SHOCK METABOLIC RESPONSE TO SURGERY Dr Mussarat Afzal
SHOCK & METABOLIC RESPONSE TO SURGERY Dr Mussarat Afzal Consultant Anesthesiologist PMAH
Objectives • Definition of shock • Pathophysiology of shock • Classification of shock • Recognition of shock • Treatment objectives in shock • Metabolic response to Surgery.
Definition of shock A clinical state in which tissues do not receive adequate blood flow and O 2 to meet their metabolic needs.
Physiological principles • Systemic blood pressure • Systemic vascular resistance • Cardiac output • Oxygen supply Blood flow
Systemic blood pressure SBP = CO x SVR This relationship equates well to Ohms’s Law: V = IR
Systemic blood pressure • Control of BP in the acute phase: 1. Intrinsic regulatory properties of the heart 2. Autonomic pathways 3. Hormonal mechanisms
Systemic vascular resistance SVR = SPB CO Which is rearranged as: SVR = (MAP – CVP) x 80 CO
Cardiac output • Cardiac output is the volume of blood being pumped by the heart per minute. CO = HR x SV
Which does not affect SV? 1. 2. 3. 4. Preload Heart rate Contractility Afterload
Cardiac output CO = SV x HR SV Preload Contractility Afterload
Cardiac output
Supply v demand • O 2 supply = CO x (arterial O 2 content) • O 2 demand is dependent upon temperature, metabolic status and hormonal status
Pathophysiology of shock Inadequate tissue perfusion Decreased oxygen supply Anaerobic metabolism Accumulation metabolic waste Cellular failure
PATHOPHYSIOLOGY OF SHOCK SYNDROME Cells switch from aerobic to anaerobic metabolism lactic acid production Cell function ceases & swells membrane becomes more permeable electrolytes & fluids seep in & out of cell Na+/K+ pump impaired mitochondria damage cell death
Compensatory mechanisms • Sympathetic compensatory mechanisms may preserve organ perfusion initially.
Sympathetic activation • Tachycardia • Increased myocardial contractility (β 1) • α-adrenergic receptor-mediated vasoconstriciton (β 2 -receptor-mediated vasodilatation in skeletal muscle, coronary, pulmonary and renal circulations) • Overall increased CO and redistribution of flow: cardiac, cerebral, hepatic and muscle vascular beds
Autoregulation of coronary blood flow
Compensatory mechanism and shock AFTER-LOAD PRE-LOAD Fluid Cardiac Vascular Volume Output Diameter (CVP/JVP) (SV x HR) (SVR)
Hypovolaemic shock AFTER-LOAD PRE-LOAD Fluid Cardiac Vascular Volume Output Diameter (CVP/JVP) (SV x HR) (SVR) 1
Hypovolaemic shock AFTER-LOAD PRE-LOAD Fluid Cardiac Vascular Volume Output Diameter (CVP/JVP) (SV x HR) (SVR) 1 2
Hypovolaemic shock AFTER-LOAD PRE-LOAD Fluid Cardiac Vascular Volume Output Diameter (CVP/JVP) (SV x HR) (SVR) 1 2 3
Cardiogenic shock AFTER-LOAD PRE-LOAD Fluid Cardiac Vascular Volume Output Diameter (CVP/JVP) (SV x HR) (SVR) 1
Cardiogenic shock AFTER-LOAD PRE-LOAD Fluid Cardiac Vascular Volume Output Diameter (CVP/JVP) (SV x HR) (SVR) 1 2
Cardiogenic shock AFTER-LOAD PRE-LOAD Fluid Cardiac Vascular Volume Output Diameter (CVP/JVP) (SV x HR) (SVR) 3 1 2
Distributive shock AFTER-LOAD PRE-LOAD Fluid Cardiac Vascular Volume Output Diameter (CVP/JVP) (SV x HR) (SVR) 1
Distributive shock AFTER-LOAD PRE-LOAD Fluid Cardiac Vascular Volume Output Diameter (CVP/JVP) (SV x HR) (SVR) 2 1
Distributive shock AFTER-LOAD PRE-LOAD Fluid Cardiac Vascular Volume Output Diameter (CVP/JVP) (SV x HR) (SVR) 2 3 1
Which group of individuals cope poorly with shock? 1. 2. 3. 4. Children Pregnant women The elderly Young adults
Classification of shock • Hypovolaemic Shock • Cardiogenic shock • Distributive shock
Causes of shock • Significant blood loss: Haemorrhagic shock • Loss of ECF: Hypovolaemic shock • Myocardial infarction: Cardiogenic shock • High spinal injuries: Neurogenic shock • Severe infections: Septic shock Distributive shock • Anaphylaxis: Anaphylactic shock • Poisoning: Cytotoxic shock
Grading of haemorrhagic shock
Recognition of shock • Tachycardia • Tacypnoea • Impaired tissue blood flow – Capillary fill time – Cold peripheries? • • Hypotension Oliguria <0. 5 ml/kg/hr Increased serum [lactate] Low venous saturation ……. <70%
Treatment objectives • • Early recognition Accurate diagnosis Optimise tissue oxygen delivery early Blood gas estimation: guides metabolic status Urinary catheter Appropriate environment Invasive haemodynamic monitoring
Treatment objectives • Specific treatment will depend on the underlying cause • • • ABC approach Volume replacement: Hypovolaemic or septic Inotropes: Cardiogenic Vasopressors: Septic Adrenaline: Anaphylactic
Metabolic response to surgery • • • Surgery evokes: Hormonal response Metabolic response Psychological response Increase catabolism Decrease anabolism Salt and water retention
Metabolic response to surgery • • • Hormonal release: Hypothalamic -piyuitary axis. Anterior Pituitary hormones ACTH –cortisol 400 nmol/L raises to 3 times Posterior Pituitary Hormones ADH –distal convoluted tubule Sympathetic nervous system Insulin and glucagon. β Endorphins and Prolactin
Metabolic response to surgery • Cortisol: Anti-inflammatory effects mediated by↓inflamatory mediators Leukotrienes Cytokines Prostaglaandins. Skeletal muscle protein breakdowngluconeogenesis.
Metabolic response to surgery Glucose utilization is impairedhyperglycemia. • Sympathetic Nervous system: Catecholamines-adrenal medulla Tachycardia Hypertension Overall metabolic effect of endocrine response is mobilization of substrates from carbohydrates, lipid and prorein stores.
Metabolic response to surgery • Carbohydrate breakdown glycogenolysis and gluconeogenesis leading to ineffective regulation of glucose production and homeostasis. • Failure of insulin secretion-insulin resistance. • Glucose>12 mmol/L impairs wound healing. • ↑ infection rate • ↑ risk of ischemic damage to CNS & myocardium
Response to Surgery • Protein catabolism↑ due to cortisol Influenced by type of surgery Nutritional status of the patient. Major abdominal surgery 0. 5 kg/day lean body mass is lost. Amino acids are used for gluconeogenesis-↓ Albumin –maintenance of ECF-Edema How to measure – urea in urine
Response to surgery • Increase lipolysis-leads to ↑ ketone bodies. • Salt and water metabolism: • ADH-water retention concentrated urine and potassium loss- 3 -5 days. • Renin secreted from kidney-water and sodium retention –concentrated urine. • Cytokines: LMW glycoproteins : Interleukins, interferons and TNF-mediate immunity& inflammation
Modifying the response • Surgical technique e. g laparoscopic • Nutrition: Enteral feeding • Hormone therapy: Insulin infusions, growth hormone or anabolic steroids. • Normothermia • Anesthesia
Is this the appropriate environment?
Summary Definition of shock Causes Oxygen supply-demand balance Assess, intervene, reassess and seek help Hormonal and metabolic response to surgery is complex. • Maximum effort to reduce the deleterious effects of hypertension and tachycardia • • •
Any questions?
Evaluation 24 th Sep. 2014
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