PBL 1.2 - shock

• What is shock?


  A medical emergency characterised by inadequate blood flow and oxygen delivery to the body's organs and tissues --> organ failure and death
• What is the most common cause of shock in children?

  Dehydration -->hypovolemic shock
• What is the most common cause of shock in adults?

  Infection -->septic shock(distributive)
• What are the 4 stages of shock?

  1. Initial

  
  

  2. Compensatory/non-progressive

  
  

  3. Progressive

  
  

  4. Refractory/irreversible

  
  

  EARLY RECOGNITION IS INCREDIBLY IMPORTANT

  
• What is the initial stage of shock?

  A sudden decrease in tissue perfusion causing cells to begin to experience hypoxia

  
  

  Difficult to recognsise due to subtle or absent symptoms
• What occurs in the initial stage of shock?

  Switch from aerobic to anaerobic respiration --> inc in lactic acid production -->metabolic acidosis...
• What immediately follows the initial stage of shock?

  The compensatory/non-progressive stage
• What is the compensatory stage of shock?


  Where the body activates compensatory mechanisms in an attempt to overcome the increasing consequences of anaerobic metabolism and maintain tissue perfusion
• What occurs in the compensatory stage of shock?

  - Baroreceptor reflex

  Sudden drop in bp sensed by baroreceptors --> activation of cardioaccelratory centre and vasomotor area in the medulla -->inc HR, SVandvasoconstriction

  This maintains bp and directs blood away from non-essential areas, like the skin and gastrointestinal tract, to prioritize perfusion to vital organs

  - Inc blood volume --> inc venous return

  Dec bp -->dec capillary hydrostatic pressure--> inc fluid retention --> inc venous volume

  Dec bp --> dec GFR --> dec stretch of afferent glomerular arteriole & dec tuboglomerular feedback --> inc renin production -->activation of RAAS--> vasoconstriction and inc Na+ reabsorption...

  Baroreceptor reflex & inc plasma Na+ --> activation of posterior pituitary gland --> inc release ofADHand trigger ofthirst--> inc water reabsorption...

  - Hyperventilation

  Body attempts to compensate for dec pH shifting buffer to the left to dec conc of bicarbonate --> inc prod of CO2 --> inc RR

  These mechanisms inc CO, TPR and blood volume whilst combatting inc acidosis
• What occurs as a result of the compensatory stage of shock?

  Dec perfusion to non-essential areas, like the skin and gastrointestinal tract -->cold, clammy skin*and risk of GI paralysis

  *NOT in septic shock due to systemic vasodilation
• What can occur if shock isn't recognised and managed?


  Progressive stageof shock

  These compensatory mechanisms can only be sustained for so long due to their high energy demands... if the underlying cause of shock isn't identified and treated during the compensatory stage, or if the stressor persists, the shock can progress...

  
• What occurs during the progressive stage of shock?

  FAILURE OF COMPENSATORY MECHANISMS

  Failure of compensatory mechanisms --> low CO --> inadequate tissue perfusion --> worsening tissue damage --> multiple organ dysfunction

  Tissue damage --> inflammation --> inc capillary permeability --> major oedema --> dec in blood volume -->severe dec in CO...
• How do patients present in the progressive stage of shock?

  Severe hypoperfusion --> major organ dysfunction:

  Hypoperfusion of brain -->confusion, disorientationandslurred speech

  Hypoperfusion of heart -->cardiac arrhythmias

  Hypoperfusion of lungs and severe oedema of alveoli -->ARDS--> tachypnea and shortness of breath

  Hypoperfusion of GI -->ulcerationandsevere bleeding

  Hypoperfusion of liver --> reduced production of clotting factors -->DIC
• What follows the progressive stage of shock?


  Therefractory stage

  This occurs when organ failure is irreversible --> death
• What are the signs and symptoms of shock?

  Severe hypotension, tachycardia, tachypnea, cool clammy skin*, dec urine output, thirst, confusion

  
  

  May differ slightly depending on type*

  
• What are the 4 main types of shock?

  1. Hypovolemic

  
  

  2. Obstructive

  
  

  3. Cardiogenic

  
  

  4. Distributive

  - Anaphylactic

  - Septic

  - Neurogenic
• What is hypovolemic shock?

  Shock resulting from asignificant decrease in blood volumedue to significant blood or fluid loss --> reduced venous return --> reduced preload --> dec SV --> dec CO --> dec bp --> inadequate perfusion...
• What are some causes of hypovolemic shock?

  Caused by severe loss of body fluid e.g.

  
  

  - Dehydration

  - Hemorrhage (internal/external)

  - Fluid loss from burns

  - Vomiting

  - Diarrhea

  ...
• How does hypovolemic shock affect CO, HR, JVP and peripheral temperature?

  At first JVP and CO maintained by compensatory mechanisms BUT as blood volume continues to decrease both dec

  
• How do we manage hypovolemic shock?

  Increase blood volume by managing cause and administeringIV fluids--> inc venous return --> inc CO
• How are fluids given to patients in hypovolemic shock? Why?

  Often viacentral venous catheter- enables us to administer fluids and medications whilst assessing central venous pressure (pressure in vena cava)

  Dont use peripheral venous catheter due to peripheral vasoconstriction - limits ability to measure venous pressure and effectively administer meds

  
• What is obstructive shock?


  Shock caused by obstruction to filling or ejection of the heart
• What are some causes of obstructive shock?

  - PEResults in increased resistance to bloodflow to lungs --> reduced bloodflow --> reduced oxygenation

  Inc resistance --> inc pressure in right ventricle --> reduced venous return --> reduced SV --> reduced CO...

  
  

  - Cardiac tamponadeRapid accumulation of fluid in pericardium --> compression of heart --> reduced ability to expand and fill --> reduced preload --> reduced SV --> reduced CO...

  - Tension pneumothoraxAccumulation of air in pleural space --> inc intrapleural pressure --> compression of lung and vena cava --> dec venous return --> dec SV --> dec CO...
• How does obstructive shock affect CO, HR, JVP and peripheral temperature?

  JVP incdue to impaired venous return often due to raised right ventricle pressure as a consequence of impaired blood flow due to obstruction

  
• What is cardiogenic shock?


  Inadequate perfusion of tissues due to the heart's inability to effectively pump blood, often resulting from severe heart failure or other cardiac conditions
• What are some causes of cardiogenic shock?

  - Myocardial infarcationSudden blockage of bloodflow to portion of myocardium --> ischaemic damage --> impaired pumping --> dec CO

  - Congestive heart failureStructural or functional abnormalities of the heart --> inadequate pumping ability of the heart --> dec CO

  Compensatory mechanism of inc blood volume towards dec bp --> inc workload - worsens condition!
• How does cardiogenic shock affect CO, HR, JVP and peripheral temperature?

  JVP incdue to impaired venous return often due to raised right ventricle pressure as a consequence of inadequate pumping ability of the heart

  
• What is distributive shock?

  Shock caused by widespread vasodilation leading to severe hypotension and poor tissue perfusion

  
  

  3 main subtypes including:

  - Septic

  - Neurogenic

  - Anaphylactic
• How does septic shock affect CO, HR, JVP and peripheral temperature?

  At first compensatory mechanisms cause CO to increase by inc HR and contractility of the heart

  Peripheral temperature inc due to systemic vasodilation

  HOWEVER as septic shock progresses, loss of blood volume due to inc vasuclar permeability and myocardial depression --> dec CO and JVP

  
• How does neurogenic shock affect CO, HR, JVP and peripheral temperature?

  Inability to activate SNS --> dec HR, systemic vasodilation and dec CO

  
• How does anaphylactic shock affect CO, HR, JVP and peripheral temperature?

  Severe allergic reaction --> systemic release of histamine and other vasoactive inflammatory mediators --> systemic vasodilation and inc vasc permeability

  At first compensatory mechanisms cause CO to increase by inc HR and contractility of the heart

  Peripheral temperature inc due to systemic vasodilation

  HOWEVER as anaphylactic shock progresses, loss of blood volume due to inc vascular permeability and myocardial depression --> dec CO and JVP