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WHO-defined tachypnea predicted pneumonia in children
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Children with tachypnea, as defined by WHO, were more likely to have radiographic pneumonia than children without tachypnea, according to a study. When WHO guidelines were not used, the presence of tachypnea generally failed to predict pneumonia.
In resource poor areas, WHO recommends tachypnea as a proxy to the diagnosis of pneumonia. However, “the use of tachypnea alone as a predictor of pneumonia has not been evaluated in a modern and readily accessible medical system,” the researchers wrote.
The study prospectively examined 1,622 patients aged 5 years and younger who underwent chest radiography for pneumonia at an urban academic hospital. Patients were excluded if they were suspected of having indications beyond pneumonia or if they had a pre-existing condition that heightened their risk of pneumonia.
Before chest radiography, the presence of tachypnea in each child was defined in three ways: mean triage respiratory rate by age group; age-defined respiratory rate thresholds defined by WHO; and subjective clinical impression.
Chest radiography revealed 235 children (14.5%) had radiographic pneumonia. The mean triage respiratory rate was 39 breaths per minute in the pneumonia group, compared with 38 in the children without pneumonia. In a subgroup of children aged 1 to 5 years, however, mean triage respiratory rate was higher in the pneumonia group (37.6 vs. 34.5 breaths per minute, respectively; P=.002).
Tachypnea predicted pneumonia most accurately when diagnosed with WHO respiratory rate thresholds. In this case, 20.4% of children with tachypnea had pneumonia vs. 12.1% of non-tachypneic children with pneumonia (P<.001). Among children aged 1 to 5 years, the difference remained significant, with 25.5% of tachypneic children having pneumonia vs. 14.9% of non-tachypneic children having pneumonia (P<.001).
When tachypnea was diagnosed subjectively by the treating physician, the condition failed to predict pneumonia. A total of 16.7% of children with tachypnea had pneumonia vs. 13.3% of non-tachypneic children. The difference remained insignificant across all age groups.
When wheezing patients were excluded from the study group, however, tachypnea diagnosed by clinical impression became a statistically significant predictor of pneumonia (P=.03).
“The presence of wheeze is likely to be a confounder in the relationship between respiratory rate and pneumonia,” the researchers wrote. “Infants and young children with wheeze are more likely to be tachypneic as a result of the disease process [that] led to the wheezing and are less likely to have pneumonia compared with children who are tachypneic for reasons other than airway hyper-responsiveness.”
For this reason, WHO recommends that physicians in resource poor areas deliver a dose of bronchodilator to patients with tachypnea and wheeze to see if the tachypnea improves, the researchers noted.
“We observed that the WHO case definition for tachypnea is a useful discriminator of children with and without radiographic pneumonia. The association … was strongest for children >1 year of age,” the researchers concluded, adding that certain viral illnesses causing tachypnea were less likely to confound results in this age group, and that the quality of examinations were inherently superior in older children. – by Andy Moskowitz
Shah S. Pediatr Infect Dis J. 2010;29:406-409.
This article looks at the predictive value of tachypnea for a radiologically supported diagnosis of pneumonia. The authors relate this to the WHO guidelines for diagnosis of pneumonia. I don’t think it is too surprising that the predictive value was low. The WHO guidelines are meant for management of infants and young children in resource poor areas where the triage may be done by a person with very little or no medical training. Also, the WHO criteria rely not solely on tachypnea but include cough as an entry criterion and chest indrawing (retractions) as well as tachypnea to decide which children should receive antibiotics. In such settings a lower predictive value than what would be expected in an Emergency Department in Boston would be acceptable.
– Robert S. Baltimore, MD
Infectious Diseases in Children Editorial Board