Experimental hypoxia in fetal lambs
Oh et al. (1975) conducted experiments with sheep
to determine the effect of hypoxia on fetal-placental
blood flow [1]. These experiments can be compared
with those of Myers (1972) on intrauterine hypoxia
and brain damage in monkeys [2].
Surgery was performed to implant catheters for
blood sampling and infusions of radioactive iodine
and indocyanine green dye. After a 5-day recovery
period maternal hypoxia was induced by covering
the ewe's head with a 5-liter plastic bag.
After 15 minutes of hypoxia, maternal blood oxygen
fell from 82 to 47 mmHg and fetal oxygen fell from 20
to 11 mmHg. Carbon dioxide and pH were
essentially unchanged during or after hypoxia.
Only a slight reduction in maternal blood flow to the
placenta was recorded, but fetal blood volume was
significantly increased, and remained high during the
30 to 60 minute recovery period. Placental blood
volume decreased during hypoxia and remained
lower during the recovery period. Thus the fetus
received a placental transfusion during the period of
maternal hypoxia.
Oh et al. stated at the beginning of this paper:
"numerous studies in the past have shown that
delayed clamping of the umbilical cord during vaginal
delivery could result in a sizable amount of placental
vlood transfusion to the fetus.
...In preterm infants who developed respiratory
distress syndrome, the increment in blood volume
may increase the mortality rate, although some
studies suggested that higher blood volume may
favor the outcome of premature infants with this
disease." [1, p316]
Thus delayed clamping of the cord appears to have
been a deviation from protocol, and uncertainty
about the safety of allowing a placental transfusion
was expressed.
The experimental finding suggests that hypoxia-
induced shift of blood from placenta to fetus might
be protective for the fetus. Oh et al concluded this
paper with the remark:
"The clinical implication is that in delivering a fetus
who shows signs of intrauterine fetal asphyxia,
postnatal placental transfusion (for example by
milking the umbilical cord) should probably be
discouraged since a marked increase in neonatal
blood volume is in many respects nonbeneficial to
the physiologic adaptation during the immediate
neonatal life." [1, p321]
The fear of blood volume overload during this period
appears related to the perceived danger of the
blood breakdown product bilirubin, which was
associated with the form of cerebral palsy known as
kernicterus [3].
(in progress)
- Oh W et al. (1975) Placenta
to lamb fetus transfusion in
utero during acute hypoxia.
- Myers RE (1972) Two
patterns of perinatal brain
damage and their conditions
of occurrence.
- Saigal S et al. (1972)
Placental transfusion and
hyperbilirubinemia in the
premature. Pediatrics. 1972
Mar;49(3):406-19.
- Oh W, Omori K, Emmanouilides GC, Phelps DL. Placenta to lamb fetus
transfusion in utero during acute hypoxia. Am J Obstet Gynecol. 1975 Jun
1;122(3):316-22.
- Myers RE. Two patterns of perinatal brain damage and their conditions of
occurrence. Am J Obstet Gynecol. 1972 Jan 15;112(2):246-76.
- Saigal S, O'Neill A, Surainder Y, Chua LB, Usher R. Placental transfusion
and hyperbilirubinemia in the premature. Pediatrics. 1972 Mar;49(3):406-
19.