Setting: ED
CC: “My muscles hurt and my urine is dark.”
VS: BP: 112/70 mm Hg; P: 108 beats/minute; T: 98°F; R: 18 breaths/minute
HPI: A 27-year-old man arrives at the ED by ambulance after undergoing the physical fitness test for being a firefighter. He had to lift a 150-lb bag, run up a flight of stairs while carrying it, and proceed across a balance beam. He then had to do 50 pushups and 50 sit-ups. At the end, he developed dark urine and diffuse muscle pain.
PMHX/Medications: none
PE:
General: weak, tired, and in pain
Heart, Lung, Abdomen: normal
What would be the most likely cause of death in this patient?
a. Dehydration
b. Renal failure
c. Hyperkalemia
d. Hyperphosphatemia
e. Hypocalcemia
Answer c. Hyperkalemia
The single most important fact about rhabdomyolysis is knowing that hyperkalemia causes death when it is severe. Everything in this list occurs, but the one that kills you is hyperkalemia.
• High Potassium Level = ECG
• Ninety-five percent of potassium in the body is intracellular.
Rapidly Destroyed Cells = Hyperkalemia
Initial Orders:
ECG
CHEM-7
Bolus IV saline
Urinalysis (UA)
Creatine phosphokinase (CPK)
Calcium
Phosphate
Rhabdomyolysis is a case where timing is essential. Exclude hyperkalemia and cardiac toxicity immediately. Order potassium level and ECG even before the PE.
Peaked T Waves = Give Calcium Chloride (or Gluconate)
Reports:
ECG: peaked T waves
CHEM-7: potassium 6.8 mEq/dL; BUN 26 g/dL; creatinine 1.5 mg/dL
UA: dipstick + blood
Calcium level: 6.8 mg/dL (low)
Phosphate: elevated
Why do we give patients calcium to protect the heart?
a. It drives calcium back into the cells.
b. It blocks norepinephrine release.
c. It raises the threshold for depolarization.
d. It decreases conduction velocity in His-Purkinje tissue.
Answer c. It raises the threshold for depolarization.
Calcium makes it harder for neural tissue to depolarize. This is a good thing if the myocardium might abnormally depolarize and lead to arrhythmia. This is sometimes referred to as “membrane stabilization.” To depolarize, neural and muscle tissue must become more positive until it hits a “threshold” or trigger point to depolarize. Resting or baseline membrane potential is often at −70 to −90 mV. The cells must increase to −50 or −45 mV before the threshold for depolarization is reached. Calcium raises the level so the threshold is more “out of reach” and depolarization does not occur.
High Calcium = Harder to Depolarize
Low Calcium = Easier to Depolarize
There is no maximum rate of calcium infusion. Calcium channels are closed at baseline.
IV calcium is given and IV fluids are running. Now you must give medication to lower the blood potassium level.
Orders:
Insulin
Glucose
Repeat chemistry
Urine myoglobin
Insulin drives potassium into cells by stimulating Na+/K+-ATPase.
The type of fluids in rhabdomyolysis is not clear. Use normal saline (NS) for now.
Urine dipstick cannot distinguish between
• Red blood cells (RBCs)
• Hemoglobin
• Myoglobin
Move the clock forward 15 minutes.
Repeat potassium level: 6.2 mEq/L
Urine microscopic: no RBCs seen
CPK: 28,000 units/L
CPK levels are not dangerous until above 5000 to 10,000 units/L.
What causes hypocalcemia?
a. Decreased parathyroid hormone (PTH).
b. Binding by sarcoplasmic-endoplasmic reticulum calcium adenosine triphosphatase (SERCA).
c. Urinary loss.
d. Suppression of vitamin D.
Answer b. Binding by sarcoplasmic-endoplasmic reticulum calcium adenosine triphosphatase (SERCA).
SERCA has calcium adenosine triphosphatase (ATPase) pumps that pull calcium into storage. When muscles are damaged by rhabdomyolysis, the exterior membrane becomes permeable to calcium in blood. The muscle then binds up all the calcium by pumping it into SERCA. Normally SERCA only has contact with the interior of the muscle cells. In rhabdomyolysis, the interior now contacts blood calcium.
Damaged muscle binds calcium.
Where in the hospital should this patient be placed?
a. Place the patient in the intensive care unit (ICU).
b. Keep the patient in ED for the first 24 to 48 hours.
c. Place the patient in the hospital ward.
d. Discharge the patient after his potassium level is corrected.
Answer a. Place the patient in the intensive care unit (ICU).
After initial administration of fluids and correcting the potassium level, you can move the patient to the ICU. The indication for ICU placement is hyperkalemia with ECG changes. Patients can go to a regular hospital ward just for hydration for rhabdomyolysis. Renal insufficiency is not an indication for ICU placement. Even in rhabdomyolysis, the creatinine level cannot rise more than 1 to 2 points a day.
What is the mechanism of hyperphosphatemia?
a. Binding to muscle
b. Release from muscle
c. Renal insufficiency
d. Hyperparathyroidism
Answer b. Release from muscle
The majority of phosphate is in muscles and inside cells. Destroyed cells and muscle release phosphate and potassium and bind calcium.
Continue IV fluids at high volume to “flush out” the kidneys. It is not clear if bicarbonate or mannitol make a clear difference in outcomes. The proposed mechanism of bicarbonate is that it prevents precipitation of CPK and myoglobin in the kidney tubule. The idea of mannitol is to decrease the duration of contact of myoglobin with the kidney tubule—like taking your hand off a hot stove.
Move the clock forward 4 hours and repeat the potassium and chemistry levels.
Keep the patient in the ICU until the potassium level is repeatedly normal and the ECG is normal. Move the patient to the floor. When on the floor, you do not need to do the chemistry more often than twice a day.
Move the clock forward until you see:
No rise in creatinine level and no need for dialysis
CPK levels drop below 1000 units/L
At that point you can discharge the patient from the hospital if the case has not ended already.
Do not be dismayed if many acute cases give you the “this case will end in 5 minutes of real time” screen before you can send the patient home. In those cases, the emphasis is simply on initial management.