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Access: Acid-Base, Fluids, and Electrolytes - part 6

thận HCO3-Loss-xa RTA Mặc dù loại cổ điển xa RTA bước đầu đã được đặc trưng bởi một suy yếu trong quá trình axit hóa nước tiểu, kết quả tất cả các RTAs xa trong một suy yếu trong Nae này phần lớn là do nước tiểu giảm NH4 + bài tiết loại I xa RTA có thể liên quan hoặc hạ kali máu, tăng kali máu | METABOLIC ACIDOSIS 235 TABLE 6-40 Renal HCO3- Loss Distal RTA Although classic type I distal RTA was initially characterized by an impairment in urinary acidification all distal RTAs result in an impairment in NAE this is largely due to reduced urinary NH4 excretion Type I distal RTA may be associated with either hypokalemia or hyperkalemia RTA associated with hyperkalemia is the most common form generally resulting from hypoaldosteronism All distal RTAs are characterized by a positive UAG in the setting of acidosis reflecting inadequate NH4 excretion Abbreviations RTA renal tubular acidosis NAE net acid excretion UAG urine anion gap 236 METABOLIC ACIDOSIS TABLE 6-41 Renal HCO3- Loss Distal RTA Hypokalemic Hypokalemic type I distal RTA is best considered a disorder of collecting duct capacity for effective proton secretion such that patients cannot achieve the necessary NAE to maintain acid-base balance Patients with hypokalemic type I distal RTA usually present with hyperchloremic metabolic acidosis but are unable to acidify their urine below pH 5.5 despite systemic acidosis Two mechanisms were suggested for impaired acidification by distal nephron in hypokalemic distal RTA back leak of acid through a leaky epithelium and proton pump failure i.e. the H ATPase cannot pump sufficient amounts of H Hypokalemic type I distal RTA may be inherited or may be associated with other acquired disturbances Some of the same conditions that can cause hypokalemic distal RTA e.g. urinary obstruction autoimmune disorders can also cause hyperkalemic distal RTA due to a defect in Na reabsorption suggesting that the mechanistic analysis discussed above might be somewhat artificial In its primary form hypokalemic type I distal RTA is unusual and generally diagnosed in young children afflicted children typically present with severe metabolic acidosis growth retardation nephrocalcinosis and nephrolithiasis Hypokalemia which is usually present may actually be caused by associated Na .