Inferior vena cava compression in the pregnant dog.

Attempts were made to produce inferior vena cava (IVC) compression in 14 pregnant and 12 nonpregnant bitches. Ligation of the iliac veins, the IVC below the renal veins, or the left renal vein separately produced minimal hemodynamic disturbances. Only ligation of the two renal veins or of the IVC above the renal veins produced a moderate drop in blood pressure and blood flow. Shock and bradycardia, characteristic of the supine hypotension syndrome (SHS) as observed in human subjects, were never observed. Satisfactory collateral circulation was demonstrated radiologically. Since human SHS was not reproduced in the pregnant bitch by compression of the IVC alone, one may conclude that the SHS is not solely caused by the compression.