Calling Trendelenburg into Question


 
 

Howard Rodenberg, MD, MPH, Dip(FM) | | Thursday, December 13, 2007


I value family more as I get older. It's not that I want to make sure people actually show up at the funeral. It's that I feel a growing link to the past. It's important to me that one grandfather beat Johnny Weismuller in a swim race and another was a combat medic in WWII. A great-grandfather won a Purple Heart in the Spanish-American War and was head of the Burlap Bag Board during WWI. (Where do you think sandbags come from?) A thrice-removed relative invented the shopping cart. I even have an uncle in the distant past who loaned Abe Lincoln an axe and never got it back (Honest Abe, indeed). And, of course, it's especially important to me that my father married my mother (or my mother told him to I get it mixed up).

I was always kind of hoping that the Trendelenburg position was named after some distant relative who just didn't get the name right. I knew I was never going to have anything named after me. During my tenure as the local medical director, we tried to find something to establish my place in history. The best anyone could come up with was "Rodenberg Rectal Valium," an honor that was politely declined. So it's with a heavy heart that I must take poor Uncle Trend to task, for I think his namesake is on the way out.

Defining Trendelenburg

First, a definition is in order. It's important to note what the Trendelenburg position actually is. The full Trendelenburg position involves the entire supine body tilted head-downward at a 45_ angle. In practice, most EMS stretchers only tilt to an angle of 15 20 degrees, but the term is still applicable in that the entire body of the patient is involved in the change of horizontal axis. The term is often used interchangeably with the "first aid" position, in which the patient lies supine and the legs are elevated by flexion of the hips. They are not the same in practice or effect.

(By the way, what we call the Trendelenburg position is not actually the one used by Trendelenburg. He elevated the lower half of the body by slinging the patient's knees over the shoulders of a standing assistant. It's so hard to find good help these days.)

The concept of the Trendelenburg position is exceedingly simple. Gravity pushes blood down. If the patient is sitting up, relatively more blood pools in the lower extremities than in the central circulation. As the patient lies down, the blood volume equilibrates throughout all portions of the body. But in the patient with hypotension, one wants to maximize perfusion of the core organs of the body (heart, brain, and kidneys the body really doesn't care about much else). So why not move blood more centrally by using gravity to push more blood to the core in effect, to provide an autotransfusion.

If the word autotransfusion looks familiar, it's because that was part of the theory behind MAST suit use. Inflate the pants, and not only will the compression of the vascular tree raise systemic vascular resistance and blood pressure, but any blood lodged in the leg vessels will be squeezed centrally. Unfortunately, studies showed that the amount of blood shunted centrally was minimal at best, and not hemodynamically significant. This lack of effect is even more pronounced in the Trendelenburg position, where gravity is your only mechanical aid. The lack of circumferential compression of the extremities means that some venous pooling may still occur. In the true Trendelenburg position with the entire supine body tilted head-downward 45_, up to 1 L of blood may be returned into the central circulation. However, in the more usual 15 20_ tilt, patients who are hypotensive actually exhibit no change or decreased cardiac outputs. To complicate matters, the elevation in blood pressure seen after use of the Trendelenburg position may be related to movement of the upper extremity blood pressure cuff from a position level with or above the heart to a plane beneath it.

The lack of efficacy should be enough to remove the procedure from our handy quiver of medical arrows. But to get rid of tradition, we need more than to say it simply doesn't work. We need to show that it has problems as well, and the Trendelenburg position has quite a few.

Problems

These difficulties might be anticipated from both the mechanism of the Trendelenburg position and previous studies of means to raise prehospital blood pressure. It's been fairly well demonstrated that in certain trauma patients, aggressive fluid resuscitation or MAST suit use leads to worse outcomes. If the goal of the Trendelenburg is to raise systolic BP, then it's use would pose a danger to these patients as well. In addition, patients with pre-existing volume overload states, such as cardiac failure, may decompensate as more blood is presented to the impaired heart.

There are other, more subtle problems with this positioning technique. Full application of the Trendelenburg position tends to shift abdominal and pelvic organs toward the head. The intra-abdominal contents then press against the diaphragm, limiting diaphragmatic excursion. The limited tidal volumes and inspiratory capacities may provoke respiratory compromise. In addition, limitations of diaphragmatic excursion may cause the lower lobes of the lung to be unable to fully inflate. Hypoventilation and hypoxia are likely results. In the head-injured patient, the migration of blood towards the head may result in deleterious increases in intracranial pressure. And if one believes that changes in intrathoracic pressure are the primary cause of blood circulation during CPR, than restricted diaphragmatic excursion limits both the negative pressure generated to bring blood into the heart and the positive pressure differential producing forward blood flow.

The use of the Trendelenburg position also merits some technical considerations. As bodies are inclined, they slide. Some form of restraint must be provided to keep the patient from slipping. The use of restraints, in turn, carries with it risks of aspiration should the patient vomit and be unable to be turned. Procedures may be more difficult to perform when the patient is in the position. A portion of the mechanical force of CPR is lost when compressions are applied at an angle. Visualization of the glottis and vocal cords when performing intubation is also more complex as the anterior hypopharynx is removed from the line of sight. Successful intubation will require creative technique.

Finally, let's note that being placed upside down is just darned uncomfortable. Besides the lack of claws on the feet, there's another reason we don't hang from the ceiling like bats. The shift of volume towards the head results in nasal congestion, headache, anxiety and restlessness. If this is coupled with hypoxia, altered mental status or head injury, the patient may become frankly combative, and now you've got a restraint issue on your hands.

In the context of first aid, raising the extended legs by flexion at the hip alone is probably benign. Where no spinal trauma is suspected, I doubt that a simple elevation of the legs alone does much harm, and it might do a bit of good. At least it gives the rescuer the feeling of doing something. It's of interest to note that the evidence-based guidelines for First Aid as promulgated in the 2000 AHA ECC Guidelines fail to recommend any particular positioning techniques (including the Trendelenburg). This is presumably due to a lack of formal efficacy studies.

As we put the Trendelenburg to a supine rest, let me say one final benediction over this legend with a modified joke:

An Asian man was sitting in a bar when suddenly a grizzled old EMS veteran lodged nearby hauled off and slapped him across the face. Surprised, the man asked what that was all about. "That was for Pearl Harbor," growled the vet.

"But that was the Japanese. I'm Korean!" exclaimed the man,

"Japanese, Korean, Chinese they're all the same to me," retorted the old street warrior.

The man thought for a minute, than walloped the veteran. "Hey, what's that for?" cried the vet.

"That was for the Titanic," proclaimed the man.

The ex-grunt stuttered, "But the Titanic was sunk by an iceberg!" The man smiled and said, "Iceberg, Trendelenburg, Rodenberg they're all the same to me."

(PS: For those interested in medical eponyms, may I offer these additional bits gleaned from my battered 1976 Edition of Steadman's Medical Dictionary: Scultetus' Position: Patient tilted on an inclined plane with the head low, recommended for castration. Leapfrog Position: A stooping position taken as when playing leapfrog, used for rectal examination. No comments necessary. You make the connections.)


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