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LETTER TO THE EDITOR

Prolonged Decrease of Regional Cerebral Saturation Readings with the INVOS® Device After Continuous Intravenous Methylene Blue Administration

Division of Cardiothoracic Anesthesiology; The Mount Sinai Medical Center; New York City, New York; alexander.mittnacht{at}msnyuhealth.org

To the Editor:

McDonagh et al.1 provide important information on the technical limitations of using cerebral near-infrared spectroscopy (NIRS) with the INVOS® (Somanetics Corp., Troy, MI) device. The IV injection of indigo carmine dye led to a rapid decrease in regional cerebral saturation (rSO₂) that could not be explained by other hemodynamic or oxygenation parameters. In their discussion, they point out that methylene blue (maximum light absorption 668 nm) also absorbs light at wavelengths close to the wavelengths emitted by the INVOS device (730 and 805 nm). They quote one report in which the bolus administration of methylene blue apparently did not alter cerebral oximetry readings using the INVOS device.2 In another letter to the editor which McDonagh et al. would not have seen due to its recent publication, we reported on our experience with methylene blue administration in patients with vasoplegic syndrome undergoing cardiac surgery.3 In contrast to the above-mentioned case report, we found and documented an immediate decrease in rSO₂ readings after methylene blue bolus administration (2 mg/kg over 20 min), followed by continuous methylene blue infusion (0.5 mg · kg^–1 · h^–1). When our letter to the editor was accepted for publication, our experience was limited to two cases. Since that time, we have used methylene blue with increasing frequency in patients with vasoplegic syndrome and an immediate decrease in rSO₂ readings using the INVOS cerebral oximeter was seen in all cases. Unlike the findings of McDonagh et al., rSO₂ readings remained low without returning to pre-dye administration levels. This could possibly be explained by the administration of methylene blue as a continuous infusion (0.5 mg · kg^–1 · h^–1) after the loading dose.

REFERENCES

1. McDonagh DL, McDaniel MR, Monk TG. The effect of intravenous indigo carmine on near-infrared cerebral oximetry. Anesth Analg 2007;105:704–6[Abstract/Free Full Text]
2. Taylor K, Holtby H. Methylene blue revisited: management of hypotension in a pediatric patient with bacterial endocarditis. J Thorac Cardiovasc Surg 2005;130:566[Free Full Text]
3. Mittnacht AJC, Fischer GW, Reich DL. Methylene blue administration is associated with decreased cerebral oximetry values. Anesth Analg 2007;105:549–50[Free Full Text]

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