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The Anesthetic Management of a Patient with Hemoglobin MIwate

2001; Lippincott Williams & Wilkins; Volume: 93; Issue: 5 Linguagem: Inglês

10.1097/00000539-200111000-00028

1526-7598

Akiyoshi Kuji, Yu Satoh, K Kikuchi, Kenichi Satoh, Shigeharu Joh,

Renal function and acid-base balance

Hemoglobin (Hb) MIwate, a Hb M variant with tyrosine instead of histidine–87 in the α chain, is acceleratedly auto-oxidized into the met-form and loses O2-binding ability (1). This hemoglobinopathy is inherited in an autosomal dominant pattern and characterized by marked cyanosis, but it may be missed by the patient and the doctor because there are no associated health obstacles in daily life and it is very rare. In Japan approximately 35 patients with Hb MIwate lived almost exclusively in Iwate prefecture (2); the trait has been occasionally documented in the United States, Germany, Israel, and Switzerland (1,3). This hemoglobinopathy affects anesthetic management, however, because the anomalous absorption spectrum of Hb MIwate renders standard pulse oximetry useless, as reported in different Hb forms (4-8). We report our experience with the anesthetic management of a patient with Hb MIwate. Case Report A 50-yr-old woman presented with a carcinoma in the right side of the tongue. Though she had been treated for appendicitis and acute hepatitis at 17 and 20 yr of age, she had never undergone general anesthesia. Treatment for her ventricular arrhythmia started at 47 yr of age, and when being admitted, she received an antiarrhythmic 1-(2,6-dimethylphenoxy)-2-propanamine and an antineoplastic 5-fuluoro-1-(tetrahydro-2-furyl)-uracil; the former was continued except during a period mentioned below. We noticed her systemic cyanosis, low hemoglobin (10.7 g/dL), and high pseudocholinesterase values (1483 IU/L) by preoperative laboratory analysis, but she experienced neither fatigue nor any serious problems. Arterial blood gas values obtained while she was breathing room air were normal (Table 1). Her blood type was O and D-positive with no detectable abnormalities. The slightly heightened QRS wave and depressed ST segment were observed in her electrocardiographic leads II, III, aVR, and V4-6. Like the other doctors who had treated her, we did not suspect her Hb MIwate trait, and gave anesthesia for the operation for tongue carcinoma.Table 1: Blood Gas Analyses at Different Oxygen ConcentrationsAs a pulse oximeter using the wavelengths 660 and 940 nm (PB1410, NEC San-ei Instrument, Tokyo) did not respond to the patient, who lay supine and breathed room air after being premedicated with atropine (0.1 mg IV) and midazolam (3 mg IV), we prepared to manage the patient without relying on pulse oximetry. Anesthesia was induced with thiopental (200 mg IV) and vecuronium (5 mg IV) and maintained with N2O/O2 (4L/2L), sevoflurane, and fentanyl. With a Fio2 of 0.33, the pulse oximeter occasionally indicated either values of 31%–36% or did not respond, so we switched to the O2-saturation monitoring by analysis of arterial blood gases. After 30 min of anesthesia, her Pao2 was 155 mm Hg and calculated SaO2 99.1% at the Fio2 of 0.33. At 75 min of anesthesia, to attain a safer O2-delivery, we increased the Fio2 to 0.5; the Pao2 reached 266 mm Hg and the calculated SaO2 99.7%. After the IV drip of the antiarrhythmic was stopped because of bradycardia, there were no anomalous heartbeats. The operation lasted over 215 min without blood transfusion and was completed successfully. We referred the patient to our blood clinic, where her hemoglobinopathy was confirmed to be Hb MIwate. Of her two sisters, the younger is suspected of the trait, but does not have confirmation. Our patient is now in good health. Discussion Though the extinction coefficient of Hb MIwate at 660 nm–the critical wavelength for the pulse oximeter–is unavailable, the absorbance at the wavelength of Hb MIwate, whether at the oxygenated or met state, is as high as that of MetHb A (1). Hb MIwate accounts for 30% of the total Hb (9). For patients with this hemoglobinopathy, pulse oximetry is useless, as a MetHb A concentration of 5% affects pulse oximeter readings (4). The usefulness of a co-oximeter would be limited because at a broad range of wavelength from 350 nm to 650 nm, which includes the wavelengths a co-oximeter uses, both met and oxygenated Hb MIwate show similar absorption spectra that differ from those of the Hb A counterparts (1). Nonetheless, unlike hemoglobinopathies such as Hbs S, H and MHyde Park(10–12), Hb MIwate does not accompany increased hemolysis, so we can maintain sufficient O2 delivery by keeping a high Fio2 and periodically checking the O2-delivery state by blood gas analysis. The oxygenation of Hb MIwate is 60% at 100 mm Hg Po2 at pH 7.0–7.5 (13). Taking into account the proportion of Hb MIwate, the O2-carrying capacity under ordinary respiration conditions may be reduced in the blood to <90% of that in normal blood. Care must be taken to maintain sufficient O2 delivery allowing for this degree of dysfunction. A lesson can be drawn from this rare case. Like some other variants of Hb M, Hb MIwate rarely appears only within single kindreds or in single individuals with no associated clinical signs except cyanosis (2,11); therefore patients do not need counseling for the trait because counseling may produce anxiety about social discrimination because of rare heritable traits. Indeed, our patient hesitated to inform us about her cyanosis, and we failed to consider its cause. The doctor must build a trusting relationship with a patient so that health problems can be openly discussed.