title: The accuracy of noninvasive hemoglobin measurement by multiwavelength pulse oximetry after cardiac surgery.
abstract: BACKGROUND
  In March 2008, a new multiwavelength pulse oximeter, the Radical 7 (Rad7; Masimo Corp., Irvine, CA), was developed that offers noninvasive measurement of hemoglobin concentration. Accuracy has been established in healthy adults and some surgical patients, but not in cardiac surgery intensive care patients, a group at high risk of postoperative bleeding events and anemia in whom early diagnosis could improve management.
  
  
  METHODS
  In this prospective, observational study conducted in a cardiovascular intensive care unit, we compared hemoglobin concentrations shown by the Rad7 with arterial hemoglobin concentrations determined by an automated hematology analyzer, XE-2100 (Roche, Neuilly sur Seine, France). Two software versions of Rad7 (V 7.3.0.1 [42 points of comparison in 14 patients] and the updated V 7.3.1.1 [61 points of comparison in 27 patients]) were studied during two 1-week periods. Bias, defined as the difference between the 2 methods (Masimo SpHb-XE-2100 laboratory hemoglobin), was calculated. A negative bias indicated that the Masimo underestimated hemoglobin compared with the laboratory analyzer. Correlation between the perfusion index given by Rad7 and the hemoglobin bias was also studied.
  
  
  RESULTS
  Correlations between Rad7 and XE-2100 were weak for both software versions (R2=0.11 for V 7.3.0.1 and R2=0.27 for V 7.3.1.1). Mean bias was -1.3 g/dL for V 7.3.0.1 and -1.7 g/dL for V 7.3.1.1, with wide 95% prediction intervals for the bias (respectively, -4.6 to 2.1 g/dL and -5.7 to 2.3 g/dL). The absolute hemoglobin bias tended to increase when the perfusion index decreased. For the V 7.3.0.1 software, the average absolute bias was 1.9 g/dL for perfusion index<2 and 0.8 g/dL for perfusion index>2 (P=0.03). For V 7.3.1.1, the mean absolute bias was 2.1 g/dL when the perfusion index was <2, and 1.6 g/dL when the perfusion index was >2 (P=0.26).
  
  
  CONCLUSIONS
  Our study demonstrates poor correlation between hemoglobin measured noninvasively by multiwavelength pulse oximetry and a laboratory hematology analyzer. The difference was greater when the pulse oximetry perfusion index was low, as may occur in shock, hypothermia, or vasoconstriction patients. The multiwavelength pulse oximetry is not sufficiently accurate for clinical use in a cardiovascular intensive care unit.
authors.affiliation: Department of Anesthesiology and Critical Care Medicine, University Hospital, CHU Brest, and Université de Brest, Faculté de Médecine et des Sciences de la Santé, Laboratoire de Physiologie, Brest, France.
authors.forename: Ba-Vinh
authors.initials: BV
authors.lastname: Nguyen
authors.forename: Jean-Louis
authors.initials: JL
authors.lastname: Vincent
authors.forename: Emmanuel
authors.initials: E
authors.lastname: Nowak
authors.forename: Michelle
authors.initials: M
authors.lastname: Coat
authors.forename: Nicolas
authors.initials: N
authors.lastname: Paleiron
authors.forename: Pierre
authors.initials: P
authors.lastname: Gouny
authors.forename: Mehdi
authors.initials: M
authors.lastname: Ould-Ahmed
authors.forename: Maité
authors.initials: M
authors.lastname: Guillouet
authors.forename: Charles Christian
authors.initials: CC
authors.lastname: Arvieux
authors.forename: Gildas
authors.initials: G
authors.lastname: Gueret
mesh_terms: D000368:Aged; D006348:Cardiac Surgical Procedures / Q000379:methods*; D003422:Critical Care; D005260:Female; D006452:Hemoglobinometry / Q000295:instrumentation*; D006801:Humans; D008297:Male; D008875:Middle Aged; D008991:Monitoring, Physiologic; D010092:Oximetry / Q000295:instrumentation*; D011184:Postoperative Period; D011446:Prospective Studies; D012039:Regional Blood Flow / Q000502:physiology; D015203:Reproducibility of Results; D012984:Software