Severe Oxyhemoglobin Desaturation during Induction of Anesthesia in a Patient with Congenital Methemoglobinemia

Metemoglobinemia: do diagnóstico ao tratamento

“…O Fe 3+ provoca ainda mudança alostérica na porção heme da Hb parcialmente oxidada, aumentando sua afinidade pelo O 2 . Assim, além de a MetHb não se ligar ao O 2 , ela desvia a curva de dissociação da Hb parcialmente oxidada para a esquerda [8][9][10][11] , prejudicando também a liberação de O 2 para os tecidos. A hipóxia tecidual provocada pela MetHba é conseqüência não só da diminuição da Hb livre para transportar O 2 (anemia relativa), mas também pela dificuldade de liberação de O 2 para os tecidos 11 .…”

“…Os agentes oxidantes aceleram a oxidação da Hb de 100 a 1.000 vezes e acabam sobrepujando a capacidade dos sistemas redutores endó-genos 17 . O contato com essas substâncias ocorre pelo tratamento com inúmeros fármacos 1,5,7,11,14,[18][19][20][21][22][23] , intoxicação por pesticidas, herbicidas, fertilizantes 3 , fumaça de escapamento de automóveis 13 e substâncias químicas industriais 24,25 . Entre os fármacos mais implicados, destacam-se os anestésicos locais (benzocaína, lidocaína e prilocaína), a dapsona, os derivados da fenacetina e os antimaláricos 16 .…”

“…Each Hb chain is formed by a globin polypeptide linked to a prosthetic heme group, which is formed by a complex of a protoporfirin IX ring and one atom of ferrous iron (Fe +2 , hindering the release of O 2 in the tissues. Tissue hypoxia caused by MetHba is secondary to a reduction in free Hb to transport O 2 (relative anemia) and the difficulty to release O 2 in the tissues 11 . In theory, any oxidizing agent can lead to the formation of MetHb 6 .…”

L’administration prophylactique de bleu de méthylène chez un patient atteint de méthémoglobinémie congénitale

“…In patients with congenital methemoglobinemia, oxygen delivery is already compromised, and hence even a mild degree of respiratory depression, which would go unnoticed in normal patients, can result in serious hemoglobin desaturation. 4 Preoxygenation increases the oxygen reserve in the lungs' functional residual capacity as well as the plasma oxygen in physical solution, counteracting any decrease of PaO 2 during induction of anesthesia. However, following preoxygenation in this patient, the methemoglobin level remained high and the fractional oxygen concentration low.…”

“…3 The present report presents a patient with congenital methemoglobinemia who previously developed severe oxyhemoglobin desaturation during induction of anesthesia, resulting in the cancellation of surgery. 4 This report evaluates, for the first time, the beneficial effect of the prophylactic iv administration of methylene blue before induction of anesthesia in the same patient when he was rescheduled for surgery four years later.…”