Methylene blue can cause a marked artifactual elevation in StO2 and THI measurements from the InSpectra™ StO2 Tissue Oxygenation Monitor.1 This elevation is more pronounced when StO2 is low1 (see tables below) and can reasonably be expected to persist until methylene blue is sufficiently cleared from the blood. The terminal half-life of intravenous methylene blue is 5.25 hours.2
It should be noted that methylene blue caused a reduction in pulse oximetry measurements.3,4 This is important as we have occasionally seen cases in which the SpO2 is lower than StO2. This is not possible physically and should be an alert that there is an artifact in the StO2 and/or SpO2 measurement.
Methylene blue is a chemical compound used in biology, chemistry and medicine. Treatment of methemoglobinemia and cyanide poisoning are examples of common medical uses. In the treatment of methemoglobinemia, methylene blue is administered intravenously as a 1% solution in doses of 1 to 2 mg/kg bodyweight (BW) injected over a period of several minutes.5
Effect of Methylene Blue (MB) on StO2 and THI Measurements1
1 Bjork K, internal HTI study, 2010 (#5025183).
2 Peter C, Hongwan D, Kupfer A, Lauterburg BH, Pharmacokinetics and organ distribution of intravenous and oral methylene blue. Eur J Clin Pharmacol. 2000;56:247-50.
3 Gorman ES, Shnider MR. Effect of methylene blue on the absorbance of solutions of haemoglobin. Br J Anaesth. 1988;60(4):439-44.
4 Paulus SA, Gravenstein RW, Davis RF. Methylene blue and indocyanine green artifactually lower pulse oximetry readings of oxygen saturation. Studies in dogs. J Clin Monit. 1987;3(4):249-56.
5. MEDSAFE Data Sheet, www.medsafe.govt.nz/profs/datasheet/m/MethyleneBlueinj.htm.
6. InSpectra™ StO2 Tissue Oxygenation Monitor User Manual (#5024798)