A patient experiencing cardiac arrest (VF, pVT, asystole, and PEA) must be diagnosed and managed quickly. By identifying and treating a reversible condition, responders can help the patient to quickly achieve ROSC. This is the primary importance of treating asystole or PEA. 

To achieve this goal, providers should:

• remember to assess for H & Ts
• quickly assess the cardiac rhythm
• evaluate volume status
• assess for exposure to toxins/drug overdoses.

Responders can use the Hs & Ts to remember the most common and reversible reasons that cardiac or pulmonary arrest occurs in adults.

Cardiac and Pulmonary Arrest Hs and Ts

Related Video: Introduction to the Hs and Ts

The conditions outlined in the H and Ts mnemonic are those that can be treated quickly to reverse potential causes and manage cardiac arrest. There are other conditions that can lead to cardiac arrest; the Hs and Ts are simply ones that can be ruled out quickly. 

While diagnostic tests can help to assess for these conditions, they should not delay the appropriate cardiac arrest management. 

Managing underlying conditions

These H and T conditions should be diagnosed and treated quickly to reverse cardiac arrest.

Related Video: Treating Reversible Causes of PEA and Asystole

Hypovolemia

Common reasons for hypovolemia include hemorrhage (internal or external) and dehydration. Low circulating blood volume can precipitate cardiac arrest and often presents with sinus tachycardia and hypotension with low systolic and high diastolic pressures. With progression, hypotension becomes severe with the sinus tachycardia converting to PEA. Quick restoration of blood volume via IV infusion can temporize the patient until the underlying cause can be treated.

Related Video: Hs and Ts – Hypovolemia

Heart and Lung Conditions

Acute coronary syndromes that cause damage to much of the heart muscle can lead to PEA. This often occurs following to blockage of either the left anterior descending or left main coronary arteries. However, it should be noted that patients with cardiac arrest but no evidence of a pulmonary embolus do not benefit from routine fibrinolytic therapy. 

A large pulmonary embolus (PE) can block blood flow to the lungs, causing a sudden overload on the right heart—and its failure. Fibrinolytic medications should be initiated when providers believe that cardiac arrest is secondary to a suspected large PE. 

Pericardial tamponade can be reversed with fluid resuscitation in the early stages, and subsequent pericardiocentesis should be performed if needed. 

Tension pneumothorax can be treated well if treated urgently with needle thoracostomy and chest tube. 

All of these conditions require a swift diagnosis and management. These conditions (although the evidence for tension pneumothorax is in its infancy) can be diagnosed with well-performed bedside ultrasound.

Related Video: Hs and Ts – Pulmonary Embolism

Related Video: Hs and Ts – Cardiac Tamponade

Related Video: Hs and Ts – Tension Pneumothorax

Related Video: Hs and Ts – Hydrogen Ions

Toxin Exposure and Overdose

Some drugs and toxins can lead to a sudden drop in peripheral vascular resistance and cardiac dysfunction, leading to severe hypotension. If there is a concern for exposure, patients must be treated quickly and aggressively as these agents can cause dysfunction rapidly but then often reverse after their physiological effect is completed.

There are specific procedures that may allow the patient to survive until the condition becomes reversible. Such procedures include:

• Extended CPR
• Extracorporeal CPR (ECPR)
• Intravenous lipid emulsion
• Intra-aortic balloon pump
• Antidotes specific to the toxin
• Transcutaneous pacing
• Management of significant electrolyte imbalances
• Hemodialysis.

Related Video: Hs and Ts – Hypo-Hyperkalemia

Once there is evidence of ROSC, providers should begin post-arrest management.