Circulatory Shock

Types of Shock

Circulatory shock is a life-threatening medical condition that occurs due to inadequate substrate for aerobic cellular respiration.

Learning Objectives

Differentiate among the types of shock

Key Takeaways

Key Points

  • Circulatory shock, commonly known simply as shock, is a life-threatening medical condition that occurs due to the provision of inadequate substrates for cellular respiration.Typical symptoms of shock include elevated but weak heart rate, low blood pressure, and poor organ function, typically observed as low urine output, confusion, or loss of consciousness.
  • There are four subtypes of shock with differing underlying causes and symptoms: hypovolemic, cardiogenic, obstructive, and distributive.
  • Distributive shock can be further divided into septic, anaphylaxis, and neurogenic shock.

Key Terms

  • shock: A medical condition that occurs due to an inadequate supply of substrates required for aerobic respiration by the bodies tissues.

Circulatory shock, commonly known simply as shock, is a life-threatening medical condition that occurs due to inadequate substrates for aerobic cellular respiration. In the early stages, this is generally caused by an inadequate tissue level of oxygen. The typical signs of shock are low blood pressure, a rapid heartbeat, and signs of poor end-organ perfusion or decompensation (such as low urine output, confusion, or loss of consciousness). In some people with circulatory shock, blood pressure remains stable.

This schematic of the manifestation of shock includes vasoconstriction, failure of precapillary sphincters, peripheral pooling of blood, inadequate perfusion, cell hypoxia, energy deficit, lactic acid accumulation and fall of pH, anaerobic metabolism, metabolic acidosis, cell membrane dysfunction and failure of sodium pump, intracellular lysosomes release digestive enzymes, efflux of potassium, influx of sodium and water, toxic substances enter circulation, capillary endothelium damage, destruction, dysfunction, and cel death.

Shock: The scheme depicts the cell metabolic response as a result of inadequate blood delivery during circulatory shock.

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 low blood pressure, decreased urine output, and confusion, these may not always be present. Specific subtypes of shock may have additional symptoms.

Hypovolemic Shock

Hypovolemic shock, the most common type, is caused by insufficient circulating volume, typically from hemorrhage although severe vomiting and diarrhea are also potential causes.

Hypovolemic shock is graded on a four-point scale depending on the severity of symptoms and level of blood loss. Typical symptoms include a rapid, weak pulse due to decreased blood flow combined with tachycardia, cool, clammy skin, and rapid and shallow breathing.

Cardiogenic Shock

Cardiogenic shock is caused by a failure of the heart to pump correctly, either due to damage to the heart muscle through myocardial infarction or through cardiac valve problems, congestive heart failure, or dysrhythmia.

Obstructive Shock

Obstructive shock is caused by an obstruction of blood flow outside of the heart. This typically occurs due to a reduction in venous return, but may also be caused by blockage of the aorta.

Distributive Shock

Distributive shock is caused by an abnormal distribution of blood to tissues and organs and includes septic, anaphylactic, and neurogenic causes.

Septic

Septic shock is the most common cause of distributive shock and is caused by an overwhelming systemic infection that cannot be cleared by the immune system, resulting in vasodilation and hypotension.

Anaphylactic

Anaphylactic shock is caused by a severe reaction to an allergen, leading to the release of histamine that causes widespread vasodilation and hypotension.

Neurogenic

Neurogenic shock arises due to damage to the central nervous system, which impairs cardiac function by reducing heart rate and loosening the blood vessel tone, resulting in severe hypotension.

Homeostatic Responses to Shock

An organism responds with numerous reactions during each of the four stages of shock in an attempt to maintain cellular homeostasis.

Learning Objectives

Describe the homeostatic response to shock

Key Takeaways

Key Points

  • 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.
    The initial stage of shock is characterized by hypoxia and anaerobic cell respiration leading to lactic acidosis.
  • The compensatory stage is characterized by the employment of neural, hormonal, and biochemical mechanisms in the body’s attempt to reverse the condition.
  • The progressive stage is the point at which the compensatory mechanisms will begin to fail. If the crisis is not treated successfully, vital organs might be compromised.
  • The refractory stage is when vital organs have failed and the shock can no longer be reversed leading to imminent death.

Key Terms

  • hypoperfusion: Decreased perfusion of blood through an organ.
  • hypoxia: A condition in which tissues (especially the blood) are deprived of an adequate supply of oxygen; anoxia.

Circulatory shock, commonly known simply as shock, is a life-threatening medical condition that occurs due to inadequate substrate for aerobic cellular respiration. In the early stages this is generally an inadequate level of oxygen in the tissues.

This diagram of the process of shock indicates inadequate perfusion, cell hypoxia, energy deficit, lactic acid accumulation and fall in pH, anaerobic metabolism, metabolic acidosis, vasoconstriction, failure of precapillary sphincters, peripheral pooling of blood, cell membrane dysfunction and failure of sodium pump, intracellular lysosomes release digestive enzymes, efflux of potassium, influx of sodium and water, toxic substances enter circulation, capillary endothelium damaged, destruction, dysfunction, and cell death.

Shock: The scheme depicts the cell metabolic response as a result of inadequate blood delivery during circulatory shock.

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.

Initial Stage

During the initial stage, the state of hypoperfusion causes hypoxia. Due to the lack of oxygen, the cells perform anaerobic respiration. Since oxygen is not abundant, the Kreb’s cycle is slowed, resulting in lactic acidosis (the accumulation of lactate).

Compensatory Stage

The compensatory stage is characterized by the employment of neural, hormonal, and biochemical mechanisms in the body’s attempt to reverse the lactic acidosis. The increase in acidity will initiate the Cushing reflex, generating the classic symptoms of shock. The individual will begin to hyperventilate to rid the body of carbon dioxide to raise the blood pH (lower the acidity). As a result, the baroreceptors in the arteries detect the hypotension and initiate the release of epinephrine and norepinephrine to increase heart rate and blood pressure.

Progressive Stage

Should the cause of the crisis not be successfully treated, the shock will proceed to the progressive stage, in which the compensatory mechanisms begin to fail. As anaerobic metabolism continues, increasing the body’s metabolic acidosis, the arteriolar smooth muscle and precapillary sphincters relax. Blood remains in the capillaries, leading to leakage of fluid and protein into the surrounding tissues. As fluid is lost, blood concentration and viscosity increase, causing blockage of the microcirculation. The prolonged vasoconstriction will also cause the vital organs to be compromised due to reduced perfusion. If the bowel becomes sufficiently ischemic, bacteria may enter the blood stream, resulting in the additional complication of endotoxic shock.

Refractory Stage

At the refractory stage, the vital organs have failed and shock can no longer be reversed. Brain damage and cell death are occurring, and death is imminent. Shock is irreversible at this point since a large amount of cellular ATP has been degraded into adenosine 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 vasodilation, and then is transformed into uric acid. 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 phosphorylate into ATP.

Signs and Symptoms of Shock

The clinical manifestation of shock varies depending on the type of shock and the individual, but there are some general symptoms.

Learning Objectives

Differentiate among the types of shock and the signs and symptoms associated with each

Key Takeaways

Key Points

  • The general signs for all types of shock are low blood pressure, decreased urine output, and confusion. However, these may not always be present.
  • Hypovolemic shock is characterized by loss of effective circulating blood volume, which leads to rapid pulse, cool skin, shallow breathing, hypothermia, thirst, and cold mottled skin.
  • Cardiogenic shock is characterized by distended jugular veins, weak or absent pulse, and arrhythmia.
  • Distributive shock includes septic shock, characterized by fever or anaphylaxis, and neurogenic shock, characterized by a reduced heart rate and vasodilation of superficial vessels warming the skin.

The presentation of shock varies. Some people presenting only minimal symptoms, such as confusion and weakness. Typical symptoms of shock include elevated but weak heart rate, low blood pressure, and poor organ function, typically observed as low urine output, confusion or loss of consciousness.

While a fast heart rate is common, those on beta blockers and those who are athletic may have a normal or slow heart rate. This also occurs in 30% of cases of shock caused by abdominal bleeding. Specific subtypes of shock may have additional symptoms.

Hypovolemic shock results from the direct loss of effective circulating blood volume. This leads to a rapid, weak pulse due to decreased blood flow combined with tachycardia, stimulation of vasoconstriction, and cool, clammy skin. It also presents with acidosis as well as rapid, shallow breathing due to sympathetic nervous system stimulation. Hypothermia due to decreased perfusion and evaporation of sweat, and thirst and dry mouth due to fluid depletion, may also be present.

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Anaphalactic Hives: Hives and flushing on the back of a person with anaphylaxis.

The symptoms of cardiogenic shock are similar to those of hypovolemic shock. Additional symptoms may include arrhythmia of the heart beat and visibly distended jugular veins.

Distributive shock includes septic, anaphylactic, and neurogenic causes. With septic shock, fever may occur and the skin may be warm and sweaty. With anaphylaxis, hives may present on the skin, and there may localized edema, especially around the face, and weak and rapid pulse. Breathlessness and cough due to narrowed airways and swelling of the throat may also occur. The symptoms of neurogenic shock are distinct from those of classical shock, as the heart rate slows and and superficial vessels vasodilate and warm the skin. These symptoms are caused by neural damage and resultant loss of muscle control.