Ch 6 - Shock Flashcards
List and briefly describe the 4 main types of shock
- Hypovolaemic - Reduction in curculating intravascular volume
- Cardiogenic - Inability of heart to propel blood through circulation. Includes obstructive shock by decreasing to preload
- Distributive - Maldistribution of vascular volume and massive vasodilation resulting in relative hypovolaemia. Sepsis and SIRS, anaphylaxis, drugs, severe CNS damage
- Hypoxic - Adequate perfusion but inadequate arterial oxygen content or cellular oxygen utilisation
What are the basic factors determining oxygen delivery?
- Cardiac output
- Arterial oxygen content
What is the Frank-Starling mechanism?
In an intact heart, an increase in end-diastolic volume (pre-load) augments the strength of cardiac contractions
What factors influence the affinity of Hb for Oxygen
pH, temperature, 2,3-DPG, CO2
List the ALTS (Advanced Trauma Life Support) classed of haemorrhage
- Class 1 - loss of up to 15% blood volume. Clinical signs absent or mild
- Class 2 - Loss 15-30%. Tachycardia, tachypnoea, weak pulses
- Class 3 - Loss 30-40%. mms pale, CRT prolonged, arterial hypotension
- Class 4 - Loss of >40%. Severe and immediately life-threatening. Cold extremities, altered mentation, profound hypotension
List the possible defect of oxygen uptake in which the central venous oxygen saturation can be normal but tissue oxygenation can be impaired
- Diffussional shunting - slow blood velocity cause diffusion of oxygen from arterial into venous blood instead of into the tissues
- Diffusional resistance - Tissue oedema increases diffusion distance and limits oxygen availability
- AV shunting - Loss of capillary bloodflow due to SIRS/sepsis, thrombi etc
- Perfusion/metabolic mismatch - increased metabolic oxygen demands
- Cytopathic hypoxia - mitochondrial dysfunction such as in sepsis
What is the normal resting oxygen extraction ratio?
20%
Can increase to 60-70% in cases of increased metabolic demand or decreased oxygen delivery
What are the three main hypotheses to explain acute coagulopathy of trauma?
- A fibrinolytic variant fo DIC
- Enhance thrombomodulin-thrombin protein C pathway (decreased thrombin degradation and increased activation of anticoagulant and profibrinolytic protein C)
- Neurohumoral response (Catecholamine induced glycocalyx damage and expression of prothrombotic phenotype. Counterregulatory increase in anticoagulants and fibrinolytics leads to systemic anticoagulation and hyperfibrinolysis
What are considered the shock organs in the dog and cat?
dog - GIT
cat - Lungs
Over what MAP ranges will perfusion be maintained to the kidneys, myocardium and the brain?
Kidneys - 70-130mmHg
Myocardium - 60-140mmHg
Brain - 50-180mmHg
What is the recommended blood pressure cuff width?
40% limb circumference in dogs, 30-40% in cats
What is considered physiologic central venous pressure for dogs and cats?
0-5cmH20
What is a Swan-Ganz catheter?
A pulmonary artery catheter for the measurement of cardiac output
What factors effect lactate measurement?
- Liver and kidney clearance can cause normal lactate in hypoperfusion
- Severe hepatic failure can cause hyperlactataemia with normal production
- Inadequate collection and handling
What are the 2 types of lactic acidosis?
- Type A - inadequate oxygen delivery
- Type B - mitochondrial dysfuntion with normal oxygen delivery (sepsis, DM, neoplasia, drugs, toxins)
Prolonged hypoxia can lead to mitochondrial damage leading to complex (Type A and B) lactic acidosis
