Abstract

Although late survival has been occasionally reported for patients with cyanotic congenital heart disease (CCHD), the complexity of the cardiac malformations and the complications of cyanosis prove often lifethreatening at an early age. 1 It has been documented that chronic cyanosis affects renal glomerular structure and function, causing progressive glomerulopathy with eventual proteinuria. 2,3 Adverse effects of chronic hypoxia on renal tubular function have been less frequently documented. 4,5 Secondary renal tubular acidosis (sRTA) seems to be an acquired complication in patients with chronic cyanosis. The aim of this study was to evaluate the association of CCHD and renal tubular acidosis in a Guatemalan population. Patients and Methods Seventy-three of 110 patients with cyanosis (study group) with congenital heart disease were selected on the basis of an arterial oxygen saturation less than 80%. In these patients, arterial pH and blood gas values, as well as plasma anion gap (PAG) and urinary anion gap (UAG) were measured to evaluate the origin of metabolic acidosis. Patients with diarrhea in the previous 15 days or receiving prolonged treatment with diuretics or laxatives were also excluded. The diagnosis of sRTA should be suspected in all patients with a normal PAG and hyperchloremic metabolic acidosis. Differentiation of sRTA from other metabolic disorders is facilitated by the determination of the UAG. A UAG greater than 0 is indicative of an acidification defect at the distal tubular level (distal sRTA), whereas a UAG less than 0 suggests the presence of gastrointestinal or renal loss of bicarbonate (proximal sRTA). Fifty-six of the 73 patients included in the study (77%) had metabolic acidosis (plasma bicarbonate 22 mmol/L); of these, 48 (86%) also had a normal PAG (sRTA group). The remaining 17 patients (23%) had normal arterial pH and blood gas values (reference group). Metabolic acidosis originated from the distal renal tubule (UAG 0) in 39 patients (81%, distal sRTA) and from the proximal tubule (UAG 0) in 9 patients (19%, proximal sRTA; Figure 1 and Table 1). Patients with distal renal tubular acidosis were significantly older than patients in th e reference group (P .05). Differences in other variables analyzed in this study, such as patient nutritional status, altitude (meters above sea level), and renal function, were not significant. Ten patients with sRTA who underwent surgical repair of their congenital heart disease with elimination of cyanosis (mean postoperative arterial oxygen saturation increased from 70.3% 7.94% to 95.3% 3.19%) were evaluated at 48 postoperative hours. They had a normal arterial pH and blood gas profile .

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