Shock (circulatory)
Shock is the state of insufficient blood flow to the tissues of the body as a result of problems with the circulatory system.[1][2] Initial symptoms of shock may include weakness, fast heart rate, fast breathing, sweating, anxiety, and increased thirst.[1] This may be followed by confusion, unconsciousness, or cardiac arrest, as complications worsen.[1]
For other uses, see Shock (disambiguation).Shock
Initial: Weakness, fast heart rate, fast breathing, sweating, anxiety, increased thirst[1]
Later: Confusion, unconsciousness, cardiac arrest[1]
Low volume: Severe bleeding, vomiting, diarrhea, dehydration, or pancreatitis[1]
Cardiogenic: severe heart attack (especially of the left or right ventricles), severe heart failure, cardiac contusion[1]
Obstructive: Cardiac tamponade, tension pneumothorax[1]
Distributive: Sepsis, spinal cord injury, certain overdoses[1]
Based on symptoms, physical exam, laboratory tests[2]
Based on the underlying cause[2]
Risk of death 20 to 50%[3]
1.2 million per year (US)[3]
Shock is divided into four main types based on the underlying cause: hypovolemic, cardiogenic, obstructive, and distributive shock.[2] Hypovolemic shock, also known as low volume shock, may be from bleeding, diarrhea, or vomiting.[1] Cardiogenic shock may be due to a heart attack or cardiac contusion.[1] Obstructive shock may be due to cardiac tamponade or a tension pneumothorax.[1] Distributive shock may be due to sepsis, anaphylaxis, injury to the upper spinal cord, or certain overdoses.[1][4]
The diagnosis is generally based on a combination of symptoms, physical examination, and laboratory tests.[2] A decreased pulse pressure (systolic blood pressure minus diastolic blood pressure) or a fast heart rate raises concerns.[1] The heart rate divided by systolic blood pressure, known as the shock index (SI), of greater than 0.8 supports the diagnosis more than low blood pressure or a fast heart rate in isolation.[5][6]
Treatment of shock is based on the likely underlying cause.[2] An open airway and sufficient breathing should be established.[2] Any ongoing bleeding should be stopped, which may require surgery or embolization.[2] Intravenous fluid, such as Ringer's lactate or packed red blood cells, is often given.[2] Efforts to maintain a normal body temperature are also important.[2] Vasopressors may be useful in certain cases.[2] Shock is both common and has a high risk of death.[3] In the United States about 1.2 million people present to the emergency room each year with shock and their risk of death is between 20 and 50%.[3]
Diagnosis[edit]
The diagnosis of shock is commonly based on a combination of symptoms, physical examination, and laboratory tests. Many signs and symptoms are not sensitive or specific for shock, thus many clinical decision-making tools have been developed to identify shock at an early stage.[25] A high degree of suspicion is necessary for the proper diagnosis of shock.
The first change seen in shock is increased cardiac output followed by a decrease in mixed venous oxygen saturation (SmvO2) as measured in the pulmonary artery via a pulmonary artery catheter.[26] Central venous oxygen saturation (ScvO2) as measured via a central line correlates well with SmvO2 and are easier to acquire. If shock progresses anaerobic metabolism will begin to occur with an increased blood lactic acid as the result. While many laboratory tests are typically performed, there is no test that either conclusively makes or excludes the diagnosis. A chest X-ray or emergency department ultrasound may be useful to determine volume status.[7][8]
Epidemiology[edit]
Septic shock (a form of distributive shock), is the most common form of shock. Shock from blood loss occurs in about 1–2% of trauma cases.[33] Overall, up to one-third of people admitted to the intensive care unit (ICU) are in circulatory shock.[41] Of these, cardiogenic shock accounts for approximately 20%, hypovolemic about 20%, and septic shock about 60% of cases.[42]
History[edit]
There is no evidence of the word shock being used in its modern-day form prior to 1743. However, there is evidence that Hippocrates used the word exemia to signify a state of being "drained of blood".[44] Shock or "choc" was first described in a trauma victim in the English translation of Henri-François LeDran's 1740 text, Traité ou Reflexions Tire'es de la Pratique sur les Playes d'armes à feu (A treatise, or reflections, drawn from practice on gun-shot wounds.)[45] In this text he describes "choc" as a reaction to the sudden impact of a missile. However, the first English writer to use the word shock in its modern-day connotation was James Latta, in 1795.
Prior to World War I, there were several competing hypotheses behind the pathophysiology of shock. Of the various theories, the most well regarded was a theory penned by George W. Crile who suggested in his 1899 monograph, "An Experimental Research into Surgical Shock", that shock was quintessentially defined as a state of circulatory collapse (vasodilation) due to excessive nervous stimulation.[46] Other competing theories around the turn of the century included one penned by Malcom in 1907, in which the assertion was that prolonged vasoconstriction led to the pathophysiological signs and symptoms of shock.[47] In the following World War I, research concerning shock resulted in experiments by Walter B. Cannon of Harvard and William M. Bayliss of London in 1919 that showed that an increase in permeability of the capillaries in response to trauma or toxins was responsible for many clinical manifestations of shock.[48][49] In 1972 Hinshaw and Cox suggested the classification system for shock which is still used today.[50][43]