Ambulatory BP Monitors Helpful in Children


SEATTLE — Take-home, ambulatory blood pressure monitors for children ensure more accurate blood pressure assessments and rule out white-coat hypertension, nephrologists at Seattle Children's Hospital's hypertension clinic have found.

The clinic ruled out white-coat hypertension in about 30%–40% of the roughly 200 children sent home with the monitors in 2009, according to Dr. Jodi Smith of the clinic.

Although more expensive than an office blood pressure reading, “if used as first-line, before doing a bunch of other diagnostic tests, it can decrease costs” overall, Dr. Smith said at a conference sponsored by the North Pacific Pediatric Society.

The clinic uses ambulatory monitors made by SpaceLabs Medical, Inc., of Issaquah, Wash. They cost about $3,000 each.

Dr. Smith, along with her nephrologist colleagues, sees patients in the hospital's hypertension clinic due to the correlation of pediatric hypertension and renal problems. The hypertension clinic started using the monitors about a year ago, switching from office readings and automated blood pressure cuffs that caretakers used to take a few measurements a day at home.

The units consist of a blood pressure cuff and an iPod-sized monitor that is worn around the waist and easily concealed under a sweatshirt. The cuffs inflate every 20–30 minutes for 24 hours. Older children adapt well to the frequent squeezes, Dr. Smith said, but the approach would not be appropriate for children under age 7.

The read-outs go far beyond a listing of systolic and diastolic pressures, and are complicated to interpret, she said. “They look for patterns,” including blood pressure load, and the presence—or not—of a normal drop in blood pressure at night.

Children also keep an activity log, so a spike in blood pressure during a soccer game, for instance, isn't misinterpreted.

It's a first-line assessment at the clinic, especially to confirm hypertension in otherwise healthy children.

Schedulers get prior insurance authorization for an ambulatory monitor before the child comes in, so they can be sent home with one after the first visit.

Her clinic matches readings to a chart in the National Heart, Lung, and Blood Institute's Fourth Report on the Diagnosis, Evaluation, and Treatment of High Blood Pressure in Children and Adolescents (Pediatrics 2004;114:555-76).

“We get calls all the time [from pediatricians wondering] what's normal and what's not,” she said. “Normals change through childhood. It is hard to define what level is dangerous.”

The chart helps. At her clinic, blood pressures at or above the 90th percentile trigger intervention. Kids who fall between the 90th and 94th percentile are considered pre-hypertensive, the point at which lifestyle changes are initiated along with medication if there are comorbidities.

At or above the 95th percentile, children are deemed hypertensive. Treatment and drug selection depends on cause, symptoms, the presence of end-organ damage or diabetes, and other considerations.

With increasing rates of obesity, primary hypertension is on the rise in the pediatric population, but hypertensive children are still more likely than adults to have definable causes for the condition.

Renal problems are most likely, followed by renovascular, endocrine, and genetic problems, Dr. Smith said.

Although rare, post-streptococcal glomerulonephritis is the most common cause of acute glomerulonephritis in kids. Other causes of acute nephritis, with more uncertain outcomes—lupus, bacterial endocarditis, shunt nephritis, membranoproliferative glomerulonephritis—will typically depress both C3 and C4.

IgA nephropathy and Henoch-Schnlein purpura nephritis are associated with normal C3 and C4, said Dr. Smith, who had no conflicts of interest to report.

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