What are the factors that make shock progressive?

In the progressive stage, there is hypotension indicating that even the maximum compensatory responses are inadequate. Moreover, the blood pressure falls continuously, which indicates that a vicious cycle has started? Somewhere along this vicious cycle is a point of no return. Therapeutic interventions before this point can restore normalcy.

However, beyond this point, all interventions are ineffective and the shock is called irreversible.

The vicious cycle occurs due to the following reasons:

Cardiac Depression:

When the arterial pressure falls low enough, coronary blood flow decreases below that required for adequate nutrition of the myocardium itself. This weakens the heart and thereby decreases the cardiac output still more. Thus, a positive feedback cycle develops whereby the shock becomes more and more severe.

Vasomotor Failure:

In the late stages, the diminished blood flow to the vasomotor center depresses the center itself so that it becomes progressively less active and sympathetic discharge decreases.

Thrombosis and sludging:

The sluggish blood flow during shock leads to thrombosis in the micro-vessels. The cells stick to each other makes it more difficult for blood to flow through the microvasculature (sludging of blood).

Increased capillary permeability:

Prolonged capillary hypoxia results in increase in capillary permeability, and large quantities of fluid begin to transude into the tissues. This further decreases the blood volume, aggravating the shock.

Release of toxins by ischemic tissues:

Endotoxin is a toxin released from dead gram-negative bacteria in the intestines. Diminished blood flow to the intestines causes enhanced formation and absorption of this toxic substance. Endotoxin causes extensive vascular dilatation, increased cellular metabolism despite the inadequate nutrition of the cells, and cardiac depression. It plays a major role in septic shock.

Acidosis in shock

The poor delivery of oxygen to the tissues greatly diminishes oxidative metabolism and the cells switch to anaerobic glycolysis. This leads to accumulation of lactic acid in the blood. Moreover, the sluggish blood flow through tissues also results in accumulation of CO2in tissues. The CO2 dissolves in water to produce H⁺ ions and causing acidosis. Acidosis causes vasodilatation which aggravates the shock, which in turn causes more acidosis. Thus, another vicious cycle is initiated.