perfusing the brain, as determined by the infrared spectrophotometric method. It appears that, if blood pressure is maintained and cardiac output and maternal hyperoxia are increased, oxygen is readily released and transferred across the placenta in the presence of a perfluorochemical maternal blood mixture. The oxygen uptake and delivery properties of Fluosol-DA (20%) are rapid (almost twice that of hemoglobin), reversible, and temporary. The emulsion is taken up by the reticuloendothelial system of the liver and spleen and is excreted mainly by the lungs and skin without any catabolism. The emulsion is not metabolized in vivo, has a blood half-life of approximately 12 to 18 hours, and a body half-life of 7 to 8 days. Under conditions of acute hypovolemia secondary to loss of blood, in a patient who refuses blood, the administration of FluosoI-DA (20%) may allow for maternal resuscitation and stabilization and in utero resuscitation prior to delivery. In addition, other candidates for the use of erythrocyte substitutes in pregnancy may include patients whose pregnancies are complicated by carbon monoxide poisoning, sickle cell crisis, or drug overdose, in which situations an emergency exchange transfusion might be lifesaving for both mother and fetus. Further studies are necessary to test Fluosol-DA (20%) and its component parts as oxygen carriers and volume expanders in acute hypovolemic animal models. In addition, uteroplacental circulation, metabolic, and coagulation studies are necessary prior to clinical use of Fluosol-DA (20%) in the acute hypovolemic pregnant patient who refuses blood or blood products. These preliminary studies do seem to demonstrate that Fluosol-DA (20%) is effective in maintaining maternal
Exchange transfusion with red blood cell substitute
865
cardiodynamic function, and that fetal oxygenation appears to increase despite a decrease in maternal blood oxygen content under the conditions of our study. We wish to thank Mr. Patrick Nash and Mr. William Palladino for their invaluable assistance with the research. REFERENCES I. Ohyanagi, H., Toshima, K., Sekita, M., Okamoto, M., Itah, T., Mitsuno, T., Naito, R., Suyama, T., and Yokoyama, K.: Clinical studies of perfluorochemical whole blood substitutes: Safety of Fluosol-DA (20%) in normal human volunteers, Clin. Ther. 2:306, 1979. 2. Tremper, K. K., Papin, R., Levine, E., Friedman, A., and Shoemaker, W. C.: Hemodynamic and oxygen transport effects of perfluorochemical blood substitute, Fluosol DA (20%), Crit. Care Med. 8:738, 1980. 3. Gould, S. A., Rosen, A. L., Sehgal, L. R., Sehgal, H. L., Rice, C. L., and Moss, G. S.: How good are fluorocarbon emulsions as O 2 carriers? Surg. Forum 32:299, 1981. 4. Tremper, K. K., Friedman, A. E., Levine, E. M., Lapin, R., and Camarillo, D.: The preoperative treatment of severely anemic patients with a perfluorochemical oxygentransport fluid, Fluosol-DA, N. Eng!. J. Med. 307:277, 1982. 5. Mitsuno, T., Ohyanagi, H., and Naito, R.: Clinical studies of a perfluorochemical whole blood substitute (FluosolDA), Ann. Surg. 195:60, 1982. 6. Seeds, J. W., Cefalo, R. C., Proctor, H. J., and Jobsis, F.: Near infrared spectrophotometry: A new technique for assessing fetal hypoxia, presented at the Thirtieth Annual Meeting of the Society for Gynecologic Investigation, Washington, D. C., March 17-20, 1983. (Abst. 543.) 7. Jobsis, F. F.: Non-invasive infrared monitoring of cerebral and myocardial oxygen sufficiency and circulatory parameters, Science 198:1264, 1977. 8. Rosen, A. L., Sehgal, L. R., Gould, S. A., Dalton, L., Rice, C. L., and Moss, G. S.: Fluorocarbon emulsions methodology to assess efficacy, Crit. Care Med. 10:149, 1982. 9. Bartels, H. P., Heinz, A., Hilpert, P., and Riegel, K.: In: Ditmer, D. S., editor: Blood and Other Body Fluids, Federation of the American Society of Experimental Biology, pp. 155, 159. ro. Kirschbaum, T. H., Brinkman, C. R., and Assali, N. S.: Effects of maternal-fetal blood exchange transfusion in fetal lambs, AM. J. OBSTET. GYNECOL. 110: 190, 1971. II. Glogar, D. H., Kloner, R. A., Muller,J., De Boer, L. W. V., Braunwald, E., and Clark, L. C., Jr.: Fluorocarbons reduce myocardial ischemic damage after coronary occlusion, Science 211:1439,1981. 12. Peerless, S. J., Ishikawa, R., Hunter, I. G., and Peerless, M. J.: Protective effects of Fluosol-DA in acute cerebral ischemia, Stroke 12:548, 1981. 13. Vercelotti, G., Hammerschmidt, D., Craddock, P., and Jacob, H.: Activation of plasma complement by per f1uorocarbon artificial blood: Probable mechanism of adverse pulmonary reaction in treated patients and rationale for corticosteroid prophylaxis, Blood 56: 1299, 1982. 14. Nuwayhid, B., Vaughn, D., Brinkman, C. R., III, and Assali, N. S.: Circulatory shock in pregnant sheep, AM. J. OBSTET. GYNECOL. 132:658, 1978. 15. Longo, L. D., Hill, E. P., Power, G. G.: Factors affecting placental oxygen transfer, in Longo, L. D., and Bartels, H., editors: Respiratory Gas Exchange and Blood Flow in the Placenta, DHEW Publication No. 73-361:345, Bethesda, Maryland, 1972. 16. Meschia, G.: Evolution of thinking in fetal respiratory physiology, AM. J. OBSTET. GYNECOL. 132:807, 1978.
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Cefalo et al.
Discussion DR. Roy M. PITKIN, Iowa City, Iowa. Perftuorochemicals, organic compounds in which hydrogen atoms have been replaced by fluorine, bind with oxygen, and emulsified forms have been tested as a substitute for the oxygen-carrying role of blood. The first perfluorochemical produced for this purpose, Fluosol-DA (20%), has been widely publicized in the laypress, where it has been referred to, dramatically but inaccurately, as "artificial blood." The agent is currently being tested in humans under Investigational New Drug protocols in a few United States centers. To date, it has been used only in patients whose religious beliefs lead them to refuse blood transfusions under any circumstances. One such case was an obstetric patient, and I am indebted to Dr. Dwight P. Cruikshank, of the Medical College of Virginia, for providing me with the details of her course, so that I may relate them to you. She was a 34-year-old woman who experienced massive postpartum hemorrhage, probably from a low-lying placenta, immediately after vaginal delivery of twins. The use of ecbolic agents and bilateral hypogastric artery ligation was unsuccessful, and total hysterectomy was necessary for hemostasis. Extensive volume replacement with crystalloid solutions was given, and the postoperative hemoglobin and hematocrit values were 2.3 gm/dl and 7%, respectively. The patient was transferred by jet aircraft to Chicago and to Michael Reese Hospital, where she was given two units of Fluosol-DA (20%). This stabilized her hemodynamically, and she made a fairly uneventful, albeit prolonged, recovery. The potential for this exciting new approach is enormous, particularly in the practice of obstetrics, where the threat of hemorrhage is always present. Much more work needs to be done to investigate both safety and efficacy, but this preliminary study by Dr. Cefalo and his colleagues is encouraging. In acute experiments in sheep, induction of severe anemia by isovolemic replacement of the maternal volume with Fluosol-DA (20%) maintained maternal blood pressure and arterial oxygen content. More importantly, because it has not previously been demonstrated, fetal oxygenation was maintained as well. Thus, it seems to be clear that Fluosol-DA (20%) is capable of delivering oxygen effectively to the placenta and thence to the fetus. Moreover, Fluosol-DA (20%) itself was found not to cross the placenta. This study represents an important step in the evaluation of a new and potentially valuable therapeutic weapon. The project was well conceived and executed. The results are clearly described and interpreted. I have only two questions for Dr. Cefalo. The first is to ask him to speculate on any physiologic implications of his findings, with particular reference to the mechanism(s) of maternal-fetal oxygen transport. Fetal blood binds oxygen more avidly than does adult blood, presumably because of the differential binding characteristics of hemoglobin A and hemoglobin F to 2,3diphosphoglycerate. An increased oxygen affinity of
April 1, 1984 Am. J. Obstet. Gynecol.
fetal over adult erythrocytes is regarded as the principal mechanism that favors the transfer of oxygen from mother to fetus. What-if anything-does the finding that oxygen transfer to the fetus also occurs from a perfluorochemical on the maternal side of the placenta mean in this regard? Second, perhaps Dr. Cefalo would comment on any potential clinical significance involved in the remarkable degree of pulmonary hypertension observed with Fluosol-DA (20%) treatment. DR. CHARLES BRINKMAN, Los Angeles, California. I am also curious about the increase in both pulmonary arterial and systemic arterial pressures. You mentioned that you hypothesize that the intravascular volume had increased, probably secondary to the increased oncotic pressure. I wonder whether you have looked at either intravascular volumes or, with your Swan-Ganz catheter, pulmonary capillary wedge pressure which might give you some idea of what was going on the other side of the vascular tree. DR. THOMAS H. KIRSCHBAUM, East Lansing, Michigan. Several years ago, I experimented with a mathematical model of the sheep placental oxygen transfer system and demonstrated an argument that it is the nonlinear shape of the oxyhemoglobin dissociation curves of mother and fetus that limits oxygen transfer! and predicted that, to the extent that one could replace those dissociation curves with linear functions of P0 2 , a barrier to diffusibility across the placenta would diminish proportionally. Your work supports that argument, of course, just as did the work which my associates and F did with hyperbaric oxygenation of pregnant ewes. I wonder whether you have replaced fetal blood with Fluosol-DA, since we would predict the same facilitative effects on oxygen transfer across the placenta there. REFERENCES 1. Kirschbaum, T. H., and Shapiro, N. Z.: A mathematical model of placental oxygen transfer, J. Theoret. BioI. 25:380, 1969. 2. Kirschbaum, T. H., Dilts, P. V., Jr., and Assali, N. S.: Placental oxygen transfer in pregnant ewes during hyperbaric oxygenation, Pediatr. Res. 3:398, 1969.
DR. RICHARD P. PERKINS, Albuquerque, New Mexico. We had a patient of similar religious preference who had severe Rh isoimmunization, and the question came up about whether this product might serve some useful purpose in replacing fetal blood or being used in place of fetal transfusion. Thanks to the people at North Carolina, we were put in touch with the distributors of the product in this country and discussed with them the possibility of its use. We were told that an Act of Congress would constitute the initial step in getting this product for use in the fetus and children under 18 years of age. It appears that the oxygen affinity of this particular product is relatively low, in that it does take up oxygen readily when exposed to high concentrations and releases it readily. However, for use in the fetus, where P0 2
Volume 148 Number 7
availability at the placental level would be limited, it would seem, even if it does become approved, that it will not solve our problems of treating the affected fetus of the woman with this particular religious belief. DR. CEFALO (Closing). The questions asked by Dr. Pitkin are most appropriate. We must consider that Fluosol-DA 20% solution is very different from blood in that it carries a high partial pressure of oxygen in a biologic fluid with a high and useful concentration of dissolved oxygen. When we think about maternal-fetal transport of oxygen, we think about the mechanism of diffusion, and we must consider the role of partial pressure. The interesting thing with Fluosol is that the increase in the blood P0 2 that one sees with a blood/Fluosol mixture with high oxygen tension or high Flo" is greater than that which would be expected from the Flo, alone. This may be related to the fact that there are decreased pulmonary shunts secondary to the Fluosol with subsequent improved microcirculation of the pulmonary circulation, which may allow for a partial pressure of oxygen greater than expected from the Flo" level. This greater partial pressure allows for a higher gradient for transfer of oxygen from mother to fetus. The second factor that contributes to the increased partial pressure of oxygen is that the amount of oxygen dissolved in the Fluosol is greater than that of plasma and the amount that is released is faster. With an increased amount of dissolved oxygen, there is less oxygen released from the hemoglobin. This is very important because it allows for a higher venous blood oxygen saturation. Previously published work has indicated that the fetal blood oxygenation depends, in part, upon the venous oxygen saturation leaving the placental uterine veins. If a significant amount of oxygen transferring across the placenta is coming from the dissolved oxygen and if the venous oxygen saturation remains high, which our studies demonstrate, then that would allow for a better transfer of oxygen to the fetus. More important, we must think of the Fluosol as an acellular colloidal suspension and, as such, it is not flow limited. Therefore, we are thinking about an oxygen transfer medium that is not flow limited, which is unique. In fact, in a bloodlFluosol mixture, with its low shear rates, there is less increase in viscosity than with whole blood alone. This, combined with the fact that perfluorochemical tends to flow in low-flow areas
Exchange transfusion with red blood cell substitute 867
rather than high-flow areas where red blood cells are prone to travel, could allow oxygen transfer in vasoconstricted areas, which would also enhance maternalfetal oxygen transfer. In fact, ischemic cerebral and myocardium studies of various animals, together with Fluosol administration, has decreased the amount of damage secondary to the ischemia. The surface area is another factor in oxygen transfer. The surface area with the perfluorochemical particles is greater than that associated with red blood cells in an equal quantity of blood, again allowing for greater increase in oxygen transfer. Also in favor of oxygen transfer is the fact that the release of oxygen from Fluosol is twice as fast as that from hemoglobin. The increased pulmonary artery pressure has been very consistently demonstrated in animals and humans. In humans, even with a test dose of 0.5 ml of Fluosol, an increase in the pulmonary artery pressure has been noted. This sustained response is transitory, lasting only 60 to 75 minutes. When wedge pressures have been measured, they have been in the range of 18 to 20 torr. The immediate increase in the pulmonary artery pressure is much like we see with an intravenous bolus of E. coli endotoxin in the sheep, which has been related to prostaglandin production and release. With Fluosol administration there may be pulmonary vascular damage secondary to a leukostasis within the vasculature, a margination of the granulocytes and platelets which may be associated with pulmonary vasculature damage with release of vasoactive substances. Probably the vasoactive substances are prostaglandins, e.g., prostaglandin F2a. The other possible mechanism is that there is an increase in complement C5A upon administration of the Fluosol and that this complement may be activated because of the Pluronic F -68, the emulsifying agent. This activation has been averted by the use of a glucocorticoid prior to the administration of Fluosol. As far as exchange transfusion in the fetus with Fluosol, as questioned by Drs. Kirschbaum and Perkins, we are about to engage in a protocol to study exchange transfusion of the fetus with Fluosol. I believe that Dr. Perkins' comment is pertinent in that it takes a high P0 2 in adult blood, as far as we know, to increase the oxygen capacity of Fluosol. However, we do not know what is going to happen when we use it with fetal blood.