Pathyophysiology and Classification of Shock

1. Pathyophysiology and Classification of Shock KENNEY WEINMEISTER M.D.

2. Definition • Shock is a physiologic state characterized by a significant, systemic reduction in tissue perfusion, thereby resulting in decreased tissue oxygen delivery.

3. Stages of Shock • Early, Preshock, Warm shock • Compensation by body’s homeostatic mechanisms • Tachycardia, Peripheral vasodilatation and modest decrement in systemic BP

4. Stages of Shock • Shock • Homeostatic mechanisms are overwhelmed • Signs and symptoms of organ dysfunction • Tachycardia, tachypnea, metabolic acidosis, oliguria, and cool and clammy skin • 20 to 25% fall in effective blood volume • Fall in CI to < 2.5L/min/M2 • Activation of mediators of sepsis

5. Stages of Shock • End Organ Dysfunction • Pathophysiology • AG II & NE cause increased Ca+2 in cytosol • Ca + calmodulin = P+myosin • P+myosin + actin = Myosin ATPase • Myosin ATPase = muscle contraction

6. Pathophysiology of End Organ Shock • Activation of ATP sensitive potassium channels • Activation causes hyperpolarization • Closure of Ca channels • Activated by decrease in cellular ATP and increases in cellular H+ and lactate • Natriuretic peptide and nitric oxide

7. Pathophysiology of End Organ Shock • Increased production on Nitric Oxide • activation of myosin light-chain phosphatase • leads to dephosphoralation of myosin • Vasopressin deficiency • potentiates vasoconstrictor effects of NE • directly inactivates Katp channels • blunts increase in cGMP • decreases synthesis of NO synthase

8. Pathophysiology of End Organ Shock • Vascular smooth muscle tone is lost • Resistant vasodilatation • End organ dysfunction and death

9. Classification of Shock • Hypovolemic shock • Cardiogenic shock • Distributive shock

10. Hypovolemic Shock • Results from decreased preload • Hemorrhagic • Trauma, GIB, Ruptured aneurysm • Volume loss • Third spacing, GI losses, burns, insensible losses

11. Cardiogenic Shock • Pump failure • Cardiomyopathies • Ischemic right and left ventricle, • Dilated • Stunned myocardium

12. Cardiogenic Shock continued • Arrhythmia's • Bradyarrhythmias • Tachyarrhythmias • Mechanical • Valvular; MR, AI, AS • VSD • Atrial myxoma

13. Cardiogenic Shock continued • Obstructive • Massive PE • Tension pneumothorax • Constrictive pericarditis • Tamponade • Severe pulmonary hypertension

14. Distributive Shock • Vasodilatory shock resulting in severe decrease in SVR • Septic shock • Activation of systemic inflammatory response • Toxic shock syndrome • Anaphylaxis • Drug or toxins

15. Distributive Shock continued • Addisonian crisis • Myxedema coma • Neurogenic shock

16. Evaluation • H & P • Labs • CXR • EKG

17. Treatment • Goal is early intervention to prevent irreversible organ damage • Recognize early shock • Diagnose and correct the underlying cause • Early goal directed therapy in sepsis • In hospital mortality 46.5% vs 30.5% for treatment group • NEJM, vol 345,No 19 Nov 8 2001

18. Treatment • Fluid resuscitation • CVP 8-12 • Vasopressors • Norepinephrin infuse mcg/min (4mcg/min) • Dopamine infuse mcg/kg/min • Epinephrine infuse mcg/min (range 1-10 mcg) • Vasopressin infuse units/min (range 0.01 to 0.1 units/minute)