Intraoperative Diagnosis of Unsuspected Methemoglobinemia Due to Low Pulse Oximetry Values

Abstract

Methemoglobinemia results from the oxidation of the iron in the hemoglobin molecule from the ferrous to the ferric state. Methemoglobinemia may result from congenital deficiencies of enzymes that normally convert methemoglobin (metHb) to hemoglobin, alterations in the hemoglobin molecule itself or, most commonly, from medications or toxins. As metHb cannot carry oxygen, clinical sequelae result when the concentration of metHb is high enough to compromise oxygen delivery to the tissues. With low levels, the patient may be asymptomatic or only symptomatic during periods of increased tissue oxygen demands such as exercise. With higher levels, symptoms may occur at rest. We describe an adolescent with acute leukemia who presented to the operating room for placement of a Broviac catheter for permanent central venous access. Given a persistently low oxygen saturation as measured by pulse oximetry (92% to 94%) with no response to changes in the inspired oxygen concentration and the lack of physical findings on auscultation to explain the low oxygen saturation, the diagnosis of metHb was entertained and confirmed by laboratory analysis.

The Role of Preoperative Evaluation for Congenital Methemoglobinemia

“…Using sulphonamides, nitrite-nitrate, phenytoin, quinine, and aniline-benzene derivatives may lead to methaemoglobinaemia in such patients. Some anaesthetic agents used in anaesthesia practice as well may cause asymptomatic patient with congenital methaemoglobinaemia to be symptomatic (Table 1) (10). We attributed development of methaemoglobinaemia in the present case, who had no history of drug use, to the use of 10 mL of 0.5% bupivacaine.…”

“…Methaemoglobinaemia is a serious clinical condition that presents itself with increased blood methaemoglobin concentration and is characterized by clinical symptoms such as cyanosis and hypoxia due to lack of adequate oxygen supply to the tissues (3). Methaemoglobin results from oxidation of iron in the haemoglobin molecule into ferric form (Fe +3 ) from ferrous form (Fe +2 ) (4)(5)(6). Increased methaemoglobin, which has no ability to deliver oxygen, shifts the oxyhaemoglobin dissociation curve to the left and leads to impaired tissue oxygenation.…”

Incidence of metoclopramide-induced methemoglobinemia

“…Since methemoglobin can not transport oxygen this shifts the oxygen-hemoglobin dissociation curve to the left and results in difficulties in delivering oxygen to the tissues. [1][2][3][4] Under normal physiological conditions, the methemoglobin level will not exceed 2-3% of the total hemoglobin. [5] In acute cases increases up to 20-30% in methemoglobin levels are tolerated well in patients without anemia, however, an increase to 70% or more is typically fatal.…”

Hemoglobin glutamer‐250 (bovine) in South Africa: consensus usage guidelines from clinician experts who have treated patients

“…Increased methemoglobin (metHb) levels may be encountered as metHb‐reductase contained in RBCs is not present in Hemopure. Patients will, however, remain asymptomatic unless metHb levels exceed 15% to 20% …”