Anaesthetics - Use of Intravenous Fluids

Question 1

what are the 5 Rs of fluid loss?

Answer 1

Resuscitation

Routine Maintenance

Replacement

Redistribution

Reassesment

Question 2

what are fluids? and what do you need to think about when you are going to use them?

Answer 2

Question 3

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

Answer 3

60

2

type of fluid

volume

Question 4

what are the fluid compartments?

Answer 4

intracellular fluid

extracellular fluid

Question 5

what is the voume of each fluid comparmtent?

Answer 5

• TBW = 42L (70KG X 60%)
• ICF = 28L
• ECF 14L (11L ISF, 3L PLASMA)

Question 6

when giving someone fluids where will you be targeting?

Answer 6

extracellular fluid, particularly the plasma

Question 7

what makes up extracellular lfuid?

Answer 7

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

Question 8

water likes to diffuse from a dilute solution to a concentrate solution when seperated by a semi-permiable membrane, this is termed what?

Answer 8

osmosis

Question 9

water likes __________ so will try equal things out

Answer 9

balance

Question 10

how can you stop osmosis happening?

Answer 10

by applying pressure to the concentrated oslution

Question 11

what is the pressure called that prevents osmosis occuring?

Answer 11

osmotic pressure

Question 12

what is the calculation for osmosis?

Answer 12

• 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)

Question 13

what is a solute?

what is a solvent?

Answer 13

a substance dissolved into a liquid

a substance that is able to dissolve an solute

Question 14

what is an osmole?

Answer 14

reflects the concentration of osmotically active particles in solution

Question 15

what is osmolality?

Answer 15

• Number of osmoles of solute/kg
• 1 osmole contains 6.02 x 10²³ particles
• Body fluids measured in millimolar concentrations (mosm/kg)

Question 16

what is osmolarity?

Answer 16

• 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

Question 17

what is NICEs guidlines for the algorithm for IV fluid therapy in adults

Answer 17

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

Question 18

what is the routine maintenance?

Answer 18

Question 19

what is tonicity?

Answer 19

• 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

Question 20

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?

Answer 20

lower

higher

Question 21

• Hypotonicity = cell _________
• Hypertonicity = cellular _________

Answer 21

swelling

dehydration

Question 22

Symptoms of tonicity changes are largely neurological:

what are swelling symptoms?

Answer 22

raised icp, compromised cbf (cerebral blood flow) and herniation

Question 23

Symptoms of tonicity changes are largely neurological:

what are shrinkage symptoms?

Answer 23

ich (itracerebral haemorrhage) venous sinuous thrombosis

Question 24

there is many fluids that you can use

do all fluids distribute in the same place in the body

Answer 24

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

Question 25

what are the 2 types of IV fluids?

Answer 25

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

Question 26

what are the disdvantages and advantages of crystalloids and colloids?

Answer 26

Question 27

what are isotonic fluid sand where are they found?

Answer 27

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

Question 28

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]

Answer 28

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

Question 29

* 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 ___ \_\_\_\_\_ \_\_\_\_

Answer 29

lysis red blood cells. it is relatively isotonic so has little effect on red blooc cells

Question 30

* 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.

Answer 30

•Over 50% of 500 and 1000ml bags of fluid issued to ARI is 0.9% saline

Question 31

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?

Answer 31

Question 32

how do we measure body fluid?

Answer 32

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

Question 33

assessment of volume status

Answer 33

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

Question 34

the rates of prescribing fluids is still high so NICE done what?

Answer 34

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

Question 35

picutre showing fluid presciption chart

Answer 35

* One chart with fluid prescription on one side and intake/output on the other * Hand out fluid charts

Question 36

key point sof the fluid prescription chart

Answer 36

* 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: 1. Assess Patient - Is patient Hypovolaemic, Euvolaemic or Hypervolaemic? 2. Why give fluid? - Maintenance, Replacement or Resuscitation? 3. How much? 4. Which Fluid?

Question 37

how much fluid is given for maintenance fluid?

Answer 37

* 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

Question 38

what is the preffered choice of fluid to be used as maintenance fluid?

Answer 38

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

Question 39

how is fluid replacement done?

Answer 39

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

Question 40

what fluid should be used for replacement?

Answer 40

* 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!

Question 41

what is resuscitation?

Answer 41

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

Question 42

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!