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Dr. Ajith Kumar J MD
Dept. of Emergency Medicne
Travancore Medicity, Kollam
India
editor
Definition
Rhabdomyolysis is a clinical and biochemical syndrome that results from acute necrosis of skeletal muscle fibres and leakage of cellular contents into circulation.
Pathophysiology
Damage to myocyte causes an influx of sodium into cell and an accumulation of cytosolic calcium due to a combination of direct injury to the cell and to increased activity of the sodium-calcium exchange mechanism that attempts to extrude sodium from the cell in exchange for calcium.
The high intracytoplasmic calcium concentration has a number of deleterious effect, including activation of phospholipase A2, which results in the production of toxic metabolite and cell death.
ETIOLOGY
Traumatic | Non- Traumatic |
| Infection
|
Electrolyte imbalance
| |
| Immune mediated
|
| Drugs
|
| Metabolic Disorder
|
DIAGNOSIS
Total CK
Total Creatine Kinase is the most sensitive test.
A five fold or greater increase in serum CK in the absence of cardiac or brain injury is diagnostic of rhabdomyolysis
Myoglobin
Myoglobin is an oxygen binding protein found in skeletal and cardiac muscle and is involved in oxidative metabolism.
Myoglobin elevates even before CK elevates. Myoglobin enters urine when the plasma concentration is >1.5 mg/dl .
Urine Myoglobin causes typical reddish brown discolouration of the urine.
Myoglobin is rapidly and unpredictably eliminated by hepatic metabolism.Myoglobin reaches normal value within 1 -6 hrs. Therefore test for myoglobin in plasma or urine are not a sensitive diagnostic procedure.
Red discoluration of the urine when erythrocyte cannot be detected by microscope must be hemoglobinuria or myoglobinuria unless the colour of urine is due to drugs or metabolite.
Dip stick test : Since myoglobin contains heme qualitative test such as dip stick donot differentiate among hemoglobin, myoglobin and red blood cells
Characteristic | Rhabdomyolysis | Hemolysis | Hematuria |
Red discolouration | - | + | - |
Positive benzidine dipstick | + | + | + |
Presence of erythrocyte by urine microscopy | - | - | + |
Elevated CK concentration in blood | + | - | - |
Serum electrolytes including phosphorus and calcium should be determined.
Uric acid level
CBC, PT, aPPT, Fibrinogen levels has to checked.
ABG : Wide anion gap acidosis
Causes for reddish brown discolouration of the urine |
Myoglobinuria
Hemoglobinuria
Hematuria
External factors
|
Complication
Acute renal failure :
It is due to renal vasconstriction, intraluminal cast formation and direct heme induced cytotoxicity
Myoglobin is usually bound to plasma, when large amount of myoglobin exceeding the capacity to bind is released, it gets filtered by glomeruli and reaches tubules, where it may cause obstruction and renal dysfunction.
Metabolic disarrangement
Hyperkalemia
Hyperphosphatemia : Due to release of phosphorus from the damaged cells.
Hyperuricemia : Nucleosides are released from disintegrating cell nuclei into blood and metabolized in the liver to purines such as xanthine, hypoxanthine and uric acid which causes tubular obstruction.
Hypocalcemia : Occurs early in rhabdomyolysis. It is due to deposition of calcium salts in necrotic muscles, due to the hyperphosphatemia and decreased levels of 1,25 dihydroxycholecalciferol.
Hypercalcemia : Occurs during recovery period due to secondary hyperparathyroidism and extrusion of calcium from recovering muscle cells.
Hypophosphatemia
Albumin
Initially patient may have hyperalbuminemia but once the patient is hydrated plasma volume expands and there will be leak of albumin due to capillary leak leading to hypoalbuminemia.
DIC
Mechanical complication
Compartment syndrome
Peripheral neuropathy
RISK SCORING for Predicting Renal failure or Death ; Mc mahon etal |
Age
|
Female sex : 1 points |
Initial creatinine level
|
Initial calcium level <7.5 mg/dl ; 2 points |
Initial CPK level >40,000 U/L : 2 points |
Origin not seizures, syncope, exercise, statin or myositis : 3 points |
Initial phosphate level
|
Initial bicarbonate level <19 meq/L : 2 points |
|
Treatment
Hydration
Aggressive IV rehydration for first 24 -72 hrs.
Rapid infusion of IV crystalloids at a rate of 2.5 ml/kg/h with a goal of maintaining urine output of 2ml/kg/h.
Potassium or lactate containing fluid must be avoided.
Correction of electrolytes
Alkalinisation of urine
Alkalination of urine may inhibit myoglobin induced lipid peroxidation.
It is achieved by continuous IV Infusion of sodium bicarbonate aiming for a urinary Ph >7.
Suggested regimen is 0.9% NaCl with 1 amp of sodium bicarbonate at 100ml/hr
OR Each litre of NS alternate with 1L of 5% Dextrose with 100 mmol of bicarbonate.
Disadvantage : Hypocalcemia
Mannitol :
Mannitol is controversial. Efficacy is not proven. Currently not recommended
10 ml/hr if urine output >20ml/hr
Advantages of using mannitol
Mannitol increases renal blood flow and GFR
It is an osmotic agent that attracts fluid from interstitial compartment
Mannitol is an osmotic diuretic that increases urinary flow and prevents obstructive myoglobin cast.
Myoglobin scavenges free radicals.
Diuretics
Loop diuretics increases tubular flow and decrease the risk of precipitation of myoglobin, while simultaneously acidifying urine and calcium losses.
Reference
Tintinalli
Rhadomyolysis, By John D hunter ;Oxford journal 2006
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emmedonline
Dr. Ajith Kumar J MD
Dept. of Emergency Medicne
Travancore Medicity, Kollam
India
editor