SHOCK
Shock
Oxygen content
• Factors involved in oxygen content
– Carrier (amount) – Hb
– Carrier saturation – SaO2
– Carrier capacity – 1.34ml O2/Hb molecule
CaO2 = Hb x SaO2 x 1.34
Oxygen Delivery DO2
• Additional factor of a pump (L/min)
• Pump – Cardiac output
DO2 = CO x Hb x SaO2 x 1.34
VO2
• VO2 – Oxygen consumption at tissues
(170ml/min/m2)
• VO2 = difference in arterial oxygen and
venous oxygen
• VO2 = CO x Hb x 1.34 x (SaO2 – ScvO2)
• In one “loop” of the circulatory system the
body extracts 25% of oxygen for use
• Normal SaO2 = 100%
• Normal ScvO2 = 75%
Maintaining VO2 when delivery
fails
• VO2 = CO x Hb x 1.34 x (SaO2 – ScvO2)
• When either CO fails
– Inadequate preload
– Excessive afterload
– Impaired contractility
• Hb drops
– Haemorrhage/haemoglobinopathies
• SaO2 falls
– Respiratory compromise
• The body compensates and maintains VO2 by
increasing O2 extraction from haemoglobin
O2 extraction ratio
• Max O2ER = 50-60% (ScvO2 = 40-50%)
• When DO2 reaches ~ 330ml/min/m2
Types of shock – A physiologic
perspective
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DO2 = CO x Hb x SaO2 x 1.34
Stagnant/cardiogenic
Anaemic shock
Hypoxic shock
Histocytotoxic (sepsis/cyanide poisoning)
(doesn’t fit with the equation) – myocardial
depression but also mitochondrial
dysfunction
Types of shock – a clinical
perspective
• Septic
• Hypoxic/Hypovolaemic
• Obstructive
– PE
– Tamponade
– Pneumothorax
• Cardiogenic
• Distributive
– Anaphylactic
– Neurogenic
Shock in the haemodynamically
“normal”, “afebrile” patient
• Beware the haemodynamically normal
patient
• HaemoDYNAMICS
– Follow trends. Some patients are hypertensive
in the community so may be shocked at a SBP
of 120
– Beware the cardioactive drugs
• Elderly patients may not mount a febrile
response and may in fact become
hypothermic
Assessing the shocked patient
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• Formulate vital signs
• Obtain IV access
• Make an early diagnosis and initiate early
management
Investigating the shocked patient
• Investigate the cause of the shock
• Septic screen
– Pan culture
– Imaging
– Targeted examination
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SaO2
ABG
ECHO
Lactate (sensitive but not specific)
Invasive and non-invasive
monitoring
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NIPB
SaO2
Arterial lines
Central lines
IDC
Optimising oxygen delivery
(managing the shocked patient)
• Optimise oxygen delivery in all shocked
patients
• U/O > 0.5ml/kg/hr
• SBP >90/ MAP >65
• ScvO2 >70%
• SaO2 > 92%
• Hb > 100
Treating shock
• Treat the cause!
• CO
– Augment preload with fluids (20ml/kg bolus).
Colloids are preferred
– Reduce afterload (in APO etc..)
• Hb – give blood
• SaO2 – give oxygen
Fluids in shock
• Crystalloids/colloids have no evidence
based difference in terms of mortality
• Colloids augment cardiac output better
• Reduce (short term) risk of symptomatic
overload
• Can be safe when chosen correctly
• Otherwise give crystalloids
• Practical note: get hold of a recent ECHO
Vasopressors and inotropes in
shock
• Vasopressors are required in states of
systemic vasodilation
– Neurogenic shock
– Anaphylaxis
– Septic shock
• Inotropes required in states of cardiac
depression
• Management of septic shock?
Surviving sepsis campaign
• Early resuscitation
• Early administration of antibiotics
• Source control
– Don’t let the sun set on pus
– Remove all infected foreign bodies
Compartmentalised shock
• Shock doesn’t always have to be global
• Pressure ≠ Flow
• Good systemic pressures ≠ good compartment
pressures
• Be aware of this an investigate your
compartments when worried
– Abdomen (bladder pressures)
– Peripheral limb compartments (examine, image)
– Intracranial compartments (Papilloedema, Cushings
sign)
• Ensure you optimise compartment perfusion
(MAP – compartment pressure)
Judging resuscitation efforts
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Improvement in BP/HR
Improvement in urine output
Meeting evidence based targets
Reduction in serum lactate
Questions?