Shock is a critical medical emergency that occurs when the body's tissues don't receive adequate blood flow and oxygen. This leads to cellular dysfunction and can rapidly progress to organ failure if not treated promptly. Understanding shock requires examining both its underlying causes and the complex pathological processes that follow.
Shock can be classified into four main categories based on its underlying cause. Hypovolemic shock results from significant blood or fluid loss, such as hemorrhage or severe dehydration. Cardiogenic shock occurs when the heart fails to pump effectively, often due to heart attack or severe heart failure. Distributive shock involves widespread blood vessel dilation, commonly seen in sepsis or severe allergic reactions. Finally, obstructive shock is caused by physical blockages that prevent normal blood flow, such as blood clots in the lungs or fluid around the heart.
The pathophysiology of shock involves a cascade of cellular events. When tissue perfusion decreases, cells become hypoxic and must switch from efficient aerobic metabolism to less efficient anaerobic metabolism. This produces lactic acid instead of adequate ATP, leading to metabolic acidosis. As ATP levels drop, cellular pumps fail, causing cell swelling and dysfunction. This cellular damage progresses to organ dysfunction and ultimately multi-organ failure if the shock state persists.
Initially, the body attempts to compensate for shock through several mechanisms. The heart rate increases to maintain cardiac output, blood vessels constrict to redirect blood to vital organs, the kidneys retain fluid to maintain blood volume, and breathing increases to improve oxygenation. Hormones like adrenaline and vasopressin are released to support these responses. However, these compensatory mechanisms are limited and eventually become overwhelmed, leading to decompensated shock where organ systems begin to fail progressively.