The measurement of carboxyhemoglobin and methemoglobin using a non-invasive pulse CO-oximeter

Department of Anesthesia, McGill University Health Centre, Montreal, Québec, Canada.
Respiratory Physiology & Neurobiology (Impact Factor: 1.97). 05/2012; 182(2-3):88-92. DOI: 10.1016/j.resp.2012.05.010
Source: PubMed


The pulse CO-oximeter (Rad-57 Masimo Corporation, Irvine, CA) allows non-invasive and instantaneous measurement of carboxyhemoglobin (COHb) and methemoglobin (MetHb) percentage level using a finger probe. However, the accuracy and reliability of the Rad-57 against the gold standard of venous or arterial blood samples have not been clearly established. Thus, the objective of this trial is to evaluate the accuracy and precision of the Rad-57 pulse CO-oximeter by comparing it with venous sampling on the same subjects. Nine healthy subjects were subjected to carbon monoxide such that it raised the COHb to 10-14% on two different days and pooled together. The COHb and MetHb were measured with a blood gas-analyzer and simultaneously with the Rad-57 as the COHb increased from 1.4 to 14%. Results were compared using linear regression and a Bland and Altman method comparison. Mean bias and precision for COHb measured with the Rad-57 was -1% and 2.5%, respectively. The mean bias and precision for MetHb measured with the Rad-57 was 0.0% and 0.3%, respectively. The ability to detect a COHb ≥ 10% occurred in 54% of the samples in which COHb was ≥ 10-14%. In conclusion, the Rad-57 provides a reading that is between -6% and +4% of the true COHb value for 95% of all samples. The Rad-57 seems to be a good substitute as a first screening test of COHb when the pulse CO-oximeter reads <15%.

  • No preview · Article · Feb 2013 · Respiratory care
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    ABSTRACT: Background: Carbon monoxide poisoning is a significant problem in most countries, and a reliable method of quick diagnosis would greatly improve patient care. Until the recent introduction of a multiwavelength "pulse CO-oximeter" (Masimo Rainbow SET(®) Radical-7), obtaining carboxyhemoglobin (COHb) levels in blood required blood sampling and laboratory analysis. In this study, we sought to determine whether hypoxemia, which can accompany carbon monoxide poisoning, interferes with the accurate detection of COHb. Methods: Twelve healthy, nonsmoking, adult volunteers were fitted with 2 standard pulse-oximeter finger probes and 2 Rainbow probes for COHb detection. A radial arterial catheter was placed for blood sampling during 3 interventions: (1) increasing hypoxemia in incremental steps with arterial oxygen saturations (SaO2) of 100% to 80%; (2) normoxia with incremental increases in %COHb to 12%; and (3) elevated COHb combined with hypoxemia with SaO2 of 100% to 80%. Pulse-oximeter (SpCO) readings were compared with simultaneous arterial blood values at the various increments of hypoxemia and carboxyhemoglobinemia (≈25 samples per subject). Pulse CO-oximeter performance was analyzed by calculating the mean bias (SpCO - %COHb), standard deviation of the bias (precision), and the root-mean-square error (A(rms)). Results: The Radical-7 accurately detected hypoxemia with both normal and elevated levels of COHb (bias mean ± SD: 0.44% ± 1.69% at %COHb <4%, and -0.29% ± 1.64% at %COHb ≥4%, P < 0.0001, and A(rms) 1.74% vs 1.67%). COHb was accurately detected during normoxia and moderate hypoxia (bias mean ± SD: -0.98 ± 2.6 at SaO2 ≥95%, and -0.7 ± 4.0 at SaO2 <95%, P = 0.60, and A(rms) 2.8% vs 4.0%), but when SaO2 decreased below approximately 85%, the pulse CO-oximeter always gave low signal quality errors and did not report SpCO values. Conclusions: In healthy volunteers, the Radical-7 pulse CO-oximeter accurately detects hypoxemia with both low and elevated COHb levels, and accurately detects COHb, but only reads SpCO when SaO2 is more than approximately 85%.
    No preview · Article · Mar 2013 · Anesthesia and analgesia
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    ABSTRACT: Background: The RAD-57 pulse CO-oximeter is a lightweight device allowing noninvasive measurement of blood carboxyhemoglobin (S(pCO)). We assessed the diagnostic value of pulse CO-oximetry, comparing S(pCO) values from the RAD-57 to standard laboratory blood carboxyhemoglobin (COHb) measurement in emergency department patients with suspected carbon monoxide (CO) poisoning. Methods: This was a prospective, diagnostic accuracy study according to the Standards for the Reporting of Diagnostic Accuracy Studies criteria in consecutive adult emergency department patients with suspected CO poisoning. S(pCO) was measured with the RAD-57 simultaneously with blood sampling for laboratory blood gas analysis. We made no changes to our standard management of CO poisoning. Blood COHb > 5% for non-smokers, and > 10% for smokers were applied as the reference standard. Results: We included 93 subjects: 37 smokers and 56 non-smokers. CO poisoning was diagnosed in 26 subjects (28%). The S(pCO) values ranged from 1% to 30%, with a median of 4% (IQR 2.7-7.3%). The COHb values ranged from 0% to 34%, with a median of 5% (IQR 2-9%). The mean differences between the COHb and S(pCO) values were -0.2% ± 3.3% (95% limits of agreement of -6.7% and 6.3%) for the whole cohort, -0.7% (limits of agreement -7.7% and 6.2%) for the non-smokers, and 0.6% (limits of agreement -5.0% and 6.2%) for the smokers. The optimal thresholds for detecting CO poisoning were S(pCO) of 9% and 6% for smokers and non-smokers, respectively. Conclusions: S(pCO) measured with the RAD-57 was not a substitute for standard blood COHb measurement. However, noninvasive pulse CO-oximetry could be useful as a first-line screening test, enabling rapid detection and management of CO-poisoned patients in the emergency department.
    Full-text · Article · Mar 2013 · Respiratory care
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