What are the Hs and Ts?

The Hs and Ts are a mnemonic aid used to remember the possible reversible causes of cardiac arrest. A variety of disease processes can lead to cardiac arrest. However, they usually boil down to one or more of the Hs and Ts that will be outline below.

The Hs and Ts are just one small part of a greater systematic approach to patient assessment. This systematic approach can be summed up as:

  1. BLS Assessment
  2. Primary Assessment (A, B, C, D, and E)
  3. Secondary Assessment (SAMPLE, Hs and Ts)

As you can see above, the Hs and Ts are part of an ACLS provider’s secondary assessment. A secondary assessment in ACLS is the process of differentiating between two or more conditions that share similar signs and symptoms. This includes a focused medical history, as well as thoroughly searching through the Hs and Ts for any intriguing underlying causes that may have contributed to the patient’s condition.

In a nutshell, the Hs and Ts help healthcare providers make sure they aren’t overlooking any likely or dangerous possibilities. The Hs and Ts help create a road map for ACLS providers as they attempt to find possible diagnoses and the ensuing interventions and treatment options for their patients.

The Hs and Ts are a tried and true reminder that can help ACLS providers rule out some possibilities and also confirm other possibilities.

While the Hs and Ts are part of a healthcare provider’s secondary assessment, there are a few specific conditions or scenarios in which they could be more valuable. These include:

Hs and Ts: Common Causes of Cardiac Arrest

Now that you understand what the Hs and Ts are, when they are used by ACLS providers, and specific situations when they may be most valuable, let’s get into the specific Hs and Ts.

The Hs

  1. Hypovolemia – can often be corrected with fluid replacement.
  2. Hypoxia – can be corrected with appropriate oxygenation and tissue perfusion.
  3. Hydrogen ion or acidosis (respiratory or metabolic) – if respiratory, you can correct it with oxygen and respirations, and if metabolic, you might need sodium bicarbonate to correct it.
  4. Hypokalemia – when dealing with hypokalemia, you may need to administer potassium.
  5. Hyperkalemia – when dealing with hyperkalemia, you need to administer calcium chloride.
  6. Hypothermia

The Ts

  1. Tension pneumothorax – can often be relieved with needle decompression and later with a chest tube.
  2. Cardiac tamponade – this would require surgical intervention to correct.
  3. Toxins
  4. Pulmonary thrombosis – this would require a corrective procedure or thrombolytic therapy.
  5. Coronary thrombosis – the same as above is applicable, but additionally, treatment may also include percutaneous coronary intervention, commonly known as PCI.

It should be noted that the most common causes of pulseless electrical activity (PEA) are hypoxia and hypovolemia, and both are potentially reversible. Which is why ACLS providers must look for evidence of these problems when assessing their patients.

The importance of the Hs and Ts cannot be overstated. Healthcare providers should attempt to identify and correct an underlying cause of cardiac arrest if one is present. It’s vital that healthcare providers stop, think, and ask, Why did this person have this cardiac arrest at this time? It is essential to search for and treat any and all reversible causes.

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