Week 107: Hypovolaemia Flashcards
What is hypovolaemia?
20% loss of circulatory volume (can be caused by dehydration or blood loss)
Why would you not try to normalise blood pressure in cases of hypovolaemia?
Because the medication needed would wash out clotting factors
What are the four types of shock?
- Hypovolaemia
- Maldistributive (anaphylactic)
- Cardiogenic
- Obstructive
What test can you do to assess the severity of shock?
Lactic acid test
Glucose
Check SATS - 98%
What would you do when a hypovolaemic patient is anaemic?
Give them EPO
Vitamin D
What is a portal system?
Two capillary beds in series - heart > capillary bed > capillary bed > heart
- Occurs in kidneys around each nephron
What is the juxtaglomerular apparatus?
Macula densa cells in distil tubules, granular cells found in blood vessels next to distil tubules
- Produce renin as part of monitoring sodium excretion in urine
What is blood pressure?
Product of cardiac output x resistance
Where is the antidiuretic hormone produced?
In the pituitary gland in the brain
What is the function of the antidiuretic hormone (ADH)?
- Reserves water and sodium
- Stops peeing
Where is atrial natriuretic peptide produced?
Right atrium
When is atrial natriuretic peptide produced?
In response to high blood pressure
- High blood pressure causes increased sodium excretion and water loss
What is ADH?
A vasopressin
What is Starling’s Law of the Heart?
- As the heart expands more (actin and myosin fibres come together and spread under tension) it has to contract more
- The greater the filling, the greater the contraction
- Stroke volume increases as end diastolic pressure increases
What is the Windkessel effect?
- The beginning of aorta is the Windkessel device which causes the effect
- Heart pumping out causes a rise in blood pressure
- If arteries were non-elastic then would shoot blood
- Device absorbs some of the shock and recoil
- Maintains systolic going through elastic protection
- Without effect: high systolic blood pressure 200/80
- Windkessel smooths out the two
What is the baroreceptor reflex?
- A fast response that deals with blood pressure very quickly
- In carotid arteries the stretch is detected: if increase then reduce heart rate and stroke volume which relaxes the heart and reduces blood pressure
- In carotid arteries chemo receptor complex: determines how oxygenated - fast response and can increase heart rate
What percentage of total body water occurs in the plasma?
13% (3.5l)
What percentage of total body water occurs in the interstitial fluid?
22% (9.5l)
What percentage of total body water occurs intracellularly?
65% (27l)
What is osmolality?
The concentration of a solution expressed as the total number of solute particles per kilogram
What is the osmolality of plasma?
290 mosmol/kg H2O
What is the osmolality of interstitial fluid?
290 mosmol/kg H2O
What is the osmolality of intracellular fluid?
290 mosmol/kg H2O
What is a capillary wall permeable to?
Everything except plasma proteins
What is interstitial fluid?
Fluid between cells
What comprises extracellular fluid?
Interstitial fluid
Plasma
What does the barrier between interstitial fluid and plasma consist of?
Walls of the capillaries
What are the intracellular and extracellular fluids separated by?
Plasma membranes of cells
What is an isotonic fluid?
A fluid at the same osmotic potential as plasma
What is a hypertonic fluid?
A fluid at a higher osmotic potential than plasma
What is a hypotonic fluid?
A fluid at a lower osmotic potential that plasma
Define osmotic potential
Depends on the number of osmotically active particles (molecules) per litre irrespective of their identity
What is osmotic potential expressed in?
Osmoles: 1 osmole = 1 mole of particles
What types of substances diffuse easily across capillaries?
Crystalloid fluids
- Glucose
- Urea
What does not pass through capillary walls?
Proteins
There are three main fluid compartments. Within each single one what is it important to maintain?
Electrical neutrality: the total number of positively charged ions must equal the total number of negatively charged ions
What does the Na+ - K+ ATPase or Na+ pump do?
Prevents the steady movement of ions across membranes with Na+ and K+ following their concentration gradients from leading to an equalisation of the compositions of intracellular and extracellular compartments - if they equalised then all bioelectrical signalling would stop
What is normal blood volume?
70ml/kg
What is normal plasma volume?
40ml/kg
What percentage of body weight is total fluid volume?
60% in men
50% in women
What percentage of body fluid does intracellular fluid account for?
65%
What percentage of body fluid does extracellular fluid account for?
34%
