Shock Flashcards
What is shock?
A state of cellular and tissue hypoxia due to either reduced oxygen delivery, increased oxygen consumption, inadequate oxygen utilisation or a combo
How is MAP calculated?
CO x SVR
DBP + 1/3 (pulse pressure = SBP - DBP)
What are the causes of shock?
Hypovolaemia Cardiogenic Distributive - septic, anaphylactic, neurogenic Obstructive Endocrine
Mechanism behind hypovolaemic shock
Volume depletion - reduced SVR
Reduced pre-load = reduced CO
What mediates cardiogenic shock?
Ischaemia induced myocardial dysfunction mainly
But can be caused by cardiomyopathies, valvular problems, dysrhythmias
If cardiogenic shock due to MI; suggests that >40% of LV involved, mortality of >75%
Mechanism of distributive shock
Disruption of normal vascular autoregulation and profound vasodilation
Poor perfusion; despite increased CO
Regional perfusion differences
Alteration of oxygen extraction
What can cause endocrine shock?
Myxoedema coma
Addisonian crisis
Thyrotoxicosis crisis
What is the effect of the sympathetic nervous system on the heart?
Positive chronotropy and inotropy
Increased vasoconstriction
What is the role of cortisol in shock?
Fluid retention
Antagonises insulin to maintain adequate sugar levels
What inflammatory response is involved in shock?
Activation of complement cascade; attraction and activation of leukocytes
Cytokine release; interleukins, TNF-alpha
Platelet activating factor; increased vascular permeability, platelet aggregation
Lysosomal enzymes; myocardial depression
Adhesion molecules; damaged vessel walls
Endothelium derived mediators; NO
Imbalance between antioxidants and oxidants
What haemodynamic changes are seen in shock?
Vascular abnormalities; vasodilation or constriction. Often massive venodilataion
Maldistribution of blood flow
Microcirculatory abnormalities
Inappropriate activation of coagulation system
DIC
Reperfusion injuries
What mediates the loss of vascular reactivity seen in shock?
Massive release of NO; vasodilation
What myocardial dysfunction will result from shock?
Reversible biventricular systolic and diastolic dysfunction
Circulating cytokines have a direct myocardial effect
Beta-receptor down regulation
Decreased cardiac myofilament calcium sensitivity
Class 1 hypovolaemia
<15% blood loss
HR, BP, pulse pressure, RR, urine, GCS and base deficit normal
Monitor
Class 2 (mild) hypovolaemia
15-30% blood loss Tachycardic, decreased pulse pressure BP, RR, urine, GCS normal Base deficit -2 to -6 Possible need for blood transfusion
Class 3 (moderate) hypovolaemia
31-40% blood loss
Tachycardic, hypotensive, decreased pulse pressure, tachypnoeic, decreased urine output, decreased GCS
Base deficit -6 to -10
Blood transfusion required
Class 4 (severe) hypovolaemia
> 40% blood loss
Tachycardic, hypotensive, decreased pulse pressure, tachypnoeic, anuric, low GCS
Base deficit -10 or less
Massive Transfusion Protocol required
How can BP be measured?
Cuff
Arterial line
What is CVP useful for?
Assessment of fluid responsiveness
Look at trend
What is the gold standard for monitoring cardiac output?
Thermodilution with pulmonary artery catheter
What MAP is aimed for?
65-70 mmHg
How is oxygen delivery calculated?
CO x (1.39 x Hb x SpO2) + (PaO2 x 0.003)
What is the goals with fluid resuscitation in shock?
Increase preload
Fine balance between rapid volume replacement and fluid overload (pulmonary oedema)
How is a fluid challenge given?
500ml over 15 mins
Want to see increased MAP, decreased HR, increased urine output
What fluid can be given?
Crystalloids (saline, hartman’s) - good, cheap, safe BUT rapidly lost from circulation to extravascular spaces so significant volumes required
Colloids - reduced volumes required but can cause anaphylaxis
Blood; probs best
NEVER use dextrose
What pharmacological management options are available for management of BP?
Adrenaline; alpha/beta adrenergic agonists. At low dose primarily beta (positive chronotropy and inotropy, vasodilation. Alpha has vasoconstrictive effects) NA; alpha agonist Vasopressin Dopamine Dobutamine/ dopexamine
What is a massive haemorrhage?
50% blood volume within 3 hours
Blood loss of 150ml/min
Obstetrics; minor (500-1000ml), major (<1000ml)
What blood samples are required in a major haemorrhage protocol?
FBC Coag screen Fibrinogen Crossmatch U+Es Calcium
What will the blood bank supply in a major haemorrhage protocol?
4 units red cell
4 units FFP
1 unit platelets
What markers do you want to aim for in blood transfusionn?
Hb 80 g/L
APTT and PT ratio <1.5
Platelets >50
Fibrinogen >1.5 g/L (obstetric >2 g/L)
When should you transfuse cryoprecipitate (factor 7, fibrinogen, von Willebrand factor)?
Fibrinogen <1 g/L or <2g/L in obstetric haemorrhage
What is important to think about post blood transfusion?
Thromboprophylaxis
