Transcript Medical Students_files/medstudentfluidsnov

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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)
Too much given
Wrong stuff
Or
Not enough given
•
•
Estimated 8315 excess deaths / year USA due to
iatrogenic pulmonary oedema
?number with renal failure / underperfusion
– easier to see and treat
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
50kg
ASA I
Elective Total Abdominal Hysterectomy
Fasted from midnight
Prescribe an IV fluid regimen for the next 24
hours
Case 2
80 year old male
Dx 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
Energy
Nitrogen
Sodium
Potassium
Chloride
Phosphate
Calcium
Magnesium
30 - 40ml/kg
30 – 40kcal/kg
0.2g/kg
1-2mmol/kg
1mmol/kg
1.5mmol/kg
0.2-0.5mmol/kg
0.1-0.2mmol/kg
0.1-0.2mmol/kg
Water and Na Homeostasis
illness / injury / starvation
•Pain and sympathetic stimulation
•Inflammatory mediators
•Normal mechanisms overridden
• Water
• Non-physiological ADH
release
• Water retention
• Hyponatraemia
• 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 ClSimilar 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
Albumin
HAS = 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
HES
(like Voluven)
in a
balanced electrolyte solution
(like Hartmann’s)
•
•
•
•
•
•
Na 137
K 4
Ca 1.5
Cl 110
Acetate 34
Significantly lower chloride levels
– Minimise hyperchloraemic acidosis
Body Compartments
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Clinical Fluid Management
Options are:
copy what went before
or
prescribe a logical regimen
Clinical Fluid Management
• Individualise
•
•
•
•
Assess
Replace deficit
Maintenance
Replace ongoing
losses
Case 1
55 year old female
50kg
ASA I
Elective Total Abdominal Hysterectomy
Fasted 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
• Na
•K
40ml/kg/day
1.5 mmol/kg/day
1 mmol/kg/day
2000ml
75mmol
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
Case 2
•
•
•
•
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
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)