Circulatory Shock Overview

Shock Definition

• Shock is a general term referring to the depression or suppression of body functions caused by any disorder.
• Circulatory shock describes shock from inadequate blood flow throughout the body.
• Circulatory shock is life-threatening and, if untreated, can result in death.

Manifestations of Circulatory Shock

• A key feature of all forms of circulatory shock is inadequate blood flow to the tissues, particularly the brain.
• Reduced cardiac output is a primary cause of decreased blood flow.
• Manifestations include a drop in arterial blood pressure following decreased cardiac output.
• Low blood pressure triggers reflex tachycardia and vasoconstriction.
• Tachycardia shortens the diastolic phase of the heart cycle, decreasing stroke volume and systolic pressure.
• Pulse pressure typically falls below 20 mm Hg, and the pulse becomes weak.

Further Manifestations of Circulatory Shock

• Stagnant hypoxia develops due to the slow blood flow.
• Skin becomes pale and cold because of vasoconstriction.
• Cyanosis appears in areas like earlobes and fingertips along with hypoxia.
• Reduced glomerular filtration rate (GFR) and urine output result from decreased blood pressure and constricted renal blood vessels.
• Myocardial activity increases to compensate for low blood flow, generating lactic acid and causing acidosis.
• Acidosis decreases heart function and further reduces cardiac output.
• Blood flow to vital organs becomes significantly impaired.
• Brain tissue ischemia leads to fainting and irreversible brain damage.
• Cardiac arrest often follows, resulting in death.

Stages of Circulatory Shock

• Circulatory shock occurs in three stages:
• Compensated Stage (First Stage)
• Progressive Stage (Second Stage)
• Irreversible Stage (Third Stage)

First Stage (Compensated Stage)

• Blood loss less than 10% of total volume typically causes only moderate reductions in blood pressure.
• Body's regulatory mechanisms successfully restore normal blood pressure and flow.
• The shock remains nonprogressive, and the patient recovers.
• Baroreceptor, renal, and ADH mechanisms are key regulatory components in this stage.

Second Stage (Progressive Stage)

• Severe shock characterized by a failing positive feedback mechanism.
• Regulatory mechanisms become inadequate to compensate.
• Blood pressure decreases significantly, insufficient for adequate cardiac muscle blood flow.
• Myocardial function deteriorates from lack of nutrition and oxygen.
• Bacterial toxins (endotoxins) severely damage the myocardium.
• Vasomotor and sympathetic systems fail, leading to further blood pressure drops.
• Capillary permeability increases, fluid leakage into interstitial spaces.
• Thrombosis occurs in small blood vessels,
• Severe symptoms emerge, signaling a progression to irreversible shock

Third Stage (Irreversible Stage)

• Brain fails due to severe cerebral ischemia.
• Blood pressure drops dramatically.
• Blood infusion often fails to restore adequate pressure.
• Myocardial activity declines, and arteriolar tone decreases significantly.
• Death results.

Types and Causes of Circulatory Shock

• Shock is categorized into four major types:
• Hypovolemic shock (decreased blood volume)
• Vasogenic shock (increased vascular capacity)
• Cardiogenic shock (cardiac disease)
• Obstructive shock (blood flow obstruction)

Hypovolemic Shock

• Caused by decreased blood volume.
• Includes hemorrhage, trauma, surgery, burns, and dehydration.
• Important manifestations: decreased cardiac output, low blood pressure, thin/weak pulse, and pale/cold skin.
• Associated with restlessness and elevated respiratory rate.

Vasogenic Shock

• Results from increased vascular capacity.
• Includes neurogenic shock (loss of vasomotor tone), anaphylactic shock (severe allergic reaction), and septic shock (body invasion by pathogens).
• Symptoms often include vasodilation, reduced blood pressure, and other signs of circulatory instability.

Cardiogenic Shock

• Arises from cardiac diseases that reduce heart output.
• Examples include arrhythmias, myocardial ischemia, and congestive heart failure.
• Symptoms typically include lowered cardiac output, reduced blood pressure, and compromised tissue perfusion.

Obstructive Shock

• Triggered by impeding blood flow through the circulatory system.
• Often linked to cardiac tamponade (fluid in the pericardial sac compressing the heart), tumors in the myocardium or lung embolism.
• Obstructive shock prevents adequate cardiac output and causes significant decline in blood pressure and perfusion of tissues.

Shock Treatment

• Treatment depends on the cause.
• Common treatments include blood transfusions (especially in hypovolemic shock), plasma transfusions (if plasma loss is significant).
• Blood plasma substitutes can be used.
• Oxygen therapy addresses reduced oxygenation.
• Glucocorticoids can be given to manage tissue damage and reduce stress.

Additional treatment considerations include: altering posture (raising or lowering the patient's extremities) to support circulatory function and monitoring for symptoms.