Shock - Comprehensive Notes

Shock

Introduction

  • Shock, also known as hypoperfusion, is defined as inadequate cellular perfusion.
  • Any compromise in perfusion can lead to cellular injury or death.
  • In the early stages of shock, the body attempts to maintain homeostasis.

Pathophysiology

Diffusion

  • Diffusion is a passive process where molecules move from an area of high concentration to an area of low concentration.
  • Oxygen and carbon dioxide move across the walls of the alveoli through diffusion.

Impaired Perfusion

  • In cases of poor perfusion (shock), the transportation of carbon dioxide out of tissues is impaired, leading to a buildup of waste products and potential cellular damage.

Cardiovascular System Failure

  • Shock is a state of collapse and failure of the cardiovascular system, resulting in inadequate circulation.
  • Early recognition and rapid treatment are crucial for saving lives.

Components of the Cardiovascular System

  • The cardiovascular system consists of three main parts:
    • Pump (heart)
    • Set of pipes (blood vessels or arteries)
    • Contents (the blood)

Perfusion Triangle

  • The heart, blood vessels, and blood represent the three parts of perfusion, often referred to as the "perfusion triangle."
  • When a patient is in shock, one or more of these components is not working correctly.

Blood Pressure

  • Blood pressure is the pressure of blood within the vessels.
    • Systolic pressure: Peak arterial pressure.
    • Diastolic pressure: Pressure in the arteries when the heart rests between beats.

Pulse Pressure

  • Pulse pressure is the difference between systolic and diastolic pressures.
  • It signifies the force the heart generates with each contraction.
  • A pulse pressure less than 25 mm Hg may be seen in patients with shock.

Capillary Beds

  • Blood flow through the capillary beds is regulated by capillary sphincters, controlled by the autonomic nervous system.
  • Regulation of blood flow is determined by cellular needs.

Requirements for Adequate Perfusion

  • Perfusion requires adequate:
    • Oxygen exchange in the lungs.
    • Nutrients, particularly glucose, in the blood.
    • Waste removal, primarily through the lungs.

Support Mechanisms

  • Mechanisms are in place to support the respiratory and cardiovascular systems when the need for perfusion of vital organs increases. These include the autonomic nervous system and hormones.

Hormonal Response

  • Hormones are triggered when the body senses pressure falling, leading to:
    • Increased heart rate.
    • Increased strength of cardiac contractions.
    • Peripheral vasoconstriction.
  • This response causes the signs and symptoms of shock.

Causes of Shock

  • Many different types of shock result from three basic causes:
    • Pump failure.
    • Poor vessel function.
    • Low fluid volume.

Cardiogenic Shock

  • Caused by inadequate function of the heart.
  • A major effect is the backup of blood into the pulmonary vessels, resulting in pulmonary edema.
  • Cardiogenic shock develops when the heart cannot maintain sufficient output to meet the body's demands.
  • Cardiac output depends on:
    • Contractility of the heart muscle.
    • Amount of blood to pump (preload).
    • Resistance to flow in peripheral circulation (afterload).
  • Patients in cardiogenic shock should not receive nitroglycerin because they are hypotensive.
  • Patients usually have low blood pressure, a weak/irregular pulse, cyanosis, anxiety, and nausea.

Obstructive Shock

  • Caused by a mechanical obstruction that prevents adequate blood volume from filling the heart chambers.
  • Common examples include:
    • Cardiac tamponade.
    • Tension pneumothorax.
    • Pulmonary embolism.

Cardiac Tamponade

  • Collection of fluid between the pericardial sac and the myocardium (pericardial effusion) becomes large enough to prevent ventricles from filling with blood.
  • Caused by blunt or penetrating trauma. Signs and symptoms may be referred to as Beck Triad.

Tension Pneumothorax

  • Caused by damage to lung tissue.
  • Air normally held within the lung escapes into the chest cavity, collapsing the lung and applying pressure to organs, including the heart and great vessels.

Pulmonary Embolism

  • A blood clot blocks blood flow through pulmonary vessels.
  • If massive, it can result in complete backup of blood in the right ventricle, leading to catastrophic obstructive shock and complete pump failure.

Distributive Shock

  • Results from widespread dilation of small arterioles, small venules, or both.
  • Circulating blood volume pools in the expanded vascular beds, decreasing tissue perfusion.

Septic Shock

  • Occurs due to severe infections where toxins are generated by bacteria or infected body tissues.
  • Toxins damage vessel walls, causing increased cellular permeability.
  • Vessel walls leak and are unable to contract well, leading to widespread dilation and plasma loss, resulting in shock.

Neurogenic Shock

  • Usually results from high spinal cord injury.
  • Nerve impulses to blood vessels below the injury are blocked.
  • Vessels cut off from nerve impulses dilate, causing blood to pool.

Anaphylactic Shock

  • Occurs when a person reacts violently to a substance to which they have been sensitized.
  • Sensitization means becoming sensitive to a substance that did not initially cause a reaction.
  • Subsequent exposures tend to produce more severe reactions.

Psychogenic Shock

  • Caused by a sudden reaction of the nervous system, producing temporary, generalized vascular dilation that results in fainting (syncope).
  • Life-threatening causes include irregular heartbeat and brain aneurysm.
  • Non-life-threatening events include receiving bad news or experiencing fear or unpleasant sights.

Hypovolemic Shock

  • Results from an inadequate amount of fluid or volume in the circulatory system.
  • Can be caused by hemorrhagic (bleeding) and nonhemorrhagic (dehydration, burns) factors.
  • Occurs with severe thermal burns.

Progression of Shock

  • Stages in the progression of shock:
    • Compensated shock: early stage when the body can still compensate for blood loss.
    • Decompensated shock: late stage when blood pressure is falling.
  • It is impossible to assess when effects are irreversible, so early recognition and treatment are essential.
  • Blood pressure may be the last measurable factor to change, especially in infants and children where a drop in blood pressure indicates they are close to death.
  • Also expect shock if a patient has multiple severe fractures, abdominal or chest injury, spinal injury, a severe infection, a major heart attack, or anaphylaxis.

Patient Assessment

Scene Size-Up

  • Be alert to potential hazards.
  • Use gloves and eye protection for trauma scenes or if bleeding is suspected.
  • Consider the mechanism of injury/nature of illness.

Primary Assessment

  • Perform a rapid exam.
  • Determine the level of consciousness.
  • Identify and manage life-threatening concerns.
  • Determine the priority of the patient and transport.
  • Provide high-flow oxygen to assist in perfusion.
  • Treat aggressively for hypoperfusion and provide rapid transport.
  • Request advanced life support (ALS) as necessary.
  • Increased respiratory rate is often an early sign of impending shock.
  • A rapid pulse suggests compensated shock.
  • In shock or compensated shock, the skin may be cool, clammy, or ashen.
  • Assess for and identify any life-threatening bleeding and treat it immediately.
  • Trauma patients with shock or a suspicious MOI generally should go to a trauma center.

History Taking

  • Determine the chief complaint.
  • Obtain a SAMPLE history.

Secondary Assessment

  • Repeat the primary assessment, followed by a focused assessment.
  • Treat any immediate life-threatening problems.
  • Obtain a complete set of baseline vital signs.
  • Use monitoring devices.

Reassessment

  • Reassess the patient’s:
    • Vital signs
    • Interventions
    • Chief complaint
    • ABCs (Airway, Breathing, Circulation)
    • Mental status
  • Determine what interventions are needed.
  • Focus on supporting the cardiovascular system.
  • Treat for shock early and aggressively by:
    • Providing oxygen
    • Keeping the patient warm

Emergency Medical Care for Shock

  • As soon as you recognize shock, begin treatment.
  • Follow standard precautions.
  • Control all obvious bleeding.
  • Make sure the patient has an open airway.
  • Maintain manual in-line stabilization if necessary, and check breathing and pulse.
  • Comfort, calm, and reassure the patient.
  • Never allow patients to eat or drink anything.
  • If spinal immobilization is indicated, splint the patient on a backboard.
  • Provide oxygen and monitor the patient’s breathing.
  • Place blankets under and over the patient.
  • Consider the need for ALS.
  • Accurately record the patient’s vital signs approximately every 5 minutes throughout treatment and transport.

Treating Specific Types of Shock

Cardiogenic Shock

  • Patient cannot generate the necessary contraction to pump blood.
  • Patients may present with chest pain.
  • Place the patient in a position that eases breathing.
  • Assist ventilations as necessary.
  • Provide prompt transport.
  • Consider meeting ALS en route to hospital.

Obstructive Shock

  • Cardiac tamponade: Increasing cardiac output is the priority. Apply high-flow oxygen. Surgery is the only definitive treatment.
  • Tension pneumothorax: Apply high-flow oxygen to prevent hypoxia. Chest decompression is required. Request ALS early in call if available, but do not delay transport.

Septic Shock

  • Hospital management is required.
  • Use standard precautions and transport.
  • Administer high-flow oxygen; ventilatory support may be necessary.
  • Use blankets to conserve body heat.
  • Notify “sepsis team” if available.

Neurogenic Shock

  • Emergency treatment includes:
    • Obtaining and maintaining a proper airway.
    • Providing spinal immobilization.
    • Assisting inadequate breathing.
    • Conserving body heat.
    • Ensuring the most effective circulation.
    • Transporting promptly.

Anaphylactic Shock

  • Administer epinephrine.
  • Promptly transport the patient.
  • Provide high-flow oxygen and ventilatory assistance en route.
  • A mild reaction may worsen suddenly.
  • Consider requesting ALS backup, if available.

Psychogenic Shock

  • In an uncomplicated case of fainting, circulation to the brain is restored once the patient collapses.
  • Psychogenic shock can worsen other types of shock.
  • If the patient reports being unable to walk, suspect another problem.
  • Transport the patient promptly.

Hypovolemic Shock

  • Control all obvious external bleeding.
  • Keep the patient warm.
  • Recognize internal bleeding and provide aggressive support.
  • Secure and maintain an airway and provide respiratory support.
  • Transport as rapidly as possible.

Treating Shock in Older Patients

  • Older patients have more serious complications than younger ones.
  • Illness is not just a part of aging.
  • Many older patients take medications that mask or mimic signs of shock.