Chapter 4 

Shock

COURSE CONTENT

I. The generality and clinical feature of shock

Shock is not a disease but rather a clinical syndrome leading to reduced perfusion of tissues and organs and, eventually, organ dysfunction and failure. The classical signs and symptoms of shock include changes of blood pressure (hypotension or decrease of pulse pressure ), overbreathing (hyperventilation), a weak rapid pulse, cold clammy grayish-bluish (cyanotic) skin, decreased urine flow (oliguria), and mental changes (a sense of great anxiety and foreboding, confusion and, sometimes, combativeness). Even with treatment, shock has a high mortality rate once the body's compensatory mechanisms fail.

Ⅱ. Shock Classification

⑴ Based on the etiology, shock can be classified into seven major categories: ① hemorrhagic shock; ② traumatic shock; ③ infectious shock; ④ burn shock; ⑤ cardiogenic shock; ⑥ anaphylactic shock;  ⑦ neurogenic shock

⑵ Shock can be classified into three major categories according to starting segment that influences the perfusion of tissue: ① hypovolemic shock; ② vasogenic shock; ③ cardiogenic shock

⑶ Shock can be classified into two major categories based on the changes of blood dynamics: ① hypodynamic shock; ② hyperdynamic shock

Ⅲ. Pathophysiology of shock

There are three basic stages common to hemorrhagic shock: the compensatory, progressive, and irreversible or refractory stages.

1. Compensatory stage (Ischemic hypoxia stage)

In the stage, the manifestation of microcirculation is the velocity of capillary blood flow decreased gradually due to local arteriolar and precapillary sphincter constriction.

When arterial pressure and tissue perfusion are reduced, compensatory mechanisms are activated to maintain perfusion to the heart and brain. As the baroreceptors in the carotid sinus and aortic arch sense a drop in blood pressure, epinephrine and norepinephrine are secreted to increase peripheral resistance, blood pressure, and myocardial contractility. Reduced blood flow to the kidney activates the renin-angiotensin-aldosterone system, causing vasoconstriction and sodium and water retention, leading to increased blood volume and venous return. As a result of these compensatory mechanisms, cardiac output and tissue perfusion of important organ, such as heart and brain, are maintained.

The effects on body-compensatory are maintain of BP and redistribution of blood flow. Clinical signs in this stage: blood pressure is maintained even though cardiac output has fallen.

2. Progressive stage (Stagnant hypoxic stage)

The manifestation of microcirculation in this stage: blockade of the micro-vessels.

This stage of shock begins as compensatory mechanisms fail to maintain cardiac output. Tissues become hypoxic because of poor perfusion. As cells switch to anaerobic metabolism, lactic acid builds up, producing metabolic acidosis. This acidotic state depresses myocardial function and blunts the vasomotor response to catecholamines. Tissue hypoxia also promotes the release of endothelial mediators, which produce vasodilation and endothelial abnormalities, leading to venous pooling and increased capillary permeability. Sluggish blood flow increases the risk of disseminated intravascular coagulation. The effects on body: decompensation causes decreased blood flow return and constantly decreasing BP. Clinical signs of this stage: blood pressure is decreased.

3. Microcirculatory failure stage (irreversible stage, refractory stage or DIC stage)

The manifestations of microcirculation at this stage include congestion of microcirculation, no reaction of micro-vessel, formation of micro-thrombus, no-reflow of capillary, hemorrhage and DIC, obstinate low blood pressure, severity damage of important tissues and organs, severity anoxia and acidosis.

As the shock syndrome progresses, permanent organ damage occur as compensatory mechanisms can no longer maintain cardiac output. Reduced perfusion damages cell membranes, lysosomal enzymes are released, and energy stores are depleted, possibly leading to cell death including necrosis and apoptosis. As cells use anaerobic metabolism, lactic acid accumulates, increasing capillary permeability and the movement of fluid out of the vascular space. This loss of intravascular fluid further contributes to hypotension. Perfusion to the coronary arteries is reduced, causing myocardial depression and a further reduction in cardiac output. Eventually, circulatory and respiratory failure occurs. Death is inevitable.

Effect on body: ①multiple organ failure (MOF); ② DIC

Ⅳ. Functional and metabolic changes

Organ failures includes shock lung, shock kidney, functional changes of heart, brain, digestive system and multiple organ failure syndrome.

Possible complications of shock include: ①acute respiratory distress syndrome; ②acute tubular necrosis; ③disseminated intravascular coagulation (DIC); ④cerebral hypoxia

Disturbance of cellular metabolism of nutrients such as glucose and the activities of some hormones are depressed as well include a depression in the action of insulin.

Ⅴ. Types of shock

Ⅵ. Treatment

Correction of shock typically involves the following measures:

1. Identifying and treating the underlying cause, if possible

2. Maintaining a patent airway; preparing for intubation and mechanical ventilation if the patient develops respiratory distress

3. Supplemental oxygen to increase oxygenation

4. Continuous cardiac monitoring to detect changes in heart rate and rhythm; administration of antiarrhythmics, as necessary

5. Initiating and maintaining at least two intravenous lines with large-gauge needles for fluid and drug administration

6. Intravenous fluids, crystalloids, colloids, or blood products, as necessary, to maintain intravascular volume. Fluids such as normal saline or lactated Ringer's solution, initially, to restore filling pressures

EXERCISES

Ⅰ. True or false questions (mark √ for true question, mark ´ for false question. If it is false, correct it. )

1. Change of blood pressure is the important sign and symptom for diagnosis of shock.

2. At early stage, shock can develop acute functional renal failure, but at late stage always develops parenchymal.

3. Shock is not a disease but rather a clinical syndrome with high mortality rate.

4. MDF only has the role of inhibiting cardiac muscle.

5. At progressive stage of shock, no-reflow can be seen.

Ⅱ. Fill in blanks

1. There are three basic stages in the process of hemorrhagic shock, they are        ,        , and       .               

2. The immature immune system of        ,         and the weakened immune system of        , often accompanied by chronic illness, make these populations more susceptible to septic shock.

3. The classification of shock according to the cause of shock is        ,        ,          ,         ,         ,         

and         .

4. Based on major determinants that influence the tissue perfusion, shock is divided into three types, they are        ,          and         .                                                    

5. Based on peripheral vascular resistance and cardiac output shock is divided into two types, they are         and        .                   

6. Reduced blood flow to the kidney activates the        system, causing vasoconstriction and sodium and water retention, leading to increased blood volume and venous return.

7. The principle of supplying fluid for treating shock is according to the        , not according to the        .

Ⅲ. Multiple choice questions of type A

1. The most common cause of cardiogenic shock is

A. Arrhythmias                     B. Obstruction

C. Heart failure                     D. Myocardial infarction

E. Pulmonary embolism

2. The most common cause of hypovolemic shock is:

A. Blood loss                       B. Burns

C. Fluid shifts                      D. Peritonitis

E. Ascites

3. Most common cause of septic shock is

A. gram-positive bacteria             B. gram-negative bacteria

C. Protozoa                        D. ABO-incompatible blood

E. Viruses.

4. Which factor of the following keeps balance with TXA₂?

A .NO                            B. SOD 

C. ADH                           D. MDF

E. PGI₂                                                        

5. What is the major clinical signs in irreversible stage of shock?

A. Cold clammy grayish-bluish         B. Oliguria

C. Overbreathing                    D. Hypotension

E. Hyperventilation

6. Anaphylactic shock is triggered by an allergic reaction, anaphylactic shock occurs when a person is exposed to an antigen to which he has already been sensitized. Which kind of cells play important role in this kind of shock?

A. White blood cells                 B. Red blood cells

C. Mast cells                       D. Acidocyte

E. Myocyte                                                   

7.Which factor directly trigger the septic shock?

A. Tumor necrosis factor (TNF)        B. Endotoxin

C. Thromboxane A₂                  D. Leukotrienes

E. Platelet-activating factor (PAF)

8. What is the manifestation of microcirculation at early stage of shock?

A. Precapillary sphincter constriction    B. Blockade of the micro-vessels

C. No-reflow                       D. Formation of micro-thrombus

E. Blood flow stop

9. For drug administration of early hypovolemic shock, the better choice is:

A. Avidin                          B. Medicine of dilatating vessel

C. Medicine of constricting vessel      D. Antibiotics

E. Anticoagulant

10. For septic shock, which kind of medicine is absolutely necessary?

A. Antibiotics                     B. Diuretic

C. Histamine                      D. Manitol

E. Heparin

Ⅳ. Multiple choice questions of type X

1. Causes of neurogenic shock may include

A. Spinal cord injury                 B. Spinal anesthesia

C. Vasomotor center depression        D. Hypoglycemia

E. Medications                                              

2. Causes of septic shock may include

A. Gram-negative bacteria             B. Gram-positive bacteria

C. Protozoa                        D. ABO-incompatible blood

E. Viruses

3. What factors can cause hypovolemic shock?

A. Blood loss                                          B. Burns

C. Fluid shifts                                         D. Gastrointestinal fluid loss 

E. Dehydration caused by excessive perspiration    

4. Causes of anaphylactic shock may include

A. Vaccines                         B. Spinal anesthesia

C. ABO-incompatible blood            D. Hypoglycemia

E. Venom

5. What can cause cardiogenic shock?

A. Myocardial infarction                           B. Cardiomyopathy

C. Heart failure                                        D. Pericardial tamponade

E. Tension pneumothorax.                 

6. In ischemic hypoxia stage of shock, besides hyperactivity of sympathetic- adrenal medulla system, some other vasoconstrictors also have effects on microcirculation. These vasoconstrictors include

A. AngiotensinⅡ                                           

B. Antidiuretic,hormone (ADH)

C. Myocardial depressant factor (MDF)           

D. Thromboxane A₂ (TXA₂)

E. Endothelin (ET)                                        

7. Which factors are relative to septic shock?

A. Tumor necrosis factor (TNF)         B. Endotoxins

C. Thromboxane A₂                            D. Leukotrienes

E. Platelet-activating factor (PAF)

8. What are the manifestations of microcirculation at DIC stage of shock?

A. Congestion of microcirculation       B. Microvessel contraction

C. No-reflow of capillary              D. Formation of micro-thrombus

E. Blood flow became slow

9. In the compensatory stage of shock, which signs and symptoms can be observed?

A. Tachycardia and bounding pulse due to sympathetic stimulation

B. Restlessness and irritability related to cerebral hypoxia

C. Tachypnea to compensate for hypoxia

D. Reduced urinary output secondary to vasoconstriction

E. Cool, pale skin associated with vasoconstriction, warm, dry skin in septic shock due to vasodilation.

Ⅴ. Term explanations

1. shock                                                  2. shock lung

3. hypodynamic shock                              4. hypovolemic shock

5. MDF                                              

Ⅵ. Questions to be answered briefly

1. In compensatory stage of shock, what are the compensatory significances?

2. Why does the body can maintain the BP in normal level in the ischemic hypoxia stage of shock?

3. What factors are released into blood during progressive stage of shock?

4. What are the manifestations of microcirculation at DIC stage of shock?

5. What are the principles of treatment for shock?

6. What are the complications of shock?

Ⅶ. Questions to be answered in detail

1. What changes of microcirculation can occur in the ischemic hypoxia stage of shock? Please describe the mechanisms of these changes and significances of these changes.

2. What are pathophysiology changes of progressive stage?

3. Try to explain the clinical signs and microcirculatory changes in DIC stage of shock.