Article

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: 2.05). 05/2012; 182(2-3):88-92. DOI: 10.1016/j.resp.2012.05.010
Source: PubMed

ABSTRACT 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%.

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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 (Arms).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 Arms 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 Arms 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%.
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