Identifying the most common causes of cardiac arrest and how to properly treat them.
The H’s and T’s are a mnemonic used to help remember the causes of cardiac arrest that are most frequently seen in patients experiencing heart failure. Because these underlying causes are oftentimes reversible, the ability to identify what contributed to arrhythmia, and then follow the proper steps to treat that particular cause is a critical aspect of Advanced Cardiac Life Support (ACLS) training.
Although the H’s and T’s are primarily associated with pulseless electrical activity (PEA), they can also be the cause of asystole, ventricular fibrillation (VF), and ventricular tachycardia (VT). It’s important to utilize the patient’s medical history, ECG, and any environmental or situational clues to help diagnose and treat the patient to increase the likelihood of a successful outcome (Return of Spontaneous Outcome or ROSC).
Table of Contents
The H’s of ACLS:
Hypovolemia
What is it?
- A sudden and significant decrease in the volume of blood and fluids in your body.
What causes it?
- Loss of blood (internal or external)
- Inadequate fluid intake
- Excessive diarrhea or vomiting
How to treat it?
- Obtain IV/IO access
- Administer fluids/blood products
Hypoxia
What is it?
- When the body is deprived of sufficient oxygen supply
What causes it?
- Lack of oxygen (due to high altitude, fire, drowning, etc.)
- Lung disease
- Chemical or gas poisoning
How to treat it?
- Ensure the airway is open
- Increase oxygen intake
- Ventilate/intubate
Hydrogen Ions (Acidosis)
What is it?
- Improper pH level caused by too much acid (lactic acidosis) in the body.
What causes it?
- Respiratory: lung disease, the buildup of carbon dioxide, etc.
- Metabolic: DKA/AKA, cancer, liver failure, etc.
How to treat it?
- Respiratory: ventilate
- Metabolic: sodium bicarbonate
Hyper / Hypokalemia (Potassium)
What is it?
- Too much (hyperkalemia) or too little (hypokalemia) potassium in the body
What causes it?
- Kidney disease/failure
- Diuretics
- DKA
How to treat it?
- Hypokalemia: potassium (rapid infusion)
- Hyperkalemia: calcium chloride, sodium bicarbonate, dialysis
Hypothermia
What is it?
- When the body loses the ability to keep itself warm. By definition, hypothermia occurs when body temperature drops below 95˙ F (35˙ C).
What causes it?
- Extreme and/or prolonged exposure to cold weather and/or water.
How to treat it?
- Passive and active warming measures to restore the body to normal temperature.
The T’s of ACLS:
Tension Pneumothorax
What is it?
- When air enters the pleural space but is unable to exit, causing a buildup in the pleural space.
What causes it?
- Mechanical ventilation
- Chest trauma
How to treat it?
- Needle decompression
Tamponade (Pericardial Tamponade)
What is it?
- A buildup of blood or fluid in the pericardial space.
What causes it?
- Chest trauma
- Myocardial rupture
- Pericarditis
How to treat it?
- Pericardiocentesis
Toxins
What is it?
- Intentional or accidental overdose.
What causes it?
- Street drugs (overdose)
- Prescription or CTC drugs (overdose)
- Chemical exposure
How to treat it?
- Specific antidote based on overdose agent
- Support circulation
Thrombosis (Pulmonary Embolus)
What is it?
- Blockage of the lung’s main artery (pulmonary artery).
What causes it?
- Blood clot(s)
- Pulmonary embolism
How to treat it?
- Fibrinolytics
- Thrombolytics
- Embolectomy
Thrombosis (Acute Coronary Syndrome)
What is it?
- Blockage of the heart’s coronary artery/arteries.
What causes it?
- Blood clot(s)
- Myocardial infarction
How to treat it?
- Fibrinolytics
- Percutaneous coronary intervention (PCI)
Related Article: ACLS H's And T's Video
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