Original Contributions
The reliability of vital sign measurements*,**,*

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Abstract

Study objective: Vital sign measurements, specifically heart rate, respiratory rate, and blood pressure, play a fundamental role in many medical evaluations, yet little is known about the reliability of noninvasive vital sign measurements. We sought to determine whether trained observers can reproducibly assess vital signs in the clinical setting. Methods: Two trained observers independently measured vital signs on 140 patients presenting to an urban emergency department with acute medical complaints. Heart rate and respiratory rate were each measured by auscultation of heart and breath sounds for 1 minute. Systolic and diastolic blood pressures were determined by auscultating Korotkoff sounds while viewing pressure measurements from a standard cuff and mercury manometer. The mean value of each vital sign and Bland-Altman statistics (mean difference between observers [MDO], expected range of agreement [ERA]) were used to provide absolute and relative indices of reliability. Results: The observers found a mean heart rate of 78.5 beats/min, with an MDO of 0.02 beats/min (0.03%), and an ERA of ±10.6 beats/min (±13.5%). Respiratory rate exhibited a mean of 17.5 breaths/min, an MDO of 0.04 breaths/min (0.2%), and an ERA of ±6.2 breaths/min (±35.5%). The mean systolic blood pressure of 127.1 mm Hg was associated with an MDO of 1.3 mm Hg (1.0%), and an ERA of ±24.2 mm Hg (±19.0%). Diastolic blood pressure exhibited a mean of 77.4 mm Hg, an MDO of 0.3 mm Hg (0.4%) with an ERA of ±19.9 mm Hg (±25.7%). Conclusion: The reproducibility of vital sign measurements may be limited by significant interobserver variability. Clinicians should recognize this inherent variability and interpret vital signs with caution. [Edmonds ZV, Mower WR, Lovato LM, Lomeli R. The reliability of vital sign measurements. Ann Emerg Med. March 2002;39:233-237.]

Introduction

The measurement of standard vital signs (heart rate, blood pressure, respiratory rate, and temperature) is a core component of the physical assessment of most emergency patients.1 These values play a fundamental role in emergency assessments, but to date, the reproducibility of these measures has not been assessed. Existing data suggest that respiratory rates may be difficult to measure and that problems may arise in assessing blood pressure.2, 4 There is currently no documentation of the interobserver variability of vital signs measurements, or of their reliability in assessing for the presence or absence of tachycardia, bradycardia, systolic hypertension, diastolic hypertension, or systolic hypotension.

The purpose of this study is to examine the interobserver variability of vital sign measurements and to determine whether trained observers, using careful technique, can reproducibly assess the presence or absence of tachycardia, bradycardia, systolic hypertension, diastolic hypertension, or systolic hypotension.

Section snippets

Methods

The study enrolled consecutive patients presenting to an urban emergency department with an annual census of 35,000 visits, during defined representative observation periods between June 1 and August 30, 1999. Patients were excluded from the study only if they were unwilling to provide informed consent or were unable to do so (those exhibiting intoxication, altered mentation, language barriers, or pediatric patients ≤6 years old). The study was reviewed and approved by the institutional Human

Results

Of 174 patients who met enrollment criteria, 140 (80%) agreed to participate in the study, including 78 (56%) women and 62 (44%) men. The age of the participants ranged from 7 to 86 years, with a mean of 49 years. The study population consisted of 93 (66%) white patients, 18 (13%) black patients, 14 (10%) Hispanic patients, 11 (8%) Asian-American patients, and 4 (3%) patients from other races.

Table 1 summarizes the results of the Bland-Altman analysis.

. Variability of vital sign measurements

Discussion

Clinical assessments are most useful when they provide information that is both valid and reproducible. Validity reflects the ability of a measurement to provide information on the true value of the phenomenon being assessed, whereas reproducibility, or reliability, relates to the ability to perform repeated measurements of the phenomenon.7 We designed this study to evaluate the reliability of standard vital sign measurements, and we did not undertake an assessment of validity. Prior research

Acknowledgements

We thank the staff of the UCLA Emergency Department for facilitating this research effort.

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Supported in part by the UCLA School of Medicine Short-Term Training Program.

**

Reprints not available from the authors. Address for correspondence: William R. Mower, MD, PhD, UCLA Emergency Medicine Center, 924 Westwood Boulevard, Suite 300, Los Angeles, CA 90024; 310-794-0582, fax 310-794-0599; E-mail: [email protected]

*

Author contributions are provided at the end of this article. Author contributions: ZVE and WRM conceived the study and designed the trial. ZVE, WRM, LML, and RL undertook patient recruitment, enrollment, and data collection. WRM provided statistical advice on study design and analyzed the data. ZVE drafted the manuscript, and all authors contributed substantially to its revision. WRM takes responsibility for the paper as a whole.

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