SHOCK, not the zappy kind, the uh oh kind.

SHOCK:

Shock is a term used to refer to a state of inadequate tissue perfusion, leading to cellular hypoxia, anaerobic metabolism, and acidosis. Hypoperfusion of tissues has several causes, including traumatic, volume depletion, pump failure, vasodilation, etc. Shock is not a specific illness in itself, but represents the systemic manifestation of a pathological process.

Tissue perfusion requires 3 components:

1. A functioning heart

2. Adequate fluid volume

3. A vascular system capable of dynamic changes to maintain circulatory pressures.

If any of these 3 mechanisms is affected, shock will occur.

Stages of shock:

• Compensated shock: This occurs immediately following the insult that initiates a shock state. Compensatory mechanisms in the body take over to maintain Mean Arterial Pressure (MAP). On average, MAP is approximately 65mmHg. In response to decreased BP, baroreceptors trigger vasoconstriction, increase in heart rate, and activation of the RAAS. Early signs may be pallor, and tachycardia, with a relatively normal blood pressure.

• Decompensated Shock: Because compensatory mechanisms are energy expensive, they do eventually fail. We typically say a patient is in the decompensated phase when we begin to notice a drop in blood pressure.

• Irreversible shock: Once BP becomes terminally low, CO falls, and vascular collapse occurs. There is significant end organ damage. During compensation, blood was shunted away from the liver, kidneys, and other organs in order to maintain cerebral perfusion. At this point we start to see cell death in these organs, that is irreversible. The end result is MODS, and ultimately the patient will die.

Types of shock:

There are 4 broad categories of shock:

1. Hypovolemic

2. Cardiogenic

3. Obstructive

4. Distributive

Hypovolemic Shock:

This occurs due to depletion of vascular fluid volume, resulting in drop in MAP, and vascular collapse. There are several causes including: hemorrhage, dehydration, and fluid third spacing to name a few. There is not enough fluid in the pipeline, and increases in CO and SVR are not capable of improving MAP.

Cardiogenic shock:

Failure of the pump. The heart itself becomes unable to beat effectively enough to maintain MAP. This can be due to ischemia, arrhythmia, cardiomyopathy, or even fluid overload.

Obstructive shock:

This is mechanical impedance to blood flow in the vasculature. Common causes include: PE, Tamponade, Tension Pneumothorax, and compressive forces.

Distributive shock:

This occurs when the blood vessels lose tone, dilating and reducing SVR. This causes a drop in MAP. Common causes are anaphylaxis, spinal injury, neurological disorders, and electrolyte imbalances.

Treatment of shock:

Ultimately the definitive treatment involves addressing the cause of the shock state. A patient with a heart block will be in a state of cardiogenic shock. Our treatment is to pace this patient and improve CO, raising MAP. The patient with profound hemorrhage needs a transfusion of blood products and fluids in order to correct a hypovolemic state. Anaphylaxis can be corrected by stopping the immune response with Epinephrine and Benadryl, and providing isotonic fluid replacement.

Regardless of the cause, the goal is to raise MAP to levels sufficient to perfuse the brain and the organs, reversing the trajectory toward irreversible shock. ALS providers may make use of vasopressors such as Norepi, or dopamine, to improve SVR, while utilizing IV fluid replacement. A good assessment and identification of the cause is our primary goal.