What is shock?
Shock is a condition in which the systemic blood pressure is inadequate to deliver oxygen and nutrients to cellular function and vital organs. It is an acute medical condition associated with reduced perfusion to body tissues.https://www.google.com/url?sa=t&source=web&rct=j&opi=89978449&url=https://www.icd10data.com/ICD10CM/Codes/R00-R99/R50-R69/R57-/R57.9&ved=2ahUKEwiBvvmM68eAAxX1cmwGHZNOAXsQFnoECBQQAQ&usg=AOvVaw2fMHgwWxACvHjPVEiHugTl
Stages of shock:
Initial stage: Decreased cardiac output results in reduced mean arterial pressure. Increase in heart rate due to stimulation of sympathetic nervous system. Characterized by increased heart rate, decreased blood pressure, thirst, pale, cool, moist skin over the face.
Compensatory stage: Stimulation of sympathetic nervous system releases epinephrine and norepinephrine to maintain homeostasis. Peripheral vasoconstriction caused by stimulation of a1 adrenergic fibers assures more blood available for heart and brain. Coronary and cerebral artery dilation occurs due to stimulation of beta adrenergic fibers. This results in increased cardiac output. Increased renal sodium and water reabsorption results in increased cardiac output.
Compensatory stage of shock
Progressive stage: Compensatory mechanisms become ineffective. Impaired perfusion results in anaerobic metabolism and cellular hypoxia. Renal ischemia stimulates renin-angiotensin-aldosterone system, which further causes vasoconstriction.
Irreversible stage: Compensatory mechanisms are ineffective. Coronary and cerebral tissue perfusion drops, and organ system fail.
Classification of Shock Based on Etiology:
Hypovolemic shock, Cardiogenic shock and Circulatory or Disruptive shock
Hypovolemic shock: Occurs because of low blood pressure.
Causes: External fluid loss such as Vomiting, Diarrhea, diuresis, Diabetes Insipidus, Trauma, Surgery. Internal fluid shift such as hemorrhage, burns, ascites, peritonitis and dehydration.
Manifestations: Rapid, irregular and thready pulse. Urine output less than 20 ml/hr or 400 ml/24 hrs.
Management:
Crystalloids: Ringer Lactate and Normal Saline are commonly used for fluid replacement.
Colloids: Albumin, Dextran and Hectastarch can also be used to replace fluid volume.
Cardiogenic Shock: Heart is not able to perform its function. https://www.google.com/url?sa=t&source=web&rct=j&opi=89978449&url=https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8405485/&ved=2ahUKEwimyrWl6seAAxVw1jgGHUwUB5E4ChAWegQICxAB&usg=AOvVaw1wh7mxYswxR_pXOIDcEMf2
Causes: Myocardial infarction, Cardiomyopathy, Valve disease, Cardiac tamponade , Arrhythmia.
Manifestations: Anginal pain, Dysrhythmias, Cyanosis of Skin, Jugular Vein Distension, Pulmonary Crackles.
Management: Supplemental oxygen, Pain management, Selected fluid support, Vasoactive medications, e.g. Dobutamine, Nitroglycerin, Norepinephrine, Desmopressin, Amrionone and Anti-arrhythmic drugs.
Cardiac supportive measures such as Pacemaker, Ventricular assistive devices,Intra- aortic balloon pump or Extracorporeal cardiopulmonary bypass.
Circulatory or Distributive shock: It includes septic shock, anaphylactic shock, neurogenic shock and hypodynamic shock.
Septic shock: Occurs because of infection. Manifestation include rapid heart, warm, pink extremities and widening pulse pressure.
Anaphylactic shock: Occurs because of allergic reaction. Manifestation include feeling warm, abdominal pain, diarrhea, flushing, pruritus, urticaria.
Management: Remove the causative antigen. Epinephrine to restore vasoconstrictive action. Albuterol (if histamine induced bronchospasm present)
Neurogenic Shock: Dilatation of blood vessels because of the damage to sympathetic nervous system controlling it. Signs and symptoms include bradycardia, hypotension, hypothermia, dry warm skin.https://www.google.com/url?sa=t&source=web&rct=j&opi=89978449&url=https://www.medicalnewstoday.com/articles/neurogenic-shock&ved=2ahUKEwi_nbrx6ceAAxV_yTgGHeEmC5EQFnoECCwQAQ&usg=AOvVaw3vgDVfKDX2mEf68LD5cUwv
Management: Treatment of the underlying cause and restore sympathetic tone.
Hypodynamic shock: Narrowing pulse pressure, Oliguria, Cold extremities.
Key Points: If the cause for hypovolemic shock is hemorrhage, then the use of Dextran is contraindicated because it interferes with the platelet aggregation.
Calculation of Mean Arterial Pressure:
Method 1:
Mean Arterial Pressure(MAP)= DBP+⅓(SBP-DBP) Where, SBP- Systolic Blood Pressure and DBP- Diastolic Blood Pressure
For e.g. if the SBP= 120 mm Hg and DBP= 75 mm Hg, the MAP is :
MAP= 75+⅓(120-75)
= 75+45/3 = 75+15=90
Method 2:
Mean Arterial Pressure (MAP)= SBP+(2*DBP)/3
e.g. if the SBP= 120 mm Hg and DBP= 75 mm Hg, the MAP is :
MAP= 120+(2*75)/3
= (120+150)/3 = 270/3 = 90
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