Shock

Shock is the state of not enough to the s of the body as a result of problems with the. Initial symptoms may include weakness,, , , anxiety, and increased thirst. This may be followed by confusion,, or as complications worsen.

Shock is divided into four main types based on the underlying cause:, , , and. Low volume shock may be from bleeding,, vomiting, or. Cardiogenic shock may be due to a or. may be due to or a. Distributed shock may be due to, , or certain s.

The diagnosis is generally based on a combination of symptoms,, and laboratory tests. A decreased ( minus ) or a fast heart rate raises concerns. The heart rate divided by systolic blood pressure, known as the (SI), of greater than 0.8 supports the diagnosis more than  or a  in isolation.

Treatment of shock is based on the likely underlying cause. An open and sufficient  should be established. Any ongoing bleeding should be stopped, which may require surgery or. , such as or, is often given. Efforts to maintain a normal are also important. may be useful in certain cases. Shock is both common and has a high risk of death. 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%.

Signs and symptoms
The presentation of shock is variable with some people having only minimal symptoms such as confusion and weakness. While the general signs for all types of shock are, decreased , and confusion, these may not always be present. While a fast heart rate is common, those on, those who are athletic, and in 30% of cases of those with shock due to intra abdominal bleeding may have a normal or slow heart rate. Specific subtypes of shock may have additional symptoms.

Dry, reduced , prolonged , weak peripheral pulses and cold extremities can be early signs.

Low volume
is a direct loss of effective circulating blood volume leading to:
 * A rapid, weak, thready pulse due to decreased blood flow combined with tachycardia
 * Cool, clammy skin due to and stimulation of vasoconstriction
 * Rapid and shallow breathing due to sympathetic nervous system stimulation and acidosis
 * due to decreased perfusion and evaporation of sweat
 * Thirst and dry mouth, due to fluid depletion
 * Cold and mottled skin, especially extremities, due to insufficient perfusion of the skin

The severity of hemorrhagic shock can be graded on a 1–4 scale on the physical signs. This approximates to the effective loss of blood volume. The (heart rate divided by systolic blood pressure) is a stronger predictor of the impact of blood loss than heart rate and blood pressure alone. This relationship has not been well established in pregnancy-related bleeding.

Cardiogenic
Symptoms of include:
 * Distended s due to increased
 * Weak or absent pulse
 * , often a
 * in case of
 * Reduced blood pressure

Distributive
is low blood pressure due to a dilation of blood vessels within the body. This can be caused by systemic infection, a severe allergic reaction , or spinal cord injury ( shock). Like any type of shock, the result is the same: inadequate perfusion pressure resulting in inadequate cellular oxygenation. The features typically occur in early septic shock.

Septic shock
Main manifestations are produced due to massive release of which causes intense dilation of the blood vessels. People with septic shock will also likely be positive for the SIRS criteria. The most generally accepted treatment for these patients is early recognition of symptoms, and early administration of broad spectrum and organism specific antibiotics.
 * Systemic adhesion to endothelial cells
 * Reduced contractility of the heart
 * Activation of the coagulation pathways, resulting in
 * Increased levels of

Cause
Shock is a common end point of many medical conditions. Shock itself is a life-threatening condition as a result of compromised. It has been divided into four main types based on the underlying cause: hypovolemic, distributive, cardiogenic, and obstructive. A few additional classifications are occasionally used including: endocrinologic shock.

Low volume
is the most common type of shock and is caused by insufficient circulating. Its primary cause is (internal or external), or loss of fluid from the. and are the most common cause in children. Other causes include burns, and excess urine loss due to and.

Cardiogenic
is caused by the failure of the heart to pump effectively. This can be due to damage to the heart muscle, most often from a large. Other causes of cardiogenic shock include s, /, (CHF),, or  problems.

Obstructive
is due to a physical obstruction of the great vessels or the heart itself. Several conditions can result in this form of shock.


 * in which fluid in the pericardium prevents inflow of blood into the heart (venous return)., in which the shrinks and hardens, is similar in presentation.
 * Through increased intrathoracic pressure, bloodflow to the heart is prevented (venous return).
 * is the result of a thromboembolic incident in the blood vessels of the s and hinders the return of blood to the heart.
 * hinders circulation by obstructing the
 * is overly thick ventricular muscle dynamically occludes the.

Distributive
is due to loss of muscle tone in the arteries or inflammation and dilation of the capillaries. Examples of this form of shock are:
 * is the most common cause of distributive shock. Caused by an overwhelming systemic infection resulting in leading to hypotension. Septic shock can be caused by  bacteria such as (among others) ', Proteus species, ' which have an  on their surface which produces adverse biochemical, immunological and occasionally neurological effects which are harmful to the body, and other  cocci, such as  and, and certain fungi as well as Gram-positive bacterial toxins. Septic shock also includes some elements of cardiogenic shock. In 1992, the ACCP/SCCM Consensus Conference Committee defined septic shock: ". . .sepsis-induced hypotension (systolic blood pressure < 90 mmHg or a reduction of 40 mmHg from baseline) despite adequate fluid resuscitation along with the presence of perfusion abnormalities that may include, but are not limited to, lactic acidosis, oliguria, or an acute alteration in mental status. Patients who are receiving inotropic or vasopressor agents may have a normalized blood pressure at the time that perfusion abnormalities are identified."
 * is caused by a severe to an, ,  or foreign protein causing the release of  which causes widespread vasodilation, leading to hypotension and increased capillary permeability.
 * High spinal injuries may cause . The classic symptoms include due to loss of cardiac  and warm skin due to dilation of the peripheral blood vessels. (This term can be confused with  which is a recoverable loss of function of the  after injury and does not refer to the haemodynamic instability per se.)

Endocrine
Based on disturbances such as:
 * (can be considered a form of ) in people who are critically ill patients, reduces and can lead to  and respiratory insufficiency.
 * may induce a reversible cardiomyopathy.
 * Acute  is frequently the result of discontinuing  treatment without tapering the dosage. However, surgery and intercurrent disease in patients on corticosteroid therapy without adjusting the dosage to accommodate for increased requirements may also result in this condition.
 * Relative adrenal insufficiency in critically ill patients where present  are insufficient to meet the higher demands

Pathophysiology
There are four stages of shock. As it is a complex and continuous condition there is no sudden transition from one stage to the next. At a cellular level, shock is the process of oxygen demand becoming greater than oxygen supply.

One of the key dangers of shock is that it progresses by a mechanism. Poor blood supply leads to cellular damage, which results in an inflammatory response to increase blood flow to the affected area. This is normally very useful to match up blood supply level with tissue demand for nutrients. However, if enough tissue causes this, it will deprive vital nutrients from other parts of the body. Additionally, the ability of the circulatory system to meet this increase in demand causes saturation, and this is a major result, of which other parts of the body begin to respond in a similar way; thus, exacerbating the problem. Due to this chain of events, immediate treatment of shock is critical for survival.

Initial
During this stage, the state of hypoperfusion causes. Due to the lack of oxygen, the cells perform. Since oxygen, the terminal electron acceptor in the electron transport chain, is not abundant, this slows down entry of into the, resulting in its accumulation. Accumulating pyruvate is converted to lactate by lactate dehydrogenase and hence lactate accumulates (causing ).

Compensatory
This stage is characterised by the body employing physiological mechanisms, including neural, hormonal and bio-chemical mechanisms in an attempt to reverse the condition. As a result of the, the person will begin to in order to rid the body of carbon dioxide (CO2). CO2 indirectly acts to acidify the blood and by removing it the body is attempting to raise the pH of the blood. The in the  detect the resulting, and cause the release of  and. Norepinephrine causes predominately with a mild increase in, whereas  predominately causes an increase in  with a small effect on the  tone; the combined effect results in an increase in. The is activated, and  (ADH) is released to conserve fluid via the kidneys. These hormones cause the vasoconstriction of the, , and other organs to divert blood to the heart, and. The lack of blood to the system causes the characteristic low  production. However the effects of the renin–angiotensin axis take time and are of little importance to the immediate mediation of shock.

Progressive
Should the cause of the crisis not be successfully treated, the shock will proceed to the progressive stage and the compensatory mechanisms begin to fail. Due to the decreased perfusion of the cells, ions build up within while  ions leak out. As anaerobic metabolism continues, increasing the body's metabolic acidosis, the arteriolar smooth muscle and precapillary relax such that blood remains in the. Due to this, the hydrostatic pressure will increase and, combined with release, this will lead to leakage of fluid and  into the surrounding tissues. As this fluid is lost, the blood concentration and increase, causing sludging of the micro-circulation. The prolonged vasoconstriction will also cause the vital organs to be compromised due to reduced perfusion. If the bowel becomes sufficiently, bacteria may enter the blood stream, resulting in the increased complication of.

Refractory
At this stage, the vital organs have failed and the shock can no longer be reversed. and cell death are occurring, and death will occur imminently. One of the primary reasons that shock is irreversible at this point is that much cellular has been degraded into  in the absence of oxygen as an electron receptor in the mitochondrial matrix. Adenosine easily perfuses out of cellular membranes into extracellular fluid, furthering capillary, and then is transformed into. Because cells can only produce adenosine at a rate of about 2% of the cell's total need per hour, even restoring oxygen is futile at this point because there is no adenosine to into ATP.

Diagnosis
The first change seen in shock is an increased followed by a decrease in  (SmvO2) as measured in the  via a. (ScvO2) as measured via a central line correlates well with SmvO2 and are easier to acquire. If shock progresses will begin to occur with an increased blood  as the result. While many laboratory tests are typically performed there is no test that either makes or excludes the diagnosis. A or emergency department ultrasound may be useful to determine volume state.

Management
The best evidence exists for the treatment of in adults and as the pathophysiology appears similar in children and other types of shock treatment this has been extrapolated to these areas. Management may include securing the airway via if necessary to decrease the work of breathing and for guarding against respiratory arrest. Oxygen supplementation, intravenous fluids, (not ) should be started and blood transfusions added if blood loss is severe. It is important to keep the person warm to avoid as well as adequately manage pain and anxiety as these can increase oxygen consumption. Negative impact by shock is reversible if it's recognized and treated early in time.

Fluids
Aggressive intravenous fluids are recommended in most types of shock (e.g. 1–2 liter bolus over 10 minutes or 20 ml/kg in a child) which is usually instituted as the person is being further evaluated. and appear to be similar with respect to outcomes. Thus as crystalloids are less expensive they are recommended. If the person remains in shock after initial resuscitation should be administered to keep the  greater than 100 g/l.

For those with haemorrhagic shock the current evidence supports limiting the use of fluids for penetrating thorax and abdominal injuries allowing mild to persist (known as ). Targets include a of 60 mmHg, a  of 70–90 mmHg, or until their adequate mentation and peripheral pulses. may also be an option in this group.

Medications
may be used if blood pressure does not improve with fluids. There is no evidence of substantial superiority of one vasopressor over another; however, using dopamine leads to an increased risk of arrhythmia when compared with norepinephrine. Vasopressors have not been found to improve outcomes when used for from  but may be of use in. (Xigris) while once aggressively promoted for the management of has been found not to improve survival and is associated with a number of complications. Xigris was withdrawn from the market in 2011, and clinical trials were discontinued. The use of is controversial as it has not been shown to improve outcomes. If used at all it should only be considered if the pH is less than 7.0.

Mechanical support

 * (IABP)
 * (VAD)
 * (TAH)
 * (ECMO)

Treatment goals
The goal of treatment is to achieve a urine output of greater than 0.5 ml/kg/h, a of 8–12 mmHg and a  of 65–95 mmHg. In trauma the goal is to stop the bleeding which in many cases requires surgical interventions.

Epidemiology
Haemorrhagic shock occurs in about 1–2% of trauma cases. Up to one-third of people admitted to the (ICU) are in circulatory shock. Of these, cardiogenic shock accounts for approximately 20%, hypovolemic about 20%, and septic shock about 60% of cases.

Prognosis
The prognosis of shock depends on the underlying cause and the nature and extent of concurrent problems. Hypovolemic, anaphylactic and neurogenic shock are readily treatable and respond well to medical therapy. , however, is a grave condition with a mortality rate between 30% and 50%. The prognosis of is even worse with a mortality rate between 70% and 90%.

History
In 1972 Hinshaw and Cox suggested the classification system for shock which is still used today.