A description of the preterm fetal sheep systemic and central responses to maternal general anesthesia.
BACKGROUND
The second trimester is recommended as the optimal time to conduct a surgical procedure on pregnant patients, even though the fetal responses to anesthesia at this age are not known. Here we assessed the responses of preterm fetal sheep to a standard anesthetic regimen of midazolam, thiopental, and isoflurane.


METHODS
Variables were monitored in previously instrumented preterm pregnant sheep before, during, and after 4 h of general anesthesia. Isoflurane produced moderate fetal hypotension and bradycardia, whereas extubation was accompanied by increases in fetal heart rate and mean arterial blood pressure.


RESULTS
We observed an initial increase in fetal Sao2 followed by a gradual decline to baseline. Within the fetal brain, oxygenated hemoglobin changed by <10% (nonsignificant) and deoxygenated hemoglobin and total hemoglobin varied by <5%. Overall, although O2 levels within the preterm fetal brain were not independently enhanced by isoflurane (as occurs in the older fetus and in the adult), they did remain constant even as fetal mean arterial pressure decreased by more than 20%. By extension, we failed to identify changes in cerebral oxygenation that could be construed as injurious.


CONCLUSIONS
Any adverse preterm fetal response to maternal surgery should not be attributed solely to the actions of general anesthesia upon the fetus.
McClaine
Rebecca J
RJ
Department of Anesthesiology, Duke University Medical Center, Durham, North Carolina 27710, USA.
Uemura
Kenichiro
K
McClaine
Deborah J
DJ
Shimazutsu
Kazufumi
K
de la Fuente
Sebastian G
SG
Manson
Roberto J
RJ
White
William D
WD
Eubanks
William S
WS
Benni
Paul B
PB
Reynolds
James D
JD
D000768:Anesthesia, General / Q000009:adverse effects / Q000379:methods; D000818:Animals; D001784:Blood Gas Analysis; D005260:Female; D005333:Fetus / Q000187:drug effects* / Q000502:physiology*; D007530:Isoflurane / Q000008:administration & dosage / Q000009:adverse effects; D008431:Maternal-Fetal Exchange / Q000187:drug effects* / Q000502:physiology*; D011247:Pregnancy; D012756:Sheep
D007530:Isoflurane