Sample · ACEM
Return of spontaneous circulation after VF arrest: gas, ECG and the first hour
Resuscitation and critical care · 4 parts · 14 marks. Decide what you would write, then compare with the rubric and model answer. In the app you write it under time and it comes back marked.
A 58-year-old man collapsed at a suburban bowls club. Bystander cardiopulmonary resuscitation (CPR) was started within two minutes and a public-access defibrillator delivered one shock. Paramedics found ventricular fibrillation (VF), gave two further shocks and 300 mg of amiodarone, and achieved return of spontaneous circulation (ROSC) 18 minutes after collapse. Paramedics placed an i-gel supraglottic airway, which was replaced by an endotracheal tube on arrival in your resuscitation bay.
On arrival: heart rate 104/min sinus rhythm, blood pressure 92/58 mmHg, SpO2 100% on FiO2 1.0, Glasgow Coma Scale (GCS) score 3 with no sedation, pupils 3 mm and sluggish, temperature 35.9 °C, blood glucose 14.2 mmol/L.
Arterial blood gas on FiO2 1.0:
pH 7.12 | PaCO2 58 mmHg | PaO2 382 mmHg | HCO3- 18 mmol/L | base excess -10 | lactate 7.8 mmol/L | K+ 3.4 mmol/L
12-lead electrocardiogram (ECG) 10 minutes after ROSC: sinus rhythm 104/min; 3 mm ST elevation V1 to V4 and 1 mm in I and aVL; reciprocal ST depression in III and aVF; QRS 100 ms; QTc 460 ms.
(a) Interpret the arterial blood gas. 3 marks
Show the rubric and model answer
- Acidaemia with mixed respiratory acidosis (PaCO2 58) and metabolic acidosis (HCO3 18, BE -10) (1)
- Raised lactate 7.8: type A lactic acidosis from low-flow state during arrest; expect clearance if perfusion restored (1)
- Marked hyperoxia (PaO2 382 on FiO2 1.0): wean FiO2 now; mild hypokalaemia (3.4) relevant to arrhythmia risk (1)
- Severe acidaemia (pH 7.12) from a mixed respiratory and metabolic acidosis.
- Respiratory: PaCO2 58 mmHg = hypoventilation; the ventilator minute ventilation is inadequate.
- Metabolic: HCO3- 18, base excess -10, lactate 7.8 = lactic acidosis (type A) from the no-flow and low-flow periods. It should clear over hours if perfusion is restored; failure to clear suggests ongoing shock.
- Hyperoxia: PaO2 382 mmHg. Harmful after ROSC; reduce FiO2 immediately.
- K+ 3.4: mild hypokalaemia (partly adrenergic). Replace to 4.0-4.5 to reduce re-arrest risk.
(b) List your physiological targets for the next six hours, with values. 5 marks
Show the rubric and model answer
- Oxygenation: titrate FiO2 to SpO2 94-98% (or PaO2 about 75-100 mmHg); avoid both hypoxaemia and hyperoxia (1)
- Ventilation: normocapnia, PaCO2 35-45 mmHg; increase minute ventilation (rate first), lung-protective tidal volume 6-8 mL/kg predicted body weight (1)
- Haemodynamics: mean arterial pressure at least 65 mmHg (systolic above 100 mmHg); fluid then noradrenaline via arterial line monitoring (1)
- Temperature: active prevention of fever (no higher than 37.5-37.7 °C) for at least 72 hours; do not rewarm above this; treat shivering (1)
- Glucose 6-10 mmol/L (treat above 10, avoid hypoglycaemia); K+ 4.0-4.5, Mg2+ above 1.0; seizures treated if present (EEG when available) (1)
- Sedation and analgesia started once haemodynamics allow (e.g. fentanyl and propofol or midazolam) to facilitate ventilation and temperature control (1)
- Oxygen: FiO2 down to SpO2 94-98% (PaO2 roughly 75-100 mmHg).
- Ventilation: PaCO2 35-45 mmHg. Increase the rate (e.g. 14 to 20/min) at tidal volume 6-8 mL/kg predicted body weight; repeat gas in 20-30 minutes. Avoid hyperventilation (cerebral vasoconstriction).
- Blood pressure: mean arterial pressure at least 65 mmHg, systolic above 100 mmHg. Arterial line; 250-500 mL crystalloid boluses if fluid-responsive, then noradrenaline (start 5 microgram/min and titrate).
- Temperature: core temperature monitoring; prevent fever (keep no higher than 37.5 °C) for at least 72 hours; no active rewarming of his current 35.9 °C.
- Glucose: 6-10 mmol/L; insulin infusion if persistently above 10.
- Electrolytes: K+ 4.0-4.5 mmol/L, Mg2+ above 1.0 mmol/L.
- Neurological: sedation (e.g. propofol and fentanyl infusions, cautious with blood pressure); watch for seizures and myoclonus; head of bed 30 degrees.
(c) Outline the indications for, and your decision about, emergency coronary angiography in this patient. 3 marks
Show the rubric and model answer
- Post-ROSC ECG shows anterolateral ST-elevation myocardial infarction (STEMI); likely proximal left anterior descending occlusion as cause of the VF arrest (1)
- ST elevation after ROSC (with presumed cardiac cause) is an indication for emergency coronary angiography and primary percutaneous coronary intervention, regardless of coma (1)
- Decision: activate the cath lab now; aspirin 300 mg (via nasogastric tube or IV), heparin per interventional cardiologist; coma and GCS 3 are not a contraindication; fibrinolysis only if PCI not achievable in time (1)
- The ECG shows an anterolateral STEMI (ST elevation V1-V4, I and aVL with inferior reciprocal change), most likely a proximal left anterior descending occlusion. This is the probable cause of his VF.
- ST elevation after ROSC with a presumed cardiac cause is an indication for emergency coronary angiography and primary percutaneous coronary intervention (PCI). Without ST elevation, early angiography is decided case by case (haemodynamic or electrical instability, ongoing ischaemia).
- Decision: activate the cath lab now, before transfer to the intensive care unit (ICU). Aspirin 300 mg via orogastric tube (or 100-300 mg IV), heparin as directed by the interventional cardiologist. His coma is not a reason to withhold PCI; it is too early to prognosticate. If PCI could not be achieved within 120 minutes, fibrinolysis would be considered (prolonged CPR is a relative, not absolute, contraindication).
Forty minutes later, before he leaves for the cath lab, his wife arrives and asks you whether he will wake up "back to normal".
(d) Outline what you would tell her about his neurological prognosis at this stage. 3 marks
Show the rubric and model answer
- Honest that it is too early to know; reliable neurological prognostication is not done before at least 72 hours after ROSC (off sedation, normothermic) (1)
- Favourable features named: witnessed arrest, early bystander CPR, early defibrillation, shockable rhythm, presumed cardiac cause; unfavourable: 18 minutes to ROSC, GCS 3 (1)
- Explains next steps (cath lab, ICU, multimodal assessment: examination, EEG, imaging, biomarkers) and offers support and frequent updates; asks about his values (1)
- I would tell her honestly that it is too early to know. He is in a coma now, which is expected straight after a cardiac arrest, and the brain often takes days to show what has happened.
- There are good signs: the arrest was witnessed, CPR started within two minutes, a defibrillator was used early, and his rhythm was a shockable one caused by a heart attack that can be treated. A concerning feature is that it took 18 minutes to restart his heart.
- Doctors do not make firm predictions until at least 72 hours after the heart restarts, once sedation has worn off and his temperature is controlled, using several tests together: examination, brain wave monitoring (EEG), brain scans and blood markers.
- Next: he is going for an angiogram to open the blocked artery, then to the ICU. The ICU team will update her regularly. I would ask whether he had expressed wishes about treatment, offer a social worker, and check who else needs to come in.
Where candidates lose marks here
- Writing "maintain oxygenation and blood pressure" without numbers: examiners want SpO2 94-98%, PaCO2 35-45 mmHg, MAP at least 65 mmHg, fever prevention for at least 72 hours, glucose 6-10 mmol/L.
- Leaving FiO2 at 1.0: failing to recognise the hyperoxia on the gas loses an easy mark.
- Withholding or delaying angiography because the patient is comatose.
- Giving the family a firm prognosis (good or bad) in the first hour.
- Over-writing part (a) in prose and running short of time for later parts: the gas needs five crisp lines, not a paragraph.
Original content written for Fellowship Ready, for exam preparation only, not clinical advice. Not affiliated with the Australasian College for Emergency Medicine.