Acute Tubular Necrosis Treatment & Management

The main goal of treatment of acute tubular necrosis (ATN) is to prevent further injury to the kidney. Extracellular fluid (ECF) volume should be assessed promptly, either on clinical grounds or by invasive means (Swan-Ganz catheter), and repletion of any deficit should be initiated promptly. The 2011 UKRA guidelines recommend optimizing hemodynamic status by appropriate fluid therapy, giving vasopressors and/or inotropes and treating any underlying sepsis.^[2]

All possible nephrotoxic drugs should be stopped. In addition, doses of all medications that are eliminated by the kidney should be adjusted.

Any complications that develop must be aggressively treated.

Visit the Pediatric Acute Tubular Necrosis article for additional information.

Despite some controversy in the literature, in general, if oliguria is present, make an attempt to increase urine output using intravenous loop diuretics. Use diuretics only if ECF volume and cardiac function are first carefully assessed and found adequate.

Intravenous furosemide or bumetanide in a single high dose (ie, 100-200 mg of furosemide) is commonly used, although little evidence indicates that it changes the course of ATN. The drug should be administered slowly because high doses can lead to hearing loss. If no response occurs, the treatment should be discontinued.

Dopamine, a selective renal vasodilator, has also been used to increase urine output, but this treatment has little benefit and is no longer recommended.

In general, there is no clear consensus on when or how often to perform hemodialysis in the setting of acute kidney injury (AKI). Some studies have suggested that early initiation may be beneficial, but in one prospective trial, aggressive dialysis did not improve recovery or survival rates. However, hemodialysis is still considered standard therapy in severe AKI. In addition, continuous hemodialysis (continuous venovenous hemodiafiltration [CVVHD] and continuous arteriovenous hemofiltration with dialysis [CAVHD]) and peritoneal dialysis are also available.

The 2011 UKRA AKI guidelines recommend starting renal replacement therapy (hemodialysis, CVVHD, CAVHD, or peritoneal dialysis) once AKI is firmly established but before overt complications arise.^[2] .

No compelling studies suggest that one mode of dialysis is better than another. In general, patients with multiorgan failure and hemodynamic instability may benefit from a continuous mode because it is typically less hemodynamically taxing. The 2011 UKRA AKI guidelines recommend lowering the threshold for starting dialysis in the case of multiorgan failure.^[2]

Some studies suggest that the use of biocompatible membranes instead of cuprophane membranes may improve the recovery rate and decrease the mortality rate in AKI. The 2011 UKRA AKI guidelines recommend using synthetic or modified cellulosic membranes rather than unmodified celluloid membranes if a choice is available. In addition, UKRA guidelines recommend bicarbonate as the preferred buffer for dialysate and replacement fluid in continuous dialysis.^[2]

According to the 2011 UKRA guidelines, regardless of whether dialysis is performed intermittently or continuously, the prescribed dose should be assessed at each hemodialysis session.^[2]

The 2011 UKRA guidelines recommend venovenous access rather than arteriovenous access for dialysis. Access should be placed by an experienced or supervised staff member, using real-time ultrasound as a guide to placement.^[2]

Generally, the treatment of choice for nephrotoxic ATN is to stop all nephrotoxic agents to prevent further damage to the kidney. Of note, calcium channel blockers may have some use in cyclosporine toxicity, where they may reduce the vasoconstrictive action of the drug. However, their use is typically avoided because of possible hypotension.

Aggressive and early nutritional support improves survival rates. Adequate protein and caloric intake is essential because marked increase in protein catabolism is often observed, especially in patients with shock, sepsis, or rhabdomyolysis. The risks of this catabolism include malnutrition and an impaired immune system. According to the 2011 UKRA AKI guidelines, patients with AKI who are receiving dialysis should be referred to a dietician for individual evaluation. The UKRA also recommends nutritional support with 25-35 kcal/kg/day, and up to1.7 g amino acids/kg/day, for patients receiving dialysis who are hypercatabolic.^[2]

The approach to prevention differs with ischemic ATN and nephrotoxic ATN.

Prevention of ischemic acute tubular necrosis

Be attentive to optimizing cardiovascular function as well as to maintaining intravascular volume, especially in patients with preexisting risk factors or those taking nephrotoxic medications. Medicines that reduce systemic resistance (eg, afterload reducers) may cause renal vasoconstriction or affect the kidney’s autoregulatory response (eg, angiotensin-converting enzyme [ACE] inhibitors, cyclooxygenase [COX] inhibitors) and also should be used with caution.

Prevention of nephrotoxic acute tubular necrosis

Prevention of nephrotoxic ATN depends on the possible nephrotoxin under consideration.

With aminoglycosides, studies have demonstrated that once-daily dosing decreases the incidence of nephrotoxicity. In one study, 24% of patients receiving 3 daily doses developed clinical nephrotoxicity, compared to only 5% of patients receiving 1 daily dose. However, other studies comparing a single daily dose to multiple daily doses have failed to find a difference in the incidence of nephrotoxicity. Therapeutic efficacy is not diminished by single daily dosing.

With amphotericin B, efforts should be made to minimize the use of the drug and ensure that ECF volume is adequate. By saline loading, maintenance of a high urine flow rate has been shown to be helpful. Likewise, various lipid formulations of amphotericin B have been developed, namely, amphotericin B colloid dispersion (ABCD), amphotericin B complex (ABLC), and liposomal amphotericin B; these lipid formulations are believed to be less nephrotoxic intrinsically.

Whereas amphotericin B is suspended in bile salt deoxycholate, which has a detergent effect on cell membranes, the lipid formulations do not contain deoxycholate. The lipid formulations also bind more avidly to fungal cell wall ergosterol as opposed to the cholesterol in human cell membranes. Liposomal amphotericin B is preferred in patients with renal insufficiency or evidence of renal tubular dysfunction.

With cyclosporine and tacrolimus (calcineurin inhibitors), regular monitoring of blood levels can help maintain therapeutic levels and prevent nephrotoxicity. Usually, renal insufficiency is easily reversed by a reduction of the dosage. On the other hand, persistent injury can lead to interstitial fibrosis.

With cisplatin, the key to preventing renal injury is volume loading with saline. Some investigators advocate the use of amifostine, a thiol donor that serves as an antioxidant. Others prefer using carboplatin, a less nephrotoxic alternative.

Prevention of contrast-induced nephropathy

For contrast-induced nephropathy (CIN) from the use of radiocontrast dye, isotonic sodium chloride solution infusion has proven benefits as a preventive measure.^[10] Typically, isotonic sodium chloride solution (0.9%) administered at a rate of 1 mL/kg/h 12 hours before and 12 hours after the administration of the dye load is most effective, especially in the setting of prior renal insufficiency and diabetes mellitus. This has been shown to be superior to half normal saline infusions.

A single-center, randomized, controlled trial demonstrated that isotonic sodium bicarbonate (3 mL/kg of body weight/h given 1 h prior to the contrast-requiring procedure and then continued at 1 mL/kg of body weight/h for 6 h post procedure) may offer even greater protection than isotonic sodium chloride.^[11] The postulated mechanism is being attributed to the inhibition of oxidant injury by the administered alkali.

Nonionic contrast media are also protective in patients with diabetic nephropathy and renal insufficiency. In susceptible patients, the use of nonionic, low-osmolar contrast media reduces the likelihood of clinical nephrotoxicity.

Some investigators recommend the avoidance of contrast-requiring procedures, if at all possible. Magnetic resonance imaging (MRI) studies usually necessitate the use of gadolinium as a contrast agent, which, in several studies, has been shown to be less nephrotoxic than conventional contrast media. Using the lowest possible amount of contrast media in the procedure is also recommended.

To date, several interventions have been suggested to decrease the risk of CIN, such as furosemide, mannitol, dopamine, and fenoldopam, but none of these agents have been shown to be significantly effective.

The use of N -acetylcysteine (NAC) as a prophylactic agent has gained popularity, on the basis of the theory that contrast media cause direct renal tubular epithelial cell toxicity via exposure to reactive oxygen species (ROS), and NAC is believed to have antioxidant properties that potentially counteract the effects of ROS.^[12] Studies have also suggested that pretreatment with oral NAC (600 mg or 1200 mg bid on the day prior to and on the day of the contrast-requiring procedure) acts as an antioxidant, scavenging ROS, thereby reducing the nephrotoxicity of contrast media.

Based on what is known now, making a strong, evidence-based recommendation for the use of NAC in the prevention of CIN is not possible. Recognizing that NAC is inexpensive and is not associated with significant complications, in the absence of other effective pharmacologic therapy, its use in clinical practice is not entirely inappropriate. Additional large randomized, controlled trials of NAC are needed to better define its proper role in preventing CIN.

Theophylline, an adenosine antagonist, with a similar mechanism of action as NAC, is viewed as another potential agent to prevent CIN, the main difference being the lower risk profile associated with the latter. Based on the idea that contrast media cause local release of adenosine, a known vasoconstrictor considered by some to have a potential role in the pathogenesis of CIN, theophylline is a known adenosine antagonist. Although theophylline appears to be promising, further randomized trials are required to show any proven benefit in the prevention of CIN.

Aside from the recommended prophylactic medications discussed above, other guidelines recommend withholding potential nephrotoxic agents, such as nonsteroidal anti-inflammatory drugs (NSAIDs) and COX-2 inhibitors. In those patients with underlying volume depletion, withholding ACE inhibitors and/or angiotensin receptor blockers (ARBs) may even be necessary. Metformin should be withheld at least 48 hours before the procedure and until CIN has been ruled out.

Angiotensin II and prostaglandins play central roles in the maintenance of the glomerular filtration rate (GFR) in the face of volume depletion. ACE inhibitors and ARBs have gained popularity not only as antihypertensive agents but also as renoprotective agents that either slow or halt the progression of diabetic and nondiabetic kidney disease. They have also been shown in several studies to have a role in chronic heart failure as well as ventricular remodeling.

The use of ACE inhibitors and ARBs is limited by the tendency to cause prerenal failure, especially in patients who are considered to be at high risk; risk factors include advanced age, underlying renovascular disease, concomitant use of diuretics or vasoconstrictors (eg, NSAIDs, COX-2 inhibitors, and calcineurin inhibitors), and elevated baseline serum creatinine.

Serum creatinine and electrolytes, especially potassium, should be measured before and at least 1 week after starting or changing the dose of the medication. A threshold for discontinuation of therapy has been suggested to be (1) an increase in serum creatinine of more than 0.5 mg/dL if the initial serum creatinine is less than 2.0 mg/dL or (2) an increase in serum creatinine of more than 1.0 mg/dL if the baseline serum creatinine is greater than 2.0 mg/dL.

An increase in serum creatinine of up to 30% is acceptable, but a continued rise of over 30% should prompt immediate discontinuation of the medication. Alternatively, discontinuation of ACE inhibitor or angiotensin receptor blocker therapy is not necessary if smaller increases in serum creatinine occur.

If and when prerenal AKI does develop, one should commence looking for underlying heart disease, volume depletion, hypotension, concomitant use of vasoconstrictors, or renovascular disease.

Prevention of rhabdomyolysis

Preventive strategies for rhabdomyolysis include aggressive volume resuscitation with normal saline at 1000-1500 mL/h with a goal urine output of 300 mL/h. Caution should be exercised to avoid producing a compartment syndrome, especially in those patients who remain oligoanuric despite infusions of large volumes of fluid.

In the presence of sufficient urine output, urine alkalinization to achieve a urine pH of greater than 6.5 is recommended to increase the solubility of the heme proteins within the tubules. This has also been shown to reduce the generation of ROS. Mannitol has not been shown to be more efficacious than volume expansion with normal saline alone.