Accuracy of Noninvasive Multiwave Pulse Oximetry Compared With Carboxyhemoglobin From Blood Gas Analysis in Unselected Emergency Department Patients

Study objective

Accurate and timely diagnosis of carbon monoxide (CO) poisoning is difficult because of nonspecific symptoms. Multiwave pulse oximetry might facilitate the screening for occult poisoning by noninvasive measurement of carboxyhemoglobin (COHb), but its reliability is still unknown. We assess bias and precision of COHb oximetry compared with the criterion standard blood gas analysis.

Methods

This was a prospective diagnostic accuracy study according to STARD (Standards for the Reporting of Diagnostic accuracy studies) criteria, performed at a tertiary care hospital emergency department. We included all patients for whom both invasive and noninvasive measurement within 60 minutes was available, regardless of their complaints, during a 1-year period.

Results

One thousand five hundred seventy-eight subjects were studied, of whom 17 (1.1%) received a diagnosis of CO poisoning. In accordance with this limited patient cohort, we found a bias of 2.99% COHb (1.50% for smokers, 4.33% for nonsmokers) and a precision of 3.27% COHb (2.90% for smokers, 2.98% for nonsmokers), limits of agreement from −3.55% to 9.53% COHb (−4.30% to 7.30% for smokers, −1.63% to 10.29% for nonsmokers). Upper limit of normal cutoff of 6.6% COHb had the highest sensitivity in screening for CO poisoning. Smoking status and COHb level had the most influence on the deviation between measurements.

Conclusion

Multiwave pulse oximetry was found to measure COHb with an acceptable bias and precision. These results suggest it can be used to screen large numbers of patients for occult CO poisoning.

Introduction

Carbon monoxide (CO) poisoning is a major cause of morbidity and mortality. Official data from the United States indicate approximately 20,000 exposures¹ and 439 deaths² per year, including only non−fire-related and unintentional cases. Large registry trials, however, show much higher numbers than those officially reported, with approximately 50,000 visits per year to emergency departments (EDs) alone, representing 0.05% of all patients.3, 4 Data from other countries are limited, but higher rates than in the United States are expected.⁵

Symptoms of CO poisoning are nonspecific, ranging from mild headache, nausea, confusion, and dizziness to end-organ injury such as myocardial infarction,⁶ stroke,⁷ and death.8, 9 Diagnosis is therefore difficult and relies on clinical suspicion and confirmation by measurement of carboxyhemoglobin (COHb), using either venous or arterial¹⁰ blood gas analysis. However, COHb analyzers are not ubiquitously available.¹¹ As a result, many victims of CO poisoning might be overlooked and misdiagnosed.12, 13

Conventional pulse oximetry uses 2 different wavelengths of light only and is not able to explicitly determine COHb or methemoglobin levels, leading to wrong results.¹⁴ Recent technologic advancements allow for noninvasive measurement of COHb by multiwave pulse oximetry.¹⁵ Multiwave pulse oximeters use 8 different wavelengths to overcome this problem. This technique has been tested on healthy volunteers¹⁵ and small groups of selected patients.16, 17, 18, 19 To date, however, the accuracy of this method has not been studied in daily clinical use with large numbers of unselected patients.

The aim of our study was to assess bias and precision of multiwave pulse oximetry compared with blood gas analysis as reference standard in a cohort of unselected patients presenting to a large tertiary care ED. We further aimed to identify the upper limit of normal cutoff values of noninvasively measured COHb to aid in the diagnosis of CO poisoning and identify factors that influence its accuracy. Subgroup analyses were performed for smokers and nonsmokers.