A systemic state of low tissue perfusion that is inadequate for normal cellular respiration
- Pathophysiology
Cellular
- Low perfusion leads to anerobic metabolism which leads to accumulation of lactic acid in the blood producing systemic metabolic acidosis
- Glucose exhausted , anerobic metabolism also ceases and Na/K pump fails
- Intracellular lysis by release of lysosomal autodigestive enzymes , cell lysis ensues.
- Intracellular contents including K released in the blood
Microvascular
- Tissue ischemia progresses , activation of the immune and coagulation systems
- Hypoxia & acidosis activate complement and prime neutrophils - generation of free radicals, cytokine release , endothelial injury
- Leaky endothelium leads to tissue edema , exacerbating tissue hypoxia
Systemic
Cardiovascular
- Preload, after load decreases , compensatory baroreceptors response
- Increased catecholamines into circulation
- Tachycardia and systemic vasoconstriction ( Except in sepsis)
Respiratory
- Metabolic acidosis , increased sympathetic response
- Tachypnea , minute ventilation
- Increased excretion of CO2 ( produce a compensatory respiratory alkalosis)
Renal
- Decreased perfusion , decreased Urine output
- RAAS axis stimulation , further vasoconstriction
- Increased sodium & water reabsorption by renal tubules
Endocrine
- Decreased preload , release of RAAS , vasopressin
- Vasoconstriction and resorption of H²O
- Cortisol - Na , H²O resorption
- Sensitising cells to catecholamines ( permissiveness)
Ischemia- reperfusion syndrome
- Systemic hypoperfusion , activation of inflammation - damage to cells and tissue
- Acid and K + accumulation leads to myocardial depression , vascular dilatation & further hypotension
- Cellular & humoral elements activated by hypoxia
- Neutrophils, complement, microvascular thrombi rush back to circulation- endothelial injury
- Lungs and kidneys affected
Classification of shock
- Hypovolemic shock
- Carduogenic shock
- Obstructive shock
- Distributive shock
- Endocrine shock
Hypovolemic shock
- Reduce circulating volume
- Hemorrhagic and non hemorrhagic ( poor hydration , fluid loss due to vomiting, diarrhea, urinary loss (eg diabetes) , evaporation , third spacing)
- Third spacing- loss of fluid into GI & interstitial ( bowel obstruction & Pancreatitis)
Cardiogenic shock
- Failure of heart to pump the blood
- Cause : MI , Arrythmia , valcular heart disease, trauma, cardiomyopathy, drugs, toxins
- Venous HTN , pulmonary or systemic edeman- classical sign of shock
Obstructive shock
- Reduction in preload due to obstruction in mechanical filling
- Cause - Cardiac tamponade, tension pneumothorax, massive pulmonary or air embolus
Distributive shock
- Vasodilation due to (histamine release , failure of sympathetic outflow , adequate
- Maldistritbution of blood flow at Microvascular level with AV shunting and dysfunction of cellular utilization of O2
Endocrine shock
- Hypo /hyperthyroid , adrenal insufficiency