title: Methemoglobin measurements are underestimated by the Radical 7 co-oximeter: experience from a series of moderate to severe propanil poisonings.
abstract: BACKGROUND
  In Asia methemoglobinemia (MetHb) is commonly caused through self-poisoning with the pesticide propranil. MetHb can cause hypoxia, coma and death, but usually responds to methylene blue. It is therefore vital to have accurate methods to measure blood MetHb to guide appropriate treatments. The gold standard to measure MetHb utilizes a spectrophotometer, but recent bedside tests have been developed e.g., pulse co-oximeter probe and blood color chart.
  
  
  METHODS
  Nine propanil poisoned patients had data collected from hospitals in Sri Lanka during 2008. Several MetHb readings were taken from each patient from admission up to 50 hours using spectrophotometry (Unico UV-Vis model no. 2800), pulse co-oximetry (Radical-7, Masimo, CA), and color chart.
  
  
  RESULTS
  The co-oximeter underestimated the MetHb percentage when compared with spectrophotometry and the color chart, especially when the average MetHb was greater than 20%. The color chart demonstrated acceptable accuracy compared with formal spectrophotometry with the majority of values showing no more than 10% difference.
  
  
  CONCLUSIONS
  This small cohort highlights the potential for extreme inaccuracy of the Radical-7 co-oximeter, especially with a MetHb greater than 20%. Pulse co-oximeters should be required to be validated for the complete range of MetHb prior to regulatory approval.
authors.affiliation: a Pharmacology, Toxicology and Therapeutics, University/BHF Centre for Cardiovascular Science, University of Edinburgh , UK.|b South Asian Clinical Toxicology Research Collaboration (SACTRC) , Kandy , Sri Lanka.
authors.forename: Elspeth
authors.initials: E
authors.lastname: Hulse
authors.affiliation: c Faculty of Medicine , University of Peradeniya , Kandy , Sri Lanka.
authors.forename: Fathima
authors.initials: F
authors.lastname: Shihana
authors.affiliation: b South Asian Clinical Toxicology Research Collaboration (SACTRC) , Kandy , Sri Lanka.|d School of Medical Sciences, University of Sydney , Sydney , Australia.
authors.forename: Nicholas A
authors.initials: NA
authors.lastname: Buckley
mesh_terms: D006540:Herbicides / Q000506:poisoning*; D006801:Humans; D008706:Methemoglobin / Q000032:analysis*; D008708:Methemoglobinemia / Q000175:diagnosis*; D008751:Methylene Blue / Q000627:therapeutic use; D010092:Oximetry / Q000295:instrumentation / Q000379:methods*; D011411:Propanil / Q000506:poisoning*; D011446:Prospective Studies; D015203:Reproducibility of Results; D012720:Severity of Illness Index; D013053:Spectrophotometry / Q000379:methods; D013188:Sri Lanka
chemical_list: D006540:Herbicides; D011411:Propanil; D008706:Methemoglobin; D008751:Methylene Blue
keywords: Methemoglobinemia; SpMet; diagnostic accuracy; non-invasive co-oximeter spectrophotometry; pulse oximetry