Circulatory Shock MBBS PDF

Circulatory Shock Dr. Ikemefuna 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...

Circulatory Shock Dr. Ikemefuna 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 it may result in death if the affected person is not treated immediately. MANIFESTATIONS OF CIRCULATORY SHOCK A characteristic feature of all types of circulatory shock is the insufficient blood flow to the tissues, particularly the brain. The major cause of decreased blood flow is the reduction in cardiac output. Following are the manifestations of circulatory shock: 1. Whenever cardiac output is decreased, arterial blood pressure drops down 2. Low blood pressure produces reflex tachycardia and reflex vasoconstriction 3. Tachycardia decreases the diastolic period. So, the filling of the heart is reduced leading to a decrease in stroke volume and systolic pressure. This decreases the pulse pressure below 20 mm Hg. Pulse also becomes feeble.  4. Stagnant hypoxia develops because of decreased velocity of blood flow 5. Skin becomes pale and cold due to the vasoconstriction 6. Along with hypoxia, cyanosis also develops in many parts of the body, particularly ear lobes and fingertips 7. Glomerular filtration rate (GFR) and urinary output are reduced due to fall in blood pressure and constriction of renal blood vessels 8. Metabolic activities of myocardium are accelerated because of reduced blood flow and increased heart rate. A large amount of lactic acid is produced, resulting in acidosis. 9. Acidosis decreases myocardial efficiency and pumping action of the heart leading to further reduction in cardiac output 10. So, the blood flow to vital organs is severely affected 11. Lack of blood flow to brain tissues produces ischemia resulting in fainting and irreparable damage of brain tissues 12. Finally the damage of brain tissues and cardiac arrest kill the victim.  Circulatory shock occurs in three stages: 1. First stage or STAGES OF CIRCULATORY compensated stage SHOCK 2. Second stage or progressive stage 3. Third stage or irreversible stage.  The first stage is also called a non-progressive stage. When blood loss is less than 10% of total volume, the blood pressure decreases only moderately. And the regulatory mechanisms in FIRST STAGE the body operate successfully to reestablish normal blood pressure and normal blood flow throughout OR the body. COMPENSATED Thus, the shock becomes nonprogressive and the person recovers. STAGE Regulatory mechanisms involve negative feedback control. Regulatory mechanisms are: i. Baroreceptor mechanism ii. Renal mechanism iii. ADH mechanism.  Baroreceptor Mechanism Ischemic response by baroreceptors initiates strong sympathetic stimulation, which causes vasoconstriction and tachycardia Renal Mechanism Kidneys release large amount of renin that increases the angiotensin II formation. Angiotensin II produces intense vasoconstriction and increases release of aldosterone from adrenal cortex. Aldosterone in turn promotes retention of water and salts by kidneys. This helps in restoration of blood volume.  ADH Mechanism Antidiuretic hormone (ADH) released from posterior pituitary increases retention of water by kidneys. ADH also enhances vasoconstriction. Because of 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 shock is not severe enough to progress further. With proper treatment, the progression can be arrested completely.  Second stage is also called decompensated stage. When the shock is severe, positive feedback system develops so that regulatory mechanisms become inadequate to compensate. And the shock enters progressive stage. SECOND STAGE With immediate and appropriate treatment, this stage OR of shock can be reversed. PROGRESSIVE During this stage, blood pressure falls to a low level, which is not adequate to maintain the STAGE blood flow to cardiac muscle. So the myocardium starts deteriorating because of lack of nutrition and oxygen. Toxic substances released from tissues also suppress the myocardium. Particularly, the bacterial toxin called endotoxin 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 Third stage is the last stage prior to the collapse. It is also called refractory stage. Irreversible stage leads to death regardless of 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 decrease in the myocardial activity and reduced arteriolar tone resulting in death of the affected person. TYPES AND CAUSES OF CIRCULATORY SHOCK Circulatory shock is primarily classified into four types A. Shock due to decreased blood volume B. Shock due to increased vascular capacity C. Shock due to cardiac disease D. Shock due to obstruction of blood flow. SHOCK DUE TO DECREASED BLOOD VOLUME – HYPOVOLEMIC SHOCK Shock due to decreased blood volume is called hypovolemic shock or cold shock. It occurs when there is acute loss of at least 10% to 15% of blood. Loss of blood less than 10% may not produce any significant effect because of immediate compensatory mechanism Important Manifestations of Hypovolemic Shock 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..  Pathological Conditions when Hypovolemic Shock Occurs 1. Hemorrhage: Hemorrhagic shock 2. Trauma: Traumatic shock 3. Surgery: Surgical shock 4. Burns: Burn shock 5. Dehydration: Dehydration shock. 1. Hemorrhagic Shock Hemorrhagic shock is the shock due to hemorrhage. Acute hemorrhage as in the case of accident causes shock. Chronic hemorrhage as in ulcers does not produce shock.  2. Traumatic Shock Trauma means serious injury or wound caused by some external force. Shock caused by trauma is called traumatic shock. Shock occurs due to the damage of muscles and bones, which is common in battlefields and road accidents. Apart from loss of blood, the plasma escapes to the tissue spaces. 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 Burn shock is the shock produced by the effects of burn. In burns, 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 decrease in 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. Capacity of the vascular system increases by the extensive dilatation of blood vessels. It is also known as vasogenic or low resistance or distributive shock. Causes and Types of Vasogenic Shock 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 nervous system due to extensive vasodilatation caused by loss of vasomotor tone. Conditions when neurogenic shock develops i. Ischemia of brain: Severe ischemia in medulla depresses the activity of vasomotor center ii. General anesthesia iii. Spinal anesthesia iv. Emotional conditions: Extreme emotions cause sudden and exaggerated activity of autonomic nervous system, the subject faints because of neurogenic shock.  Syncope (Fainting) Syncope or fainting is the sudden and transient (shorttime) loss of consciousness and postural tone with spontaneous recovery. It occurs due to temporary inadequate cerebral blood flow. Types of syncope: i. Vasovagal syncope or emotional fainting: Fainting is caused by sudden stimulation of vagus nerve. It is also called neurocardiogenic syncope. ii. Postural syncope: Loss of consciousness because of prolonged standing. iii. Micturition syncope: Fainting during micturition. It is common in the patients who suffer from orthostatic hypotension. Fall in blood pressure while standing is called orthostatic hypotension iv. Effort syncope: Fainting caused during exercise or any other strain  v. Cough syncope: Fainting while coughing. Sometimes, severe cough increases intrathoracic pressure, which reduces the venous return and cardiac output leading to fainting. vi. Carotid sinus syncope: Fainting in persons wearing dress with tight collar. Tight collar of the dress exerts pressure over the region of carotid sinus  2. Anaphylactic Shock Anaphylaxis means exaggerated allergic reaction to a foreign protein or antigen or any other substance to which the person has been previously sensitized. 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 the chemical mediators such as histamine that are secreted during anaphylactic reaction. 3. Septic Shock Sepsis is the pathological condition characterized by the presence of pathogenic organisms or their toxins in blood or tissues. Shock developed during sepsis is known as septic shock or blood poisoning.  Conditions when septic shock occurs i. Infection of the uterus and fallopian tube, commonly occurring in abortion by instrumentation ii. Infection of peritoneum iii. Spreading of skin infection due to bacteria like streptococci or staphylococci iv. Spread of infection from any other part of the body. Septic shock develops due to the depression of myocardium, dilatation of blood vessels and increased permeability of capillary membrane. All these effects occur due to the toxic substances released by bacteria. Septic shock is also called as vasogenic, cardiogenic or hypovolemic shock.  Endotoxin shock Endotoxin shock 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 alimentary tract by gram-negative bacteria like colon bacilli. It is actually released from dead bacteria. Endotoxin shock can also occur in urinary tract infection. SHOCK DUE TO CARDIAC DISEASES – CARDIOGENIC SHOCK Shock due to cardiac disease is also called cardiogenic shock. Conditions when Cardiogenic Shock Occurs 1. Arrhythmia, particularly those which lead to reduced cardiac output 2. Depressed activity of 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 circulatory system is called obstructive shock. Conditions when Obstructive Shock Occurs 1. Tumor in myocardium 2. Cardiac tamponade 3. Obstruction of blood vessels in lungs due to embolism TREATMENT FOR CIRCULATORY SHOCK Treatment for shock is based on the cause of the shock. Following are the various measures taken during the treatment of shock. BLOOD TRANSFUSION Transfusion of whole blood is done in hypovolemic shock except burn shock. PLASMA TRANSFUSION Plasma transfusion is very useful in burns or other shocks in which there is loss of more plasma. ADMINISTRATION OF PLASMA SUBSTITUTES 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. Commonly used Plasma Substitutes i. Plasma expanders (solutions of sugar with high molecular weight such as dextran); such substances do not escape through capillary membrane ii. Concentrated human serum albumin iii. Hypertonic solutions, which cause drawing of fluid into blood from interstitial space. 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 the blood pressure by vasoconstriction. However, the sympathomimetic drugs should not be used for longer period since, these drugs induce severe myocardial activity. In traumatic and cardiogenic shocks, dopamine is used. OXYGEN THERAPY Oxygen therapy is given only in severe conditions involving reduced oxygenation of tissues. ADMINISTRATION OF GLUCOCORTICOIDS Glucocorticoids are administered in serious conditions. Glucocorticoids increase the glucose metabolism in damaged tissues, prevent further damage of tissues and increase the myocardial activity. 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 prolonged head down position might affect the ventilation. It is because of effect of the increased pressure exerted by abdominal viscera on diaphragm. Thank You