Purpose: Pulse oximetry (SpO(2)) measured at finger site via transmission mode may fail in situations of hypoperfusion. Forehead sensors using reflectance technology might be useful in these circumstances. We hypothesized that reflectance SpO(2) would be more accurate than finger SpO(2) in patients with severe shock.
Methods: A prospective observational study was conducted in an intensive care unit of a university hospital of patients in shock who were treated with high norepinephrine and/or epinephrine doses (≥0.1 μg kg(-1) min(-1)). When blood gas determinations were requested, forehead SpO(2) and finger SpO(2) values were simultaneous recorded. Agreement between SpO(2) measurements with arterial saturation (SaO(2)), obtained by blood analysis with a co-oximeter, was assessed using the Bland-Altman method. The number of outliers, defined by the formula SaO(2) - SpO(2) > ±3 %, indicated the proportion of measurements considered to be clinically unacceptable.
Results: Thirty-two patients were enrolled in the study. With the forehead sensor no reading failure occurred, and 140 paired data sets (forehead SpO(2) vs. SaO(2)) were obtained. Bias and precision were +1.0 and +2.5 %, respectively, and the limits of agreement ranged from -4.0 to 6.0 %. The finger sensor failed to give a value in four cases, thus providing 136 paired data sets (finger SpO(2) vs. SaO(2)) for analysis. Bias and precision were +1.4 and +4.8 %, respectively, and the limits of agreement ranged from -8.0 to 10.9 %. There were 21 (15 %) outliers for the forehead sensor and 43 (32 %) for the finger sensor (P < 0.001).
Conclusions: Forehead SpO(2) measurements were more accurate than finger SpO(2) when compared with SaO(2) in critically ill patients requiring high-dose vasopressor therapy and should therefore be the preferred method considered.