Approach Considerations
In clinical situations in which renal hypoperfusion or toxic injury is anticipated, therapy with fluids, mannitol, diuretics, and renal-dose dopamine is used to prevent or reverse renal injury. Although these maneuvers do not alter the natural history of acute kidney injury, they are capable of converting the oliguric state to a nonoliguric acute kidney injury, which is more easily managed because it obviates the need for fluid restriction and allows for maximal nutritional support.
Vigorous fluid administration has been successfully used to prevent acute kidney injury following cardiac surgery, cadaveric renal transplantation, hemoglobinuria, myoglobinuria, hyperuricosuria, radiocontrast infusion, and therapy with amphotericin B or cisplatinum.
A trial of intravenous (IV) mannitol or furosemide should be attempted in a patient with oliguria for less than 48 hours who has not responded to adequate hydration (although meta-analysis studies have failed to document a clear benefit that can be associated with the use of either furosemide or mannitol therapy). [20]
The benefit of renal-dose dopamine therapy is controversial. [21] Current recommendations are that it be considered for use in patients who are adequately hydrated and resistant to furosemide.
Once oliguria is established, mannitol may precipitate congestive heart failure; the risk of ototoxicity from furosemide and adverse hemodynamic changes from dopamine is significant.
Atrial natriuretic peptide
During the past decade, experimental studies in animals and humans have focused on restoration of renal hemodynamics and tubule cell integrity. Atrial natriuretic peptide (ANP) has been shown to improve renal function in animal models of ischemic acute kidney injury, predominantly via afferent arteriolar dilatation. In a large study of adults, ANP reduced the need for dialysis and improved survival in some patients with oliguric acute kidney injury. Further clinical trials with ANP are required to better define its therapeutic profile and optimal target population.
Other ongoing clinical trials include investigations into the role of growth factors such as insulinlike growth factor, nitric oxide inhibitors, antioxidants, and antagonists of endothelin receptors in human acute renal failure. However, in current practice, the efficacy of therapies such as dopamine, fenoldopam, and natriuretic peptides for the treatment of established acute kidney injury remains unproven and their routine use is not recommended.
Considerations in pharmacotherapy
Nephrotoxic agents should be avoided because they may worsen the renal injury and delay recovery of function. Such agents include contrast media, aminoglycosides, and NSAIDs.
Prescribing medication requires knowledge of the route of elimination and adjustments in dose or frequency based on residual renal function. Patients in the early phase with a rising creatinine should be assumed to have a glomerular filtration rate (GFR) of less than 10mL/min, irrespective of the absolute value for serum creatinine.
Consultations
Consult a pediatric nephrologist for management of all cases of oliguria, except in children with prerenal insufficiency from dehydration who have promptly responded to fluid therapy or those with mild nephrotoxic injury who have responded to discontinuation of the drug. Consult a pediatric urologist for the management of obstruction.
Transfer
If the patient with oliguria requires close monitoring of hemodynamic status or if indications for acute dialysis are present, transfer the patient to a center with ICU facilities.
Fluid Management
The major goal of fluid management is to restore and maintain normal intravascular volume. Patients with oliguric acute kidney injury may present with hypovolemia, euvolemia, or volume overload, and an estimation of fluid status is a prerequisite for initial and ongoing therapy. This is accomplished by determination of input and output, body weights, vital signs, skin turgor, capillary refill, peripheral edema, cardiopulmonary examination, serum sodium, and fractional excretion of sodium (FENa).
Children with intravascular volume depletion require prompt and vigorous fluid resuscitation. Initial therapy includes isotonic sodium chloride or lactated Ringer solution at 20mL/kg over 30 minutes, which can be repeated twice if necessary. This therapy should result in increased urine output within 4-6 hours. If oliguria persists (confirmed with bladder catheterization), central venous monitoring may be required to guide further management. Potassium administration is contraindicated until urine flow is established.
Oliguria with volume overload requires fluid restriction and intravenous furosemide. Failure to respond to furosemide suggests the presence of acute tubular necrosis rather than renal hypoperfusion, and fluid removal by dialysis or hemofiltration may be required, especially if signs of pulmonary edema are evident.
Potassium should be withheld until the oliguria improves and serum potassium levels begin to fall.
Monitoring treatment progress
Input and output records, daily weights, physical examination, and serum sodium guide ongoing therapy. When appropriate fluid therapy is administered, the body weight should decrease by 0.5-1.0% daily as a result of caloric deprivation, and the serum sodium concentration should remain steady. A more rapid weight loss and increasing serum sodium indicate inadequate fluid replacement. An absence of weight loss with decreasing serum sodium suggests excess free-water replacement.
Management of Hyperkalemia
In practice, the definitive therapy for significant hyperkalemia accompanying oliguric acute kidney injury frequently includes dialysis. The other forms of therapy outlined in this section serve primarily to tide over the crisis.
Serum potassium levels of 5.5-6.5 mEq/L should be treated by eliminating all sources of potassium from the diet or IV fluids and administration of a cation exchange resin, such as sodium polystyrene sulfonate (Kayexalate). Kayexalate requires several hours of contact with the colonic mucosa to be effective, and the rectal route of administration is preferred. Complications of this therapy include hypernatremia and constipation.
Emergency treatment of hyperkalemia is indicated when serum potassium exceeds 6.5mEq/L or if peaked T waves are present. In addition to Kayexalate, patients should receive calcium gluconate (with continuous electrocardiographic monitoring) to counteract the effects of hyperkalemia on the myocardium.
Uptake of potassium by cells can be stimulated by infusion of glucose and insulin or by beta-agonists (albuterol by nebulizer). The efficacy and convenience of nebulized albuterol has been well described in hemodialysis patients with hyperkalemia, but it can cause tachycardia.
Sodium bicarbonate, which also causes a rapid shift of potassium into cells, was the drug of choice in the past. However, the current recommendation is to use this therapy only in the concomitant presence of severe acidosis. Such therapy should be used with caution because it can precipitate hypocalcemia and sodium overload.
Management of Other Electrolytes and Acid-Base Balance
The primary treatment for hyponatremia is free water restriction; however, a serum sodium level of less than 120 mEq/L or accompanied central nervous system (CNS) dysfunction may require 3% sodium chloride infusion.
The management of hyperphosphatemia includes dietary restriction and oral phosphate binders (calcium carbonate or calcium acetate). Hypocalcemia usually responds to the oral calcium salts used for control of hyperphosphatemia but may require 10% calcium gluconate infusion if severe.
Mild metabolic acidosis is treated with oral sodium bicarbonate or sodium citrate. Severe acidosis (pH < 7.2), especially in the presence of hyperkalemia, requires IV bicarbonate therapy. Recognize that bicarbonate therapy requires adequate ventilation (to excrete the carbon dioxide produced) to be effective, and it may precipitate hypocalcemia and hypernatremia. Patients who cannot tolerate a large sodium load (eg, those with congestive heart failure) may be treated in an ICU setting with IV tromethamine (THAM), with provision of adequate ventilatory support pending institution of dialysis.
Management of Hypertension
Mild hypertension usually responds to salt restriction and diuretics. Moderate, asymptomatic hypertension is most commonly treated with oral or sublingual calcium channel blockers or with IV hydralazine.
For patients with hypertensive encephalopathy, treatment may require continuous sodium nitroprusside infusion with monitoring of thiocyanate levels. Because nitroprusside therapy requires careful drip calculations and administration, other immediate alternatives include a nicardipine drip or labetalol. Once the hypertensive crisis has been controlled, oral long-acting agents can be initiated.
Dialysis
The general goal of dialysis is to remove endogenous and exogenous toxins and to maintain the fluid, electrolyte, and acid-base balance until renal function returns. The indications for acute dialysis are not absolute, and the decision to use this modality depends on the rapidity of onset, duration, and severity of the abnormality to be corrected. Common indications include the following:
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Fluid overload that is unresponsive to diuretics or a hindrance to adequate nutrition
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Symptomatic acid-base imbalance, electrolyte imbalance, or both (especially hyperkalemia) that is unresponsive to nondialytic management
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Refractory hypertension
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Symptomatic uremia (CNS symptoms, pericarditis, pleuritis)
The choice between hemodialysis, peritoneal dialysis, and continuous venovenous hemodialysis (CVVH) depends on the overall clinical condition, the availability of technique, the etiology of the renal failure, institutional preferences, and specific indications or contraindications.
Peritoneal dialysis
In general, peritoneal dialysis is a gentler continuous method that was a more preferred technique in children in the past. It is not the treatment of choice for acute, severe fluid overload or hyperkalemia, however, because the onset of action is slower. Specific contraindications include abdominal wall defects, bowel distention, perforation or adhesions, and communications between the chest and abdominal cavities.
Hemodialysis
Hemodialysis requires vascular access, heparinization, a large extracorporeal blood volume, and skilled personnel, but it has the advantage of rapid correction of fluid, electrolyte, and acid-base imbalances. This therapy may be difficult to accomplish in hypotensive patients with multiorgan damage
CVVH
CVVH has emerged as an alternative therapy for children who require fluid removal in an unstable, critically ill setting. The major advantage of these techniques is in their potential ability to remove fluid, even in a hypotensive child in whom hemodialysis may be contraindicated and peritoneal dialysis may be inefficient. However, patients require the presence of trained personnel and specialized equipment that are available only at select tertiary care centers.
Management of Urologic Obstruction
Patients with oliguria secondary to obstruction frequently require urologic care. The site of obstruction determines the primary therapy.
Obstruction of the bladder neck due to posterior urethral valves should be immediately relieved by gentle insertion of a fine urethral catheter. Foley catheters should not be used because the balloon may become lodged in the dilated prostatic urethra, resulting in incomplete bladder emptying.
The subsequent management of choice is endoscopic ablation of the valves. A temporary cutaneous vesicostomy may be required in a small infant whose urethra may not accept an endoscope or when hydronephrosis and renal function do not improve after catheterization.
Relief of obstruction is often followed by postobstructive diuresis. The resultant polyuria, hypokalemia, and hyponatremia should be managed with vigorous fluid replacement guided by frequent determinations of urinary flow rate, urinary electrolytes, and serum electrolytes.
Diet
Children with oliguric acute kidney injury are frequently in a highly catabolic state; therefore, aggressive nutritional support is important. Adequate calories should be provided to allow for maintenance requirements, and supplements should be provided to combat excessive catabolism. Children should be administered at least 150% of maintenance caloric intake and at least 3 g/kg/d of daily protein intake.
Protein of high biologic value should be administered in amounts that are sufficient to maintain neutral nitrogen balance, reflected by steady BUN levels.
Oral feeding is the preferred route. Infants should be placed on a low-phosphorus formula (Similac PM 60/40), and older children should be fed a low-phosphorus/low-potassium diet.
Additional calories may be supplied by fortifying foods with Polycose and medium-chain triglycerides.
Children who are nauseous or anorexic may benefit from enteral feedings. If these are not possible, central IV hyperalimentation may be used to deliver concentrated dextrose (25%) and lipids (20%).
If adequate nutrition cannot be achieved because of fluid restriction, early institution of ultrafiltration or dialysis should be considered.
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Pathogenesis of prerenal failure
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Compensatory mechanisms for preventing a fall in glomerular filtration rate (GFR) in the presence of prerenal failure
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Mechanisms of intrinsic acute renal failure.
Tables
| Stage | Serum creatinine | Urine output |
|---|---|---|
| 1 | Increase by 1.5-1.9 times baseline within 7 days OR Increase by 0.3 mg/dL (26.5 µmol/L) or more within 48 hours |
Less than 0.5 mL/kg/h for 6-12 hours |
| 2 | Increase by 2-2.9 times baseline | Less than 0.5 mL/kg/h for 12 hours or longer |
| 3 | Increase by 3 times baseline or greater OR Increase to 4 mg/dL (353.6 µmol/L) or greater OR Renal replacement therapy initiation OR In patients younger than 18 years, decrease in estimated GFR to less than 35 mL/min/1.73m2 |
Less than 0.3 mL/kg/h for 24 hours or longer OR Anuria for 12 hours or longer |
