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Canadian Journal of Anesthesia 52:885 (2005)
© Canadian Anesthesiologists' Society, 2005

Correspondence

REPLY

Anis S. Baraka, MD FRCA, Chakib M. Ayoub, MD, Vanda Yazbeck-Karam, MD, Roland N. Kaddoum, MD, Frederic J. Gerges, MD, Ussama M. Hadi, MD and Carla M. Dagher, MD

American University of Beirut, Beirut, Lebanon, E-mail: abaraka{at}aub.edu.lb

Thank you for referring the letter of Charma et al. concerning our report "Prophylactic methylene blue in a patient with congenital methemoglobinemia.1

Our patient had severe congenital methemoglobinemia as evidenced by a methemoglobin level of 15.9%. The case was scheduled on two previous occasions for turbinectomy, but was cancelled because of the development of severe hypoxemia during induction of anesthesia.1,2

On this occasion, the patient was preoxygenated prior to induction of anesthesia resulting in an increase of the PaO2 from 81.3 to 543 mmHg, associated with an increase of the functional oxygen saturation (SaO2) [O2Hb / O2HB + RHb x 100%] from 96.2% to 99.7%. However, as shown in the TableGo, the fractional oxygen saturation (SfO2) [O2Hb / O2Hb + RHb + COHb + MetHb x 100%] which reflects the actual oxyhemoglobin saturation, only increased from 80.9% to 84.1%. Thus, preoxygenation alone did not provide an adequate margin of safety against hypoxemia. It was only after the administration of methylene blue that SfO2 increased up to 94.7%, associated with a significant decrease of the methemoglobin level from 15.9% to 5%.


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  		TABLE Values of oxygen partial presure (PaO2), saturation (SaO2) and fractional saturation (SfO2) and methemoglobin concentrations on room air, after preoxygenation, and after methylene blue administration
 
The increase in SfO2 and the decrease in methemoglobin levels following prophylactic methylene blue were maintained postoperatively, which increased the safety margin against perioperative hypoxemia not only during induction of anesthesia, but also intraoperatively and during the postoperative period.

References

1 Baraka AS, Ayoub CM, Yazbeck-Karam V, et al. Prophylactic methylene blue in a patient with congenital methemoglobinemia. Can J Anesth 2005; 52: 258–61.[Abstract/Free Full Text]

2 Baraka AS, Ayoub CM, Kaddoum RN, Maalouli JM,Chehab IR, Hadi UM. Severe oxyhemoglobin desaturation during induction of anesthesia in a patient with congenital methemoglobinemia. Anesthesiology 2001; 95: 1296–7.[Medline]


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