Advanced Life Support (ALS) Level 3 (VTQ)

117 videos, 6 hours and 42 minutes

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The 4 H's

Video 41 of 117
3 min 38 sec
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Identifying and Reversing Reversible Causes of Cardiac Arrest


Cardiac arrest can often be caused by reversible factors known as the 4 Hs and 4 Ts. In this discussion, we will explore each of these individually to understand how we can identify and potentially reverse the causes of cardiac arrest.

The 4 Hs


Hypoxia is a common contributor to cardiac arrest, especially in younger patients and children. Providing high-quality ventilation as part of our management can reverse hypoxia.


Hypovolemia, often caused by trauma, anaphylaxis, or cardiogenic shock, can lead to cardiac arrest. Administering fluids as part of cardiac arrest management can reverse hypovolemia. Note that traumatic hypovolemic arrest should not be overlooked, and patients require transport to a hospital for further evaluation, especially in cases of gunshot or shrapnel wounds.

In some cases, hemostatic dressings or zoledronic acid may be used to control bleeding in pre-hospital settings.


Hypothermia is a concern in colder environments, and immersion in cold water can lead to cardiac arrest. Patients with hypothermia may have undetectable pulses, and continuous CPR is essential until the patient is normothermic. Take precautions when moving hypothermic patients, as they are at risk of ventricular fibrillation. Limiting shocks and adrenaline doses during the arrest scenario is advisable.

Remember, "They are not dead until they are warm and dead."

The 4 Ts

Metabolic Imbalances (Hyperions)

Metabolic imbalances such as hyperkalemia or hypokalemia can contribute to cardiac arrest. In pre-hospital settings, it may be challenging to confirm these imbalances. They can be suspected in acidotic patients, but definitive diagnosis often requires blood gas analysis in a hospital setting.

Blood gas results can help identify the cause of the arrest and guide appropriate management.