Reversible Causes of Cardiac Arrest – The H’s and T’s

Reversible Causes of Cardiac Arrest – The H’s and T’s

In cardiac arrest, once ACLS algorithms are followed but ROSC is not achieved, evaluate for reversible causes. These are the H’s (6) and T’s (5) — 11 total causes to systematically assess and treat.

The H’s

1. Hypovolemia

   • Causes: blood loss, dehydration, vomiting, diarrhea, burns, sepsis (relative).

   • Signs: tachycardia, hypotension, history of fluid loss, possible fever.

   • Treatment: establish IV/IO access, give fluids; blood products if hemorrhage.

2. Hypoxia

   • Causes: respiratory failure, airway obstruction.

   • Signs: low SpO₂, cyanosis, ABG abnormalities.

   • Treatment: provide O₂, ventilate, intubate if needed, confirm tube placement (equal chest rise, ETCO₂). Consider VV-ECMO if refractory.

3. Hydrogen ions (acidosis)

   • Causes:

     • Respiratory → CO₂ retention.

     • Metabolic → sepsis, DKA, ingestions, alcoholic ketoacidosis.

   • Assessment: ABG to differentiate respiratory vs metabolic.

   • Treatment:

     • Respiratory: ventilate.

     • Metabolic: treat underlying cause; consider sodium bicarbonate.

4. Hypo-/Hyperkalemia

   • Hypokalemia (<3.5, symptoms often <2.7): causes = vomiting, diarrhea, diuretics.

     • Signs: flat/inverted T-waves, U-waves.

     • Treatment: K⁺ replacement (not too rapidly).

   • Hyperkalemia (>5.5): causes = renal failure, DKA, trauma, burns, hemolysis, rhabdo.

     • Signs: peaked T-waves, wide QRS.

     • Treatment: calcium (cardiac protection), insulin + D50, albuterol, bicarbonate, diuretics/Kayexalate, dialysis if severe.

5. Hypoglycemia

   • Signs: very low glucose on POC check.

   • Treatment: administer D50 IV immediately.

6. Hypothermia

   • Definition: <35°C; cardiac depression pronounced <30°C.

   • Causes: exposure, environmental.

   • Treatment: active/passive rewarming (blankets, Bair Hugger, warm IV fluids).

The T’s

1. Toxins

   • Examples: CCBs, beta-blockers, digoxin, TCAs, cocaine.

   • Assessment: EKG (QT prolongation, arrhythmias), history, pupils, tox screen.

   • Treatment: supportive care, administer antidotes if available.

2. Tamponade (cardiac)

   • Causes: post-op cardiac surgery, post-cath, aortic dissection, trauma (penetrating), malignancy, pericarditis.

   • Signs: Beck’s triad (JVD, muffled heart sounds, hypotension), PEA arrest, echo.

   • Treatment: pericardiocentesis or surgical drainage.

3. Tension Pneumothorax

   • Causes: trauma, central line placement, barotrauma from ventilation.

   • Signs: JVD, tracheal deviation, unilateral absent breath sounds, difficulty ventilating, hypotension.

   • Treatment: immediate needle decompression → chest tube placement.

4. Thrombus

   • Coronary (MI): chest pain, ischemic EKG changes.

     • Treatment: cath lab PCI, thrombolytics, possible CABG.

   • Pulmonary (PE): sudden SOB, hypoxia, tachycardia, large PE may cause RV failure.

     • Treatment: embolectomy, thrombolytics, VA-ECMO if available.

5. Trauma

   • Causes: blunt/penetrating trauma, hemorrhage, airway disruption.

   • Assessment: primary/secondary survey findings.

   • Treatment: depends on cause (surgical repair, transfusion, decompression).

Quick Recall Strategy

• Monitor clues: BP (hypovolemia), SpO₂ (hypoxia), Temp (hypothermia).

• Labs: ABG (acidosis), K⁺, glucose.

• Heart/Lungs: MI (thrombus), tamponade, tension pneumothorax, hypoxia.

• Whole body: toxins, trauma.

Total: 11 causes (6 H’s, 5 T’s)
Memorize and run through systematically during every code.