Accuracy of Methemoglobin Detection by Pulse CO-Oximetry During Hypoxia
ABSTRACT Methemoglobin in the blood cannot be detected by conventional pulse oximetry, although it can bias the oximeter's estimate (Spo2) of the true arterial functional oxygen saturation (Sao2). A recently introduced "Pulse CO-Oximeter" (Masimo Rainbow SET(R) Radical-7 Pulse CO-Oximeter, Masimo Corp., Irvine, CA) is intended to additionally monitor noninvasively the fractional carboxyhemoglobin and methemoglobin content in blood. The purpose of our study was to determine whether hypoxia affects the new device's estimated methemoglobin reading accuracy, and whether the presence of methemoglobin impairs the ability of the Radical-7 and a conventional pulse oximeter (Nonin 9700, Nonin Medical Inc., Plymouth, MN) to detect decreases in Sao2.
Eight and 6 healthy adults were included in 2 study groups, respectively, each fitted with multiple sensors and a radial arterial catheter for blood sampling. In the first group, IV administration of approximately 300 mg sodium nitrite increased subjects' methemoglobin level to a 7% to 8% target and hypoxia was induced to different levels of Sao2 (70%-100%) by varying fractional inspired oxygen. In the second group, 15% methemoglobin at room air and 80% Sao2 were targeted. Pulse CO-oximeter readings were compared with arterial blood values measured using a Radiometer multiwavelength hemoximeter. Pulse CO-oximeter methemoglobin reading performance was analyzed by observing the incidence of meaningful reading errors at the various hypoxia levels. This was used to determine the impact on predictive values for detecting methemoglobinemia. Spo2 reading bias, precision, and root mean square error were evaluated during conditions of elevated methemoglobin.
Observations spanned 66.2% to 99% Sao2 and 0.6% to 14.4% methemoglobin over the 2 groups (170 blood draws). Masimo methemoglobin reading bias and precision over the full Sao2 span was 7.7% +/- 13.0%. Best accuracy was found in the 95% to 100% Sao2 range (1.9% +/- 2.5%), progressing to its worst in the 70% to 80% range (24.8% +/- 15.6%). Occurrence of methemoglobin readings in error >5% increased over each 5-point decrease in Sao2 (P < 0.05). Masimo Spo2 readings were biased -6.3% +/- 3.0% in the 95% to 100% Sao2 range with 4% to 8.3% methemoglobin. Both the Radical-7 and Nonin 9700 pulse oximeters accurately detected decreases in Sao(2) <90% with 4% to 15% methemoglobin, despite displaying low Spo2 readings when Sao2 was >95%.
The Radical-7's methemoglobin readings become progressively more inaccurate as Sao2 decreases <95%, at times overestimating true values by 10% to 40%. Elevated methemoglobin causes the Spo2 readings to underestimate Sao2 similar to conventional 2-wavelength pulse oximeters at high saturation. Spo2 readings from both types of instruments continue to trend downward during the development of hypoxemia (Sao2 <90%) with methemoglobin levels up to 15%.
[Show abstract] [Hide abstract]
ABSTRACT: We have developed a method for online monitoring of blood levels of oxyhemoglobin, deoxyhemoglobin, carboxyhemoglobin, methemoglobin, and sulfhemoglobin using the diffuse reflectance spectrum of the mucosa of the lip or tongue of the patient, measured at a distance from the area to which the exciting radiation is delivered. The method is based on simple analytical expressions approximating the dependence of the diffuse light signals on the absorption coefficient, the transport scattering coefficient, the scattering anisotropy factor, and the refractive index of the mucosa. We have estimated the uncertainties in the method when there is a priori uncertainty in the optical parameters of the tissue. We have analyzed the experimental diffuse reflectance spectra of the mucosa of the lip, demonstrating that the hemoglobin composition of the studied tissue corresponds to normal physiological data.Journal of Applied Spectroscopy 02/2014; 81(1). DOI:10.1007/s10812-014-9896-7 · 0.51 Impact Factor
[Show abstract] [Hide abstract]
ABSTRACT: BackgroundHaemolytic conditions may contribute to disease pathogenesis and severe clinical manifestations through the liberation of free haemoglobin (Hb) and production of toxic free haem. Thus, free Hb and haem should be associated with altered MetHb and COHb levels in malaria as in other conditions.MethodsThis study comprises data collected at three different sites: (i) a retrospective analysis of the first arterial blood gas result (ABGS) of any patient during 2010 at the University Hospital in Lisbon; (ii) a retrospective analysis of ABGS from patients with severe malaria admitted to the intensive care unit in Berlin, Germany; and (iii) a prospective study of non-invasive MetHb measurements in children with and without malaria in Lambaréné, Gabon.ResultsIn Lisbon, the mean MetHb level was 1.4% (SD: 0.5) in a total of 17,834 ABGS. Only 11 of 98 samples with a MetHb level of >3.0 referred to infections. COHb levels showed no particular association with clinical conditions, including sepsis. In 13 patients with severe malaria in Berlin, the mean MetHb levels on admission was 1.29%, with 1.36% for cerebral malaria and 1.14% for non-cerebral malaria (P > 0.05). All COHb measurements were below 2.3%. In Lambaréné, Gabon, 132 healthy children had a mean MetHb level of 1.57%, as compared to 150 children with malaria, with a value of 1.77% and 2.05% in uncomplicated and complicated cases, respectively (P < 0.01).ConclusionsThe data appears consistent with the methaemoglobin/haem hypothesis in malaria and sepsis pathogenesis. However, although MetHb was significantly different between healthy controls and children with malaria in Africa, the difference was rather small, also when compared to previous studies. Still, non-invasive bedside MetHb testing may warrant further evaluation as it could be a simple adjuvant tool for prognosis in resource poor settings.Malaria Journal 07/2014; 13(1):285. DOI:10.1186/1475-2875-13-285 · 3.49 Impact Factor
Indian Heart Journal 02/2015; 67(1). DOI:10.1016/j.ihj.2015.02.001 · 0.17 Impact Factor