Noninvasive Masimo carboxyhemoglobin can effectively screen ED patients for CO poisoning

Masimo (NASDAQ: MASI) announced today that a new study published in this month's issue of the peer-reviewed journal, Annals of Emergency Medicine, demonstrates that noninvasive Masimo carboxyhemoglobin (SpCO®) measurements provide an "effective means for screening at-risk populations for CO poisoning" with "acceptable bias and precision" compared to invasive blood gas analysis.  The prospective diagnostic accuracy study is more than ten times larger than any other published SpCO accuracy study to date and provides a strong rationale for clinical use of SpCO in the evaluation of emergency department (ED) patients.

Carbon monoxide (CO) poisoning is a major cause of morbidity and mortality.  At least 20,000 known exposures and 439 deaths a year are attributed to non-fire-related, unintentional CO poisoning cases in the U.S.  However, large registry trials show the prevalence of CO poisoning is far greater with approximately 50,000 ED visits per year. Because the symptoms of CO poisoning are nonspecific—ranging from mild headache, nausea, confusion, and dizziness to end-organ injury, such as myocardial infarction, stroke, and death—diagnosis is difficult and has historically relied on clinical suspicion and confirmation by measurement of carboxyhemoglobin (COHb) via invasive blood gas analysis. Unfortunately, it has been estimated that up to half of U.S. hospitals do not have invasive COHb testing ability—increasing the potential that many victims of CO poisoning could be overlooked and misdiagnosed.

The study, conducted over a year-long period in the Department of Emergency Medicine at one of the largest hospitals in Europe, the Vienna General Hospital (AKH Vienna), compared the accuracy of SpCO measured noninvasively using the Masimo Radical-7 with COHb measurements obtained via invasive blood gas analysis in 1,578 ED patients.  Results showed 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) between SpCO and lab values—demonstrating "acceptable bias and precision" for the "detection of high concentrations of COHb, found in acute CO poisoning."  Values ranged from 0-50% for SpCO and 0-39.3% for COHb with limits of agreement from -3.55% to 9.53% COHb (-4.30% to 7.30% for smokers, -1.63% to 10.29% for nonsmokers).  A total of 17 patients (9 smokers, 8 nonsmokers) with a mean COHb of 14.1% received a final diagnosis of CO poisoning.  Using a cut-off SpCO value of 6.6%, the researchers found a 94% sensitivity (ability to detect CO poisoning) and 77% specificity (ability to identify a lack of CO poisoning) and stated that the method "appears to be a reasonable upper limit of normal cutoff value for a screening test in the ED setting."

Researchers also found that several factors influence SpCO measurement accuracy as compared to COHb, including smoking, SpCO level, interval between measurements, and age.  Because cigarettes increase CO levels in the blood, users were cautioned to pay attention to "the number of cigarettes smoked."  Importantly, because CO in the blood decreases with time, researchers cited the "half-life of CO" and "time between multiwave pulse oximetry and blood gas analysis" as other possible "influencing factors on the deviation between SpCO and COHb."  The study also shows that time between measurement was still a factor within the 60-minute cut-off established by the researchers—underscoring the importance of simultaneous comparisons between SpCO and invasive blood gas measurements due to the half-life of CO.

Study authors concluded that SpCO measurement via multiwave pulse oximetry has "an acceptable bias and precision" and "keeping influencing factors in mind, it can therefore be used to screen large numbers of patients for latent CO poisoning."  They also noted the "potential for different measurement results from correct and incorrect (sensor) placement," an encouragement for users to closely follow the directions for use.  The current study follows the results by researchers in the ED of a Rhode Island Hospital, who first demonstrated that large scale population screening of ED patients using SpCO could identify patients with unsuspected CO poisoning.