Every ACLS provider can recite the H's and T's. Hypovolemia, Hypoxia, Hydrogen ion, Hypo/Hyperkalemia, Hypothermia. Tension pneumo, Tamponade, Toxins, Thrombosis pulmonary, Thrombosis coronary.
But reciting a list is not the same as recognizing one at the bedside during a code.
"Reciting a list under fluorescent classroom lights is not the same skill as finding the cause under a strip of red-flashing monitor alarms."
The 10 causes at a glance
Hypovolemia
Hemorrhage, GI losses, sepsis, burns. Fluids and blood.
Hypoxia
Airway failure, PE, pneumothorax. Secure the airway and oxygenate.
Hydrogen ion (acidosis)
DKA, renal failure, prolonged CPR. Ventilation, sodium bicarb in select cases.
Hypo/Hyperkalemia
Dialysis, diuretics, rhabdo. Calcium, insulin/D50, bicarb.
Hypothermia
Exposure, near-drowning, post-ROSC. Rewarm before calling TOD.
Tension pneumothorax
Vent patients, trauma, central line complications. Needle decompression now.
Tamponade
Malignancy, post-cardiac surgery, penetrating trauma. Pericardiocentesis.
Toxins
Overdose, envenomation. Specific antidotes change the whole algorithm.
Thrombosis (pulmonary)
Massive PE. Thrombolytics during arrest are reasonable.
Thrombosis (coronary)
Acute MI. Post-ROSC cath lab activation is the priority.
Why this matters more than you think
Pulseless Electrical Activity is one of the most survivable cardiac arrests — if the cause is found and fixed fast. The heart wants to beat. Something is stopping it. Your job is to find that something within the first 5 minutes.
The problem: most teams spend those 5 minutes running the arrest algorithm correctly but never seriously interrogating the cause. They push epinephrine every 3–5 minutes and wait. That's not a plan. That's hope.
The clinical framework that actually works
Don't run through all 10 causes sequentially. That takes too long. Instead, use a rapid three-question filter:
1. What was happening 10 minutes before the arrest?
Post-surgical patient → think hemorrhage (hypovolemia) first. Dialysis patient → think hyperkalemia. Intubated patient who suddenly arrested → think tension pneumo immediately. The context before the arrest narrows the differential faster than any physical exam finding.
2. What does the ultrasound show?
If POCUS is available — and it should be — a 10-second cardiac view tells you: Is the heart moving? Is there a pericardial effusion? Is the RV dilated (suggesting massive PE)? This single step eliminates or confirms four of your ten causes.
3. What medications is this patient on?
Toxicologic causes are underdiagnosed in arrest. Beta blockers, calcium channel blockers, digoxin, and TCA overdoses all have specific antidotes that change your resuscitation entirely. The medication list is part of your differential, not an afterthought for the chart.
The ACLSMED approach
In our PEA scenario, we force providers to articulate a cause before the algorithm proceeds. Not guess — articulate. "I think this is tension pneumo because the patient was on positive pressure ventilation and the pressure alarm fired 2 minutes ago." That clinical reasoning is what saves lives. We train it explicitly.
The difference between a provider who recites the H's and T's and one who diagnoses them under pressure comes down to one thing: deliberate practice with immediate feedback. That's what the simulator is for.
Practice finding the cause, not just reciting the list
Run the PEA scenario in the ACLSMED Clinical Suite. The simulator forces you to articulate your reasoning — and shows you what you missed.
Launch the Simulator →