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Describe fluid and electrolytes?

1. IV fluid management.
2. Types of fluids.
3. Fluid assessment.


What questions should you ask a patient before giving IV fluids?

1. Is my patient evolaemic, hypovalemic or hyprvolaemic?
2. Does my patient need IV fluid? Why?
3. How much IV fluid does my patient need?
4. What type(s) of fluid does my patient need?


What are the types of fluid?

1. Hypotonic fluid.
2. Hypertonic fluid.
3. Isotonic fluid.


Describe hypotonic fluid?

This is a hypotonic solution, where it pushes fluid into the cell and makes the cell fat.


Describe hypertonic fluid?

This is a hypertonic solution that pushes fluid out of the cells and makes the cells smaller.


Describe isotonic fluid?

This is a isotonic solution that keeps everything the same.


How do you assess volume status?

Weight is useful to assess if they are euvolaemic, dehydrate or fluid overload. Any rapid weight gain or loss will be fluid. Dry tongue may be useful if incredibly cracked. Oedema is good for fluid overload.


Does the patient need IV fluid?

1. No = they do not need it as they are drinking enough, they're on enteral feeding or they are already in fluid overload.
2. Yes = they do need it as they are not drinking and they have lost or they are losing fluid.


Why do patients need IV fluid?

1. Maintenance.
2. Replacement of losses.
3. Resuscitation.


Describe maintenance fluid?

This is fluid lost over the course of a normal day. You lose this fluid from sweat, urine, excretion, and breathing out. This is how much fluid you need to maintain things (2-3L/day).


Describe maintenance fluid in children?

- 4mL/kg/hr for the first 10kg of body weight.
- +2mL/kg/hr for the next 10kg of body weight.
- +1mL/kg/hr for the remainder of body weight.


Describe replacement fluid?

Extra fluid loss can come from a lot of things i.e. drain (third spacing), profound diarrhoea, and vomiting. When you are replacing fluid you want to be replacing fluid that has been lost. But also you need to continue with maintenance fluid. Weight and JVP are helpful in assessing replacement fluid; so are fluid balance charts.


Describe resuscitation fluids?

This will occur when there is a patient who has shock. Might need to give them a lot of fluid quickly to try and get their blood fluid up. Delayed capillary fluid test (pinch fingers).


What type of IV fluid do you use?

Different fluids have different tonicity, this is important as it will affect your sodium and water balance. Need to look at the following things:
1. Patient fluid status.
2. What is the serum sodium?
3. Safest fluid is generally isotonic.


What are the most common isotonic solutions used in hospital?

Plasma-lyte and saline. generally give isotonic fluid unless maintenance fluid and overload or high sodium.


Why would you sue hypotonic fluid?

You generally would not use hypnotic fluids as they push water into the cells. 5% dextrose starts as an isotonic solution however dextrose is metabolised by cells so it just becomes free water. They are useful if there is high serum sodium (i.e. not enough water) or if the patient needs maintenance fluid but is already in overload.


Why would you sue hypertonic fluid?

Fluid that will push water out of the cells. used in patients with severe hypernatraemia. However, hypertonic fluid (too much of it) could kill people.


Describe hyponatraemia?

It is low sodium. It is mainly due to excess water or it could be due to sodium loss.


Describe body compartments?

Over half of us is made up of fluids (55% females and 60% males). 2/3 of fluid is intracellular and 1/3 is extracellular. And out of that extracellular 20% is plasma.


Describe fluid electrolyte composition?

The predominate extracellular cations is sodium, but the predominate intracellular cation is potassium.


Where are IV fluids going to?

They are going extracellularly - changing the extracellular fluid.


What is the job of ADH?

To regulate the hydrations status and blood pressure.


What do osmoreceptors and baroreceptors do?

They detect increased osmotic pressure (osmoreceptors) and decreased blood pressure (baroreceptors). This will stimulate ADH in the post pituitary. Once ADH is stimulated it will increase blood pressure and volume, reabsorption of water and vasoconstriction of blood vessels.


What are the causes of hyponatraemia?

1. Sodium loss.
2. water excess.
3. Pseudohyponatraemia.


How can you lose sodium/

1. GI loss (vomiting, diarrhoea).
2. Hypo-aldosteronism.
3. sweat (not usual).
4. Diuretics.


Describe aldosterone?

It pushes sodium from the tubule into the blood. Low aldosterone there is less sodium absorbed. Sodium is lost in urine down gradient. Low sodium means high potassium in blood.


Describe pseuodhyponatraemia?

This is when your lab test says you have low sodium but you actually don't. It can occur when you have high triglycerides (hypertriglyceridemia) or high protein (hyperproteinemia).


Describe water excess?

This is syndromes with water overload: cirrhosis, heart failure and nephrotic syndrome. SIADH and polydipsia. The excess problem is water however must patients will be euvolaemic.


How do you sort out hyponatraemia?

Ask the patient about their history: what they've been doing, drinking lots, diarrhoea, medications, hospital, drips, fluid overload. they key thing is examining their fluid status and the last thing is osmolality.


What should a person with hyponatraemia's serum osmolality be?

It should be low. Normal serum osmolality is 280-300.


What happens if the osmolality is normal?

This occurs with pseudohyponatraemias. The measured osmolality is normal as its measurement is not affected by hypertriglyceridemia or hyperproteinaemia.


Describe fluid overload and low sodium?

The signs of fluid overload:
1. High BP.
2. Increase in weight.
3. Oedema.


Describe water excess with euvolaemia?

There are no signs of dehydration or oedema; JVP is not elevated. it can be due to:
2. Polydipsia.
3. Overy hydration with low sodium IV fluids (dextrose compared with saline).
4. Diuretics.


Describe polydipsia?

It is water intoxication. Urine osmolality is usually high in hyponatraemia the exception is polydipsia. Drinking too much water for the kidneys to pee it out - urine will be dilute.


Describe the syndrome of inappropriate ADH?

ADH release occurs despite not being dry or hypotensive.


What are the causes of SIADH?

1. Tumours.
2. CNS.
3. Drugs.
4. Lung disease.


Describe diuretics?

The most common diuretic is thiazide - these make you pee out sodium. This also makes bart-receptors and osmoreceptors over active (this will increase ADH).


What is the mechanism behind diuretics?

There is NaCl loss, which will reduce ECF volume. This will shift ADH curve to lower set point. ADH system now allows a decrease in sodium i.e. decrease in ECF osmolality. Adaption favours sodium instead of potassium (aldosterone) i.e. relative wasting of potassium.


What happens when you select the wrong IV fluid?

When you give somebody a whole lot of hypotonic fluids it will cause hyponatraemia.


How do you correct hyponatraemia?

The treatment depends on the cause. A dehydrated patient with sodium loss you will give them saline. If the patient has water excess; generally you will fluid restrict them (1L water daily). Rapid correction unadvisable.