Fluid Electrolyte Balance Flashcards
Describe the distribution of fluid in the body compartments
- 2/3rd inside the cell: 28L
- 1/3rd outside the cell: 11L interstitial fluid, 3L plasma
- total = 42 in 70kg male
Describe the distribution of ions in the body compartments
ICF: K+=140, Na+=15, Cl-=5
ECF: K+=5, Na+=140, Cl-=110
Describe the sources of gains and losses that contribute to total body fluid and the total expected of a 70kg man
Gains: food and water, oxidation of food
Losses: urine, faeces, sweat, insensible losses (resp tract, evaporation)
- average: 2550ml
If you have large insensible losses from a patient due to resp distress what fluid do you give?
5% glucose/dextrose (water)
How is total bodily fluid monitored and regulated?
- homeostasis: osmoreceptors in hypothalamus outside BBB (increase/decrease secretion of ADH and driving thirst)
- in a sudden event such as trauma: baroreceptors (volume) in right atria and veins and carotid sinus in aorta (pressure)
Describe how the plasma Na+ concentrations are regulated
- linked to kidney function (to manipulate volume in the body)
- if total Na+ drops (low GFR, stimualtiong of JGA): osmolality stays the same, total volume falls
- if total Na+ rises (increased GFR, increased ADH): osmolality stays the same, total volume rises
Describe how changes in osmolality affects Na+ concentration in plasma
Rise in osmolality:
- increase in thirst
- increase in release of ADH
- increase in water intake/retention
- increase in volume
Fall in osmolality:
- decrease in thirst
- decrease in release of ADH
- decrease in water intake/retention
- decrease in volume
Describe how changes in volume affect plasma Na+ concentrations
Increase in volume: increase in stretch of vascular system
- baroreceptors sense change
- decrease in renin and aldosterone release
- increased release of ANP
- decreased Na+ and water retention
Decrease in volume: decrease in stretch of vascular system
- baroreceptors sense
- if pressure falls, induces ADH release and stimulates thirst centres
- increases renin and aldosterone release
- decreased release of ANP
- increased Na+ and water retention
Describe how the plasma K+ concentrations are regulated when it is in excess
- increases activity of basolateral Na+ pump
- more K+ enters cell
- increased secretion across simple diffusion channels on apical membrane
- increased secretion of aldosterone
Describe the effect that aldosterone has on the DCT of the kidney
- increases activity of basolateral Na+ pump
- increases number of Na+ pumps
- increases number of Na+ and K+ channels in apical membrane
- results in increased reabsorption of Na+ and secretion of K+
What is Conn’s Syndrome?
hyperaldosteronism leading to hypertension due to increased fluid volume and hypokalaemia due to excessive K+ secretion
What are the risks of IV fluids?
- peripheral vascular catheter required (risk of infection, thrombophlebitis etc.)
- easy to give fluid overload
- errors in prescribing
What are the clinical signs of hypovolaemia?
- systolyic BP: <100mmHg
- HR: >90 bpm
- cap refill: >2s
- urine output: <0.5mls/kg/hr
- dry mucous membranes
- decreased skin turgor
- postural hypotension
What are the clinical signs of fluid overload?
- history of cardiac or renal problems
- raised JVP
- peripheral oedema
- inspiratory crackles at lung bases
- hypertension
Define maintenance, replacement and resuscitation fluids
- maintenance fluids: patient does not have excess losses, if no other intake then 30mls/kg/24hrs (part IV needed if some oral intake) 0.18% NaCl, 4% dextrose
- replacement fluid: previous/current abnormal losses (in addition to maintenance fluid) - 0.9% NaCl
- resuscitation fluid: hypovolaemic patient, requires urgent correction of intravascular depletion - 0.9% NaCl, plasmalyte
