What are the 5 H's (hypovolemia, hypoxia, hydrogen‑ion (acidosis), hypo/hyper‑kalemia, hypothermia) and 5 T's (tension pneumothorax, cardiac tamponade, toxins, pulmonary embolism, coronary thrombosis) in emergency medicine?

Medical Advisory BoardAll articles are reviewed for accuracy by our Medical Advisory Board
Educational purpose only • Exercise caution as content is pending human review
Article Review Status
Submitted
Under Review
Approved

Last updated: March 30, 2026 • View editorial policy

Have a follow-up question?

Our Medical A.I. is used by practicing medical doctors at top research institutions around the world. Ask any follow up question and get world-class guideline-backed answers instantly.

Ask Question

The 5 H's and 5 T's: Reversible Causes of Cardiac Arrest

During any cardiac arrest resuscitation, systematically evaluate and treat the 5 H's and 5 T's—these are the potentially reversible causes that, if identified and corrected, can restore spontaneous circulation and save lives. 1

The Framework

The 2020 American Heart Association Guidelines for CPR explicitly list these reversible causes as a critical component of advanced cardiac life support 1:

The 5 H's:

  • Hypovolemia - Severe volume depletion
  • Hypoxia - Inadequate oxygenation
  • Hydrogen ion (acidosis) - Severe metabolic or respiratory acidosis
  • Hypo-/hyperkalemia - Potassium abnormalities (and other electrolyte disturbances)
  • Hypothermia - Core body temperature below 35°C

The 5 T's:

  • Tension pneumothorax - Air trapped in pleural space causing cardiovascular collapse
  • Tamponade, cardiac - Fluid in pericardial sac restricting cardiac filling
  • Toxins - Drug overdose or poisoning
  • Thrombosis, pulmonary - Massive pulmonary embolism
  • Thrombosis, coronary - Acute myocardial infarction

Clinical Application During Resuscitation

While performing high-quality CPR cycles, actively search for and treat these reversible causes. The guidelines emphasize that identifying and correcting these conditions is performed concurrently with standard ACLS interventions—not after CPR fails 1.

Practical Approach:

During each 2-minute CPR cycle, the team should:

  • Maintain continuous chest compressions (100-120/min, depth ≥2 inches)
  • Establish IV/IO access for medication delivery
  • Administer epinephrine every 3-5 minutes
  • Simultaneously assess for reversible causes

Key Diagnostic Clues:

Hypovolemia: History of trauma, GI bleeding, or known fluid losses; ultrasound showing collapsed IVC

Hypoxia: Cyanosis, low/absent ETCO2, difficult ventilation; ensure patent airway and adequate oxygenation

Hydrogen ion: Prolonged arrest, diabetic ketoacidosis history; consider sodium bicarbonate in specific scenarios

Hypo-/hyperkalemia: Renal failure, characteristic ECG changes (peaked T-waves for hyperkalemia, flattened T-waves for hypokalemia)

Hypothermia: Environmental exposure, cold to touch; rewarm actively

Tension pneumothorax: Unilateral absent breath sounds, tracheal deviation, difficult ventilation; perform needle decompression

Tamponade: Trauma, recent cardiac procedure, distended neck veins; perform pericardiocentesis or thoracotomy

Toxins: Known ingestion, specific toxidromes; administer antidotes (naloxone, calcium, etc.)

Thrombosis (pulmonary): Risk factors for PE, sudden collapse; consider thrombolytics

Thrombosis (coronary): Chest pain history, ST-elevation on monitor; prepare for emergent catheterization

Critical Pitfalls to Avoid:

  • Don't wait to search for reversible causes—begin evaluation immediately upon starting resuscitation
  • Don't assume "just another cardiac arrest"—young patients, traumatic arrests, and those with known risk factors demand aggressive evaluation for reversible causes
  • Don't delay definitive interventions (needle decompression, pericardiocentesis) if clinical suspicion is high—these are time-critical
  • Don't forget to reassess after each intervention to determine if ROSC has been achieved

The 2024 consensus guidelines further emphasize that in specific populations (such as pediatric pulmonary hypertension), ECMO should be considered before cardiac arrest occurs or for refractory arrest when reversible causes are suspected 2.

References

Related Questions

What is the best time of day to take dutasteride?
What is an appropriate oral prednisone taper regimen for a 100‑lb (≈45‑kg) woman?
In a patient with dysphasia, which specialists should be referred to for evaluation and management?
What is Osteo‑Bi‑Flex oral (dietary supplement)?
When can risperidone be discontinued in a bipolar II patient who was recently hospitalized for a hypomanic episode and is now receiving lithium 300 mg twice daily, quetiapine 50 mg at bedtime, and lorazepam 1 mg as needed for anxiety?
When should patients on systemic corticosteroids receive prophylaxis for Pneumocystis jirovecii pneumonia?

Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.