Study highlights uncertain value of tachypnea at triage

By Eleanor McDermid, Senior MedWire Reporter

The usual method of assessing respiratory rate at triage in the emergency department (ED) is highly insensitive for the presence of tachypnea, say researchers.

William Bianchi (Johns Hopkins University School of Medicine, Baltimore, Maryland, USA) and colleagues suggest that EDs should adopt the World Health Organization (WHO) standard of directly observing patients' breathing for a full minute, rather than assessing it for 15 seconds and multiplying the result by four, as is the usual practice.

The usual method was just 23% sensitive for the presence of tachypnea in 191 patients, the researchers report in the Annals of Emergency Medicine. It identified 10 as having tachypnea (>20 breaths/minute), compared with 44 according to the WHO standard, which was performed within 10 minutes of the usual-care method. The usual-care measurements tended to fall at 16 or 18 breaths/minute and correlated poorly with WHO standard measurements.

However, editorialists Richelle Cooper (University of California, Los Angeles, USA) and Steven Green (Loma Linda University Medical Center and Children's Hospital, California) question the value of accurate respiratory measurements per se, saying that, in a previous study, experienced nurses altered triage decisions based on accurate vital sign measurements in just 7% of patients, with respiratory rate influencing just 0.1% of decisions.

"Given this rarity of influence, even if we could measure respiratory rate more accurately would it really be worth the cost and effort?"

They also note an "ironic" problem arising from more accurate respiratory measurements, in that current practice, including risk scores, is based on the usual and therefore inaccurate method of respiratory measurement. "How would emergency physicians respond to suddenly having four times more patients identified as tachypneic?" they ask. "Would they simply order more low-yield tests?"

Bianchi and team also assessed an electronic respiratory rate sensor (BioHarness, Zephyr Technology Corp., Annapolis, Maryland), finding this to be 91% sensitive and 97% specific when compared against the WHO standard.

But Cooper and Green question the worth of such electronic sensors, which, in addition to being "time-consuming and expensive," would be difficult to keep "clean and fomite free" between patients.

"Although new technology can allow us to be more and more precise, there is not always a theoretical or empiric reason to assume that this will translate to improved patient-centered outcomes," they conclude. "Just because you can measure something more accurately does not mean you need to, and just because one can buy a BioHarness or other device to do this doesn't mean one should."

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