Episode 24: Shock

A useful way to think about shock is to start with one question: Why is oxygen delivery failing? Oxygen delivery to tissues, abbreviated as DO2, can fail for four major circulatory reasons.

The patient may have lost intravascular volume, blood volume may be maldistributed, the heart may be unable to pump effectively, or venous return and cardiac filling may be obstructed.

Those mechanisms correspond to the four classic circulatory shock categories, hypovolemic, distributive, cardiogenic, and obstructive shock.

But circulatory failure isn't the only way tissues become oxygen starved.

Shock can also develop when arterial oxygen content is inadequate or when tissues can't appropriately utilize oxygen being delivered.

But circulatory failure isn't the only way tissues become oxygen starved.

Shock can also develop when arterial oxygen content is inadequate or when tissues can't appropriately utilize the oxygen being delivered.

Hypoxic shock occurs when oxygen content is too low, such as with severe anemia, severe pulmonary disease, carbon monoxide toxicity, or methemoglobinemia.

Metabolic shock occurs when tissues can't effectively use oxygen despite adequate delivery, such as with hypoglycemia, cyanide toxicity, mitochondrial dysfunction, or the cytopathic hypoxia seen in sepsis.

So right away, this is important.

A patient can have more than one kind of shock at the same time, and in fact, that's common.

Before we get into the categories, let's zoom all the way down to the cell because that's where this starts to matter.

When cells can't make enough energy, membrane ion pumps begin to fail.

One key example is the sodium potassium adenosine triphosphate pump or sodium potassium ATPase.

Once that pump fails, cells begin to retain excess sodium.

The cells swell, contents leak out, pH regulation breaks down, and the downstream consequences start stacking up.

You get systemic acidemia, endothelial dysfunction, and activation of both inflammatory and anti-inflammatory cascades.

That's why shock isn't just low blood pressure.

It's a cellular energy crisis.

A useful way to think about shock is to start with one question: Why is oxygen delivery failing? Oxygen delivery to tissues, abbreviated as DO2, can fail for four major circulatory reasons.

The patient may have lost intravascular volume, blood volume may be maldistributed, the heart may be unable to pump effectively, or venous return and cardiac filling may be obstructed.

Those mechanisms correspond to the four classic circulatory shock categories, hypovolemic, distributive, cardiogenic, and obstructive shock.

But circulatory failure isn't the only way tissues become oxygen starved.

Shock can also develop when arterial oxygen content is inadequate or when tissues can't appropriately utilize oxygen being delivered.

But circulatory failure isn't the only way tissues become oxygen starved.

Shock can also develop when arterial oxygen content is inadequate or when tissues can't appropriately utilize the oxygen being delivered.

Hypoxic shock occurs when oxygen content is too low, such as with severe anemia, severe pulmonary disease, carbon monoxide toxicity, or methemoglobinemia.

Metabolic shock occurs when tissues can't effectively use oxygen despite adequate delivery, such as with hypoglycemia, cyanide toxicity, mitochondrial dysfunction, or the cytopathic hypoxia seen in sepsis.

So right away, this is important.

A patient can have more than one kind of shock at the same time, and in fact, that's common.

Before we get into the categories, let's zoom all the way down to the cell because that's where this starts to matter.

When cells can't make enough energy, membrane ion pumps begin to fail.

One key example is the sodium potassium adenosine triphosphate pump or sodium potassium ATPase.

Once that pump fails, cells begin to retain excess sodium.

The cells swell, contents leak out, pH regulation breaks down, and the downstream consequences start stacking up.

You get systemic acidemia, endothelial dysfunction, and activation of both inflammatory and anti-inflammatory cascades.

That's why shock isn't just low blood pressure.

It's a cellular energy crisis.