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09/09/2011 - angle of Louis

posted Sep 28, 2011, 5:51 PM by Chief Resident   [ updated Sep 28, 2011, 5:53 PM by Purnema Madahar ]
Today in CRS, one of the groups was graphing the angle of Louis when interpreting the physical exam, so I thought that a little snippet about this might be a good send-off to the weekend.

A definition from Wikipedia: The sternal angle or 'angle of Louis', from the Latin angulus Ludovici is the anterior angle formed by the junction of the manubrium and the body of the sternum.
It is named after Pierre Charles Alexandre Louis, a French physician of the 19th century, who was one of the first to bring mathematics to medicine, disproving bloodletting as a practice by showing statistically that it did not work.

Some quotes from the attached review paper on the physical exam of venous pressure by Steven McGee, one of the gurus of evidence based physical diagnosis:

1. The physiologic zero point is the location in the cardiovascular system where the CVP is tightly regulated, changing little if at all during the volume shifts that occur when the patient stands or sits.

2. There are few studies of the zero point in human beings, if it even exists, although most clinicians assume that it lies in the right atrium.

3. Over the last century, investigators have proposed numerous landmarks to help clinicians locate the level of the right atrium .... The evidence for these reference points varies, resting in some cases on anatomic dissection, in others on a trial-and-error search for the zero point, but in most, unfortunately, on no data, the landmark simply representing a convenient point.

4. Sir Thomas Lewis [different from the guy who the angle is named after!] proposed in 1930 a simple bedside method for measuring venous pressure. He observed that the top of the jugular veins of normal individuals always came to lie within 1 to 2 cm of vertical distance from the sternal angle, whether the individual's position was supine, semi-upright, or upright. If neck veins were higher than this, Lewis concluded the patient had elevated venous pressure. [I attached the original paper for the historians]

5. the 'method of Lewis' states that the CVP equals the vertical distance between a point 5 cm below the sternal angle and the top of the neck veins, although Lewis did not make such a claim.

McGee goes on to discuss the disagreement of methods to quantify CVP but concludes: If the top of the neck veins is more than 3 cm above the sternal angle, venous pressure is abnormally elevated.