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.