Shock

Chapter 13:

Defining ShockDefining Shock

• Shock is best defined as inadequate tissue perfusion• Can result from a variety of disease states and

injuries• Can affect the entire organism or it can occur at a

tissue or cellular level

• Shock is not adequately defined by:• Pulse rate• Blood pressure• Cardiac function• Hypovolemia• Loss of systemic vascular resistance

Components of the Circulatory SystemComponents of the Circulatory System

• The pump (heart)• The fluid (blood)• The container (blood vessels)

Any problem with the components can lead to inadequate perfusion.

Cardiac Output Cardiac Output

• Amount of blood separately pumped by each ventricle per minute, usually expressed in liters per minute• Determined by multiplying the heart rate by the

volume of blood ejected by each ventricle during each beat (stroke volume)

• Crucial determinant of organ perfusion• Depends on:

• Strength of contraction• Rate of contraction

• Amount of venous return available to the ventricle (preload)

Baroreceptor Reflexes Baroreceptor Reflexes

• Help maintain BP by two negative feedback mechanisms:• By lowering BP in

response to increased arterial pressure

• By increasing BP in response to decreased arterial pressure

Chemoreceptor ReflexesChemoreceptor Reflexes

• Low arterial pressure may stimulate peripheral chemoreceptor cells that lie within the carotid and aortic bodies

• When oxygen or pH decreases, these cells stimulate vasomotor center of medulla

Compensatory MechanismsCompensatory Mechanisms

• CNS Ischemic Response

• Hormonal Mechanisms• Adrenal-medullary mechanism• Renin-angiotensin-aldosterone mechanism• Vasopressin mechanism• Atrial natriuretic factor

• Reabsorption of tissue fluids

• Splenic discharge of blood

Figure 7-8 A

Role of Adrenal Medulla in Regulating BPRole of Adrenal Medulla in Regulating BP

Figure 7-8 B

Renin-angiotensin-aldosterone Mechanism in BPRenin-angiotensin-aldosterone Mechanism in BP

Figure 7-8 C

Vasopressin (ADH) Mechanism in Regulating BPVasopressin (ADH) Mechanism in Regulating BP

The Body as a ContainerThe Body as a Container

• The healthy body may be viewed as a smooth‑flowing delivery system inside a container• Container must be filled to achieve

adequate preload and tissue oxygenation

Figure 19-1

The Body As a ContainerThe Body As a Container

• The external size of the container of any particular human body is relatively constant• Volume of the container is

directly related to the diameter of the resistance vessels

• Any change in vessel diameter changes the volume of the fluid the container holds, thereby affecting preload

Blood VolumeBlood Volume

• Average adult male has a blood volume of 7% of total body weight

• Average adult female has a blood volume of 6.5% of body weight• Volume increases significantly during

pregnancy

• Normal adult blood volume is 4.5‑5 L• Remains fairly constant in the healthy body

PlasmaPlasma

• Approximately 92% water• The liquid portion of blood

• Circulates salts, minerals, sugars, fats, and proteins throughout the body

• Contains 3 major proteins: • Albumin• Globulins (alpha, beta, and gamma)• Fibrinogen

Capillary-Cellular Relationship in ShockCapillary-Cellular Relationship in Shock

• Stage 1: Vasoconstriction

• Stage 2: Capillary and Venule Opening

• Stage 3: Disseminated Intravascular Coagulation

• Stage 4: Multiple Organ Failure

Capillary-Cellular Relationship in ShockCapillary-Cellular Relationship in Shock

Classifications of ShockClassifications of Shock

• Hypovolemic shock

• Distributive shock• Neurogenic shock• Anaphylactic shock• Septic shock

• Cardiogenic shock

Compensated ShockCompensated Shock

• Characterized by signs and symptoms of early shock

• Arterial blood pressure is normal or high

• Treatment at this stage will typically result in recovery

Compensated ShockCompensated Shock

Uncompensated ShockUncompensated Shock

• Characterized by signs and symptoms of late shock

• Arterial blood pressure is abnormally low

• Treatment at this stage will sometimes result in recovery

Uncompensated ShockUncompensated Shock

Irreversible ShockIrreversible Shock

• Characterized by signs and symptoms of late shock

• Arterial blood pressure is abnormally low

• Even aggressive treatment at this stage does not result in recovery

Irreversible ShockIrreversible Shock