Types of Shock.

    SHOCK is a state of inadequate tissue perfusion, leading to tissue hypoxia and organ dysfunction. 
    Shock is classified according to one of four mechanisms:

• Hypodynamic shock:
•  hypovolemic, 
• cardiogenic, 
• obstructive.
• Hyperdynamic shock:
• distributive.

    1. Hypovolemic shock occurs with the depletion of effective intravascular volume, due to insufficient intake, excessive loss, or both. 

Common causes include:

• dehydration,
• acute hemorrhage, 
• gastrointestinal and renal losses, 
• interstitial fluid redistribution occurring in the context of severe tissue trauma, burn injuries, or pancreatitis. 

Hemorrhage is the most common cause of shock in trauma patients and has been categorized by the American College of Surgeons into four classes, providing a correlation between the percentage of total blood volume lost and the expected attendant physiologic changes in mental status, blood pressure, heart rate, respiratory rate, and urine output. Hemodynamically, hypovolemic shock is characterized by decreased cardiac output, decreased filling pressures, and increased systemic vascular resistance (SVR).

2.  Cardiogenic shock is defined as persistent hypotension and inadequate tissue perfusion due to primary cardiac dysfunction occurring in the context of adequate intravascular volume and adequate or elevated left ventricular filling pressures. It may be caused by abnormalities of heart rate, rhythm, or contractility, although it occurs most commonly after extensive acute myocardial infarction (AMI) or ischemia leading to left or right ventricular failure. Other etiologies of cardiogenic shock

include acute (e.g., tako-tsubo) and chronic cardiomyopathies, myocarditis, and myocardial contusion. The hemodynamic profile of cardiogenic shock is characterized by decreased cardiac output, increased filling pressures, and increased SVR.

3. Obstructive shock occurs as a result of an impediment to the normal flow of blood either to or from the heart, producing impairment of venous return or arterial outflow.

Common causes include tension pneumothorax, abdominal compartment syndrome, pulmonary embolism, pericardial tamponade, auto-PEEP, severe aortic stenosis, dissecting aortic aneurysm, and severe aortic coarctation. Hemodynamically, obstructive shock is characterized by decreased cardiac output, increased filling pressures, and increased SVR.

4. Distributive shock is characterized by normal or high cardiac output and a low SVR. In the critical care setting, it is most commonly caused by sepsis. Other etiologies include neurogenic shock, anaphylaxis, adrenal insufficiency, hepatic

failure, and high-output arteriovenous fistulae.

Read also:

• Acceptable blood loss in cardiac surgery

• AAGBI guidelines: the use of blood components and their alternatives 2016