Hs and Ts
As you are moving through your algorithms during ACLS and PALS, it is important to also consider reversible causes for the emergent condition. Pulseless electrical activity (PEA), asystole, ventricular fibrillation (VFib or VF), and ventricular tachycardia (VTach or VT) may have a reversible cause in your patient (though most often PEA). The reversible causes of PEA can be remembered with a mnemonic of sorts, the H’s and T’s.
The H’s and T’s are 12 reversible conditions, 7 that start with H and 5 that start with T.
- Hypovolemia
- Hypoxia
- Hydrogen ion excess (acidosis)
- Hypoglycemia
- Hypokalemia
- Hyperkalemia
- Hypothermia
- Tension pneumothorax
- Tamponade – Cardiac
- Toxins
- Thrombosis (pulmonary embolus)
- Thrombosis (myocardial infarction)
While it is important to continue to deliver compressions, ventilation, and medications according to the algorithm, it is always best to treat underlying causes of PEA and related conditions as soon as possible.
Potential Cause | How to Identify | Treatments |
| Hypovolemia | Rapid heart rate and narrow QRS on ECG; other symptoms of low volume | Infusion of normal saline or Ringer’s lactate |
| Hypoxia | Slow heart rate | Airway management and effective oxygenation |
| Hydrogen ion excess (acidosis) | Low amplitude QRS on the ECG | Hyperventilation; consider sodium bicarbonate bolus |
| Hypoglycemia* | Bedside glucose testing | IV bolus of dextrose |
| Hypokalemia | Flat T waves and appearance of a U wave on the ECG | IV Magnesium infusion |
| Hyperkalemia | Peaked T waves and wide QRS complex on the ECG | Consider calcium chloride, sodium bicarbonate, and an insulin and glucose protocol |
| Hypothermia | Typically preceded by exposure to a cold environment | Gradual rewarming |
| Tension pneumothorax | Slow heart rate and narrow QRS complexes on the ECG; difficulty breathing | Thoracostomy or needle decompression |
| Tamponade – Cardiac | Rapid heart rate and narrow QRS complexes on the ECG | Pericardiocentesis |
| Toxins | Typically will be seen as a prolonged QT interval on the ECG; may see neurological symptoms | Based on the specific toxin |
| Thrombosis (pulmonary embolus) | Rapid heart rate with narrow QRS complexes on the ECG | Surgical embolectomy or administration of fibrinolytics |
| Thrombosis (myocardial infarction) | ECG will be abnormal based on the location of the infarction | Dependent on extent and age of MI |
*Hypoglycemia is not officially one of the H’s and T’s for adults, but it still can be an important cause of PEA, especially in children. If another reversible cause has not been discovered or if the patient is known to be susceptible to hypoglycemia (e.g., brittle diabetes, past surreptitious use of insulin) then this potential cause of PEA should be considered.
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