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August 11, 2010

Understanding the fundamental nature of shock will be a paradigm shift in medicine that will enable more effective resuscitation of our sickest patients.

When a surgeon, intensivist, or other acute care practitioner uses the term “shock”, they are describing something that embodies inadequate energy supply to the body’s living cells.  There have been various descriptions and classifications of shock over the past several decades.  One of the most enduring classifications was by Alfred Blalock in 1937, who defined four principal categories of shock: hypovolemic, cardiogenic, neurogenic, and vasogenic.  To a large degree, this classification has persisted for over 70 years, with some modifications (for example, vasogenic became septic) and additions (like obstructive, anaphylactic, and distributive).   Classification has been helpful because it can guide appropriate treatment.  For example, we give volume for hypovolemic shock because that’s what’s needed.  However, volume administration can exacerbate cardiogenic shock; diuretic drugs to eliminate excess volume and other measures that help the heart pump better are best.

In the case of hypovolemic and cardiogenic shock, the reduced cardiac output delivers inadequate oxygen and nutrients relative to the net tissue demand for those fuels.  In septic shock, the circulation is actually working at a higher level than normal; the fact that we can see evidence of poor cellular metabolism in sepsis therefore suggests that cells are somehow poisoned and unable to use the fuels being delivered. 

Neurogenic shock, on the other hand, is not really shock at all, because energy supply to tissues has not changed.  With pure neurogenic “shock”, patients do not develop the signs of tissue hypoxia, such as acidosis or lactate accumulation.  They simply manifest hypotension, which, unfortunately, the modern-day clinician still believes is causative of tissue hypoperfusion.

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