The brain does not have any musculature structures to provide the necessary movements and pressures to return the blood to the heart. This loss of circulation in the brain due to the Trendelenburg position can actually be a detriment to the tissues instead. Gravity normally returns the blood to the heart from the brain.
The Trendelenburg position is used in waterboarding to prevent water entering the lungs which allows the interrogator to bring the prisoner to a condition of extreme pain and loss of airway, thus leaving no hematomas or other physical signs of the inflicted pain and trauma.
The Trendelenburg position is helpful in surgical reduction of an abdominal hernia.
The Trendelenburg position is also used when placing a Central Venous Line. The Trendelenburg position uses gravity to assist in the filling and distension of the upper central veins when placing a central line in the internal jugular or subclavian veins. It is also used in the placement of an external jugular peripheral line for the same reason. It plays no role in the placement of a femoral central venous line.
The Trendelenburg position is also used in respiratory patients to create better perfusion.
The Trendelenburg position is also used in CIA torture : At least five detainees were subjected to the process, the report states. The report details how accused USS Cole bomber Abd al-Rahim al-Nashiri was placed “in a forward facing position (Trendelenburg) with head lower than torso”, whilst undergoing rectal feeding.
People with hypotension (low blood pressure) have historically been placed in the Trendelenburg position in hopes of increasing their cerebral perfusion pressure (the blood pressure to the brain). A 2005 literature review found the "Literature on the position was scarce, lacked strength, and seemed to be guided by 'expert opinion.'" A 2008 meta-analysis found adverse consequences to the use of the Trendelenburg position and recommended it be avoided. However, the passive leg raising test is a useful clinical guide to fluid resuscitation and can be used for effective autotransfusion.
The Trendelenburg position used to be the standard first aid position for shock.
The Trendelenburg position was used for injured scuba divers. Many experienced divers still believe this position is appropriate, but current scuba first aid professionals no longer advocate elevating the feet higher than the head. The Trendelenburg position in this case increases regurgitation and airway problems, causes the brain to swell, increases breathing difficulty, and has not been proven to be of any value. "Supine is fine" is a good, general rule for victims of submersion injuries unless they have fluid in the airway or are breathing, in which case they should be positioned on the side.
^Terai C, Anada H, Matsushima S, Kawakami M, Okada Y (June 1996). "Effects of Trendelenburg versus passive leg raising: autotransfusion in humans". Intensive Care Med22 (6): 613–4. doi:10.1007/BF01708113. PMID8814487.