Treatment of Fluid and Electrolyte Imbalance Flashcards
When may a patient with fluid overload still be prescribed IV fluids?
e.g. if someone with LV failure has pulmonary oedema → doesn’t mean their TBW is high so may be situations here they need IV fluids
When do you give IV fluids/fluid replacement?
1) Maintenance
2) Replacement
3) Resuscitation
When do you give maintenance fluids?
To maintain euvolaemia when oral intake is reduced e.g. NBM< nausea, vomiting, diarrhoea (not absorbing)
When do you give replacement fluids?
- Previous ongoing or predictable future losses
- e.g. D&V, urine, drains, skin losses, sweat, third spacing, burns, surgery, polyuria
When do you give resuscitation fluids?
- To rapidly restore the intravascular compartment
- e.g. following haemorrhage, marked dehydration, vasodilation, shock
How do you diagnose dehydration>
1) High Hb → blood is haemoconcentrated → less fluid in blood
2) Low body weight → if 3kg less than 3 days ago, loss of water not fat, look at daily weight
3) Urine output → retrospective
4) Hypotension (depends on physiological state of patient) → BP tends to be one of the last things to fall bc of vasoconstriction in young people but in older people might go down quicker
What are the aims of fluid replacement?
1) Maintain normovolaemia
2) Maintain normal electrolyte concentrations
3) Compensate for any extra fluid losses with like for like → esp. with blood
How do you try and replace losses exactly?
1) Previous loss → volume, type of fluid
2) Maintenance requirement → volume (what have they lost and what extra do they need)
3) Expected future loss → volume, type of fluid
What are 5 types of IV fluids?
1) Glucose 5%
2) Sodium chloride 0.18% and glucose 4% (dextrose saline)
3) Saline 0.9%
4) Balanced crystalloids
5) Colloid
What is a feature of all IV fluids?
They are isotonic → same osmolality as plasma
Why is glucose 5% given?
It is used just for water replacement → it makes fluid isotonic but without electrolytes and glucose is broken down rapidly
Describe how glucose 5% acts in the body
1) Fluid stays in circulation for a few minutes and then is distributed into cells (so intracellular)
2) Doesn’t increase blood glucose (maybe just temp)
3) Not nutritional → doesn’t cover calorie intake
What is dextrose saline used for?
Maintenance → it covers sodium and water requriement
What is normal saline used for?
One bag (1L) meets daily sodium need in one dose
What is an example of a balanced crystalloid fluid?
Hartmann’s
What fluid does balanced crystalloid reflect?
ECF (physiological) → basically dextrose saline and potassium + buffer
What can balanced crystalloid not be used for?
Replacing potassium → only has 5mmol so not enough to replace intracellular potassium
When should you not give balanced crystalloids and why?
Hyperkalaemia → might push them over the edge into cardiac arrhythmia
What do colloids contain and therefore where does it stay?
Molecules that don’t cross semi-permeable membranes e.g. proteins → therefore the fluid mainly stays in the plasma volume
What is the ultimate colloid?
Blood
Why can colloids be better to use than balanced crystalloid?
Bc BP stays up longer
What are other colloids?
Albumin, gelatine
What is the difference between treating a healthy euvolaemic patient who is NBM and someone who is susceptible to fluid overload but is also euvolaemic and NBM?
Healthy → better to go slightly over bc otherwise they often lie there thirsty
Susceptible to fluid overload (heart/liver/kidney failure) → don’t do this
What are the principles when giving IV fluids?
1) Assess patients regularly, keeping a careful fluid balance chart
2) Stop IV fluids as soon as not required → much better to drink
3) If on IV fluids for > 3 days use oral/enteral feed or TPN (can be on IV TPN for a long time) if necessary
4) Include fluid given in IV drugs and pumps
How much volume do you give for maintenance?
Normal amount
How do you decide the composition of IV fluids?
Current and previous losses
What are examples of fluid loss?
- Nasogastric aspirate, vomit → loss of sodium, chloride, some potassium
- Drains
- Urine
- Diarrhoea/stoma
- Skin
- Blood
What are the rules of replacement therapy?
1) Prescribe for routine maintenance requirement + additional fluid and electrolyte supplements to replace the measured abnormal ongoing losses
2) Monitor and reassess fluid and biochemical status by clinical and laboratory monitoring
3) Seek expert help promptly bc getting it wrong can be fatal
What is resuscitation therapy used?
If a patient is hypotensive (shock) if the cause is hypovolaemia
How do you give resuscitation therapy in shock?
1) Test the response to fluid with a fast IV bolus of a crystalloid → 250ml over 30 mins
2) Reassess the patient using ABCDE approach and repeat the above if necessary
3) Use blood as soon as available in patient is bleeding
4) Seek expert help early
What do you use normal saline for?
Resuscitation
What do you use balanced crystalloid for?
Resuscitiation
What do you you 5% glucose for?
Maintenance
What do you use dextrose saline for?
Maintenance
What do you use colloids for?
Resuscitation
How do you treat hyponatraemia with hypovolaemia?
Correct volume depletion e.g. IV 0.9% saline
How do you treat hyponatraemia with euvolaemia?
1) Treat underlying cause
2) Fluid restriction
How do you treat hyponatraemia with hypervolaemia?
1) Underlying cause
2) Restriction
(vasopressin receptor antagonists)
When is aggressive therapy for hyponatraemia indicated?
- Severe symptoms
- Acute hyponatraemia (<24h)
What do you do in aggressive hyponatraemia therapy?
1) Careful monitoring → raise serum sodium by 4-6 mmol/L over a few hours and no more than 8 mmol/L/day
2) Hypertonic 3% saline may be indicated but seek expert help
What is the risk of rapid correction of low sodium (hyponatraemia)?
Risk of central pontine myelinolysis
How do you treat chronic hypernatraemia?
1) Treat underlying cause
2) Use of hypotonic fluid e.g. 5% dextrose given slowly
3) Lower sodium by a maximum of 10 mmol/L per day
4) Always re-assess
How do you treat hypernatraemia in an acute emergency?
1) Hypotonic fluid
2) Lower sodium by 1-2 mmol/L per hour to restore normal sodium levels within 24h
3) Bc the acute increase in plasma sodium can lead to irreversible neurology seek expert help
How do you treat hypokalaemia?
1) Correct Mg levels
2) K replacement (oral or IV) → if IV, maximum 10-20 mmol/hr and cardiac monitoring
3) Address the cause
4) Give oranges or bananas
What fruit should you give to someone in renal failure with hyperkalaemia?
Apples (not bananas or oranges)
How do you calculate HR on an ECG?
300/number of big squares
How do thiazides work?
1) Block reabsorption of sodium and chloride in DCT
2) Increase sodium to distal nephron
3) Make you pee out more
Why does caffeine make you pee more?
Bc it suppresses ADH
How do you treat hyperkalaemia?
1) IV calcium gluconate → antagonise membrane action of high K
2) IV insulin with glucose, sodium bicarbonate or beta agonists → drive K into cells
3) Remove K from the body → loop diuretics, haemofiltration or haemodialysis
4) Treat underlying cause
5) Monitor
6) Longer term → drug and diet changes
Where are IV fluids administered and how do they re-distribute?
They are administered into the intravascular space but re-distribute differently according to their composition
What should rate of correction of electrolyte disturbances be related to?
The rate of onset of electrolyte disturbance
