MRCS Part B Revision · Applied surgical science and critical care
Rhabdomyolysis — MRCS Part B Applied surgical science and critical care
By Dr Richard Miller, MBChB FRCS · Reviewed
Rhabdomyolysis is an applied surgical science and critical care station. Three of the seventeen examined stations in the MRCS Part B OSCE fall in this area. These stations ask you to interpret data and manage a sick surgical patient: a chart, a blood gas, an imaging study or a deteriorating patient on the ward, and the physiology underneath the decision.
What you need to know for the Rhabdomyolysis station
A young woman with dark urine and thigh pain after a spin class, with a creatine kinase over 5,000. The station is rhabdomyolysis, its renal complication and its treatment, ending with compartment syndrome.
Definition and mechanism
Breakdown of skeletal muscle with release of its contents — myoglobin, creatine kinase, potassium, phosphate and urate — into the circulation. Whatever the trigger, the final path is the same: the muscle cell runs out of ATP, cannot pump calcium out, and the rising intracellular calcium activates proteases and phospholipases that destroy the cell.
Causes
Crush injury and prolonged immobility (the collapsed elderly patient on the floor, the unconscious overdose), unaccustomed extreme exertion, seizures, compartment syndrome and limb ischaemia with reperfusion, burns and electrocution, heat stroke and malignant hyperthermia, drugs (statins, alcohol, cocaine, amphetamines), infections, and inherited disorders of muscle metabolism such as McArdle's disease.
Complications
Acute kidney injury, hyperkalaemia with arrhythmia, hypocalcaemia early (calcium binds in the damaged muscle) and hypercalcaemia in recovery, metabolic acidosis, disseminated intravascular coagulation, hypovolaemia from fluid sequestered in the muscle, and compartment syndrome.
Why the kidney fails
Myoglobin, filtered freely once it exceeds the plasma proteins that carry it, is toxic to the tubular cells, forms casts with Tamm-Horsfall protein that block the tubules, and constricts the renal vessels. Acid urine and hypovolaemia make all three worse.
Diagnosis
Creatine kinase more than five times normal (usually many thousands), a urine dipstick positive for blood with no red cells on microscopy (the stick reacts to myoglobin), and the typical electrolytes: high potassium, phosphate and urate, low calcium, raised creatinine. The diagnosis is clinical; the CK tracks the course.
Why this patient
Unaccustomed, sustained, high-intensity exercise in a novice, often with dehydration and heat; the cyclist's quadriceps are the muscles involved, which is why both thighs hurt.
Management
Aggressive intravenous crystalloid to keep the urine output above 200–300 ml an hour, started before the CK result if the story fits. Treat hyperkalaemia. Alkalinising the urine and mannitol are used in some units but the evidence is thin; the fluid is what matters. Monitor the electrolytes and CK, and involve the renal team early if the creatinine rises or the potassium will not settle, because dialysis may be needed. Look for and treat the cause.
Compartment syndrome
Pain out of proportion, pain on passive stretch of the muscles in the compartment and paraesthesia in the nerves crossing it are the early signs; loss of pulses is late and a poor guide. Diagnosis is clinical, supported if needed by a compartment pressure within 30 mmHg of the diastolic pressure. Treatment is immediate: remove any dressings or casts, keep the limb level with the heart, give oxygen and fluid, and carry out an urgent fasciotomy of every compartment involved, leaving the wounds open. Delay beyond a few hours costs the muscle.
What are you asked at the Rhabdomyolysis station?
The station runs to 10 questions over nine minutes. These are the questions as they are put to you; the model answers are in the question bank.
- What is the diagnosis?
- Define rhadomyolysis?
- What serious complications can it lead to?
- What are the commonest causes of rhabdomyolysis?
- What substance released from damaged muscle cells is thought to damage renal tubules leading to AKI?
- How is rhabdomyolysis diagnosed in the hospital patient?
- Why has this patient developed the condition?
- How should this patient be managed?
- If this patient had pain out of proportion to the injury, pain on passive stretching of the thigh compartment affected and parastheisa what might you suspect had developed?
- How would you manage a patient with suspected compartment syndrome?
How is the applied surgical science and critical care station marked in MRCS Part B?
Each of these three stations is marked out of 20, split 12 marks for clinical knowledge and its application, 4 for clinical and technical skill and 4 for professionalism. No communication marks are available. The three cover critical care management, interpretation of clinical data, and interpretation of visual information.
FAQ
What does the Rhabdomyolysis station ask?
It opens with "What is the diagnosis?" and runs to 10 questions over nine minutes. Each of these three stations is marked out of 20, split 12 marks for clinical knowledge and its application, 4 for clinical and technical skill and 4 for professionalism. No communication marks are available. The three cover critical care management, interpretation of clinical data, and interpretation of visual information.
What counts as applied surgical science in MRCS Part B?
Three of the seventeen examined stations: critical care management, interpretation of clinical data such as blood results and charts, and interpretation of visual information such as imaging and traces.
How is an applied science station marked?
Out of 20, with 12 marks for clinical knowledge and its application, 4 for clinical and technical skill and 4 for professionalism. Unlike the communication stations, none of the marks are for how you say it.
How much physiology do I need?
Enough to explain the decision you are making. The station rewards applying physiology to the patient in front of you rather than reciting it, so practise talking through why a number changes your management.
How many stations are in the MRCS Part B OSCE?
Seventeen examined stations of nine minutes each, with a minute to read the task before each one. Two preparation stations and at least one rest station bring the circuit to about twenty, and the exam takes about three and a half hours.
What is the pass mark for MRCS Part B?
There is no published pass mark. The cut score is set separately for Applied Knowledge and Applied Skills, for each circuit, by borderline regression. Published pass rates across the 2024/25 diets ranged from 51% to 66%.
Can I fail a station and still pass?
Yes. There is no rule about how many stations you may fail: the cut score applies to your total mark in each component, so a weak station costs the marks you lost on it and strong stations elsewhere can make them back. Applied Knowledge and Applied Skills are passed separately and must both be passed at the same sitting, so a strong anatomy performance cannot rescue a weak communication one.
Dr Richard Miller, MBChB FRCS
Station summaries are reviewed against the current intercollegiate MRCS syllabus and the published marking blueprint. Guidance changes between diets: check the royal colleges' own pages before relying on a date, a fee or a threshold.
Practise this station
The question bank carries the model answer to every question above, with the rest of the applied surgical science and critical care stations.
More applied surgical science and critical care stations