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Shock

Shock is a life-threatening condition characterized by poor oxygen delivery to the tissues for a variety of reasons. It is something we commonly see in the ICU, so recognizing it and knowing how to treat it is essential to becoming a provider in critical care medicine.

Prior to the 1930s, the main type of shock that was recognized was hypovolemic shock although they did not directly recognize it at the time. They noticed that in trauma patients, if they did not bleed to death, they would often have post-traumatic shock that was called "wound shock". The belief was that the wound would release toxins that resulted in neurogenic vasodilation and blood pooling. Later, more groups came out with the idea that it wasn't necessarily from toxins, but from loss of fluids in general.

In 1934, Dr. Blalock first defined the types of shock:

  1. Hematologic/oligemic
  2. Cardiogenic
  3. Neurogenic
  4. Vasogenic

And later in 1967 Shubin and Weil proposed more types of shock. These were added to those listed above:

  1. Hypersensitivity
  2. Bacteremic
  3. Obstructive
  4. Endocrinologic

Early Developments of Septic Shock

Dr. Swan and Dr. Ganzs noticed that there were two types of bacteremic (i.e. septic) shock - "warm shock" which was associated with high cardiac output state and "cold shock" which was associated with a low cardiac output state. They noticed that there was a period of hyperdynamic heart function, the "warm shock"; if their disease progressed past this it would develop into "cold shock". Even more importantly they noticed that the development of cold shock was associated with death, and therefore death by septic shock was subsequently from a low cardiac output state. At the time, studies they did on animals supported this.

As we know today, septic shock is a high cardiac output state, so why did they believe this?

  1. There was no way to measure CO at bedside
  2. CVP was used as a surrogate for LVEDV (heart function), which we now know is inaccurate and inappropriate

Dr. Wilson first came up with the idea that septic shock was a high CO, low SVR state, but nobody believed him because he didn't have the evidence to back it up.

The Invention of the SGC

Dr. Forssman was the first person to place a catheter in the heart - on himself. He went to the OR; inserted a catheter into his ventricle and climbed up the starwell to radiology in order to confirm its placement. He was subsequently fired by his group and decided to take up urology.

After that time, advancements were made; the first heart cath was done and they began to put catheters into the heart regularly. In 1970 Dr. Swan and Dr. Gans then had the idea to push a pulmonary artery catheter into a dogs heart in order to assess it's cardiac output. It worked - an they immediately did it to a patient with MI afterward being able to successfully measure their hearts function. With the invention of the Swan Ganz catheter, we were finally able to get cardiac output.

This is when Dr. Wilson's description of shock as a high cardiac output, low SVR state became more widely accepted. Even later it was shown by Dr. Clavin through portable radionucleide cineangiography that septic shock caused reversible myocardial dysfunction that last for 7-10 days; that CO was indeed high.

New Types of Shock Emerge

In 1972, Hinshaw and Cox proposed a classification of shock based on hemodynamics. This was primarily due to the invention of the SGC. The previous types of shock were scrapped, and the following were proposed:

  1. Distributive
  2. Cardiogenic
  3. Neurogenic
  4. Hypovolemic

These are the types of shock that we seek to understand in our practice today.

See our core content (shock) podcast: click here

Part 1: The Differentiating Different Types

FCCS Ch. 7

Marino 3rd ed: Ch 12-14; 4th ed: Ch 11-12

Medcram: Shock part 1 and 2

Part 2: In-depth interpretation and management

FCCS Ch. 6

Marino 3rd ed: Ch. 9, 10; 4th ed: Ch 7-10

Vasopressors

EmCrit Podcast 138: Vasopressor Basics

AHA 2008: Inotropes and Vasopressors (Drive)

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