• Acute Kidney Injury (AKI) is defined as an acute loss of kidney function, with subsequent accumulation of metabolic waste products.
• AKI can be divided into 3 subtypes:
  • Prerenal – Decrease in kidney perfusion
  • Intrarenal – Injury to kidney parenchyma
  • Postrenal – Urine obstruction

• Clinical presentation of AKI is varied. Patients may be asymptomatic and be diagnosed incidentally on lab investigations or imaging, or present with overt signs and symptoms such as:
  • Oliguria/anuria
  • Pulmonary edema
  • Evidence of shock

• Risk factors for AKI:
  • >65 years old
  • Volume depletion
  • Surgical procedures
  • Infections
  • Nephrotoxic agents
  • Hypertension
  • Diabetes
  • CHF
  • Atherosclerosis
  • Chronic Kidney Disease
  • Obstructive uropathy

• Life threatening complications of AKI:
  • Severe metabolic acidosis
  • Hyperkalemia
  • Pulmonary edema
• Recovery of kidney function may occur within days or require dialysis for many months depending on the severity, duration, and recurrence of the initial AKI.
• Patients may require admission to monitor for recovery of renal function, and nephrology or urology consultation for further workup and management.

• AKI is diagnosed based on serum creatinine (SCr) levels or decreased urine output.
  • eGFR is NOT applicable in AKI.
• AKI Staging criteria based on Kidney Disease: Improving Global Outcomes definitions.

• Baseline creatinine measurements may not be available. Patients at increased risk of AKI should have SCr and urine output monitored.

Clinical Evaluation

Try to determine the cause (prerenal, intrarenal, postrenal).

• Prerenal and postrenal causes are the most common and attempts should be made to rule these causes out prior to workup for intrarenal causes.

Prerenal

• Hemorrhage
• GI/urinary fluid loss
• Sepsis
• Postoperative hypotension
• ACEi/ARBs
• NSAIDs

Postrenal

• Prostate hypertrophy/cancer
• Kidney stones
• Neurogenic bladder

Intrarenal

• Nephritic syndrome
  • Hematuria
  • Proteinuria
  • HTN
• Nephrotic syndrome
  • HTN
  • Periorbital swelling
  • Lower leg edema
• Rhabdomyolysis
• Nephrotoxic agents
• Drug eruption
• Infections

Investigations

Investigations are guided based on the likely cause (prerenal, intrarenal, postrenal). Postrenal causes CANNOT be ruled out based on urine output.

Lab investigations:

• Serum creatinine
• BUN
• Electrolytes
• CBC
• CK
• ABG or VBG
  • pH
  • HCO3
  • pCO2
• ECG:
  • Hyperkalemia causing ECG changes
• Urinalysis:
  • Dipstick
  • Microscopy
  • Albumin or Protein to Creatinine ratio
  • Urine electrolytes
    • Urine sodium concentration < 20 mmol/L indicates prerenal cause (3)
  • Urine Osmolality
• Imaging:
  • Ultrasound for postrenal obstruction and post-void volume
  • CT for obstruction or unexplained cause of AKI
• Biopsy (consult nephrology)

• Management of AKI is mostly supportive.
• Life-threatening complications may arise and need to be treated promptly.
• Early nephrology consultation may be beneficial.

Discontinue Nephrotoxic Agents

• Pharmacist review or use of a drug lookup database (e.g. Lexicomp, RxTx) may be beneficial.
• Examples:
  • NSAIDs
  • ACEi/ARB
  • Aminoglycosides
• Adjust Medications for Renal Dosing
  • Pharmacist review or use of a drug lookup database (e.g. Lexicomp, RxTx) may be beneficial.
• Volume Status
  • Hypovolemia:
    • Renal perfusion needs to be balanced with fluid overload.
    • 9% normal saline or lactated Ringer’s solution are recommended over colloid solutions (1, 2). Plasmalyte can also be used.
    • Target Mean Arterial Pressure >65 mmHg.
    • Vasopressors may be used if fluid resuscitation is not successful (1, 2, 3).
  • Hypervolemia:
    • Furosemide:
      • Initial: 80 mg IV or double the patient’s usual dose if already on diuretic (5).
      • If no improvement in urine output within 2 hours, double initial dose (5).
    • Renal Replacement Therapy (Indications below)
  • Hyperkalemia
    • With ECG changes:
      • Calcium Gluconate 1 g IV, repeat as needed (3).
      • Insulin 10 Units IV with dextrose 25-50 g IV (3).
      • Salbutamol 10-20 mg nebulized (3).
      • Renal Replacement Therapy (Indications below)

Potassium-restricted diet (<2g/day).

Metabolic Acidosis

• Treat underlying cause.
• IV fluids:
  • Target serum bicarbonate 20-22 mmol/L and pH >7.2 (5).
  • 9% Normal Saline, plasmalyte or Lactated Ringer’s solution for acidosis due to reduced perfusion.
  • 3% Sodium Bicarbonate in D5W (3×50 mmol/50 mL ampules in 1L D5W) (5, 6).
    • May also decrease serum potassium.
    • Monitor for volume overload.
  • Renal Replacement Therapy preferred if hypervolemic (indications below).
• Urinary Obstruction
  • Urethral catheterization
  • Consider Urology consultation
• Glycemic Control
  • Target glucose 6.1 – 8.3 mmol/L (2)
• Renal Replacement Therapy
  • Requires Nephrology consultation
  • Indications (1):
    • Despite adequate IV fluid administration:
      • Anuria (>6 hours) or severe oliguria (< 200mL in 12 hours)
      • Hyperkalemia (>6.5 mmol/L) despite treatments as mentioned above
      • Severe metabolic acidosis (pH <7.2)
    • Dialyzable toxin/drug
    • BUN > 30 mmol/L
    • Uremic complications (Encephalopathy, neuropathy, pericarditis)
    • Volume overload unresponsive to diuretics

1. Mercado, M. G., Smith, D. K., & Guard, E. L. (2019). Acute Kidney Injury: Diagnosis and Management. American family physician, 100(11), 687–694.

   
   

2. Kidney Disease: Improving Global Outcomes (KDIGO) Acute Kidney Injury Work Group. KDIGO Clinical Practice Guideline for Acute Kidney Injury. Kidney inter., Suppl. 2012; 2: 1–138.

   
   

3. Gaibi, T., & Ghatak-Roy, A. (2019). Approach to Acute Kidney Injuries in the Emergency Department. Emergency medicine clinics of North America, 37(4), 661–677. 

   
   

4. Moore, P. K., Hsu, R. K., & Liu, K. D. (2018). Management of Acute Kidney Injury: Core Curriculum 2018. American journal of kidney diseases : the official journal of the National Kidney Foundation, 72(1), 136–148. 

   
   

5. Okusa, M.D., & Rosner, M.H. (2019). Overview of the management of acute kidney injury (AKI) in adults. UpToDate. Retrieved January 23, 2021, from uptodate.com.

   
   

6. Farkas, J. (2018, June 27). PulmCrit: pH-guided fluid resuscitation & BICAR-ICU. EMCrit.