RxPG - Shock Meltdown

In shock you cannot perfuse your body adequately. Eventually, this develops into a vicious cycle. Causes of shock that you must understand....

Cardiogenic shock (i.e., pump failure)
--Massive myocardial infarct
--Rupture (ventricle, valve)
--Diphtheria
--Bad rhythm disturbances ("arrhythmias", a misnomer)
--Certain poisons (remember massive nicotine ingestion)
--Extrinsic compression (i.e., tamponade)

Hypovolemic shock
-Heavy bleeding (4 or more of your 10 pints]
---Externally
---Internally (remember GI bleeds, hemoperitoneum)
-Other fluid loss
---Sweating
---Vomiting
---Diarrhea
---Burns
---Third-space losses (i.e., into effusions or ileus)

Loss of vascular tone (i.e., all vessels opening)
-Septic shock (i.e., from bacterial breakdown products)
-Anaphylaxis (generalized mast-cell degranulation)
-Neurogenic
---Certain poisons (notably war gases)
---Profound anaesthesia
---Spinal cord injury
---Vasovagal (i.e., extreme pain, emotion)

Pulmonary embolism

In shock, the liver enzymes go up (underperfused liver), anaerobiosis causes lactic acidosis (which is bad), and a huge host of chemicals get released which further interfere with physiologic function. Histamine, serotonin, leukotrienes, cachectin, interleukin 1, C3a, C5a, and many other substances dilate vessels, inviting blood to pool in venules (rightly called "congestion"), and/or make small vessels permeable, causing blood to leak out. Some people even blame endorphins. Damaged cells can release thromboplastin, producing DIC. Ischemia of the heart produces the familiar subendocardial infarcts, which doesn't help the pump.

Compensated shock: Blood pressure is maintained in the arms, but you're probably not perfusing your kidneys, gut ("I have stress ulcers!"), skin ("I'm cold"), or muscles. Progressive / decompensated shock: You're dropping your pressure and getting lactic-acidotic. If the cause of your shock is treatable, you will probably survive; your kidneys may be "off" for a few weeks, and "shock lung" may or may not supervene in a few days. Less-fortunate people may have brain damage (if the brain was underperfused), subendocardial heart infarcts, Irreversible shock means your body's been sufficiently damaged by low- flow that you won't recover, period. If your brain's being perfused, you will probably still be lucid, and can talk sensibly, which is a good thing at such a time.

Septic shock (i.e., from bacteria getting a foothold and growing in your bloodstream) is a major mystery of medicine. Nobody really understands what's happening. Lipid A ("endotoxin") dilating vessels and making them leak is part of the problem, but not all. The body's own chemical defenses play some role too.

Copyrights: "The Pathology Guy" - Ed Friedlander MD. Reproduced with permission.