Multi-wavelength pulse oximeter is not suitable for adjusting DLCO measurements

Abstract

BACKGROUND: Diffusing capacity of the lung for carbon monoxide (DLCO) can be affected by abnormal hemoglobin (Hb) or carboxyhemoglobin (COHb) levels. Predicted DLCO can be adjusted to reflect abnormal Hb or COHb levels. Until recently, blood sampling was required to determine Hb and COHb levels, but a new pulse oximeter, the Masimo RAD-57, can measure Hb and COHb noninvasively. We hypothesized that there would be no significant difference between the invasive and noninvasive Hb and COHb measurements for adjusting DLCO. METHODS: In patients referred to our university hospital for DLCO testing, we simultaneously took arterial blood gas samples and measured Hb and COHb with the RAD-57 (SpHb and SpCOHb, respectively). We analyzed the paired values and the Hb-adjusted and COHb-adjusted predicted DLCO values with t tests and Bland-Altman plots. We compared the differences in predicted DLCO to a clinical threshold of 3 mL/min/mm Hg. RESULTS: SpHb differed from Hb measured via arterial blood analysis (12.1 ± 2.4 g/dL vs 13.3 ± 2.1 g/dL, P 3 mL/min/mm Hg in 17% of patients. CONCLUSIONS: Pulse oximetry may be of limited usefulness for adjusting either predicted or measured DLCO values, but might be useful to screen patients for invasive testing, particularly if the DLCO is close to the lower limit of normal. © 2011 Daedalus Enterprises.