Non-invasive measurement of hemoglobin: assessment of two different point-of-care technologies

Abstract

Background: Measurement of blood hemoglobin (Hb) concentration is a routine procedure. Using a non-invasive point-of-care device reduces pain and discomfort for the patient and allows time saving in patient care. The aims of the present study were to assess the concordance of Hb levels obtained non-invasively with the Pronto-7 monitor (version 2.1.9, Masimo Corporation, Irvine, USA) or with the NBM-200MP monitor (Orsense, Nes Ziona, Israel) and the values obtained from the usual colorimetric method using blood samples and to determine the source of discordance.

Methods and findings: We conducted two consecutive prospective open trials enrolling patients presenting in the emergency department of a university hospital. The first was designed to assess Pronto-7™ and the second NBM-200MP™. In each study, the main outcome measure was the agreement between both methods. Independent factors associated with the bias were determined using multiple linear regression. Three hundred patients were prospectively enrolled in each study. For Pronto-7™, the absolute mean difference was 0.56 g.L(-1) (95% confidence interval [CI] 0.41 to 0.69) with an upper agreement limit at 2.94 g.L(-1) (95% CI [2.70;3.19]), a lower agreement limit at -1.84 g.L(-1) (95% CI [-2.08;-1.58]) and an intra-class correlation coefficient at 0.80 (95% CI [0.74;0.84]). The corresponding values for the NBM-200MP™ were 0.21 [0.02;0.39], 3.42 [3.10;3.74], -3.01 [-3.32;-2.69] and 0.69 [0.62;0.75]. Multivariate analysis showed that age and laboratory values of hemoglobin were independently associated with the bias when using Pronto-7™, while perfusion index and laboratory value of hemoglobin were independently associated with the bias when using NBM-200MP™.

Conclusion: Despite a relatively limited bias in both cases, the large limits of agreement found in both cases render the clinical usefulness of such devices debatable. For both devices, the bias is independently and inversely associated with the true value of hemoglobin.

Trial registration: ClinicalTrials.gov NCT01321580 and NCT01321593.

Figure 1. Flow chart of the studies (Pronto-7™ on panel A and Orsense on panel B).

Figure 2. Distribution of hemoglobin value in the two populations studied.

As depicted in the figure, the overlap of hemoglobin values between the two populations studied is almost complete all along the range of hemoglobin values.

Figure 3. Bland and Altman graphical representation of the concordance between the laboratory value of hemoglobin and SpHb.

Results for the Pronto-Study are displayed on the panel A and for the Orsense-Study on the panel B. The plain horizontal blue line represents the mean bias and the dashed horizontal blue lines represent the upper and the lower limits of agreement.

Figure 4. Association between true values of hemoglobin and bias.

Results for the Pronto-Study are displayed on the panel A and for the Orsense-Study on the panel B. The red line represents the linear regression relationship between the true value of hemoglobin and the bias. There is an inverse correlation between hemoglobin and bias in both studies (Spearman correlation coefficients at - 0.51, p <0.0001 and -0.37, p<0.0001 for the Pronto-Study and the Orsense-study, respectively).

Figure 5. Association between perfusion index and bias.

Results for the Pronto-Study are displayed on the panel A and for the Orsense-Study on the panel B. The red line represents the linear regression relationship between the perfusion index and the bias. Perfusion index is linearly correlated with the bias in Orsense-Study but not in the Pronto-Study (Spearman correlation coefficients at - 0.06, p = 0.36 and 0.42, p<0.0001 for the Pronto-Study and Orsense-study, respectively).

Figure 6. Three-dimensional representation of the variability of the measures obtained with the two monitors.

Results for the Pronto-Study are displayed on the panel A and for the Orsense-Study on the panel B. The coordinates of each point are the three consecutive measures. The graphical representation shows that the Orsense™ monitor seems to be associated with a higher variability compared to the Pronto-7™. This is confirmed by the fact that variations among the three consecutive measurements was lower than 2.5% in 71% of the cases when using the Pronto-7™ monitor but only in 47% of the cases when using the Orsense™ monitor