The Trendelenburg position originated as a method to improve surgical exposure of the pelvic organs by placing the patient in a head-down position of at least 45 degrees.
During World War I, an American physiologist, Walter Cannon, introduced the head-down position as a method to treat soldiers suffering from shock.1 EMS stretchers allow for passive leg-raising of 15 to 20 degrees with the legs and feet above the heart for resuscitation.2 The basis for using the Trendelenburg position and passive leg-raising is that blood can be diverted from the lower extremities to the torso to improve central circulation. 2
Passive leg-raising can help a medic determine whether a patient will respond to rapid fluid loading by observing changes in radial artery pulse pressure prior to fluid administration.3 The effects of passive leg-raising last about 10 minutes, 3 while the Trendelenburg position produces positive hemodynamic effects for approximately 15 minutes. 2 To properly perform passive leg-raising, the patient's legs must be raised 45 degrees for a minimum of 4 minutes. This position effectively mimics a rapid fluid bolus of 300ml3 with an actual increase in torso blood volume of approximately 100ml with no significant rise in preload or cardiac performance.2 Both passive leg-raising and Trendelenburg can cause dilation of upper limb arteries via stimulation of the low-pressure baroreceptors and may be why there is little to no effect on mean arterial pressure with increased stroke volume.3
Both Trendelenburg and passive leg-raising stress the right ventricle and reduce pulmonary function.1 When the patient is returned to the supine position, pulmonary function is immediately returned,3 whereas cardiac performance may decrease when the patient is moved back to the supine position.2 Obese patients often experience decreased volume and lung compliance leading to oxygen desaturation when placed in the Trendelenburg position.4
The lower esophageal sphincter works with the upper esophageal sphincter to prevent regurgitation and aspiration of stomach contents.4 When a patient is placed in the Trendelenburg position, the lower esophageal sphincter pressure increases, as does the risk of regurgitation and aspiration of stomach contents.4 Additionally, lower esophageal sphincter function is impaired with the use of propofol, remifentanil, rocuronium and sevoflurane. Therefore, using the Trendelenburg position while performing a rapid sequence intubation with any of these medications also increases the risk of regurgitation and aspiration of stomach contents.4
Children with cardiopulmonary disease may be susceptible to hypoxaemia when placed in the Trendelenburg position.5 Placing a child in a Trendelenburg position of 30 degrees is sufficient to induce atelectasis that cannot be reversed by simply repositioning the patient in the supine position.5
To summarize, prophylactic use of the Trendelenburg position has minimal to no effect on maintenance of blood pressure and does not provide positive hemodynamic effects in the critically ill.2 Use of Trendelenburg for resuscitation may cause life-threatening increases in hydrostatic venous and arterial pressures in the upper body and head.2 And, in the head-down position, the abdominal organs can weigh down the diaphragm, compromise lung volume and place the patient at a higher risk for cerebral edema, retinal detachment or brachial nerve paralysis.1 Finally, the Trendelenburg position does not significantly improve oxygen transport in hypovolemic patients.6
Passive leg-raising and modified Trendelenburg positions are useful for determining fluid response.1 A recent study found use of the Trendelenburg position may be a non-invasive treatment for supraventricular tachycardia.7 By placing the patient in a head-down position, increased venous return stimulates baroreceptors to produce an increased vagal tone and subsequent decrease in heart rate. Resolution of the supraventicular tachycardia occurs after approximately 30 seconds.7 The Trendelenburg position still has a place in the treatment of patients outside of the operating room. Maybe we should consider using Trendelenburg less for treating shock and more for evaluating fluid response and treating supraventricular tachycardia.