Supine position

When used in surgical procedures, it grants access to the peritoneal, thoracic and pericardial regions; as well as the head, neck and extremities.

In scientific literature "semi-supine" commonly refers to positions where the upper body is tilted (at 45° or variations) and not completely horizontal.

[3] The realization that infants sleeping face down, or in a prone position, had an increased mortality rate re-emerged into medical awareness at the end of the 1980s when two researchers, Susan Beal in Australia and Gus De Jonge in the Netherlands, independently noted the association.

Because of the immature state of their central chemoreceptors, infants do not respond to the subsequent respiratory acidosis that develops.

[5][6] Typical non-infants realize autonomic responses of increased rate and depth of respiration (hyperventilation, yawning).