Original Research
The vexatious vital: Neither clinical measurements by nurses nor an electronic monitor provides accurate measurements of respiratory rate in triage

https://doi.org/10.1016/j.annemergmed.2004.06.016Get rights and content

Study objective

Of all the vital signs, only respiratory rate is still measured clinically in most US triage systems. Previous studies have demonstrated the inaccuracy, poor interobserver agreement, and low variability of routine measurements of respiratory rate. We assess the variability and accuracy of triage nurses' measurements of respiratory rate against a criterion standard. Also, we assess electronic measurement of respiratory rate against the same criterion standard.

Methods

Consecutive patients presenting to an urban teaching emergency department (ED) were enrolled in this prospective study. Electronic measurement of respiratory rate was recorded throughout the triage encounter when nurses were recording measurements of respiratory rate. Electronic respiratory rate was measured using transthoracic impedance plethysmography. Immediately after each triage evaluation, criterion standard measurements of respiratory rate were made by research assistants using the World Health Organization recommendation of auscultation or observation for 60 seconds.

Results

We enrolled 159 patients. Variability was low for triage nurses' measurements of respiratory rate (SD 3.3) and electronic measurement of respiratory rate (SD 4.1) compared with criterion standard measurements of respiratory rate (SD 4.8; P<.05). Triage nurses' measurements of respiratory rate and electronic measurement of respiratory rate showed low sensitivity in detecting bradypnea and tachypnea. In a Bland-Altman analysis, triage nurses' measurements of respiratory rate and electronic measurement of respiratory rate showed poor agreement with criterion standard measurements of respiratory rate. Subgroup analysis of patients presenting with cardiac and respiratory symptoms yielded similar results.

Conclusion

Neither triage nurses nor an electronic monitor provides accurate measurements of respiratory rate in the ED. Emergency physicians should search for new electronic modalities for measuring respiratory rate to bring respiratory rate into line with other vital signs. Emergency physicians should also consider new clinical strategies for measuring respiratory rate.

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.

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