Shock and Pathophysiology of Shock

Shock and Pathophysiology of Shock

Circulatory Shock

Circulatory shock means generalized inadequate blood flow through the body, to the extent that the body tissues are damaged because of too little flow, especially because of too little oxygen and other nutrients delivered to the tissue cells such as the brain, heart, liver, kidneys, abdominal viscera and other. Shock represents an imbalance between oxygen demand and delivery. Early in its course, shock may be reversible with proper diagnosis and effective treatment. However, if shock remains untreated, irreversible shock develops and death becomes inevitable. Inadequate oxygen delivery, in severe and/or persistent shock leads to irreversible cell injury; even the cardiovascular system itself-the heart musculature, walls of the blood vessels, vasomotor system, and other circulatory parts-begins to deteriorate, so that the shock, once begun, is prone to become progressively worse thus, only rapid restoration of oxygen delivery can reverse the progression of the shock state. Three things, the heart, circulating blood volume and the peripheral resistance are needed to maintain a normal blood pressure and tissue perfusion. The heart is a driving force to eject oxygenated blood in to the systemic circulation. There must be sufficient blood volume in the body to be pumped by the heart into the arteries and thence to the tissue capillaries. The veins collect the blood and return it to the heart. If the blood volume falls then the patient can go into shock. The peripheral resistance is the state of the small arteries (arterioles) and capillaries to constrict or dilate. If the peripheral resistance is high, it means that these small vessels are constricted. If the peripheral resistance is low, these vessels are dilated. A low peripheral resistance can result in low blood pressure. The blood tends to stagnate or pool in the dilated peripheral vessels. The volume of blood returning to the heart is reduced, so the blood pressure falls.

Certain drugs, e.g. anaesthetic agents thiopentone and halothane, tend to lower blood pressure, mainly by causing peripheral vasodilatation. Sepsis may also induce shock by vasodilatation.

Pathophysiology of Shock

Shock stimulates a physiologic response. This circulatory response to hypotension is to conserve perfusion to the vital organs (heart and brain) at the expense of other tissues. Progressive vasoconstriction of skin, splanchnic (viscera or internal organ) and renal vessels leads to renal cortical necrosis and acute renal failure. If not corrected in time, shock leads to organ failure and sets up a vicious circle with hypoxia and acidosis.