Anaesthetics - Use of Intravenous Fluids Flashcards
what are the 5 Rs of fluid loss?
Resuscitation
Routine Maintenance
Replacement
Redistribution
Reassesment
what are fluids? and what do you need to think about when you are going to use them?
FLuid compartments:
- TBW is around __% of body mass
- Contained in _ body compartments
Importnat to know where the water is situated as it can affect the ____ __ _____ and ______ that you want to give
60
2
type of fluid
volume
what are the fluid compartments?
intracellular fluid
extracellular fluid
what is the voume of each fluid comparmtent?
- TBW = 42L (70KG X 60%)
- ICF = 28L
- ECF 14L (11L ISF, 3L PLASMA)
when giving someone fluids where will you be targeting?
extracellular fluid, particularly the plasma
what makes up extracellular lfuid?
interstitial fluid (ISF) - fluid in the spaces between cells
intravascular fluid
water in connective tissue
transcellular tissue - fluid that fills the cavities in the body lined by epithelium so an example of this is aqueous humor in the eye or cerebrospinal fluid
water likes to diffuse from a dilute solution to a concentrate solution when seperated by a semi-permiable membrane, this is termed what?
osmosis
water likes __________ so will try equal things out
balance
how can you stop osmosis happening?
by applying pressure to the concentrated oslution
what is the pressure called that prevents osmosis occuring?
osmotic pressure
what is the calculation for osmosis?
- n x c (c/M) RT
- n = number of dissociated particles
- c = concentration (g/l)
- M = molecular weight
- R = universal gas constant
- T = absolute temperature (K)
what is a solute?
what is a solvent?
a substance dissolved into a liquid
a substance that is able to dissolve an solute
what is an osmole?
reflects the concentration of osmotically active particles in solution
what is osmolality?
- Number of osmoles of solute/kg
- 1 osmole contains 6.02 x 1023 particles
- Body fluids measured in millimolar concentrations (mosm/kg)
what is osmolarity?
- Number of osmoles of solute/litre
- Estimated osmolarity of body fluids can be calculated
- 2([na+] + [k+]) + urea + glucose
Normal plasma osmolarity:
- 2([na+] + [k+]) + urea + glucose
- 2 ([140] + [4]) + 5 + 5
- 298 mOsml/l
what is NICEs guidlines for the algorithm for IV fluid therapy in adults
asses patientient using ABCDE patinet
if need fluid follow the red pathway and resusitate them and if no improvememtn after igving 2 litres
if no need for resisitation then stay on green
organge pathway is to help troubleshoot what is going on
what is the routine maintenance?
what is tonicity?
- Tonicity = effective osmolality
- Only particles restricted to one of the compartments will determine water distribution
- Particles which move freely will not influence water distribution
- ECF - Na+ (and accompanying anions)
- ICF - K+ and macromolecules
Tonicity is a measure of the effective osmotic pressure gradient; the water potential of two solutions separated by a semipermeable cell membrane. In other words, tonicity is the relative concentration of solutes dissolved in solution which determine the direction and extent of diffusion
hypertonic solution has a ______ osmotic pressure than red blood cells
water will flow towards the _______ concentration
what happens in a hypertonic and a hypotonic solution?
lower
higher
- Hypotonicity = cell _________
- Hypertonicity = cellular _________
swelling
dehydration
Symptoms of tonicity changes are largely neurological:
what are swelling symptoms?
raised icp, compromised cbf (cerebral blood flow) and herniation
Symptoms of tonicity changes are largely neurological:
what are shrinkage symptoms?
ich (itracerebral haemorrhage) venous sinuous thrombosis
there is many fluids that you can use
do all fluids distribute in the same place in the body
no all different, depends on things like the composition and tonicity of the fluid
we dont use 5% glucose for resusitation as you need fluid in the intervascular space but this would be metabolised quickly and diffuse equally in all the compartments
what are the 2 types of IV fluids?
crystalloids - aqeous mixutres that are soluble in water - use more of these as cheaper, less allogenic but slighlty more prone to odoema
colloids - insoluble with larger molecules
what are the disdvantages and advantages of crystalloids and colloids?
what are isotonic fluid sand where are they found?
Isotonic solutions have a concentration of dissolved particles similar to plasma, and an osmolality of 250 to 375 mOsm/L. These fluids remain within the extracellular compartment and are distributed between intravascular (blood vessels) and interstitial (tissue) spaces, increasing intravascular volume
Clinical Case:
- 30 year old female, 49kg
- Elective hysterectomy (low blood loss)
- Plasmalyte intraoperatively
- Post op fluids: 0.18% saline/4% dextrose @ 62.5ml/hr
- Speeded-up because of nausea (5L given over 16 hours [312.5ml/hr]
Mistakes:
- Tailor iv fluid to compartment requiring filling
- Excess hypotonic fluid in a patient secreting adh
- Assume sodium of 138 at end of operation
- 5l dextrose/saline (4l 5% dextrose + 1l 0.9% saline)
- Tbw = 55% of 49kg = 27l; ecf (before fluid) 9L
- Saline distributes only in ecf. Water will fill all compartments
- Ecf following fluid = 9l + 1l (saline) + 1.3 = 11.3l
- Na content before fluid = 9 x 138mmol/l = 1242mmol/l
- Na content after fluid = (9l X 138) + (154 in 1l 0.9% saline) = 1396mol/l
- [na] after fluid = 1392/11.3 = 123mmol/l
- The use of 0.9% saline originated from the in vitro studies of Hartog Jakob Hamburger (Dutch physiologist) who in 1896 found that the freezing point of 0.9% saline was the same as that of human serum and that erythrocytes were least likely to undergo _____ in this solution.
- Hamburger called this solution ‘indifferent saline’ indicating that it had no effect on the ___ _____ ____
lysis
red blood cells.
it is relatively isotonic so has little effect on red blooc cells
- If we look at IV fluid usage HMUD – Hospital Medicines Utilisation Database
- The HMUD database is based on data extracted from hospital pharmacy systems around Scotland.
•Over 50% of 500 and 1000ml bags of fluid issued to ARI is 0.9% saline
what are the different inputs an doutputs of fluid?
what are some sensible and insensible losses?
and how does input and output vary between climates?
how do we measure body fluid?
many different ways:
- DIFFICULT TO BE ACCURATE!
- THIRD SAPCE LOSS ?!?
- OESOPHAGEAL DOPPLER
- PULMONARY ARTERY CATHETER
- IVC collapsibility
- MINIMALLY INVASIVE CO MONITORS
- “THE CLINICIAN”
Clinical assessment is the one used most often
assessment of volume status
Hypovolemia is a state of abnormally low extracellular fluid in the body. This may be due to either a loss of both salt and water or a decrease in blood volume. Hypovolemia refers to the loss of extracellular fluid and should not be confused with dehydration
the rates of prescribing fluids is still high so NICE done what?
created an algorithm
In recognition of the issues surrounding IV fluid prescribing and in an effort to combat the issues surrounding current practice, the National Institute for Health and Care Excellence (NICE) published in December 2013
unfortunatley it has been shown that we dont follow these and the rates are still high
picutre showing fluid presciption chart
- One chart with fluid prescription on one side and intake/output on the other
- Hand out fluid charts
key point sof the fluid prescription chart
- 24 hr chart – ensure patients have their fluid management plan reviewed at least daily and also allow medical staff to see what has been previously prescribed when undertaking the next fluid review
- Patient weight – must ensure completed
- Guidance – structured framework to support prescribers in assessing and planning for optimal fluid management. Hand out pocket guideline.
- The guidance is suitable for the majority of patients but in special cases such as cardiac dysfunction, renal/liver failure, obstetrics & head injury consult senior– this list not exhaustive
- 4 questions:
- Assess Patient - Is patient Hypovolaemic, Euvolaemic or Hypervolaemic?
- Why give fluid? - Maintenance, Replacement or Resuscitation?
- How much?
- Which Fluid?
how much fluid is given for maintenance fluid?
- 30ml/kg/24hrs (20-25ml in frail & elderly)
- Never give over 100ml/hr due to risk of hyponatraemia (low level of sodium in blood)
- Remember to subtract other intake e.g oral
- Do not prescribe ‘x’ hourly bags
- All IV maintenance given in ml/hr via volumetric pump (note NOT S/C fluid)
- Reduce in frail and elderly
what is the preffered choice of fluid to be used as maintenance fluid?
0.18% NaCl/4% glucose/0.3% KCl (40mmol/l KCl)
- This fluid if given at the correct rate provides the daily requirements of water, Na, K and glucose to prevent starvation ketosis
- Unless:
- K+ ≥ 5.0 use 0.18% NaCl/4% glucose
- Na+ ≤ 132 use PlasmaLyte 148
•Patients fasting for ≥ 6hours for any reason should be started on maintenance
how is fluid replacement done?
How much?
- Add up losses in the last 24hrs (or sooner if required) e.g. bleeding, D & V, drain output, fistulae….
- Give this volume back
Remember:
- Urine output is a poor guide to fluid requirements
- Oliguria does not always require fluid therapy
- Replacement fluid is IN ADDITION to maintenance
Never ‘speed up’ maintenance fluid
what fluid should be used for replacement?
- PlasmaLyte 148
- Upper GI losses: use 0.9% NaCl with KCl
- Can be given through a gravity giving set or volumetric pump
Remember – If it hasn’t been lost…… don’t give it. Giving excess fluid is placing not replacing!
what is resuscitation?
every time you do something reasses
How much?
- For severe dehydration, sepsis or haemorrhage leading to hypovolaemia & hypotension
- Give fluid challenge of 250-500ml over 5-15 mins and reassess
- Fluid Challenge Algorithm
- Controlling bleeding and sepsis priority
- Which fluid? - PlasmaLyte 148/colloid/blood
Never ‘speed up’ maintenance fluid
Summary:
- Basic understanding of physiology required to safely deliver iv fluid
- Enteral route preferred
- Assess every patient who requires iv fluid. And re-assess.
- Be careful with tonicity!
