Define Shock
- Any circumstance where circulatory insufficiency results in inadequate perfusion and so insufficient oxygen delivery to the tissues of the body.
- OXYGEN DEMAND outstrips the oxygen SUPPLY
List the categories of shock
- Hypovolaemic
- Cardiogenic
- Distributive
- Obstructive
Define Hypovolaemic Shock
- Loss of blood/fluid from circulatory system
- E.g. Haemorrhage - Common cause of hypovolaemia
- Trauma e.g. Extrinsic bleed / Intrinsic body compartments - abdominal cavity, pelvic, long bones, chest
- Non-trauma - AAA, thoracic aneurysm
Give a non-traumatic cause of Hypovolaemic shock
- AAA / Thoracic aneurysm
- Spontaneous bleeding into GI tract
- Diarrhoea and vomiting
- Diabetic ketoacidosis - Via osmotic diuresis
- Burns
Give examples of Non-traumatic Haemorrhagic Hypovolaemic shock
- AAA/Thoracic aneurysm
- Spontaneous bleeds e.g. due to alcoholism / Anticoagulant drugs
Define Cardiogenic Shock
- Failure of the pump in the circulatory system - Specifically Ventricular dysfunction
- 2 causes: Affecting heart itself / Systemic
- Heart: MI, Myocarditis, Valvular heart disease, Cardiomyopathy,
- Systemic: Overdose, Sepsis, Pancreatitis
What are examples of Causes of Cardiogenic shock
- STEMI
- Ventricular Tachycardia
- Overdose
Define Distributive shock
- Category of shock defining no fluid/blood loss but have excessive vasodilation + subsequent maldistribution of blood within circulatory system
- Septic shock - Dysregulated host response to infection, inflammatory, excessive vasodilation
- Neurogenic shock - Secondary to spinal cord injury, interruption to ANS outflow, inability to raise BP/HR
- Anaphylactic shock - Excessive vasodilation due to Systemic IgE mediated hypersensitivity reaction
Define Obstructive shock
- Physical obstruction to blood flow through blood vessels
- Due to problem within blood vessels/external pressure
- e.g. Pulmonary embolism, Tension Pneumothorax, Cardiac Tamponade (can be cardiogenic), SVC (more common due to lymphatic/lung malignancy) / IVC obstruction
Compare normal short-term and long-term physiological control of blood pressure - Humoral control
- Humoral control - RAAS system
- BP falls, Na+ falls
- Renin produced by Kidneys/ Juxtoglomerular cells in Afferent arteriole
- Renin –> Angiotensinogen from liver to Angiotensin I
- ACE –> Angiotensin I to Angiotensin II
- Brain effects - Thirst centre, and ADH (Hypothalamus) - More aquaporins
- Adrenal cortex - Aldosterone - Increase Na+ reabsorption, water follows
- Arteries - Vasoconstriction
Compare normal short-term and long-term physiological control of blood pressure - Neural Control
- Neural control - Baroreceptors primarily in aortic arch and carotid sinus
- Reduced arterial pressure
- Decreased baroreceptor firing
- Increased sympathetic activity and reduced vagal activity in medulla
- Increased CO and CVR
What does Starling’s Law state?
- End Diastolic Left Ventricular blood volume determines the myocardial muscle fibre length and thus contractility to a point
- So Increasing preload/filling of heart –> Increases contractility
What is preload
- End diastolic left ventricular volume
- Determined by amount of blood returned to heart from venous system
What are the factors affecting Stroke volume?
- Preload
- Pump (contractility)
- Afterload (SVR)
What is a normal MAP?
> 65 mm Hg
What is MAP an indicator of?
- Mean arterial pressure - Indicator of Tissue perfusion
Which component of the FBC will tell you about the shape of the red blood cells, and is useful for detecting disorders such as sickle cell anaemia?
- RDW
- Red cell Distribution Width
- Uniformity and shape of the red blood cells
- The higher the value the more variability in shape and size of the red cells
Which component of the FBC might be reduced if you were taking Heparin, a drug that thins the blood to prevent clotting?
- Plt - Platelets
- Heparin could cause thrombocytopenia (reduced platelets) by triggering an immune response and causing antibodies to be produced that destroy the platelets
- NSAIDs (like aspirin) also work this way
- Newer drugs such as low molecular weight heparin (LMWH) are less likely to cause reduced platelets
A patient returns from a holiday overseas with a malaria (parasitic) infection. How do you think elements of their FBC would appear?
- RBC - Reduced - Malaria associated with haemolytic anaemia
- Platelet - Reduced - Thrombocytopenia
- WBC - Normal - But increased eosinophils
How to calculate MCV?
MCV (fl) = (Hct (%) x10) / RBC (x10^12/l)
How to calculate MCHC
MCHC (g/l) = (Hb (g/l) x 100) / Hct (%)
What does Hypochromic mean?
- Low Amount of Haemoglobin per cell - Below normal range
What does Normocytic mean?
Size of RBC is within normal range
How to calculate Hct / Haematocrit
Hct = (RBC (x10^12/l) X MCV (fl) / 10
