Original ResearchThe vexatious vital: Neither clinical measurements by nurses nor an electronic monitor provides accurate measurements of respiratory rate in triage
Introduction
Emergency physicians depend heavily on vital signs. In recent years, pulse oximetry, glucometry, the Glasgow Coma Scale, and various pain scales have all been honored with the title of “fifth vital sign.” The utility of the 4 classic vital signs is rarely questioned.
Of the 4 classic vital signs, respiratory rate is the only one that is still measured clinically, not electronically, in most emergency department (ED) settings. The reliability of triage respiratory rate measurement matters for several reasons. Respiratory rate has an important role in the early recognition of such diverse illnesses as pulmonary embolus, pneumonia, congestive cardiac failure, and toxicologic and metabolic emergencies. Respiratory rate is incorporated into guidelines and decision rules for diagnosing and managing these conditions.1, 2, 3, 4, 5 Finally, because of its role in determining diagnosis and severity, respiratory rate plays an important role in prioritizing care after triage.
We set out, therefore, to evaluate the measurement of respiratory rate in the triage of our urban teaching hospital ED. Specifically, we sought to measure the variability and accuracy of triage nurses' measurements of respiratory rate relative to criterion standard measurements. A finding of low accuracy would indicate that triage nurses' measurements of respiratory rate are unlikely to detect clinically important bradypnea or tachypnea. Low variability would indicate that triage nurses' measurements of respiratory rate are more clustered than are criterion standard measurements of respiratory rate, which might suggest conscious or unconscious result selection.
We also sought to evaluate the variability and accuracy of electronic measurements of respiratory rate recorded using a cardiac monitor equipped with transthoracic impedance plethysmography, a feature found in many cardiac monitors in common use in EDs. We sought to determine whether transthoracic impedance plethysmography might offer an alternative to clinical measurement of respiratory rate.
Section snippets
Study design
This study used a cross-sectional design to assess the accuracy of 2 methods of measuring respiratory rate and was approved by the institutional review board of Beth Israel Medical Center, New York, NY. Verbal consent was required for participation.
Setting
This study was conducted at an urban teaching ED with an annual adult census of 52,000 visits. Triage is performed independently of, and usually before, registration.
Selection of participants
Consecutive patients presenting to the ED triage during designated study periods
Results
One hundred fifty-nine adult patients were enrolled in the study (Table 1). Thirty-one adult patients qualified for the subgroup with respiratory or cardiac presenting complaints. Data were collected from 28 pediatric patients but were excluded from analysis.
Measurements of respiratory rate were missed in some patients (see bottom of Table 1). Missed criterion standard measurements of respiratory rate occurred because of patient refusal, severity of illness (patients immediately moved into the
Limitations
Nurses were aware of the purpose of the study, potentially influencing their practice in measuring respiratory rate. However, common sense would lead us to believe that a lack of blinding would produce more careful, not less careful, measurements of respiratory rate.
Criterion standard measurement of respiratory rate is not perfect. Even the most careful clinical measurement of respiratory rate may suffer from inaccuracy and poor interobserver agreement, as discussed below. Nor could electronic
Discussion
Pulse oximetry gained rapid acceptance in EDs during the 1980s. Not only was oximetry an early claimant to the title of “fifth vital sign”16, 17 but many authors began to ask whether oximetry had rendered routine measurement of respiratory rate unnecessary.
Any debate about oximetry and respiratory rate harkens to a much older discussion about ventilation versus oxygenation. There are many clinical situations in which ventilation and oxygenation are altered in tandem, and in such situations,
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Author contributions: PBL obtained equipment on loan free of charge for use in the study. PBL, JMB, and KS conceived the study, designed the trial, and supervised the conduct of the trial. PBL and JMB collected data. PB and PBL analyzed the data. PBL drafted the manuscript, and all authors contributed substantially to its revision. PBL takes responsibility for the paper as a whole.
Presented orally at the Society for Academic Emergency Medicine New York regional meeting, New York, NY, April 9, 2003; as a poster at the Society for Academic Emergency Medicine annual meeting, Boston, MA, May to June, 2003; as a finalist for Best Resident Research Paper at the Society for Academic Emergency Medicine annual meeting, Boston, MA, May to June, 2003; and as a poster at the Second Mediterranean Emergency Medicine Congress, Barcelona, Spain, September 2003.
Previously published as an abstract in Lovett PB, Buchwald JM, Stürman K, et al. The vexatious vital: a comparison of clinical vs electronic measurement of respiratory rate in triage. Acad Emerg Med. 2003;10:552-553.
Two Escort Prism monitors for transthoracic impedance plethysmography measurement were loaned free of charge for the study by Medical Data Electronics.
Reprints not available from the authors.