Cardiogenic Shock And Heart Failure

Circulatory Shock And Heart Failure Definition

Shock is a general term that refers to the depression or suppression of body functions produced by any disorder. Circulatory shock refers to the shock developed by inadequate blood flow throughout the body.

It is a life-threatening condition and if the affected person is not treated immediately it may result in death.

Read And Learn More: Medical Physiology Notes

Manifestations Of Circulatory Shock

The characteristic feature of all types of circulatory shock is insufficient blood flow to the tissues, particularly the brain.

The main cause of the decreased blood flow is the reduction in cardiac output. The following are the manifestations of circulatory shock:

1. When cardiac output reduces, the arterial blood pressure drops down
2. Low blood pressure produces reflex tachycardia and reflex vasoconstriction
3. Increased heart rate decreases the diastolic period. So, the filling of the heart is reduced leading to a decrease in stroke volume and systolic pressure.
4. This decreases the pulse pressure below 20 mm Hg. The pulse also becomes feeble
5. The velocity of the blood flow decreases
6. Due to the vasoconstriction, the skin becomes pale and cold
7. The reduction in velocity of blood flow produces stagnant hypoxia
8. Along with hypoxia, cyanosis also develops in many parts of the body, particularly ear lobes, and fingertips
9. The fall in blood pressure and constriction of renal blood vessels decrease the renal blood flow and GFR.
10. The urinary output is greatly reduced
11. Due to reduced blood flow and increased heart; the metabolic activities of the myocardium am- accelerated
12. During increased metabolic activities, there is the production and accumulation of an excess amount of lactic acid resulting in acidosis
13. Acidosis decreases the efficiency of the myocardium, and it reduces the pumping action of the heart still further leading to more reduction in cardiac output
14. So, the blood flow to vital organs is severely affected
15. The lack of blood flow to the brain tissues produces ischemia resulting in fainting and irreparable damage to the brain.
16. Finally, the damage to brain tissues and cardiac arrest kills the victim.

Stages Of Circulatory Shock

The circulatory shock occurs in three stages:

1. The first stage or compensated stage
2. The second stage or progressive stage
3. The third stage or irreversible stage.

First Stage Or Compensated Stage

• It is also called the nonprogressive stage. When a shock is not severe, the blood pressure decreases only moderately.
• The regulatory mechanisms in the body operate successfully to re-establish normal blood pressure and normal blood flow throughout the body. Thus the shock becomes nonprogressive and the person recovers.

The regulatory mechanisms involve negative feedback control. The mechanisms are:

1. Baroreceptor mechanism and ischemic response initiate strong sympathetic stimulation which causes vasoconstriction and tachycardia.
2. Kidneys release large amounts of renin that increases the angiotensin 2 formation.
3. Angiotensin 2 produces intense vasoconstriction and increases the release of aldosterone from the adrenal cortex.
4. Aldosterone in turn promotes the retention of water and salts by the kidneys. This helps in the restoration of blood volume.
   • ADH released from the posterior pituitary increases the retention of water by the kidneys. ADH also enhances vasoconstriction.
   • Because of the severe vasoconstriction caused by the regulatory mechanisms normal blood pressure is re-established.
   • Retention of water by kidneys and the consequent fluid shift mechanism that moves water from interstitial space and intestinal lumen restores the blood volume.
   • And the person recovers if the shock is not severe enough to progress further. With proper Sment the progression can be arrested completely.

Second Stage Or Progressive Stage

• The age is also called the decompensated stage. When the shock is severe, the positive feedback system develops so that regulatory mechanisms become inadequate to compensate.
• And the shock enters the progressive stage. With immediate and appropriate treatment, this stage of shock can be reversed.
• During this stage, the blood pressure falls to a low level which is not adequate to maintain the blood flow to cardiac muscle.
• So the myocardium starts deteriorating because of a lack of nutrition and oxygen.
• The toxic substances released from tissues also suppress the myocardium. Particularly, the bacterial toxin called endotoxin (see below) affects the myocardium severely.
• Loss of blood flow also causes suppression of the vasomotor system and the sympathetic system.
• This causes a further fall in blood pressure. Due to low pressure, thrombosis starts in small blood vessels like capillaries.
• Now the capillary permeability increases allowing passage of fluid from blood vessels into interstitial space.
• Finally because of tissue deterioration severe symptoms start appearing. And the shock progresses to an irreversible stage.

Third Stage Or Irreversible Stage

• It is the last stage prior to the collapse. The irreversible stage leads to death regardless of the type of treatment offered to the patient.
• It is because the brain fails to function due to severe cerebral ischemia.
• The blood pressure falls drastically. Even the infusion of blood fails to restore blood pressure.
• Finally, cardiac failure occurs due to a decrease in myocardial activity and reduced arteriolar tone resulting in the death of the affected person.

Types And Causes Of Circulatory Shock

Circulatory shock is primarily classified into four types.

1. Shock due to reduced blood volume
2. Shock due to increased vascular capacity
3. Shock due to cardiac disease
4. Shock due to obstruction of blood flow.

Shock Due To Decreased Blood Volume – Hypovolemic Shock

It is also called hypovolemic shock or cold shock. The important manifestations of this type of shock are:

1. Decrease in cardiac output
2. Low blood pressure
3. Thin thready pulse
4. Pale and cold skin
5. Increase in respiratory rate
6. Restlessness or lethargy.

Hypovolemic shock occurs in the following pathological conditions:

1. Hemorrhage – hemorrhagic shock
2. Trauma – traumatic shock
3. Surgery – surgical shock
4. Burns – burn shock

1. Hemorrhagic Shock

• It is the shock due to hemorrhage. Acute hemorrhage as in the case of an accident causes shock.
• Chronic hemorrhage as in ulcers does not produce shock. Details of effects of hemorrhage.

2. Traumatic Shock

• Trauma means injury or wound caused by some external force. The shock caused by trauma is called traumatic shock.
• The shock occurs due to the damage to muscles and bones, which is common in battlefields and road accidents.
• Apart from the loss of blood, the plasma escapes to the tissue spaces.

The common symptoms of traumatic shock are:

Crush syndrome

• Crush syndrome is a condition characterized by renal failure when the limb of a person is crushed or compressed in a traumatic condition.
• The myoglobin and some toxic substances released from affected muscles damage the renal tubular cells leading to degeneration of renal tubules.
• The stimulation of somatic afferents from the damaged muscles causes constriction of the renal vase’s AH these factors result in renal failure.

Reperfusion injury

Reperfusion injury refers to dysfunction of the myocardium, blood vessels, or any other tissue which is induced by restoration of blood flow to previously ischemic tissue. It is also called injury by reperfusion.

Due to compression or damage during traumatic conditions, the ischemic tissues release some toxic substances.

Later, when blood supply is restored to the tissues again, the toxic substances enter the tissues and cause further damage of the tissues. The common instance is myocardial reperfusion injury.

3. Surgical Shock

Surgical shock is the shock developed by surgical procedures. Surgical shock develops due to some reasons like internal hemorrhage, external hemorrhage, and dehydration that occur during or after surgical procedures.

4. Burn Shock

It is the shock produced by the effects of the burn. In burns, the loss of plasma through the burnt surface is more than the loss of whole blood.

It decreases the ECF volume and plasma volume, resulting in hemoconcentration.

This leads to sluggish blood flow, which decreases the cerebral blood flow causing shock.

5. Dehydration Shock

Shock due to dehydration is called dehydration shock. Dehydration means a decrease in the water content of the body. It decreases the blood volume resulting in shock.

Shock Due To Increased Vascular Capacity-Vasogenic Shock

• In this case, the blood volume is normal. Shock occurs because of inadequate blood supply to the tissues due to increased vascular capacity.
• The capacity of the vascular system increases by the extensive dilatation of blood vessels.

It is also known as vasogenic low resistance or distributive shock. The causes for vasodilatation are:

1. Sudden loss of vasomotor tone – neurogenic shock
2. Anaphylaxis – anaphylactic shock
3. Sepsis – septic shock.

1. Neurogenic Shock

Neurogenic shock is the type of shock characterized by sudden depression of the nervous system due to extensive vasodilatation caused by loss of vasomotor tone. It is common in:

1. Ischemia of the brain: Severe ischemia in the medulla depresses the activity of the vasomotor center
2. General anesthesia
3. Spinal anesthesia
4. Emotional conditions: Extreme emotions cause sudden and exaggerated activity of the autonomic nervous system, the subject faints because of neurogenic shock.

Fainting (Syncope)

Fainting or syncope is the sudden and transient (short-time) loss of consciousness and postural tone with spontaneous recovery.

It occurs due to temporary inadequate cerebral blood flow. It is of different types:

• Vasovagal syncope or emotional fainting: Vasovagal syncope is fainting caused by sudden stimulation of the vagus nerve. It is also called neurocardiogenic syncope.
  • It is due to extreme activation of the parasympathetic division of the autonomic nervous system.
  • There is a sudden decrease in heart rate (bradycardia) because of the inhibition of the myocardium by the vagus.
  • At the same time, the blood pressure also decreases (hypotension) due to severe vasodilatation by the parasympathetic nerve fibers.
  • Simultaneously, the sympathetic tone is decreased and it also causes vasodilatation leading to hypotension.
  • Because of bradycardia and hypotension, the cerebral blood flow decreases.
  • This results in fainting. Vasovagal syncope is common in conditions like severe emotional distress and exertion.
• Postural syncope: It is the loss of consciousness because of prolonged standing.
  • It is due to the pooling of blood in lower limbs during prolonged standing resulting in decreased blood supply to the brain.
  • Micturition syncope: It is the fainting during micturition. It is common in patients who suffer from orthostatic hypotension.
  • A fall in blood pressure while standing is called orthostatic hypotension.
• Effort syncope:
  • It is the fainting that is caused during exercise or any other strain.
  • It is a common symptom in patients with stenosis of semilunar valves.
  • These patients faint during exercise or any other physical strain. It is due to the failure of the heart to increase cardiac output when the tissues need more blood flow.
• Cough syncope:
  • Fainting while coughing is called cough syncope. Sometimes, severe cough increases intrathoracic pressure, which reduces the venous return and cardiac output leading to fainting.
• Carotid sinus syncope: It is common in persons wearing a dress with a tight collar.

 

2. Anaphylactic Shock

• Anaphylaxis means an exaggerated allergic reaction to a foreign protein antigen or any other substance to which the person has been previously sensitized.
• The shock that develops during anaphylactic reactions is called anaphylactic shock.
• Shock occurs because of vasodilatation and sudden fall in blood pressure.
• It is caused by chemical mediators such as histamine that are secreted during anaphylactic reactions.

3. Septic Shock

• Sepsis is a pathological condition characterized by the presence of pathogenic organisms or their toxins in blood or tissues.
• The shock developed during sepsis is known as septic shock or blood poisoning.

Septic shock is common in the following conditions:

1. Infection of the uterus and fallopian tube, commonly occurring in abortion by instrumentation
2. Infection of peritoneum
3. Spreading of skin infection due to bacteria like Streptococci or Staphylococci
4. Spread of infection from any other part of the body. Septic shock develops due to the depression of the myocardium, dilatation of blood vessels, and increased permeability of the capillary membrane.

All these effects occur due to the toxic substances released by bacteria. The septic shock is also called vasogenic, cardiogenic, or hypovolemic shock.

Endotoxin shock

• It is the shock developed by a bacterial toxin called endotoxin. Endotoxin is a lipopolysaccharide.
• It causes vasodilatation and depresses myocardial activity. It also activates the macrophages to release cytokines.
• Endotoxin shock is very common during the infection of an alimentary tract by gram-negative bacteria like Colon bacilli. It is actually released from dead bacteria.
• Endotoxin shock can also occur in urinary tract infections.

Shock Due To Cardiac Diseases – Cardiogenic Shock

Is also called cardiogenic shock. It occurs in cardiac disorders such as:

1. Arrhythmia, particularly arrhythmia, leads to reduced cardiac output
2. The depressed activity of the myocardium due to ischemia
3. Congestive cardiac disease.

Shock Due To Obstruction Of Blood Flow – Obstructive Shock

Shock developed due to the obstruction of blood flow through the circulatory system is called obstructive shock.

It occurs in the following conditions:

1. Tumor in myocardium
2. Cardiac tamponade
3. Obstruction of blood vessels in lungs due to embolism.

Treatment For Circulatory Shock

The treatment for shock is based on the cause of the shock.

The various measures used in the treatment of shock are:

1. Blood Transfusion

The transfusion of whole blood is done in hypovolemic shock except burn shock.

2. Plasma Transfusion

It is very useful in burns or other shocks in which there is a loss of more plasma.

3. Administration Of Plasma Substitutes

A plasma substitute is a solution of a substance that is used for transfusion instead of plasma. Plasma substitutes are used when plasma is not available.

The commonly used plasma substitutes are:

• Plasma expanders: The plasma expanders are solutions of sugar with high molecular weight like dextran.
• Such substances do not escape through the capillary membrane
• Concentrated human serum albumin
• Hypertonic solutions, cause the drawing of fluid into the blood from interstitial space.

4. Administration Of Sympathomimetic Drugs

Sympathomimetic drugs like epinephrine and norepinephrine are useful in neurogenic and anaphylactic shocks, which occur due to vasodilatation. These two drugs restore blood pressure by vasoconstriction.

However, sympathomimetic drugs should not be used for longer periods since these drugs cause extremely increased myocardial activity. In traumatic cardiogenic shocks, dopamine is used.

5. Administration Of Glucocorticoids

Glucocorticoids are administered in serious conditions. Glucocorticoids increase the glucose metabolism in damaged tissues, prevent further damage to tissues, and increase myocardial activity.

6. Oxygen Therapy

Oxygen therapy is given only in severe conditions involving reduced oxygenation of tissues.

7. By Changing The Posture

• This is the first measure to be taken in cases of hemorrhagic and neurogenic shock.
• The head-down position, by raising the bed at the foot end increases venous return, cardiac output, and cerebral blood flow.
• However, this should not be used for longer periods because a prolonged head-down position might affect the ventilation.
• It is because of the effect of the increased pressure exerted by abdominal viscera on the diaphragm.

Heart Failure

Heart Failure Introduction

Heart failure or cardiac failure is a condition in which the heart loses the ability to pump a sufficient amount of blood to all parts of the body.

Heart failure may involve the left ventricle or right ventricle or both. It may be acute or chronic.

Acute Heart Failure

Acute heart failure refers to the sudden and rapid onset of signs and symptoms of abnormal heart functions.

Its symptoms are severe initially. However, the symptoms last for a very short time and the condition improves rapidly. Usually, it requires treatment.

Chronic Heart Failure

Chronic heart failure is heart failure that is characterized by symptoms that appear slowly over a period of time and become worse gradually.

Congestive Heart Failure

• It is a general term used to describe heart failure resulting in the accumulation of fluid in the lungs and other tissues.
• When the heart is not able to pump blood through the aorta, the blood remains in the heart. It results in dilatation of the chambers and accumulation of blood in veins F/mcufar congestion).
• This condition is also manifested by fluid retention and pulmonary edema.

Causes Of Heart Failure

The common causes of heart failure are:

1. Coronary artery disease
2. Defective heart valves
3. Arrhythmia
4. Cardiac muscle diseases such as cardiomyopathy
5. Hypertension
6. Congenital heart disease
7. Diabetes
8. Hyperthyroidism
9. Anemia
10. Lung disorders
11. Inflammation of cardiac muscle (myocarditis) due to viral infection, drugs, alcohol, etc.

Signs And Symptoms Of Heart Failure

Signs And Symptoms Of Chronic Heart Failure

1. Fatigue and weakness
2. Rapid and irregular heartbeat
3. Shortness of breathing
4. Fluid retention and weight gain
5. Loss of appetite
6. Nausea and vomiting
7. Cough
8. Chest pain, if developed by myocardial infarction

Signs and Symptoms of Acute Heart Failure

• The signs and symptoms of acute heart failure may be the same as chronic heart failure.
• But the signs and symptoms appear suddenly and severely. When the heart starts to fail suddenly, the fluid accumulates in the lungs causing pulmonary edema.
• It results in sudden and severe shortness of breath, cough with pink, foamy mucus, and heart palpitations.
• It may lead to sudden death, if not attended immediately.

Types Of Heart Failure

1. Systolic Heart Failure

• It is the heart failure due to the decreased ability of the heart to contract. It may involve the right heart or left heart or both. It is caused either by muscular weakness or valvular defect.
• Ventricles may be filled with blood but cannot pump it out with sufficient force.
• The ejection fraction decreases to about 20%. So the amount of blood pumped to the body and to the lungs is decreased. As a result, more amount of blood remains in the ventricle.
• Later the blood starts accumulating in the lungs or systemic vein. or both. Usually, the ventricle enlarges in systolic heart failure.

2. Diastolic Heart Failure

• It is heart failure that occurs when the ventricles cannot relax properly due to the stiffening of cardiac muscle.
• So, there is a reduction in ventricular filling and cardiac output.

3. Right-Sided Heart Failure

It is heart failure that occurs due to the loss of pumping action of the right side of the heart.

Because of the loss of pumping action of the right ventricle, blood accumulates in the right atrium and blood vessels. It causes edema in the feet, ankles, legs, and abdomen.

4. Left-Sided Heart Failure

It is due to the failure of the pumping action of the left side of the heart. It causes congestion of the lungs.

Compensated Versus Decompensated Heart Failure

• Chronic heart failure may be compensated or decompensated.
• Compensated heart failure is heart failure with sufficient cardiac output.
• The heart tries to maintain cardiac output by normal compensatory mechanisms such as an increase in heart rate, an increase in the force of ventricular contraction, and ventricular hypertrophy.
• In compensated heart failure the symptoms are stable and features of retention and pulmonary edema are absent.
• In most of the patients the heart cannot meet the demand even by compensatory mechanisms and this condition leads to decompensated head failure.
• Decompensated heart failure is heart failure with inadequate cardiac output.
• It is characterized by deterioration and sudden and drastic worsening of cardiac function resulting in death.