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Physiology of Shock

Applied Sciences Lecture Course. Physiology of Shock. Mahesh Nirmalan MD, FRCA, PhD Consultant, Critical Care Medicine Manchester Royal Infirmary.

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Physiology of Shock

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  1. Applied Sciences Lecture Course Physiology of Shock Mahesh Nirmalan MD, FRCA, PhD Consultant, Critical Care Medicine Manchester Royal Infirmary

  2. Catastrophic deterioration of patients who are already in a hospital is frequently preceded by documented deterioration of physiological parameters • Sax FL et al Crit Care Med 1987; 15:510-515 • Smith AF et al. Resuscitation 1998;37:133-137

  3. Failure to respond Inadequate response Inappropriate response Irreversible damage Cardiac arrest Documented deterioration

  4. ShockThe final common pathway

  5. Objectives • Definition of shock • Classification of shock • Grades of shock • Recognition of shock……….in particular the early recognition of shock • Pathophysiology of shock • Treatment objectives in shock

  6. Definition of shock A clinical state in which the organs and tissues do not receive adequate blood flow to meet their metabolic needs. • Inadequate tissue perfusion • Decreased oxygen supply • Anaerobic metabolism • Accumulation metabolic waste • Cellular failure

  7. Cellular or organ failure in shock • Early: Immediate effects of hypo-perfusion → direct ischaemic damage • Late: Indirect effects • Ischaemia-Reperfusion • Oxidative stress • Pro-inflammatory cytokines • Sepsis • The late effects are directly related to the severity and duration of the early insult • Early recognition and immediate reversal of tissue ischaemia

  8. Injury MODS/ALI Reaction Second hit Reperfusion, Surgery, Infection Resolution MODS/ALI Giannoudis PV. Injury, Int.J.Care Injured 2003;34;397-404

  9. Pathophysiology of shock • Immediate hypo-perfusion→ cell damage • Ischaemia-reperfusion • Sepsis • Cytokine activation • Oxidative stress • Distal organ dysfunction: Kidney or liver • Multiple organ failure: MODS

  10. Distributive shock Causes or the classification of shock • Severe or sudden blood loss: Hypovolaemic shock • Loss of ECF: Hypovolaemic shock • Myocardial infarction: Cardiogenic shock • High spinal injuries: Neurogenic shock • Major infections: Septic shock • Anaphylaxis: Anaphylactic shock • Poisoning: Cytotoxic shock

  11. Classification of shock • Hypovolemic Shock: • haemorrhagic • non haemorrhagic • Other causes of shock • Cardiogenic Shock • Septic Shock • Neurogenic Shock • Anaphylactic Shock

  12. The following photograph depicts? • The first world war • Charge of the light brigade: Crimean War • Battle of Gettysburg; American Civil War • Battle of Waterloo • Russian Civil War

  13. Harvest of death: O’Sullivan: 1863

  14. Oxygenated arterial blood Body tissues Fixed oxygen demand Constant oxygen extraction Venous blood Venous oxygen saturation provides a good estimate of oxygen supply-demand balance in patients with shock

  15. Cardiac output • Haemoglobin content • Haemoglobin saturation • Metabolic status • Temperature: sepsis • Hormonal status Oxygen supply Oxygen demand • Metabolic acidosis • Lactate production • Low venous saturation

  16. Classical features of shock • Tachycardia • Tacypnoea • Impaired tissue blood flow • Capillary fill time • Cold peripheries? • Low blood pressure • Reduced UOP: <0.5ml/kg/hr • Increased serum [lactate] • Low venous saturation …….<70%

  17. % Blood loss Clinical Signs < 15 Slightly increased heart rate, local swelling, bleeding 15-30 Increased heart rate, increased diastolic blood pressure, prolonged capillary refill 30-50 Above findings plus: hypotension, confusion, acidosis, decreased urine output > 50 Refractory hypotension, refractory acidosis, death Signs of acute haemorrhagic shock

  18. Haemorrhage and blood pressure Blood pressure = CO * Vascular resistance

  19. CO, MAP and SvO2 Hypovolaemic shock in an animal model of shock

  20. Metabolic acidosis Typical changes in blood gases • pH: 7.19 • PCO2: 3.1KPa • PO2: 28KPa • HCO3-: 12.3mmol.l-1 • BE: -14.3mmol.l-1 • Lactate: 5.6mmol.l-1 Arterial oxygen saturation: 99-100% Venous oxygen saturation: 55%

  21. Post ganglionic sympathetic fibres: Norepinephrine (A diffuse response) Adrenals: Predominantly adrenaline Reuptake : MAO Local metabolism : Catechol-O-methyl-transferase normetepinephrine metepinephrine Systemic splillover Sympathetic response to trauma & shock A nonspecific & generalized response to a variety of stressful stimuli

  22. Effects of sympathetic activation • Tachycardia: baroreceptors & parasympathetics • Vasoconstriction: arteries and veins: 1 and 2 • MAP • CO: Increased inotropy (1) • Vasodilatation in muscle and liver vascular beds (2) at low concentrations & vasoconstriction at high concentrations (1) • Overall increased CO and redistribution of flow: cardiac, cerebral, hepatic and muscle vascular beds.

  23. Hyperglycemia Increase in plasma osmolality by 20-30mOsmol Mobilisation of extracellular fluid : upto 500ml Jarhult J. Acta Physiol Scand 1973;89:213-226 Hyperglycaemia in injury: an essential survival mechanism? Sympathetic activation Hypoinsulinaemia Corticosteroids, glucagon responses Increased glycogenolysis & gluconeogenesis

  24. CO, MAP and SvO2 Ischaemia-Reperfusion injuries in shock

  25. Even when cardiac output had been restored the blood pressure remained low: why? BP= CO* SVR Vasoplegia is a feature of ischaemia-reperfusion

  26. Centri-lobular hepatic necrosis Acute tubular necrosis Irreversible shock: distal organ injury

  27. Irreversible shock Reversible shock Reversible and irreversible shock

  28. Treatment objectives • Early recognition • Accurate diagnosis • Optimise tissue oxygen delivery early • Invasive haemodynamic monitoring • Urinary catheter • Blood gas estimation: to guide metabolic status • Appropriate environment • Specific treatment will depend on the underlying cause • ABC approach • Volume replacement: Hypovolaemic or septic • Inotropes: Cardiogenic • Vasopressors: Septic • Adrenaline: Anaphylactic

  29. Assess Intervene RE-assess Seek help Avoid over reliance on invasive haemodynamic monitoring Pulse rate Capillary fill time Core-toe temperature Blood pressure Level of consciousness Blood-gas estimation

  30. Supportive Specific Summary: be very familiar with…… • Immediate management of all forms of shock • Hypovolaemic • Septic • Anaphylactic • Cardiogenic: with and without pulmonary oedema

  31. summary • Definition of shock • Early and late effects • Causes • Oxygen supply-demand balance • Early recognition of shock: Early warning scores • Assess, intervene, reassess and seek help

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