Arterial blood pressure readings should be close to cuff

DEAR DR. ROACH: I recently had surgery, and my blood pressure was monitored with a catheter. The readings were higher by 30 to 40 points compared with cuff measurements taken at the same time. They were having a hard time getting the catheter readings down to 170. I am wondering which readings are to be used under blood pressure guidelines. — R.R.

ANSWER: A catheter (that’s just a name for a tube inserted in the body) measures blood pressure directly. When people are in the operating room or in the intensive care unit, a catheter often is placed in the artery to give instant, direct measurements of the blood pressure. Several studies have shown that these are more accurate than noninvasive blood pressure measurements, especially in people with very low blood pressure.

Cuff measurements can be higher than catheter measurements in people who have stiff blood vessels with calcium in them. These do not compress properly under the pressure of a cuff, so blood will still go through even with immensely high cuff pressures. In those people, only a catheter is accurate.

Unfortunately, even arterial catheters sometimes can be inaccurate. Bubbles in the system, blood clotting and kinks in the catheter all can lead to abnormal results. However, a difference of 30 to 40 points higher on a catheter than a cuff is beyond my experience. I suspect a technical error, either in the measurement via arterial catheter or (more likely) via the cuff.

Errors in measuring the blood pressure by cuff can come from several mistakes. The size of the cuff needs to be appropriate for the arm: Both too small and too large cuffs will be inaccurate. The cuff should be at the level of the heart, and the arm relaxed. The cuff must be deflated at a precise rate, often slower than I see done. Still, an error of 30 to 40 points is surprisingly large.

Blood pressure guidelines are based entirely on cuff measurements, but there usually is not a big difference between them and arterial catheter readings.

DEAR DR. ROACH: I was diagnosed with osteoma cutis. Any information on this condition would be appreciated. I have been told it is bone fragments that grow beneath the skin. It is my face that is affected. — R.I.

ANSWER: Osteoma cutis is a rare condition (I’ve never seen a case) where pieces of bone form in the skin. They can be minute to moderately sized, and the condition often is seen in combination with a hereditary syndrome, such as Albright’s hereditary osteodystrophy or Gardner syndrome (with colon polyps). The face seems to be a common site of involvement, possibly in association with acne, sunburn or a cosmetic procedure like dermabrasion.

It is surprising to me that the fragments under the skin are indeed bone, confirmed by microscopic evaluation, rather than calcifications, which happen in many other conditions. Fortunately, abnormal bone growth leading to bone cancer has not been reported with this condition.

Osteoma cutis usually is treated surgically to make the diagnosis (although the diagnosis also can be made by X-ray) or for painful lesions. Successful treatment with laser also has been reported.