Routine respiratory test may be inaccurate up to 40% of the time

Counting critically ill patients’ breaths over a 30-second period could misclassify up to 40% of respiratory scores, data show.

This same breathing test is often used in evaluating patients’ risk for COVID-19, according to a press release that accompanied the study, published in ERJ Open Research.

Gordon B. Drummond, an honorary senior lecturer in the department of anesthesia, critical care and pain medicine at the University of Edinburgh in Scotland, and colleagues counted the number of breaths that each of 25 hospitalized patients (11 women) took during selected time periods. The patients had a mean age of 66 years, mean weight of 81 kg and mean BMI of 28 kg/m². Most patients had a respiratory condition, but others had cardiac, neurological urinary or a combination of such conditions. Breaths were counted over a period of 30 seconds, 60 seconds and 120 seconds.

“The 30-second duration was chosen because it is common in clinical practice, 60 seconds because it is an ideal duration and 120 seconds to assess the effect of a larger sample, although this is rarely used clinically,” Drummond and colleagues wrote.

According to the researchers, the mean interquartile range of repeated estimates was 3.4 breaths per minute during the 30-second test, 3 breaths per minute during the 60-second test, and 2.5 breaths per minute during the 120-second test. Repeat measures often differed by more than 3 breaths per minute, according to the researchers. Also, as many as 40% of National Early Warning Scores — a measurement used to detect clinical deterioration, according to the United Kingdom’s National Health Service — from the 30-second test could be inaccurate.

The accuracy of the test improved with longer sample duration; however, the researchers said longer durations “may be impractical unless better measurement methods are used.”

“A future approach would be to use a device that allowed staff to make reliable measurements of respiratory rate over a suitable length of time,” Drummond and colleagues wrote. “Small wearable devices that directly measure respiratory movements and allow precise counts to be made over longer periods could improve the precision of rate measures, although such devices require adequate clinical validation.”

Reference:

• NHS. National Early Warning Score. https://www.england.nhs.uk/ourwork/clinical-policy/sepsis/nationalearlywarningscore/. Accessed Oct. 5, 2020.