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Duration and extent of the decline SpO2 after low-dose injection of methylene blue: A-66

Siebert, Ch.; Kroeber, S.; Lutter, N.

European Journal of Anaesthesiology: May 2005 - Volume 22 - Issue - p 18
Monitoring: Equipment and Computers
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Department of Anesthesiology, University of Erlangen-Nuremberg, Erlangen, Germany

Background and Goal of Study: With regard to previous studies (1) reporting of artifactual low readings of functional oxygen saturation (SpO2) after injection of methylene blue (MB), this study was designed to indi-vidually evaluate duration and extent of the spurious de-crease in SpO2 of four pulse oximeters, each representing the newest technology.

Materials and Methods: After IRB approval and in-formed consent, SpO2 of 20 patients (58-92 yrs) under-going transurethral vesical surgery and receiving 50 mg MB intraoperatively to localize the urethral orifices was simultaneously measured with four pulse oximeters (Philips IntelliVue M3001, Masimo Radical, Dolphin Medical 2100, Nellcor N-595) via four randomly placed sensors (digit II-V). Minimum SpO2 (t2) as well as be-ginning (t1) and end (t3) of the decline of SpO2 were marked offline and Δt1 = t2 − t1, Δt2 = t3 − t2 and ΔSpO2 = SpO2(t1) − SpO2(t2) were calculated.

Results and Discussions: Data (mean ± SD) are shown in the table:

Table

Table

There are only slight statistical differences of Δ t1 with all pulse oximeters. Dolphin Medical shows the largest recovery time and as well as Masimo Radical the deepest decline of SpO2, significantly differing from Nellcor N-595 and Philips IntelliVue.

Conclusion: Variably differing SpO2 readings with newest generation pulse oximeters after MB injection do not allow to conclude on pathophysiological alterations of oxygen delivery. Further investigations are needed to de-termine whether or not the decline in SpO2 may correlate to a change in arterial oxygen saturation (sO2).

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Reference:

1 Morell RC et al. Anesthesiology 1993; 78: 363-364.
© 2005 European Society of Anaesthesiology