Supine hypotensive syndrome.

To review reports of the supine hypotensive syndrome with reference to clinical presentation, suggestions on the mechanism of onset, and the possibility of advance detection.We used worldwide obstetric, anesthesia, and general medical journals from 1922 onward, a Medline search from 1966 onward, and manual cross-referencing for prior publications.We selected approximately 100 case reports of supine hypotensive syndrome and studies on supine blood pressure responses during late pregnancy.Publications that recorded novel clinical observations, specific hemodynamic or biochemical measurements, or associated complications were included.Supine hypotensive syndrome is characterized by severe supine symptoms and hypotension in late pregnancy, which compel the unconstrained subject to change position. Rarely, it may manifest even from the fifth month of pregnancy or postpartum, as well as in the pelvic tilt or sitting positions. Although inferior vena cava compression, influenced primarily by the size of the uterus and exact maternal and fetal position, is the major determinant in its development, other factors may also be important in modulating the circulatory effects of such compression. Advance recognition of susceptibility to the syndrome depends on a history of severe supine symptoms or supine intolerance and an increase in maternal heart rate and decrease in pulse pressure in the supine position. As there seems to be a spectrum of severity from minimal central cardiovascular alterations to severe syncopal shock resulting from supine inferior vena cava compression, it is difficult to define a cutoff point at which the syndrome occurs. Although usually recognizable by maternal symptoms, severe hypotension without symptoms has been reported on three occasions.