Intravenous Fluids Flashcards
What is diffusion?
The net movement of solutes from a concentration of high to low - the membrane has to be solute permeable
What is osmosis?
Movement of water from a high concentration to a low concentration - membrane has to be solue impermeable
What is osmolarity?
The measure of solute concentration per unit VOLUME of solvent.
Osmoles per litre.
Measures the osmotic pressure a solution has.
What is osmolality?
The measure of solute concentration per unit MASS of the solvent.
Osmoles of solvent per kg of water.
Takes into account only solutes that contribute to a solutions osmotic pressure.
What is tonicity?
The measure of the osmotic pressure gradient between two solutions.
This determines the direction and extent of diffusion.
4 main questions regarding fluid.
- What is my patients fluid status?
- Does my patient need IV fluid?
- How much do they need?
- What type(s) of fluid does my patient need?
What do we humans need daily in terms of fluid and electrolytes?
- Water - 25-30ml/kg/day
- Sodium - 1mmol/kg/day
- Potassium - 1mmol/kg/day
- Glucose - 50-100g/day
- However, not everyone is the same!
‘What is my patient’s volume status?’
How do we assess this?
- Airway:
- We breathe out water through airways
- Ventilators make people dry
- Breathing:
- If someone is fluid overloaded – can get pulmonary oedema
- Circulation
- Raised JVP = fluid overload
- Absent JVP = dehydrated
- Disability
- Extremities
- Look at mucous membranes – dry mouth
- BE CAREFUL SJOGRENS!!
- Sweat is a better sign than mucous membranes for dehydration
- Check skin turgor
Once we have identified our patients fluid need what do we do next?
- Identify the cause of the surplus/deficit and treat!!
What are the characteristics of euvolaemia [normal hydration]?
- Feels well, not thirsty
- Veins well filled
- Warm extremities
- Mild sweat
- Normal BP and HR
- Normal urine
- NEEDS
- No fluids (unless electrolyte deplete or low BP)
What are the characteristics of hypovolaemia? And what do they need?
- Feels nauseous, tired, dizzy, thirsty
- Flat veins
- Cool peripheries
- No sweat
- Low or postural BP and high HR
- Concentrate oliguria (dark urine)
- Responds to SLR
- NEEDS
- Resuscitation fluids (if low BP or in shock)
- Rehydration fluids
- ‘Plug the leak’- or else they will just get dehydrated again
What are the characteristics of hypervolaemia? What do they need?
- Feels breathless, not thirsty
- Veins distended
- Warm and oedematous extremities (ankles)
- Sweaty
- High BP and high HR
- Dilute urine (could be oliguric or polyuric)
- NEEDS
- No more fluids
- Possibly diuretics (if respiratory compromise)
- Haemfiltration (if anuric)
What are the 4 ‘R’s of fluid administration?
Resuscitation, Routine, Replacement, Reassessment
What is fluid resusitation and when is it recquired?
- If in shock – give fluids fast!
- 250-500ml stat of saline = a fluid bolus, reassess their BP after this
What is routine maintenance and when is it recquired?
- Given to patients who can’t eat/drink – to maintain their euvolaemic state
- All they really need is water – don’t mess with their oncotic pressure or overload them
- Don’t give nutrition through this – that’s given through TPN
What is fluid replacement and when is it recquired?
- Sometimes we need fluid specifically to replace lost electrolytes e.g. magnesium, potassium
- Such as during severe gastroenteritis (D&V)
What is reassessment and when is it recquired?
- Recquired for EVERY patient
- Basically assessing if the fluid intervention has worked
How do we assess how much fluid the patient needs?
Work out water deficit:
- Catheters, drains
- Input charts
- Vomit bowls
- Sputum pots
- Stool charts and stoma losses
Then the insensibles:
- Sepsis (sweat)
- Ventilation
- Open wounds
- Burns
- Bleeding
- This is loss of pure water, there is no associated solute loss
- Normal daily loss is 400-800mls in adults
Do the math… 24hrs:
- Vomit 600m
- Urine 1200ml
- Drank 1200ml
- Sweat??
- Approximate deficit = 600ml + insensible losses
See the table for handy guide of which fluids to give:
What are the three main types of fluids we administer?
- D5W - dextrose
- Crystalloids
- Plasma expanders - colloid = protein
What are the features of D5W?
Mostly water with some sugar in it
- Moves through all compartments – therefore doesn’t fill up someone’s BP as it moves straight out of arteries
- Not useful for blood volume expansion
- Zero sodium load, isotonic
- Depletes your sodium and potassium
- Useful in:
- Chronic dehydration, hypernatremia, CAN be used in diabetics as the sugar is very easily cleared by the body
- Not useful in:
- Resuscitation, low albumin
What are the features of crystalloids?
These are the BEST fluids and most commonly used.
- Utilitarian, come in various combinations
- E.g. Hartman’s, saline etc.
- Remain in ECF
- Usually high NA load – can cause problems over time
- Useful in:
- Acute illness, dehydration, AKI, resuscitation
- Not useful in:
- Long term maintenance, hypernatraemic patient (as they tend to contain a lot of sodium – strains the heart and can result in chronic cardiac problems)
What are the features of colloid?
Not commonly used anymore
- Most commonly blood, also TPN
- Stays exclusively in IVS
- Trials show no better than crystalloid in resuscitation
- IV albumin sometimes used in cirrhosis
- Useful in:
- Liver patients
- Select intra-operative
- Bleeding
- Not useful in:
- Much else
CASE 1
- New admission from A + E
- 58 year old man who has been complaining of breathlessness for 10 days
- He has a PMH of hypertension, though takes no regular medications
- He has fixed abode, previous admissions from alcohol withdrawal
- CXR = left lobar pneumonia
- Fluid assessment
- Dry mucous membranes
- Dehydrated (skin turgor)
- BP: 86/55
- HR: 120 bpm
- Temp: 38.8
- Sats: 90% on 6L
- What is his fluid status?
- Do we give fluids?
- What kind?
- How much?
- HYPOVOLAEMIC: High HR, low BP, skin turgor and mucous membranes = point to dehydration. He is hypotensive even though he is technically hypertensive and taking no medications – this is SERIOUS hypotension – we think he is in shock
- Yes
- IV bolus, Resuscitative fluid
- 500ml!!!!! Only exceptions to this are children/neonates/rare heart failure cases
Notes:
- For resus fluids, use ABCDE and take into account clinical examination, trends and context
- Identify cause of deficit and respond
- Give 500ml bolus over 15 mins of crystalloids containing 130-154mmol/l Na+
- Then reassess
CASE 2
- 58 year old lady, day one post right hemicolectomy
- She’s been doing well and is allowed to eat and drink
- She was seen due overnight due to low urine output
- Has high blood pressure and low sodium but otherwise well
- Assessment
- HR: 70 bpm
- BP: 142/7-
- Temp: 36.7
- Weight: 50kg
- Sats: 99% on 4L
- Normal mucous membranes and skin, normal colour urine
- What is her fluid status?
- Why does she have low urine output?
- Do we give IV fluid and how much fluid does she need?
- EUVOLAEMIC: Normal BP, normal clinical examination
- Physiological stress response to surgery = completely normal
- No IV, Eat and drink as normal
Notes:
- Maintenance fluids: depends on weight
- 25-30ml/kg/day of water (= about 2litres per day for 70 kg adult)
- Approx. 1mmol/kg/day of K, Na, Cl
- 50-100g/day of glucose to limit starvation ketosis
CASE 3
- 66 year old fishermen
- 2 day history of breathlessness
- Treated with amoxicillin and IV saline 0.9% at 150ml/hour for sepsis
- PMH: MI, hypertension, diabetes (tablet controlled)
- Assessment:
- HR: 110-150 (AF)
- RR: 24
- Sats 99% on 2L
- BP: 165/70
- Temp: 37.6
- Weight: 95kg
- What is this patients fluid status? + why?
- Why did he get fluid?
- Does he need any more fluid?
- HYPERVOLAEMIC : Moist mouth, JVP 6cm, Sat upright, Cool peripheries, Sweaty, Oedema
- Sepsis, Cool peripheries
- No
Notes:
- Remember, not everyone needs fluids
- Often the first measure in overload is to stop and/or restrict fluids
- Diuretics have a limited role
- Poor follow-up leads to iatrogenic overload
- REASSESS HIM
