107 - Hypovolemia Flashcards
Definition of shock
Failure of CVS to adequately perfuse tissues. Critically low oxygen delivery to mitochondria. 4 types.
Define hypovolaemia
Loss of ~20% of blood volume. Caused by sharp decline in cardiac output due to empty circulation.
Cardiogenic shock
Caused by failure of heart to pump correctly.
Maldistributive shock
Caused by abnormal dilation of the small arteries. Commonly due to infection (septic shock) or allergy (anaphylactic shock).
Obstructive shock
Physical blockage to heart or major vessels that reduces cardiac output. Mainly due to pulmonary embolism.
Recognising Shock
Present with features of organ failure and sympathetic activation (fight or flight). Collapse Changes to consciousness Tachypnoea Tachycardia Hypotension Poor peripheral perfusion Low urine output Raised blood
Characteristic features of hypovolemia
Evidence of blood loss
Dry, empty circulation
Characteristic features of cariogenic shock
Chest pain
EGC and rhythm changes
Rising upstream pressure
Pulmonary and peripheral oedema
Characteristic features of maldistributive shock
Source of sepsis - signs of infection.
Warm, dilated circulation unless severe.
Characteristic features of obstructive shock
Same as cardiogenic but without signs of MI etc.
Poss DVT, thoracic injury
0-15% blood loss - impact on patient.
Thirsty
15-30% blood loss - impact on patient.
Tachycardia
30-40% blood loss - impact on patient.
Hypotension
> 40% blood loss - impact on patient.
Game over
How to remember the impact on patient based on blood loss
Tennis score rules
When should fluid resuscitation be done in patients with shock
ASAP. Caution in older patients as can affect heart.
What are U&Es
Basic blood test for kidney function. Looks at levels of urea, Na and K. Creatinine levels also usually measured
Urea - acts as marker of what
Produced when body trying to rid itself of proteins. Useful as marker of dehydration or exposure to large amount of protein. Released by kidneys so marker of how efficiently kidneys are working.
Sodium and Potassium - role in blood
Involved in reabsorption of kidney, determining resting membrane potential and creating action potentials.
Low levels of urea can indicate
Liver failure. Can also result in raised ammonia which can cause confusion/coma.
High levels of urea can indicate
Dehydration
Lots of dietary protein
Bleeding into gut
Kidneys stop working
How is urea formed?
Protein breakdown produces amino acids which are either recycled or broken down into individual groups. Ammonia is harmful if free in blood so one bicarbonate molecule binds 2 ammonia to form urea.
What does the Glomerular filtration rate describe
How well the kidneys are working based on how much blood is being filtered by all of kidneys glomeruli in each Bowman’s capsule/min
Normal Glomerular filtration rate. What does abnormality indicate?
60ml/min - if lower then can indicate fluid either isn’t reaching kidneys or kidneys not functioning correctly
How to calculate Glomerular filtration rate?
Can look at filtration of particular chemical that is filtered but not reabsorbed or secreted (insulin classically) but can also use calculation to estimate from U&Es
What is the difference between Creatine and Creatinine.
Creatine is combined with phosphate to make phosphocreatine and is involved in ATP cycle.
Creatinine is the breakdown product.
What can affect the basic creatinine levels of the patient?
Muscle mass - more muscle, more ATP needed so more creatinine produced. Age Race Weight M - higher than F
What are creatinine levels a good marker of
How well the kidneys are working. Excreted in glomerulus and proximal tubule and is not reabsorbed so present in high levels in urine when kidneys functioning correctly. If kidneys not functioning correctly then will be higher in blood as not excreted.
How is Creatinine produced
When creatine phosphate breaks down (phosphocreatine) to supply energy in the ATP cycle.
Daily water intake
Dietary (~2100ml) and from carbohydrate oxidation (~200ml)
Daily water loss
Insensible water loss - continuous loss of water by evaporation from the respiratory tract and skin.
Fluid loss in sweat
Fluid loss in faeces
Fluid lost as urine
Body fluid compartments. How is the total body fluid divided?
Mainly between extracellular fluid (further divided into interstitial fluid and plasma) and intracellular fluid. Also transcellular fluid (specialised extracellular fluid - includes synovial, peritoneal, pericardial, intraocculas and cerebrospinal fluids).
Total body water in average man
~60% body weight. Age/Fat can affect.
What is blood volume comprised of?
Comprised extracellular fluid (plasma) and intracellular fluid (RBC). Generally 60% plasma, 40% RBC.
What is haematocrit?
Fraction of blood comprised RBCs. Can be only 0.1 in severe anaemia.
Difference between ionic composition of plasma and interstitial fluid?
Very similar as only separated by capillary membranes. More proteins in plasma. Consider as equal for practical purposes.
What makes up extracellular fluids?
Large concentrations of Na & Cl, some bicarbonate and small quantities of K, Ca, Mg, Pi and organic acid ions. Carefully controlled.
What makes up intracellular fluid?
Separated from extracellular fluid by cell membrane that is relatively impermeable to electrolytes. Contains lots of protein, K and Pi, some Mg and S but only small Na & Cl. Almost no Ca
What is the indication-dilution principle?
Volume of a fluid compartment in the body can be measured using an indicator substance that is added to one compartment and allowed to disperse. If disperses evenly though the compartment, is not excreted of metabolised then can calculate volume of the compartment.
How to measure blood volume
2 methods.
Total blood volume=plasma volume/(1-haematocrit)
or use indication-dilution principle with radio labelled RBCs.
How is distribution of fluid between intracellular and extracellular compartments controlled?
The osmotic effect of solutes acting across the cell membrane.
Define osmoles
Number of particles in a solution in moles.
Define osmolarity
Osmoles per kg of water
What mostly affects osmolarity of intracellular, plasma and interstitial fluids
Interstitial/plasma - mostly Na & Cl
Intracellular - mainly K
Effect of giving isotonic saline solution by IV
No change in osmolarity. Solution stays in extracellular fluid.
Effect of giving hypertonic saline solution by IV
Fluid moves from intracellular fluid volume to extracellular fluid volume.
Effect of giving hypotonic saline solution by IV
Osmolarity of extracellular fluid decreases so water moves from extracellular fluid to intracellular fluid. Results in net gain of extracellular and intracellular fluid.
In terms of IV fluids, what are isotonic solutions
Have same [solute] as intracellular/extracellular solutes.
In terms of IV fluids, what are hypotonic solutions
Lower concentrations of solutes compared to cell. Water containing solute moves into cell so cell swells.
In terms of IV fluids, what are hypertonic solutions
Higher concentrations of solutes compared to cell. Water moves out of cell and into solution. Cell shrinks.
Impact of 0.9% saline on body fluids
[Solute] is the same as extracellular fluids. Increase in extracellular but not intracellular fluid volumes. Isotonic.
Dosage of bolus for fluid resuscitation
20ml/kg
