• no single consensus definition

• 140 definitions in 4 journals between 2000-2006

• SBP < 20% decrease

• SBP < 100 +/- 30% decrease

• SBP < 80

• other variables

  • duration
  • requiring treatment

• theoretical basis for using relative thresholds

  • HTN have higher lower threshold of autoregulation

Haemorrhagic shock

• Hypotension is late (30% blood loss, 1.5L)
• Deranged clinical signs = stage II = 15% blood loss
• Tachycardia (HR 100) is early (15%, 750 mL)

• Pre-pump
  • Hypovolaemia = absolute hypovolaemia, eg. haemorrhage
  • Distributive = relative hypovolaemia, eg. sepsis, neurogenic
• Cardiac
  • Cardiogenic = MI, cardiomyopathy, arrhythmia
• Post-pump
  • Obstructive, eg. Tension pneumothorax, Cardiac tamponade

• high risk
  • MAP < 65 for 20+ minutes
  • MAP < 50 for 5+ minutes
  • any MAP< 40
• AMI / MINS
  • ⬆risk MI at MAP < 65
• renal
  • ⬆risk AKI at MAP < 65
  • duration is significant
• periop stroke
  • ⬆risk MAP < 70
• coagulopathy effects of shock
  • ⬆thrombomodulin = ⬇thrombin, ⬇Va, ⬇VIIIa
  • deactivates PAI-1 = ⬆fibrinolysis

• treat underlying CAUSE

• caution

  • pure vasoconstrictors = worsens tissue perfusion
    • esp in hypovolaemia and ⬇INO
  • excess IVF = right-edge of Starling curve; SV no longer augmented
    • risk = APO, tissue oedema, damage endothelial glycocalyx

• fluid responsiveness

  • PLR = passive leg raise
    • this is a validated assessment of volume status / fluid responsiveness
    • the auto-transfusion from this manoeuvre is similar to a 250-500 mL fluid challenge
  • recommendation = "moderately liberal" approach to fluid therapy ***
  • overall +ve FB 1-2 L over duration of surgery
  • induction = 10 mL/kg
  • intraop = 8 mL/kg/hr
  • postop = 1.5 mg/kg/hr

• vasoactive drug therapy

  • consider in patients who are not fluid responsive
  • pure alpha agonists, eg. phenylephrine
    • variable effect on CO
    • utility
      • CS
      • AS / HCM
    • caution ⬇CO if hypovolaemia and ⬇INO

• Pre-op
• Intra-op
• Post-op

• future directions
  • better understanding of microcirculation
  • trials
    • POISE-3
    • OPTIMISE-2
  • technology
    • machine alerts / machine learning
    • continuous NIBP
    • continuous ward BP monitoring
    • tissue perfusion monitoring
• strategies
  • hypotension-avoidance
  • hypertension-avoidance