Pulse oximetry is an essential diagnostic method in anesthesiology. However, if undetected hemoglobin anomalies are the underlying cause of low pulse oximetric saturation (Spo2) measurements, misleading conclusions could be drawn and lead to unnecessary, extensive, and repeat cardiopulmonary examinations. Dyshemoglobins, most commonly carboxyhemoglobin or methemoglobin, neither of which was present in this patient, are often detected as the underlying cause of low Spo2 measurements only after specific methods of examination have been performed.
Written consent for this case report was obtained from the patient.
The patient presented to the emergency department with acute abdominal pain. On ultrasound, an acute cholecystolithiasis with a gallstone and sludge was diagnosed. The gallbladder was laparoscopically removed under general anesthesia. The patient had a history of congenital spherocytic hemolytic anemia. He had no symptoms or history for cardiopulmonary impairment, easily exceeded METS >4, and had a hemoglobin of 8.2 g/dL. Breathing room air his Spo2 was 88%. During the entire surgery and anesthesia, a high-quality pulse oximetric signal with a stable, typical waveform was recorded. The capillary refill time was about 1 second. Heart and lung auscultation was normal. After 3 minutes of preoxygenation with 100% oxygen, the Spo2 was 89%. Anesthesia induction, maintenance, and emergence were uneventful from a cardiopulmonary perspective. An arterial line was placed because of the low baseline Spo2. The Sao2 values were as high as 100%, whereas the Pao2 values averaged out to 390 mm Hg (pH 7,44, Pco2 41 mm Hg, body temperature 36.5°C).
Because of the patient’s history of spherocytosis, splenectomy, and recurrent red blood cell transfusions, he met the clinical criteria for hemoglobin Köln (Hb Köln). Hb Köln is a hemoglobin variant with an unstable hemoglobin because of a mutation for the β-globin (description of typical values: Hb Köln: Spo2 89%, Pao2 101 mm Hg).
Some hemoglobin variants impress with low Spo2 and normal Sao2values. The reason for the low Spo2 measurement is the different organic heme component structure that has a different absorption spectrum from normal hemoglobin. In pulse oximetry, the oxygen saturation values only agree with the oxygenated hemoglobin if no dysfunctional hemoglobins are present. At the moment, there are 11 different types of hemoglobin variants, each named in accordance to the place they were first detected, eg, Hb Lansing, Hb Titusville, Hb Bonn.1–4 Variant hemoglobins that cause low Spo2 measurements have higher absorption rates around 660 nm. Typically, 660 nm mainly reflects deoxygenated blood. Thus, dyshemoglobin absorption around 660 nm leads to a high red/infrared ratio and finally to a low Spo2 measurement (see the Table).5
In conclusion, knowing not only the diagnostic value but also the limitations of the pulse oximetry, anesthesiologists can draw the right conclusions in combination with a blood gas analysis, after having ruled out nonhematologic factors. This leads to an increase in patient safety and an economic management if those values are recorded.
Name: Stefan Brugger, MD.
Contribution: This author helped conceive the idea and write the manuscript.
Name: Maria-Dolores Santafé-Marti, MD.
Contribution: This author helped research the literature.
Name: Malika Lakhal, MD.
Contribution: This author helped write and clinically embed the manuscript.
This manuscript was handled by: Raymond C. Roy, MD.
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