Distributive shock

Distributive shock is a critical medical condition involving the abnormal distribution of blood flow. It occurs within the smallest blood vessels of the body. This improper distribution leads to inadequate blood supply to vital tissues and organs. This lack of supply means cells do not receive enough oxygen to meet their metabolic needs. Shock is divided into four main categories. Distributive shock is unique among them. In other types of shock, the heart often fails to pump enough blood. However, in distributive shock, the heart output remains at or above normal levels.

The mechanism of this condition involves a failure in how blood vessels respond to signals. In a healthy body, blood vessels can tighten or widen to control flow. In distributive shock, vessels lose this normal responsiveness to vasoconstrictive agents. They may also undergo direct vasodilation, which means they widen too much. In septic shock, the endothelial cells lining the vessels are specifically affected. These cells lose their glycocalyx, which is a normal protective coating. They also lose their negative ionic charge. This causes the vessels to become leaky. Furthermore, these cells produce an extensive over-expression of nitric oxide. This chemical contributes to the loss of vessel tone.

Scientists Elbers and Ince have identified five distinct classes of abnormal microcirculatory flow. They used a tool called side stream dark field microscopy to observe these changes. Class I occurs when all capillaries are stagnant while venular flow is normal or sluggish. Class II features empty capillaries located next to those with flowing red blood cells. Class III involves stagnant capillaries positioned next to those with normal blood flow. Class IV is characterized by hyperdynamic flow next to stagnant capillaries. Finally, Class V involves widespread hyperdynamic flow throughout the microcirculatory system. These classes help doctors understand how blood is moving through the smallest vessels.

There are four primary types of distributive shock based on their causes. Septic shock is the most common type and is caused by infection. These infections can be caused by bacteria, viruses, fungi, or parasites. Neurogenic shock results from a loss of vascular tone. This is often due to damage to the central nervous system, such as a spinal cord injury. Anaphylactic shock is a type caused by severe allergic reactions. Finally, adrenal crisis causes distributive shock through inadequate steroid hormones.

The causes of these conditions are diverse and complex. Sepsis often starts in the chest, abdomen, or genitourinary tract. Other causes of distributive shock include systemic inflammatory response syndrome (SIRS). This can be triggered by non-infectious issues like burns, trauma, or pancreatitis. Anaphylaxis is triggered by a massive release of histamine from mast cells. This happens when antibodies called immunoglobulin E bind to antigens. Neurogenic shock can also follow the rupture of a hollow organ. This causes peritoneal irritation and strong vagal activation. This leads to widespread vasodilation and a slower heart rate, known as bradycardia.

Medical treatment focuses on two main goals: reversing the cause and achieving hemodynamic stabilization. Doctors often start with fluid resuscitation to support blood volume. They may also use vasoactive drugs, including vasopressors and inotropes. For anaphylactic shock, epinephrine is the standard treatment. In cases of septic shock, antimicrobial drugs are used to fight the infection. Some infections, such as necrotizing fasciitis or an abscess, may require surgical intervention. If a patient does not respond to fluids or vasopressors, hydrocortisone may be administered.

Research continues into how to best manage this condition. The Surviving Sepsis Campaign is an international group of experts studying these issues. They are currently researching whether crystalloid fluids are better than colloid fluids. Researchers are also investigating drugs like methylene blue. This drug may inhibit the NO-cGMP pathway, which plays a role in the shock. Another investigated drug is pyridoxalated hemoglobin polyoxyethylene, which scavenges nitric oxide from the blood. Understanding these pathways is vital because septic shock is a leading non-cardiac cause of death in intensive care units.