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
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
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
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
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
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)
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
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
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
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
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