Significance of retrograde diastolic uterine artery blood flow during regional anesthesia in instrumented pregnant sheep.
BACKGROUND
We studied the interactions between uterine and placental hemodynamics during maternal hypotension in chronically instrumented fetal sheep. In addition, we investigated maternal hemodynamic characteristics, fetoplacental hemodynamics and fetal acid-base status when a retrograde diastolic uterine artery blood flow pattern is present during maternal hypotension.


METHODS
Invasive maternal and fetal hemodynamic parameters, uterine (Q(UtA)) and placental (Q(UA)) volume blood flows and acid-base values were examined in 24 chronically instrumented sheep at baseline and during epidural-induced maternal hypotension at 117-132 (term 145) days of gestation. Uterine artery blood flow velocity waveforms were obtained by Doppler ultrasonography.


RESULTS
Maternal hypotension decreased Q(UtA) without affecting Q(UA). During hypotension, eight out of 24 sheep demonstrated a retrograde diastolic blood flow velocity waveform pattern in the uterine artery. Maternal systolic, diastolic and mean arterial blood pressures were significantly lower in the retrograde group than in the antegrade group. No statistically significant differences in Q(UtA), Q(UA) and fetal blood gas values were detected between the two groups during hypotension.


CONCLUSIONS
An acute decrease in uterine artery volume blood flow during maternal hypotension is not compensated by increased placental volume blood flow. A retrograde diastolic blood flow pattern in the uterine artery is related to lower maternal arterial pressures, especially during diastole. A uterine artery retrograde diastolic blood flow pattern does not have any additional detrimental short-term effects on fetal acid-base status.
Kavasmaa
T
T
Department of Anaesthesiology, University of Oulu, Oulu, Finland.
Mäkikallio
K
K
Erkinaro
T
T
Acharya
G
G
Haapsamo
M
M
Alahuhta
S
S
Räsänen
J
J
D000765:Anesthesia, Conduction; D000818:Animals; D001158:Arteries / Q000187:drug effects / Q000502:physiology*; D005260:Female; D007022:Hypotension / Q000503:physiopathology; D011247:Pregnancy; D012039:Regional Blood Flow / Q000187:drug effects; D012756:Sheep; D014599:Uterus / Q000098:blood supply* / Q000187:drug effects*