The effect of maternal hypothermic cardiopulmonary bypass on fetal lamb temperature, hemodynamics, oxygenation, and acid-base balance.
OBJECTIVE
To evaluate fetal-maternal temperature relationship and fetal cardiovascular and metabolic response during maternal hypothermic cardiopulmonary bypass in pregnant ewes.


METHODS
Cardiopulmonary bypass was instituted in 9 pregnant ewes, reaching 2 different levels of maternal hypothermia: 24 degrees C to 20 degrees C (deep hypothermia) in group A (5 cases) and less than 20 degrees C (very deep hypothermia) in group B (4 cases). Hypothermic levels were maintained for 20 minutes, then the rewarming phase was started. Fetal and maternal temperature, blood pressure, heart rate, electrocardiogram, blood gases, and acid-base balance were evaluated at different levels of hypothermia and during recovery.


RESULTS
Fetal survival was related to maternal hypothermia: all group A fetuses survived, while 2 of 4 fetuses of group B in which maternal temperature was lowered below 18 degrees C died in a very deep acidotic and hypoxic status. Maternal temperature was always lower than fetal temperature during cooling; during rewarming the gradient was inverted. The start of cardiopulmonary bypass and cooling was associated with transient fetal tachycardia and hypertension; then, both fetal heart rate and blood pressure progressively decreased. The reduction of fetal heart rate was of 7 beats per minute for each degree of fetal cooling. Deep maternal hypothermia was associated with fetal alkalosis and reduction of Po(2). Very deep hypothermia, in particular below 18 degrees C, caused irreversible fetal acidosis and hypoxia.


CONCLUSIONS
Deep maternal hypothermic cardiopulmonary bypass was associated with reversible modifications in fetal cardiovascular parameters, blood gases, and acid-base balance and therefore with fetal survival. On the contrary, fetuses did not survive to a very deep hypothermia below 18 degrees C.
Pardi
Giorgio
G
Department of Obstetrics and Gynecology, San Paolo Hospital, Milan, Italy. Giorgio.Pardi@unimi.it
Ferrari
Maria M
MM
Iorio
Fiore
F
Acocella
Fabio
F
Boero
Veronica
V
Berlanda
Nicola
N
Monaco
Ario
A
Reato
Claudio
C
Santoro
Francesco
F
Cetin
Irene
I
D000136:Acid-Base Equilibrium / Q000502:physiology*; D000818:Animals; D001831:Body Temperature / Q000502:physiology*; D002315:Cardiopulmonary Bypass / Q000009:adverse effects / Q000379:methods*; D005260:Female; D005313:Fetal Death; D005323:Fetal Monitoring / Q000379:methods; D006439:Hemodynamics / Q000502:physiology*; D007036:Hypothermia, Induced / Q000009:adverse effects / Q000379:methods*; D008431:Maternal-Fetal Exchange; D010101:Oxygen Consumption / Q000502:physiology*; D011247:Pregnancy; D011270:Pregnancy, Animal; D011659:Pulmonary Gas Exchange; D012680:Sensitivity and Specificity; D012756:Sheep