Saturday, May 03, 2014

Rhabdomyolysis: what the hospitalist needs to know

These are some of the take home points from a recent review.

The causes are diverse

In addition to the originally described physical injuries there is a long list of other causes:

Prolonged down time
Numerous endocrine and metabolic disorders
Seizures, agitation
Hyperthermia syndromes (NMS, heat stroke, etc. The review fails to mention serotonin syndrome).
And many others

The list of causative drugs is long

Usually we think of recreational drugs, alcohol, statins, daptomycin and psych drugs but there are many more.

How do you diagnose it?

The diagnosis is based on clinical circumstances and an elevated CK level. Urine myoglobin may be unhelpful, as it is a “send out” test in many hospitals. A positive urine dipstick for heme with few or no RBCs on microscopic is a clue to the presence of myoglobin.

What level of CK elevation puts the patient at risk for AKI?

From the review:

The CK level for clinical concern is uncertain; an arbitrary value of 500 to 1,000 IU/L, or five to 10 times the upper limit of normal is frequently used to define rhabdomyolysis. Higher CK levels correlate with a greater degree of muscle injury, but levels correlate marginally with the development of AKI or mortality.3,4,6,40-43 A reasonable consensus recommendation suggests close monitoring of renal function in patients with CK levels greater than 5,000 IU/L and creatinine greater than 1.5 mg/dL.44 Some studies suggest that patients with CK levels less than 5,000 IU/L are not at risk of developing AKI42,44; otherwise, it is difficult to use the magnitude of the CK value to estimate the risk of kidney injury. Serial CK measurements should be monitored; increasing levels, or failure of levels to decline despite therapy, suggest ongoing muscle injury or the development of renal failure.

Treatment: don't forget the basics

Remove/correct the underlying cause.
Monitor and address complications (electrolyte disturbances, compartment syndrome).
Involve nephrology early.

What volume of resuscitation fluid?

From the review:

IVF should be administered rapidly as an initial bolus...
Large amounts of IVF within the first 24 h are associated with improved outcomes.1 No specific rate of infusion or target urine output has been demonstrated to be superior to another. For the first 24 h after presentation, as little as 3 L to as much as 24 L have been administered effectively. A target of 6 to 12 L within 24 h is a reasonable goal, as long as complications from volume overload can be avoided.

What type of resuscitation fluid?

It has been debated whether normal saline or Ringers lactate is better but there is no high quality evidence to suggest one over the other.

What about bicarb and urinary alkalinization?

This approach has been suggested in some publications but high quality evidence in support of it is lacking.

Is there a role for diuretics (loop or mannitol)?

The review mentions the option of using loop diuretics to maintain urine flow but, absent high quality evidence, makes no strong recommendation.

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