Porth's Pathophysiology, 9e

Chapter 42 Acute Renal Injury and Chronic Kidney Disease    1113

Acute renal injury is a common threat to seriously ill people in intensive care units, with a mortality rate rang- ing from 40% to 90%. 2,3 Although treatment methods such as dialysis and renal replacement therapies are effective in ­correcting life-threatening fluid and electrolyte disorders, the mortality rate from acute renal failure has not improved sub- stantially over the last few decades. 4 This probably is because acute renal injury is seen more often in older adults than before, and because it frequently is superimposed on other life-threatening conditions, such as trauma, shock, and sepsis and comorbidities such as cardiovascular disease, diabetes, and respiratory disease. 4 The most common indicator of AKI is azotemia, an accu- mulation of nitrogenous wastes (urea nitrogen, uric acid, and creatinine) in the blood and a decrease in the glomerular fil- tration rate (GFR). New biomarkers for more accurate diag- nosing of acute renal kidney injury are discussed. As a result, excretion of nitrogenous wastes is reduced, and fluid and elec- trolyte balance cannot be maintained. ACUTE RENAL FAILURE/INJURY •  Acute renal failure/injury is caused by conditions that produce an acute shutdown in renal function. •  It can result from decreased blood flow to the kidney (prerenal failure), disorders that disrupt the structures in the kidney (intrarenal failure), or disorders that interfere with the elimination of urine from the kidney (postrenal failure). •  Acute renal failure, although it causes an accumu- lation of products normally cleared by the kidney, is a potentially reversible process if the factors causing the condition can be corrected. Types of Acute Renal Injury Acute renal injury can be caused by several types of condi- tions, including a decrease in blood flow without ischemic injury; ischemic, toxic, or obstructive tubular injury; and obstruction of urinary tract outflow. The causes of acute renal failure commonly are categorized as prerenal, intrarenal, and postrenal 2 (Fig. 42.1). Collectively, prerenal and intrarenal causes account for 80% to 95% of acute renal failure cases. 3 Causes of renal failure within these categories are summa- rized in Chart 42.1. Prerenal Failure Prerenal failure, the most common form of acute renal fail- ure, is characterized by a marked decrease in renal blood flow. It is reversible if the cause of the decreased renal blood flow can be identified and corrected before kidney damage occurs. Causes of prerenal failure include profound depletion Key Points

Prerenal (marked decrease in renal blood flow)

Intrinsic (damage to structures within the kidney)

Postrenal (obstruction of urine outflow from the kidney)

FIGURE 42.1  •  Types of acute renal failure.

of vascular ­volume ( e.g., hemorrhage, loss of extracellular fluid volume), impaired perfusion due to heart failure and cardiogenic shock, and decreased vascular filling because of increased vascular capacity ( e.g., anaphylaxis or sep- sis). Older adults are ­particularly at risk because of their

Chart 42.1

CAUSES OF ACUTE KIDNEY INJURY

Prerenal Hypovolemia

Hemorrhage Dehydration

Excessive loss of gastrointestinal tract fluids Excessive loss of fluid due to burn injury Decreased vascular filling Anaphylactic shock Septic shock Heart failure and cardiogenic shock Decreased renal perfusion due to sepsis, vasoactive mediators, drugs, diagnostic agents Intrarenal Acute tubular necrosis/acute renal injury Prolonged renal ischemia Exposure to nephrotoxic drugs, heavy metals, and organic solvents Intratubular obstruction resulting from hemoglo- binuria, myoglobinuria, myeloma light chains, or uric acid casts Acute renal disease (acute glomerulonephritis, pyelonephritis) Postrenal Bilateral ureteral obstruction Bladder outlet obstruction