General medicine/original research
Revitalizing a Vital Sign: Improving Detection of Tachypnea at Primary Triage

Presented as a poster at the American College of Emergency Physicians Research Forum, October 2011, San Francisco, CA.
https://doi.org/10.1016/j.annemergmed.2012.05.030Get rights and content

Study objective

This study evaluates the accuracy of emergency department (ED) triage respiratory rate measurement using the usual care method and a new electronic respiratory rate sensor (BioHarness, Zephyr Technology Corp.), both compared to a criterion standard measurement.

Methods

This is a cross-sectional study with convenience sampling conducted in an urban academic adult ED, including 3 separate respiratory rate measurements performed at ED triage: usual care measurement, electronic BioHarness measurement, and criterion standard measurement. The criterion standard measurement used was defined by the World Health Organization as manual observation or auscultation of respirations for 60 seconds. The resultant usual care and BioHarness measurements were compared with the criterion standard, evaluating accuracy (sensitivity and specificity) for detecting tachypnea, as well as potential systematic biases of usual care and BioHarness measurements using a Bland Altman analysis.

Results

Of 191 analyzed patients, 44 presented with tachypnea (>20 breaths/min). Relative to criterion standard measurement, usual care measurement had a sensitivity of 23% (95% confidence interval [CI] 12% to 37%) and specificity of 99% (95% CI 97% to 100%) for tachypnea, whereas BioHarness had a sensitivity of 91% (95% CI 80% to 97%) and specificity of 97% (95% CI 93% to 99%) for tachypnea. Usual care measurements clustered around respiratory rates of 16 and 18 breaths/min (n=144), with poor agreement with criterion standard measurement. Conversely, BioHarness measurement closely tracked criterion standard values over the range of respiratory rates.

Conclusion

Current methods of respiratory rate measurement at ED triage are inaccurate. A new electronic respiratory rate sensor, BioHarness, has significantly greater sensitivity for detecting tachypnea versus usual care method of measurement.

Introduction

Obtaining accurate vital signs is essential for the clinical assessment of patients.1, 2, 3, 4, 5 Of the 5 vital signs collected during emergency department (ED) triage (respiratory rate, pulse rate, pulse oximetry, temperature, and blood pressure), respiratory rate remains the only vital sign that is not routinely measured electronically. The usual care method for measuring respiratory rate at triage, direct observation of respirations, has been found to be inaccurate, suggesting the need for an alternate technique for determining respiratory rates.5, 6 Previous attempts to electronically measure respiratory rate with transthoracic impedance monitors have demonstrated poor accuracy.5 Accordingly, there remains a need to investigate alternative devices that can aid in the objective assessment of respiratory rate in the ED.

Initial clinical evaluation of respiratory function includes assessment of the patient's airway patency, efficiency of breathing and ventilation, and their relative level of distress. Objective measurement of respiratory rate is one important component of this initial assessment and has been designated as one of the core components of triage systems for determining patients' acuity level and urgency of physician evaluation.7 For example, the Emergency Severity Index, one of the most commonly used triage scores, uses a cutoff of greater than 20 breaths/min to define a patient's priority level.8, 9 Respiratory rate is also one of the core components of several decision support tools that can help clinicians in early recognition of potentially serious disease (eg, systemic inflammatory response syndrome criteria for early detection of sepsis) and in making safe patient disposition decisions (eg, Pneumonia Severity Index, which predicts mortality and outcomes in patients with pneumonia).10, 11 The use of an imprecise method for determining respiratory rate may negatively affect the application of triage and clinical decision support tools, as well as overall treatment delivered to ED patients.5

A newly developed device, BioHarness (Zephyr Technology Corp., Annapolis, MD), recently approved by the Food and Drug Administration, uses a thoracic pressure sensor to detect respirations and has potential utility in the ED triage setting. Previous use has been restricted to real-time performance monitoring of athletes, military personnel, and first responders. One of the more recent applications of the BioHarness was during the rescue of 33 trapped miners in northern Chile's San Jose Mine. Throughout the rescue, the BioHarness provided physiologic data of the miners for analysis by on-site physicians.12 However, the performance characteristics of the BioHarness have not yet been systematically studied in a clinical setting. Accordingly, here we conduct a cross-sectional study to evaluate the sensitivities of both the BioHarness and usual care measurement for detecting tachypnea in a clinical environment, using the World Health Organization (WHO) method for respiratory rate measurement as the criterion standard comparator.13 Additionally, we evaluate the agreement of each of these measurements in reference to the criterion standard measurement.

Section snippets

Study Design

This is a cross-sectional study with convenience sampling to determine the sensitivity and agreement of both the BioHarness and usual care measurement, each in reference to the criterion standard measurement. The study was approved by the institutional review board.

Setting

The study was conducted at an urban academic adult ED with an annual census of approximately 60,000 patients. Enrollment occurred between 7 am and noon daily from February 1, 2011, to June 1, 2011.

Selection of Participants

We used convenience sampling of

Characteristics of Study Subjects

Two hundred fourteen adult patients were approached for study participation. Five patients (2%) declined, leaving 209 (98%) for evaluation. Of these, 18 (9%) were excluded from analysis because of incomplete criterion standard or BioHarness data collection, as follows: excessive coughing or pain interfered with the patient's ability to remain still (N=7), triage clinicians terminated data collection because of triage reassessment as critically ill (N=5), patient noncompliance with study

Limitations

This study does not reflect the true population of the ED, and specific groups of patients were excluded. Further, patients with severe illness are not well represented in this study. In addition to acuity level 1 patients, who bypass the triage process, 5 patients were excluded from analysis because of rapid triage evaluation, and an additional 7 patients were excluded because of the nature of their illness. Patients who were physically unable to have the device applied (ie, patients

Discussion

As indicated by the mantra “ABC: airway, breathing, circulation,” assessment of respiration and respiratory rate is essential to the initial evaluation of any patient but is especially important in a triage setting that requires rapid patient assessment and stabilization. The importance of respiratory rate is further emphasized by its inclusion in triage acuity and trigger systems. Accurate measurement of respiratory rate in triage is vital to fully assess whether a patient needs immediate

References (19)

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Cited by (0)

Supervising editor: Steven M. Green, MD

Author contributions: WB and RER conceived the study and designed the trial. AT and RER obtained research funding. WB managed patient enrollment and data collection. MS, PH, and CL supervised the conduct of the trial. AFD and Y-HH analyzed the data. WB and AFD drafted the article, and all authors contributed substantially to its revision. RER takes responsibility for the paper as a whole.

Funding and support: By Annals policy, all authors are required to disclose any and all commercial, financial, and other relationships in any way related to the subject of this article as per ICMJE conflict of interest guidelines (see www.icmje.org). The authors have stated that no such relationships exist. Funded by National Science Foundation grant CNS-0855191.

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Publication date: Available online June 26, 2012.

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