Shock

Definition:  Shock is a state in which there is failure of the circulatory system to maintain adequate cellular perfusion resulting in widespread reduction in delivery of oxygen & other nutrients to tissues. In shock, the mean arterial pressure is less than 60 mmHg or the systolic blood pressure is less than 90 mmHg. 

 • Regardless of the underlying pathology, shock constitutes systemic hypoperfusion due to reduction either in cardiac out put or in the effective circulating blood volume.

The end results are hypotension followed by impaired tissue perfusion and cellular hypoxia. 

•  Adequate organ perfusion depends on arterial blood pressure (BP) which, in turn, depends on: 

1.  Cardiac output (CO) 

2.  Peripheral vascular resistance (PVR) 

•  CO = stroke volume X heart rate 

In turn, stroke volume depends on:

a)  Preload i.e. blood volume, 

b)  Afterload i.e. arterial resistance, &

c) Myocardial contractility.

•  Therefore, shock (i.e. widespread decreased perfusion of tissues) occurs when the preload (i.e. the blood volume) is decreased, or when the afterload (the peripheral vascular resistance) is decreased, or when the myocardium fails to contract. These basic mechanisms of shock are used to classify it. Next, we will look at the classification of shock.

 Classification of shock 

 Shock can be divided into:

A. Hypovolemic shock

B. Cardiogenic shock

C. Distributive shock

References

Bezabeh ,M. ; Tesfaye,A.; Ergicho, B.; Erke, M.; Mengistu, S. and Bedane,A.; Desta, A.(2004). General Pathology. Jimma University, Gondar University Haramaya University, Dedub University.