Methods for the Measurement of Respiratory Rate

Respiratory rate is among the first vital signs to change when a deterioration in patient conditions occurs, and that it is highly useful in identifying high-risk patients, patients in pain, risk of death in patients treated for myocardial infarctions and medical patients at risk of cardiac arrest.

Respiratory rate is one of the seven physiological parameters included in the Early Warning Score (EWS), an aggregated track- and trigger-system for risk-stratification of patients in hospital wards at risk of imminent clinical deterioration. EWS includes an escalation protocol, defining when it is necessary for the ward staff to call for assistance and when vital parameters should be measured again.

Manual measurement of respiratory rates is the standard in hospital wards in the Capital Region of Denmark. During the measurement of respiratory rate, patients ideally have to lie still and refrain from talking. This poses a difficulty in daily, clinical practice. Several studies in hospital wards both using and not using an EWS-system report that respiratory rate is often omitted when vital signs are measured.

Even if the respiratory rate is measured regularly, poor inter-observer agreement and reproducibility of measured respiratory rates have been found. Respiratory rates recorded by nurses have been reported to be generally higher than those measured by observers using a standardised approach.

The EWS currently in use is validated using measurements obtained by normal nursing practise. If there is an element of human influence on the measurement of respiratory rate, automation could affect the prognostic properties of EWS in an unpredictable way, even if the automatically measured respiratory rates more reliably reflect the patients' physiology than current clinical practise.

If a systematic difference between the recordings by staff and the electronic devices currently on the market exists, this could have an implication on the EWS scores and subsequently, escalation protocols for patients with elevated EWS could be affected. If this is the case, EWS might even have to be re-validated using machine-measured respiratory rates.

Thus, even as there could be a number of advantages of automating the measurements of respiratory rates in hospital wards, due considerations are required before ward staff's manual measurement of respiratory rate can be replaced by measurements obtained from electronic devices. The purpose of this study is to evaluate if there is a systematic difference in the respiratory rate measurements performed by an electronic device (SensiumVitals® system, Sensium Healthcare) compared with the measurements performed by a research assistant using a criterion standard approach and the ward staff's usual measurements.