The four types of shock include distributive shock, cardiogenic shock, hypovolemic shock, and obstructive shock.

Shock is a multisystem phenomenon that disrupts the body’s physiology and causes reduced tissue perfusion (oxygenation).

Physiological shocks are classified into four main categories:

1. Distributive shock
2. Cardiogenic shock
3. Hypovolemic shock
4. Obstructive shock

What is distributive shock?

Distributive shock is characterized by a significant drop in peripheral vascular resistance and, as a result, hypotension.

6 subclassifications of distributive shock

1. Septic shock
   • Septic shock is a potentially fatal condition that occurs when blood pressure drops dangerously low following an infection.
   • The infection might be caused by any bacteria. The shock is triggered by the bacteria toxins. Rarely, fungi (such as candida) and viruses are the cause.
   • Toxins created by bacteria, if left untreated, can trigger an inflammatory cascade in the body, affect the liver and kidney function, rupture small blood vessels, and cause fluids inside organs to leak into the surrounding tissues.
   • This can impair the heart's capacity to pump blood to organs, lowering blood pressure and preventing the blood from reaching key organs, such as the brain and liver.
   • Septic shock is mostly seen in conditions with compromised immunity, such as:
     • Neonatal sepsis
     • Elderly
     • Long-lasting medical conditions, such as cancer, human immunodeficiency virus
     • Use of immunosuppressants
2. Neurogenic shock
   • Neurogenic shock occurs due to a lack of equilibrium between parasympathetic and sympathetic stimulation. Neurogenic shock could be a potentially fatal medical condition.
   • Neurogenic shock is most typically seen after a severe spinal cord injury (SCI) although it can occur after serious brain damage.
   • Neurogenic shock occurs when sympathetic fibers are disrupted, basal vascular sympathetic tone causes the muscles to contract is lost. This leads to an unopposed parasympathetic tone that causes relaxation of the blood vessel walls for a long period. This results in severe hypotension (low blood pressure) and bradycardia (reduced heart rate), which can cause brain damage and other organ damage due to a lack of sufficient blood circulation.
   • Understanding the physiologic and anatomic changes that occur during neurogenic shock can aid in the direction of proper resuscitation efforts. The physiologic goals should be to reverse hypotension, prevent hypoxia and improve the blood circulation of the damaged central nervous system and other vital organs.
3. Anaphylactic shock
   • Anaphylactic shock is a severe life-threatening condition, which is a medical emergency.
   • Anaphylactic shock is caused by the release of chemical compounds in the body as a result of a reaction to an antigenic stimulus. This usually occurs if a person is previously sensitized to such reactions.
   • This stimulation could be caused by food, medications, blood products, insect venom, or pollen contact. If a person goes into anaphylactic shock, there could be respiratory symptoms, itching, severe skin rash, or the person may faint because the pulse drops off.
4. Endocrine shock
   • Adrenal failure caused by mineralocorticoid deficiency (Addisonian crisis), and myxedema can cause hypotension and shock. Vasodilation can occur in mineralocorticoid deficit due to increased vascular tone and aldosterone deficiency-mediated hypovolemia.
   • Although thyroid hormone plays a role in blood pressure regulation, the specific mechanism of vasodilation in myxedema patients is unknown. Concomitant myocardial depression or pericardial effusions are likely to contribute to hypotension and shock.
5. Drug and toxin-induced shock
   • Overdoses of drugs, snake bites, insect bites that contain venom, transfusion reactions, heavy-metal poisoning, and infections associated with toxic shock syndrome are all examples of drug or toxin reactions that can be associated with shock or systemic inflammatory response syndrome.
6. Systemic inflammatory response syndrome (SIRS)
   • SIRS is a clinical syndrome defined by a strong inflammatory response, which is usually triggered by a substantial body insult that could be infectious or noninfectious.
   • Most patients with SIRS in the emergency room are not in shock and will not acquire shock during their stay. However, if SIRS is present, the doctor will monitor the patient for disease severity development.

What is cardiogenic shock?

Cardiogenic shock is a condition in which the circulatory system fails due to decreased cardiac output caused by left, right, or biventricular failure. Cardiogenic shock can develop because of acute ischemia or nonischemic cardiac event or as a result of the advancement of underlying heart disease.

Acute myocardial infarction is the most prevalent cause of cardiogenic shock, accounting for up to 70 percent of cases and occurring in 5 to 10 percent of patients with acute myocardial infarction.

Cardiogenic shock can cause severe cellular and metabolic malfunction, multisystem organ dysfunction, and death.

3 subclassifications of cardiogenic shock

1. Cardiomyopathic
   • The shock is caused by cardiomyopathic causes, such as myocardial infarction, acute exacerbation of heart failure, cardiac arrest, prolonged ischemia, or cardiopulmonary bypass.
2. Arrhythmic
   • Atrial and ventricular tachyarrhythmias and bradyarrhythmia can cause hypotension, which frequently contributes to states of shock. When cardiac output is badly harmed by major rhythm disruptions, a person may go into cardiac arrest.
3. Mechanical
   • Severe aortic or mitral valve insufficiency and acute valvular defects caused by the rupture of a papillary muscle or chordae tendineae (mitral valve defect) or retrograde dissection of the ascending aorta into the aortic valve ring or an abscess of the aortic ring are mechanical causes of cardiogenic shock (aortic insufficiency).

Severe ventricular septal abnormalities or abrupt rupture of the intraventricular septum, atrial myxomas, and a ruptured ventricular free wall aneurysm are other reasons.

Though a burst ventricular aneurysm can cause cardiogenic shock due to decreased left ventricle output, it can present with obstructive shock when bleeding is confined to the pericardial sac or catastrophic hemorrhagic shock when the pericardial sac is punctured and hemorrhage is severe.

Emotional trauma is best described as a psychological response to a deeply distressing or life-threatening experience.
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What is hypovolemic shock?

Hypovolemic shock occurs as a result of decreased intravascular volume or decreased preload, which lowers cardiac output.

Hypovolemic shock is classified into two types.

1. Hemorrhagic shock
   • Hemorrhagic shock can occur as a result of decreased intravascular volume caused by blood loss. The most common cause of hemorrhagic shock is blunt or penetrating trauma, including multiple fractures without blood vessel injury.
   • Variceal hemorrhage, peptic ulcer in the upper gastrointestinal tract or diverticular, arteriovenous malformation in the lower gastrointestinal tract cause gastrointestinal bleeding, which leads to hemorrhagic shock.
2. Non-hemorrhagic shock
   • Non-hemorrhagic shock can result from decreased intravascular volume due to fluid loss other than blood. Volume depletion can occur from a variety of anatomic locations due to salt and water loss and include:
     • Diarrhea
     • Vomiting
     • External drainage
     • Heatstroke
     • Burns
     • Severe dermatologic conditions, including Stevens-Johnson syndrome
     • Excessive drug-induced or osmotic diuresis
     • Hypoaldosteronism
     • Fluid in cavities caused by postoperative complication and trauma
     • Intestinal obstruction
     • Crush injury
     • Pancreatitis
     • Cirrhosis

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What is obstructive shock?

Obstructive shock is caused mostly by extracardiac causes of cardiac pump failure and is frequently accompanied by low right ventricular output.

2 categories of obstructive shock

1. Pulmonary vascular
   • Most obstructive shock cases are caused by right ventricular failure as a result of a hemodynamically substantial pulmonary embolism (PE) or severe pulmonary hypertension (PH). The right ventricle fails in these situations because it is unable to generate enough pressure to overcome the increased pulmonary vascular resistance associated with PE or PH.
   • Though mechanical obstruction has generally been attributed to a hemodynamic collapse in the setting of PE, pulmonary vasoconstriction mediated by vasoactive mediators, such as serotonin and thromboxane, contributes to these outcomes. Severe stenosis or acute pulmonary or tricuspid valve blockage may also fall into this category.
2. Mechanical
   • Sometimes, a mechanical obstructive shock is clinically presented as a hypovolemic shock because the main cause of both conditions is decreased preload rather than pump failure. This means preload is decreased when the right ventricle filling is inadequate even though the pumping of the heart is normal.
   • Mechanical reasons for obstructive shock include:
     • Constrictive pericarditis
     • Tension pneumothorax
     • Pericardial tamponade
     • Restrictive cardiomyopathy