Abstract
BackgroundTrends in non-invasive measurements of blood hemoglobin (Hb) may be useful for identifying the need for transfusion in the perioperative period.MethodsCrystalloid fluid (5–20 mL/kg) was administered intravenously or by mouth to 30 volunteers and 33 surgical patients in five non-randomized clinical studies where Hb was measured on 915 occasions by non-invasive (Radical-7™) and invasive methodology. The hemodilution curves were compared by volume kinetic analysis and linear regression, with the slope and scattering of the data as key outcome measures.ResultsThe slope was 1.0, indicating unity between the two modes of measuring Hb when crystalloid fluid was infused in volunteers; however, only 40–45% of the variability in the non-invasive Hb could be explained by the invasive Hb. Patients undergoing major surgery, who showed the most pronounced hemodilution (median 24 g/L); non-invasive Hb explained 72% of the variability but indicated only half the magnitude of the invasive Hb changes (slope 0.48, P < 0.001 versus the volunteers). Simulations based on volume kinetic parameters from the volunteers showed 25% less plasma volume expansion after infusion when based on non-invasive as compared to invasive Hb, while no difference was found during infusion.ConclusionsIn volunteers the non-invasive Hb had good accuracy (low bias) but poor precision. In surgical patients the non-invasive Hb had good precision but systematically underestimated the hemodilution. Despite severe limitations, the non-invasive technology can be used to follow Hb trends during surgery if supported by occasional invasive measurements to assure acceptable quality of the hemodilution curve.Trial registrationsControlledTrials.gov NCT01195025, NCT01062776, NCT01458678, NCT03848507, and NCT01360333 on September 3, 2010, February 4, 2010, October 25, 2011, February 20, 2019, and May 25, 2011, respectively.
Highlights
Trends in non-invasive measurements of blood hemoglobin (Hb) may be useful for identifying the need for transfusion in the perioperative period
Continuous measurement of Hb would be of substantial value to refine these decisions
Non-invasive Hb analysis has been commercially available for about a decade in the form of the multi-wavelength pulse oximeter Radical-7TM from Masimo Inc
Summary
Trends in non-invasive measurements of blood hemoglobin (Hb) may be useful for identifying the need for transfusion in the perioperative period. Continuous measurement of Hb would be of substantial value to refine these decisions. For this purpose, non-invasive Hb analysis has been commercially available for about a decade in the form of the multi-wavelength pulse oximeter Radical-7TM from Masimo Inc. Many studies have performed point-wise comparisons between non-invasive and invasive Hb [1,2,3,4,5,6,7,8,9,10,11,12,13], and the main problem with the non-invasive technology is its poor precision. Several studies show good accuracy but 95% limits of agreement with a range of 40 g/L or more [3,4,5,6,7,8,9], which makes non-invasive Hb measurements difficult to rely on
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