Acute kidney injury (AKI): a sudden deterioration in renal function leading to an inability to maintain fluid, electrolyte and acid-base balance
AKI has replaced the term acute renal failure (ARF) which nephrologists disliked because it implied complete failure of renal function
Oligura: reduced urine output; defined variously as <0.5 ml/kg/hour, <30 ml/hour or <400 ml/day
Anuria: complete absence of urine output
Staging of acute kidney injury
Stage 1: creatinine (Cr) ≥1.5-2 times baseline or urine output (UO) <0.5 ml/kg/hours for >6 consecutive hours
Stage 2: Cr ≥2-3 times baseline or UO <0.5 ml/kg/hours for >12 hours
Stage 3: Cr ≥3 times baseline or UO <0.3 ml/kg/h for ≥24 hours or anuria for >12 hours
Patients should be staged according to their worst criterion
Epidemiology of acute kidney injury
Common
Often accompanies other acute medical or surgical problems due to its wide range of causes
Causes of acute kidney injury (AKI)
Hypovolaemia
Inadequate fluid intake
Excess fluid loss
Vomiting
Diarrhoea
Diuresis
Early sepsis
Haemorrhage
Burns
Reduced cardiac output
Pre-renal: inadequate blood supply to the kidneys
Acute coronary syndrome (ACS)
Cardiac arrhythmia eg atrial fibrillation (AF)
Valvular heart disease
Hypertension
Cardiomyopathy
Cardiac tamponade
Late sepsis
Renal artery disease
Renal artery stenosis
Vasculitis
Intrinsic renal: direct damage to the kidneys
Glomerular
Proliferative glomerulonephritis
Typically presents as nephritic syndrome characterised by haematuria (with red cells casts on microscopy), mild proteinuria (<3.5 g/day), hypertension, oedema, elevated Cr and oligruia
Non-proliferative glomerulonephritis
Typically presents as nephritic syndrome characterised by severe proteinuria (>3.5 g/day), hypoalbuminaemia and oedema
Tubular
Acute tubular necrosis (ATN)
Usually occurs secondary to the ischaemia of pre-renal AKI
Nephrotoxic drugs
Angiotensin converting enzyme inhibitors (ACEIs)
Angiotensin receptors blockers (ARBs)
Non-steroidal anti-inflammatory drugs (NSAIDs)
Aminoglycosides eg gentamicin
Radiological contrast
Rhabdomyolysis
Multiple myeloma
Interstitial
Acute interstitial nephritis: usually caused by a drug-induced allergic reaction
Penicillin
NSAIDs
Autoimmune disease e.g. systemic lupus erythromatosus (SLE)
Infiltrative disease
Lymphoma
Sarcoidosis
Vascular
Hypertensive nephropathy
Vasculitides
Haemolytic uraemic syndrome (HUS)
Thrombotic thrombocytopenic purpura (TTP)
Disseminated intravascular coagulation (DIC)
Post-renal: obstruction to urinary flow
Ureters
Luminal
Ureteric calculi
Vesicoureteric reflux
Mural
Tumour e.g. transitional cell carcinoma
Extrinsic
Compression from abdominal/pelvic mass
Complication of abdominal/pelvic surgery
Retroperitoneal fibrosis
Bladder
Luminal
Bladder calculi
Mural
Tumour e.g. bladder carcinoma
Extrinsic
Neurogenic bladder
Diabetes mellitus
Multiple sclerosis
Spinal cord compression
Cauda equine syndrome
Anticholinergic drugs
Sympathomimetic drugs
Urethra
Luminal
Blocked urethral catheter
Mural
Urethral stricture
Extrinsic
Benign prostatic hypertrophy (BPH)
Prostatic carcinoma
Pain
Risk factors for acute kidney injury (AKI)
Age >75 years
Chronic kidney disease (CKD)
Cardiac failure
Peripheral vascular disease (PVD)
Hypertension
Hepatic disease
Diabetes mellitus
Nephrotoxic medications
History in acute kidney injury
Symptoms of dehydration
Thirst
Light-headedness
Dry mouth
Dark urine
Symptoms of excess fluid loss
Vomiting
Diarrhoea
Diuresis
Haemorrhage
Burns
Symptoms of cardiac failure
Fatigue
Worsening dyspnoea progressing from an exercise tolerance of dyspnoea on exertion to at rest
Orthopnoea
PND
Cough productive of pink, frothy sputum
Ankle swelling
Symptoms of sepsis
Fever
Rigors
Symptoms of the focus
Symptoms of malignancy
Cachexia
Anorexia
Night sweats
Symptoms of the focus
Symptoms of ureteric obstruction
Severe, colicky loin to groin pain
Symptoms of bladder obstruction
Complete
Painful suprapubic mass
Anuria
Partial
Painful suprapubic mass
Urinary frequency
Hesitancy
Poor stream
Terminal dribbling
Strangury
Drug history
Angiotensin converting enzyme inhibitors (ACEIs)
Angiotensin receptors blockers (ARBs)
Non-steroidal anti-inflammatory drugs (NSAIDs)
Aminoglycosides eg gentamicin
Anticholinergic drugs
Sympathomimetic drugs
Examination of the patient with acute kidney injury
Signs of hypovolaemia
Cold, pale peripheries
Prolonged capillary refill times (CRT >2 s)
Decreased skin turgor
Reduced jugular venous pressure (JVP)
Sunken eyes
Dry lips, mouth and tongue
Tachycardia
Postural hypotension
Absolute hypotension
Dark urine
Signs of cardiac failure
Respiratory distress
Tachypnoea
Bibasal crepitations
Cardiac wheeze
Tachycardia
Displaced apex beat
Third heart sound
RV heave
Raised JVP
Hepatomegaly
Peripheral oedema
Signs of sepsis
Pyrexia
Tachypnoea
Tachycardia
Altered mental state
Hypotension in septic shock
Signs of the focus
Signs of malignancy
Cachectic
Signs of the focus
Signs of ureteric obstruction
Unable to get comfortable
Tender loin
Signs of bladder obstruction
Tender suprapubic mass that is dull to percussion; palpation may generate the urge to urinate
Enlarged prostate on digital rectal examination
Investigation of acute kidney injury
Urea & electrolytes (U&Es)
Although there may be prior clinical suspicion, comparison of current Cr to previous values will make the diagnosis, grade the severity and identify any accompanying electrolyte abnormalities
Full blood count (FBC)
May reveal elevated white cell and neutrophil count suggesting infection
Venous blood gas (VBG)
May reveal a metabolic acidosis and will provide certain electrolytes faster than laboratory blood tests
Urinalysis
Proteinuria may be part of nephrotic syndrome and should be quantified with a urinary protein:creatinine ratio (PCR)
Haematuria may be part of nephritic syndrome and should prompt a nephritic screen
Leucocytes and nitrites suggest infection and should prompt a urine culture
Urinary & plasma osmolality and sodium: may help distinguish between pre-renal AKI and ATN
Pre-renal AKI: kidney is functioning maximally to retain salt and water; urinary osmolality is high (600-900 mosm/L) and urinary sodium is low (<10 mM)
ATN: kidney is functioning inadequately and is unable to retain salt and water; urinary osmolality approaches that of plasma(280 mosm/L) and urinary sodium rises (>30 mM)
Bladder scan
Will reveal the volume of urine in the bladder and suggests retention if >600 ml
If the patient is able to pass urine, perform a post-void bladder scan: if the volume is still significant, this suggests incomplete voiding and partial retention
Renal ultrasound scan (USS)
May reveal the source of any post-renal obstruction
Initial management of acute kidney injury (AKI)
Stop/avoid nephrotoxic drugs;
If they are absolutely necessary adjust dosages accordingly
Fluid resuscitation
Monitor fluid balance with input/output chart and daily weights
Daily U&Es
Urinary osmolality and sodium
Urinalysis +/- culture, urinary PCR or nephritic screen
When considering urethral catheterisation for urine output monitoring, weigh the benefits of accurate urine output monitoring against the risks of introducing infection
Renal USS
Consider if suspicious of post-renal obstruction, especially if not resolved by urethral catheterisation
Treat the cause
Treat any complications
Further management of acute kidney injury (AKI)
Indications for renal replacement therapy (RRT):
Urine output <0.3 ml/kg for 24 hours
Absolute anuria for >12 hours
Multi-organ failure
Refractory volume overload
Complications of uraemia
Uraemic encephalopathy
Uraemic pericarditis
Severe poisoning or drug overdose
Severe hypo/hyperthermia
Refractory hyperkalaemia >6.5 mM
Serum urea >27 mM
Refractory metabolic acidosis pH <7.15
Refractory electrolyte abnormalities
Hyponatraemia <115 mM
Hypernatraemia >165 mM
Hypercalcaemia
Types of continuous renal replacement therapy (CRRT):
Continuous venovenous haemodialysis (CVVHD)
Continuous venovenous haemofiltration (CVVHF)
Continuous venovenous haemodiafiltration (CVVHDF)
Complications of acute kidney injury
Hyperkalaemia
Hypo/hypernatraemia
Hypercalcaemia
Metabolic acidosis
Pulmonary oedema
Hypertension
Uraemic encephalopathy
Uraemic pericarditis
Prognosis of acute kidney injury
When mild and treated promptly and aggressively, AKI is usually reversible
When severe and/or unrecognised and/or treated inadequately, there is usually at least an element of chronic renal impairment
