supine

The supine position is a basic anatomical position where the body lies horizontally with the dorsal (posterior) surface against the supporting surface and the ventral (anterior) surface facing upward. Clinically, this position is essential for physical examination of the abdomen, chest, and extremities, and is the standard position for many surgical procedures. The supine position has important physiological effects including increased venous return to the heart due to gravity, which can increase preload and cardiac output in healthy individuals. However, in pregnant women (especially after 20 weeks gestation), the supine position can cause supine hypotensive syndrome (aortocaval compression syndrome) where the gravid uterus compresses the inferior vena cava and aorta, leading to decreased venous return, hypotension, and potential fetal compromise. The supine position also affects respiratory mechanics by reducing functional residual capacity due to upward displacement of the diaphragm by abdominal contents. In critical care, prolonged supine positioning can increase risk of ventilator-associated pneumonia and pressure ulcers, leading to recommendations for periodic position changes.