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FLUIDS

Aims

Understanding of human water and sodium homeostasis

Develop fluid management skills

Learning Objectives / Plan

• Why this is important?

• Body fluid compartments

• Water and sodium homeostasis– Normally– In disease states

• Intravenous fluids

• Cases / scenarios

Intravenous Fluids

• 1830s – cholera epidemic

• Late 19th Century – surgical patients

• Now – Routine– ……too routine?

Problems (first reported as early as 1911)

• Estimated 8315 excess deaths / year USA due to iatrogenic pulmonary oedema

• ?number with renal failure / underperfusion– easier to see and treat

Too much given

Wrong stuff

Or

Not enough given

Reasons• Poor understanding of normal and perioperative Na and

water physiology– <50% know Na content of NaCl 0.9% – Fluid balance charts

• infrequently checked

• Infrequently correct

– Perioperative patients frequently (in only the first few days) • 7000ml positive fluid balance

• 700mmol positive Na balance

• Poor understanding of the effect of – Age – Comorbidity – Medications

Case 1

55 year old female 50kgASA IElective Total Abdominal HysterectomyFasted from midnight

Prescribe an IV fluid regimen for the next 24 hours

Case 2

80 year old maleDx Subacute Bowel Obstruction

Booked for acute theatre list following a.m.Pulse rate 120 bpm; BP 90/60; Urine output 15ml/hr

Definitions– Solute – a dissolved substance e.g. glucose– Solvent – a liquid which is able dissolve a solute to form a solution

e.g. water

– Semipermeable membrane – freely permeable to the solvent but not the solute

– Diffusion - movement of solute down concentration gradient

– Osmosis - movement of water from less concentrated solution to a more concentrated solution

• Osmotic pressure is proportional to the number of particles in solution

• Concentration of osmotically active particles in the solution = osmolarity (unit = milliosmoles)

Fluid Compartments

• Intracellular– Proteins

• Extracellular– Sodium

• Volume of ECF directly dependent upon total body Na

• Na virtually confined to ECF• Water intake and losses regulated to hold

concentration of sodium in ECF constant

• Blood– Plasma proteins

Sodium-Potassium Pump

Body Compartments

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Water and Na Homeostasis in Health

• Water• Water loss

– increased ECF osmolarity

– Stimulates hypothalamic thirst centre osmoreceptors

• ADH release• Increased water

reabsorption at renal tubules

• Na• Baroreceptors and

sympathetic system regulate Renin-Angiotensin System– Low BP, reduced ‘stretch’

• renin • angiotensin 2• aldosterone• sodium reabsorption

• (Natriuretic hormones)– inhibit sodium pump– increased sodium excretion

Daily requirements

Water 30 - 40ml/kgEnergy 30 – 40kcal/kgNitrogen 0.2g/kgSodium 1-2mmol/kgPotassium 1mmol/kgChloride 1.5mmol/kgPhosphate 0.2-0.5mmol/kgCalcium 0.1-0.2mmol/kgMagnesium 0.1-0.2mmol/kg

Water and Na Homeostasisillness / injury / starvation

• Water• Non-physiological ADH

release• Water retention• Hyponatraemia

•Pain and sympathetic stimulation•Inflammatory mediators

•Normal mechanisms overridden

• Na• Renin release

– Etc

• Sodium (and water) retention

• Fluid overload

Intravenous Fluids

• Crystalloids – NaCl – Dextrose – DexSal – Hartmann’s / Ringer’s

• Colloids – Gelofusin – Voluven – Volulyte

• Others – Blood – Albumin (HAS)

Crystalloid

• Water soluble crystalline substance capable of diffusion through a semi-permeable membrane

• Can equilibrate across membrane

NaCl

Dextrose 5%

DexSal

Hartmann’s / Ringer’s

Crystalloid

– Can infuse rapidly in large volumes – Readily available – Cheap

• But– Equilibrate with large fluid

compartments – Short duration in circulation – Risk of over-infusion, pulmonary

oedema

0.9% NaCl‘Normal’ Saline

• 9g of NaCl per litre of water • 154 mmol/l sodium • 154 mmol/l chloride • Osmolarity 308mosm/l • pH 5

• Distributes to ECFV : – 25% intravascular; 75% interstitial – After 20 minutes only 50% in ECF – 4.7L=> 1L increase in plasma volume

Would 0.9% NaCl get past ethics committees?

• Feel rotten – Abdominal pain – Nausea

• Non-physiological – Normal people can’t handle the load

– Hyperchloraemic acidosis • Normal anion gap metabolic acidosis

– [Na+] + [K+]) – ([Cl-] + [HCO3-]

• High Cl, low Bc

– Cl inhibits Na excretion– Lowers GFR– Vasoconstriction

Hartmann’s or Ringer’s Compound Sodium Lactate (HCSL)

• Na+ 131• Cl- 111• K+ 5• Ca++ 2 • Lactate 29 • Osmolarity 279 • pH 6.5

• Similar distribution to 0.9% NaCl i.e. to ECFV – 4.7L => 1L increase in PV

• Lactate ~ Bicarbonate thanks to liver

5% Dextrose

• 50g dextrose per litre • Glucose taken up by cells • Equivalent to giving free water • Fluid rapidly lost from intravascular compartment • Distributes throughout total body water • 2/3 intracellular; 1/3 extracellular

– <10% intravascular

• 14L to increase PV by 1L – hyponatraemia

• Calorific value approx. 200 kcal

4% Dextrose/ 0.18% NaCl(DexSaline)

• 40g dextrose = 160 kcal • 30 mmol/l Na+; • 30 mmol/l Cl- • Similar distribution to 5% dextrose • Free water

– Haemodilution• Hyponatraemia

Constituents of Crystalloids

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Colloids

• a suspension of finely divided osmotically active particles in a continuous medium

Gelofusin

Voluven

Volulyte

Albumin

Blood

Colloids

• Fluid stays in circulation – If capillary permeability normal – More effective in resuscitation theoretically

(but not evidence based)

• All contain NaCl – risk of hyperchloraemic acidosis

• Volulyte is different – Watch this space

• Remember! – No oxygen carrying capacity

Gelatins Gelofusin, Haemaccel, Volplex

• Contain modified gelatin in NaCl

• Plasma half-life only 2-3 hours – Leaks

• Average MW 30-35 kDa

– Metabolised

• Small risk of allergic reactions (1/13000)

Starches Voluven

• Hydroxyethylstarch (HES) in NaCl

• Variety of different brands– Wide range of MW and concentrations– Molecular substitutions

• Voluven– mean MW 130 kDa

• Intravascular t1/2 24 hours– 90% eliminated in 40 days

• Adverse effects – Pruritis – Coagulopathy (max 50ml/kg/day) – Hyper-oncotic state

• acute kidney injury

– Allergy 1/16000

AlbuminHAS = Human Albumin Solution

• Pooled human plasma • MW 69kDa • Two strengths

– 5% iso-oncotic– 20% hyper-oncotic

• Stays within intravascular space – Unless capillary permeability abnormal

• Intra-vascular t1/2 ~ 24 hours theoretically – Initial 70% increase in intravascular volume

• Effect only lasts 1-2hours – Natural turnover

Properties of Colloids

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Volulyte

• Na 137 • K 4• Ca 1.5• Cl 110• Acetate 34 • Significantly lower chloride levels

– Minimise hyperchloraemic acidosis

HES (like Voluven)

in a balanced electrolyte solution

(like Hartmann’s)

Body Compartments

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Clinical Fluid Management

Options are:

copy what went beforeor

prescribe a logical regimen

Clinical Fluid Management

• Individualise

• Assess

• Replace deficit

• Maintenance

• Replace ongoing losses

Case 1

55 year old female 50kgASA IElective Total Abdominal HysterectomyFasted from midnight

Prescribe an IV fluid regimen for the next 24 hours

How about?

Saline 0.9% 1000mL Dextrose 5% 1000mL Dextrose 5% 1000mL

Over a day, each bag 8hrly

This gives

• 153 mmol Na

• 3000 ml Water

• 0 mmol K

Requirements

• Water 40ml/kg/day 2000ml• Na 1.5 mmol/kg/day 75mmol• K 1 mmol/kg/day

50mmol

Better choice

• DexSaline + 20mmol K 1000ml

• DexSaline + 20mmol K 1000ml

• Gives;– 60mmol Na, 40mmol K, 2000ml Water

Or

• Hartmanns CSL 500ml

• Dextrose 5% 500ml + 10mmol K

• Dextrose 5% 1000ml + 20mmol K

• Gives;– 65mmol Na, 32.5mmol K, 2000ml Water– Less Cl too

• 80 year old male, 70kg• Constipation, vomiting, abdo pain• Dx Subacute Bowel Obstruction• Booked for acute theatre list following

a.m.• Pulse 120 bpm; BP 90/60; Urine output

15ml/hr

Case 2

Clinical Fluid Management

• Individualise

• Assess

• Replace deficit

• Maintenance

• Replace ongoing losses

Assessment of Fluid Status• History

– How long starved?– How much lost?

• Ongoing losses

• Examination– Dry mucous membranes– Loss of skin turgor– Oliguria– Hypotension– Tachycardia– Decreased JVP / CVP

Assessment of Fluid Deficit • Mild

– Loss of 4% body weight– Loss of skin turgor– Dry mucus membranes

• Moderate– 5-8% body weight– Oliguria – Tachycardia– Hypotension

• Severe– >8% body weight– Profound oliguria– CVS collapse

The Fluid Challenge

• Large bore intravenous cannula

– Preferably in a proximal site – antecubital fossa

• Preferably colloid (preferably a starch)

– 250-500ml stat bolus

• Observe for clinical response

– BP– UO– JVP / CVP

Plan

• Replace Deficit– Colloid boluses according to clinical response

• Maintenance– 70kg and old:

• 100mmol Na, 60mmol K, 2500ml Water

• Replace Ongoing Losses– Replace like-with-like according to nasogastric

aspirate– ?what to use

Constituents of GI Fluids

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Abnormal Fluid Losses Common in surgical patient

• Gut– NG suction / Vomiting

• Bowel obstruction

– Bowel prep• Skin/Lungs

– Increased losses with hyperventilation– Fever

• losses increase by 12% per oC rise– Burns

• Loss proportional to %age burn

• Urine– hyperglycaemia– diuretics

Imbalances: Fluid Depletion

• Decreased intake– Elderly– Dysphagia– Unconsciousness– Fasting /Nil by

mouth

• The Third Space

Problems

Too much given

Wrong stuff

Or

Not enough given

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Wrong Stuff

• Too much Na

• Too much Cl

• Inappropriate 5% Dex

• Hartmann’s

• Volulyte

Solution

• Know physiology

• Know requirements

• Replace losses

• Give enough… but not too much

Questions?

Further reading;

GIFTASUP: British Consensus Guidelines on intravenous fluid therapy for adult surgical patients (2008)