Acute Kidney Injury (AKI) is a syndrome of decreased renal function which is reflected by an increase in serum creatinine or a decrease in urine output that occurs over hours-days.
KDIGO defines AKI as:
Rise in serum creatinine > 26 umol/L within 48 hours
Rise in serum creatinine > 1.5 times baseline within 7 days
Urine output < 0.5 mL/kg/h for > 6 consecutive hours
AKI has numerous causes which are divided into prerenal, intrarenal, and post-renal causes.
Renal insufficiency is synonymous with azotemia: which is an elevation of BUN and creatinine. If symptoms of renal failure are present the diagnosis shifts to uraemia and renal replacement therapy (RRT) is indicated. Treatment depends on the cause.
AKI has a 50-70% mortality in the setting of sepsis and multiple organ dysfunction. Uncomplicated AKI due to hypotension and drugs has a better prognosis.
Causes of AKI
| Category | Causes |
|---|---|
| Prerenal causes | Volume depletion, reduced cardiac output, systemic vasodilation, NSAIDs, and ACE inhibitors |
| Intrarenal causes | Acute tubular necrosis, acute interstitial, renal artery or vein thrombosis, malignant hypertension, vasculitides, and glomerulonephritis |
| Post-renal causes | Obstruction of the renal pelvis to urethra |
Staging of acute kidney injury
| Stage | Serum creatinine | Urine output |
|---|---|---|
| Stage I | > 26.5 umol/L (0.3 mg/dL) or 1.5 – 1.9 times baseline | < 0.5 ml/kg/h for 6 – 12 hours |
| Stage II | 2.0 – 2.9 times baseline | < 0.5 ml/kg/h for > 12 hours |
| Stage III | > 353.6 umol/L (4.0 mg/dL) or > 3 times baseline or Renal Replacement Therapy (RRT) | < 0.3 ml/kg/h for > 24 hours or anuria for > 12 hours |
Prerenal vs intrarenal vs postrenal failure
| Prerenal failure | Tubulointerstitial | Glomerular | Postrenal failure | |
|---|---|---|---|---|
| U Na | Low | High (> 40) | Low/variable | Low |
| FE Na | Low (1%) | High (> 1%) | Low/variable | Low (< 1%) |
| U Osm | High | Low (<350) or isosthenuria | Low | High |
| BUN:Cr | High (> 20:1) | ~ 10:1 | ~ 10:1 | High or high-normal |
| Urinalysis | Non-specific | Brown casts, epithelial casts (acute tubular nephritis), eosinophila (acute interstitial nephritis) | Red cell casts, hematuria, proteinuria | None |
- Common causes
- Sepsis
- Major surgery
- Cardiogenic shock
- Hypovolemia
- Drugs
- Hepatorenal syndrome
- Obstruction
- Signs and symptoms
- Urinary output changes
- Oliguria
- Anuria
- Disturbed fluids, electrolytes, and acid-base balance
- Hypovolemia
- Hypotension (late sign)
- Tachycardia
- Reduced urine output
- Reduced capillary refill (late sign)
- Non-visible JVP
- Poor skin turgor (late sign)
- Daily weight loss
- Fluid overload
- Hypertension
- Increased JVP
- Crackles
- Peripheral odema
- Gallop rhythm
- Urinary output changes
- Baseline investigations
- Serum Creatinine:
- To calculate eGFR
- KDIGO criteria for diagnosis and staging
- Extended electrolytes: Na+, K+, Cl-. Ca2+, PO4-3, Uric acid
- Complete blood count, FTS, PT/PTT, Blood Glucose
- Urinalysis
- Presence of blood cells, casts, sediments points towards intrarenal failure
- Urine osmolality (Uosm)
- Serum Creatinine:
- Investigations to determine whether AKI is prerenal, intrarenal, or post-renal
- Symptoms: Hemorrhage, Diarrhea and vomiting, Reduced fluid intake, Sepsis, Use of NSAIDs, ACEi/ARBs, CCF, Liver failure
- Fractional excretion of sodium (FeNa): percentage of sodium excreted in the kidney that is filtered in the urine (normal is 1%, not as important)
- FeNa < 1%: Tubules intact
- FeNa > 2%: Tubules damaged (ATN)
- BUN:Cr: ration of BUN in the serum to Cr in the serum (Normal is between 10:1 and 20:1)
- BUN:Cr > 20:1: Prerenal
- Urine Sodium (UNa): Concentration of sodium in the urine
- Investigations to determine whether it is Acute or Chronic kidney disease
- KUB CT/US:
- Shrunken kidney = CKD
- Normal kidney = AKI or DM/HIVAN/Amyloidosis/ Polycystic kidney disease/ Hydronephrosis
- Complete blood count for anemia due to reduced EPO
- Bone biochemistry for renal osteodystrophy or secondary hyperparathyroidism
- KUB CT/US:
- Investigations to determine the etiology
- KUB CT/US: to determine post-renal causes
- Renal biopsy: to determine intrarenal failure if pre-renal and post-renal causes have been ruled out
- Contraindications to kidney biopsy
- Coagulopathy (due to uremia)
- Solitary kidney
- Small kidney
- Severe hypertension (> 140/90 mmHg)
- Hydronephrosis
- Multiple cysts
- Renal infection (Pyelonephritis, which can develop an abscess)
- Treatment
- Treatment of acute kidney injury involves managing:
- Fluid balance
- Acidosis
- Hyperkalemia
- Early recognition of patients who require renal replacement therapy (RRT)
- Treatment of acute kidney injury involves managing:
- Treatment of Hypovolemia
- Fluid resuscitation with 250 – 500 mL boluses (up to 2L can be given)
- Large volumes of normal saline may cause hyperchloraemic acidosis
- Ringer’s lactate or Hartmanns solution is a more ****balanced fluid. It is used with caution if there is hyperkalemia and oliguria/anuria
- Blood components if there is blood loss
- Human albumin in hepatorenal syndrome and as second line to crystalloids in septic shock
- Fluid resuscitation with 250 – 500 mL boluses (up to 2L can be given)
- Treatment of hypervolemia (fluid overload)
- Oxygen supplementation
- Fluid restriction
- Diuretics if there is symptomatic fluid overload
- Diuretics are potentially harmful when they used to treat oliguria without fluid overload
- Renal replacement therapy in AKI + fluid overload + oliguria/anuria
- Treatment of acidosis
- Severe acidosis should be referred for renal/critical care and renal replacement therapy.
- Medical management of acidosis with sodium bicarbonate is controversial since bicarbonate can generate CO2 which can cause respiratory acidosis if there is inadequate ventilation.
- Treatment of Hyperkalemia
- Hyperkalemia is treated if the concentration is > 6.5 mmol/L or any EKG changes are present.
- Cardioprotection(10 10 10 )
- IV Calcium Gluconate 10% 10mL over 10 minutes. Provides carioprotection for 30 – 60 minutes.
- Bind potassium(10 50)
- IV 50mL D50 and 10 Units Insulin. Monitor q1h for hypoglycemia
- Nebulized 10 – 20 mg Salbutamol. Avoid if there is tachyarrhythmia. Low dose of 10 mg in ischemic heart disease.
- IV sodium bicarbonate 1-2meq/kg
- Excrete potassium
- Renal replacement tehrapy
- Furosemide or torsemide
- Complications
- Serositis
- Pericarditis
- Pleuritis
- Coagulopathy due to platelet dysfunction.
- This can lead to gastrointestinal bleeding
- Susceptibility to infections since WBCs cannot degranulate
- Serositis
Drugs and AKI
| Category | Examples |
|---|---|
| Safe to continue in AKI | Paracetamol, warfarin, statins, junior aspirin, clopidogrel, and beta-blockers |
| Worsens AKI | NSAIDs, aminoglycosides, ACE inhibitors, Angiotensin II receptor antagonists, and diuretics |
| Increased risk of toxicity with AKI | Metformin, lithium, and digoxin |