Tham khảo tài liệu 'chapter 045. azotemia and urinary abnormalities (part 4)', y tế - sức khoẻ, y học thường thức phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Chapter 045. Azotemia and Urinary Abnormalities Part 4 POSTRENAL AZOTEMIA Urinary tract obstruction accounts for 5 of cases of acute renal failure but it is usually reversible and must be ruled out early in the evaluation Fig. 451 . Since a single kidney is capable of adequate clearance acute renal failure from obstruction requires obstruction at the urethra or bladder outlet bilateral ureteral obstruction or unilateral obstruction in a patient with a single functioning kidney. Obstruction is usually diagnosed by the presence of ureteral and renal pelvic dilatation on renal ultrasound. However early in the course of obstruction or if the ureters are unable to dilate such as encasement by pelvic tumors or periureteral the ultrasound examination may be negative. The specific urologic conditions that cause obstruction are discussed in Chap. 283. INTRINSIC RENAL DISEASE When prerenal and postrenal azotemia have been excluded as etiologies of renal failure an intrinsic parenchymal renal disease is present. Intrinsic renal disease can arise from processes involving large renal vessels intrarenal microvasculature and glomeruli or tubulointerstitium. Ischemic and toxic ATN account for 90 of acute intrinsic renal failure. As outlined in Fig. 45-1 the clinical setting and urinalysis are helpful in separating the possible etiologies of acute intrinsic renal failure. Prerenal azotemia and ATN are part of a spectrum of renal hypoperfusion evidence of structural tubule injury is present in ATN whereas prompt reversibility occurs with prerenal azotemia upon restoration of adequate renal perfusion. Thus ATN can often be distinguished from prerenal azotemia by urinalysis and urine electrolyte composition Table 45-2 and Fig. 451 . Ischemic ATN is observed most frequently in patients who have undergone major surgery trauma severe hypovolemia overwhelming sepsis or extensive burns. Nephrotoxic ATN complicates the administration of many common medications usually by inducing a .
