Wednesday 7 December 2005
Shock is the final common pathway for a number of potentially lethal clinical events, including severe hemorrhage, extensive trauma or burns, large myocardial infarction, massive pulmonary embolism, and microbial sepsis.
Regardless of the underlying pathology, shock gives rise to systemic hypoperfusion caused by reduction either in cardiac output or in the effective circulating blood volume.
The end results are hypotension, followed by impaired tissue perfusion and cellular hypoxia. Although the hypoxic and metabolic effects of hypoperfusion initially cause only reversible cellular injury, persistence of shock eventually causes irreversible tissue injury and can culminate in the death of the patient.
low cardiac output
- cardiogenic shock
- hypovolemic shock
neurogenic shock in spinal cord injury
anaphylactic shock (generalized IgE-mediated hypersensitivity response)
The mechanisms underlying cardiogenic and hypovolemic shock are fairly straightforward, essentially involving
cardiogenic shock results from myocardial pump failure. This may be caused by intrinsic myocardial damage (infarction), ventricular arrhythmias, extrinsic compression (e.g. cardiac tamponade), or outflow obstruction (e.g. pulmonary embolism).
hypovolemic shock results from loss of blood or plasma volume. This may be caused by hemorrhage, fluid loss from severe burns, or trauma.
septic shock is caused by systemic microbial infection. Most commonly, this occurs in the setting of gram-negative infections (endotoxic shock), but it can also occur with gram-positive and fungal infections.
- visceral ishemia
- cerebral ishemia
- cardiac ishemia