Fluid Balance
Outline of Talk
• Fluid compartments• What can go wrong• Calculating fluid
requirements• Principles of fluid
replacement• Scenarios
Where is the Fluid?
• 60% of body weight is fluid
• 2/3 is intracellular and 1/3 extracellular
• 2/3 of extracellular is interstitial and 1/3 intravascular
Where is the Fluid?
Intravascular5 litres
Interstitial10 litres
Intracellular30 litres
• 60% of body weight is fluid
• 2/3 is intracellular and 1/3 extracellular
• 2/3 of extracellular is interstitial and 1/3 intravascular
So for a 75kg person…
What is normal fluid intake and output?
Intravascular5 litres
Interstitial10 litres
Intracellular30 litres
Renal losses1500ml/dayInsensible losses500ml/day
Normal intake2000ml/day
What is normal fluid intake and output?
What can go Wrong?
Intravascular5 litres
Interstitial10 litres
Intracellular30 litres
XS lossesVomitingDiarrhoeaDrainsFever
Poor OutputOliguria
Inadequate or overhydration
What can go wrong? 1. Imbalance between input and
output
Intravascular
Interstitial
Intravascular pressure
Capillary leakage
Plasma oncotic pressure (hypoalbiminaemia)
Peripheral +/- pulmonary oedema
What can go wrong? 2. Redistribution
Interstitial
Intracellular
Hypertonic fluid causes water to move out
of intracellular space
What can go wrong? 3. Osmolar problems
Hypotonic fluid causes water to move into intracellular space
Water move in and out of intracellular space with changes in extracellular osmolarity
Purpose of Fluid Replacement
Purpose of Fluid Replacement
To maintain tissue perfusion by:1) Maintaining intravascular fluid volume of about 5 litres2) Correcting any deficits3) Allowing for ongoing losses
How to Calculate Daily Fluid Requirements?
How to Calculate Daily Fluid Requirements
Requirement =
Deficit + Maintenance + Ongoing Losses
Assessment of the Deficit (Volume Status)
Assessment of Volume Status – are they dry, wet or euvolaemic?
• History• Pulse• BP incl Postural BP• Skin Turgor• Mouth Dryness• Capillary Refill• JVP• Third sound and MR
Assessment of Volume Status – are they dry, wet or euvolaemic?
• Lung bases• SpO2• Body Weight• Urine Output• Fluid Balance Chart• Serum Biochem• Urine Biochem
Assessment of Volume Status – are they dry, wet or euvolaemic?
• Lung bases• SpO2• Body Weight• Urine Output• Fluid Balance Chart• Serum Biochem• Urine Biochem
Serum Biochem- The Urea:Creatinine Ratio
• Normal Blood Urea =• Normal Serum Creatinine =
• Normal Urea:Creatinine Ratio =
Urea:Creatinine Ratio• Normal Blood Urea = 2-7mmol/l • Normal Serum Creatinine = 40-
120umol/l• Normal Urea:Creatinine Ratio = 60-80:1
• Raised Ratio >100:1 suggests patient dehydrated. Why?
Why U:C Ratio >100:1 suggests Dry
• Both urea and creatinine freely filtered by glomerulus
• Urea reabsorbed passively with Na and water by PCT when dehydrated
• No such mechanism exists for creatinine which instead is secreted by PCT
• This leads to U:C ratio >100:1 when dry
Urine Biochemistry
Pre-Renal<20mmol/l>500mmol/
Established ATN>40mmol/l
<350mmol/l
Urine Na
Urine Osm
In practice we hardly ever request urine biochem
Assessment of volume status
Hypovolaemic (dehydrated)
Hypervolaemic (overloaded)
Assessment of volume status
Hypovolaemic (dehydrated)
• Reduced skin turgor• Dry mouth• Tachycardia• Postural fall BP • Poor cap refill
Hypervolaemic (overloaded)
• Raised JVP• S3 with functional MR• Bibasal crackles• Periph/sacral oedema• Hypertension
How to Calculate Daily Fluid Requirements
Requirement =
Deficit + Maintenance + Ongoing Losses
Maintenance Requirements/day in
Healthy Adult?Water = Sodium =Potassium =
Maintenance Requirements/day in
Healthy AdultWater 1.5 - 2.5 litresSodium 50 - 100mmolPotassium 40 - 80mmol
How to Calculate Daily Fluid Requirements
Requirement =
Deficit + Maintenance + Ongoing Losses
Measuring Losses• Fluid balance charts notoriously
inaccurate• Insensible losses can increase
significantly with exercise, fever, raised ambient temperature
• Interstitial (third space) losses difficult to quantify
Composition of Losses
• Vomit is mostly HCl – contains very little K and a lot of chloride (hypokalaemia is due to renal K wasting)
• Diarrhoea is more alkaline – contains quite a lot of K and no chloride
Two Other Things it Helps to Know when Judging Fluid Requirements?
Deficit Maintenance Ongoing Losses +
Two Other Things it Helps to Know when Judging Fluid Requirements
Deficit Maintenance Ongoing LossesCardiac StatusKidney Function
What Replacement Fluids are Available?
What Replacement Fluids are Available?
Crystalloid Colloid Blood
What Replacement Fluids are Available?
Crystalloid
• Saline 0.9%• Hartmanns• Dextrose 5%
So What’s in the Fluid?
So What’s in the Fluid?
Sodiummmol/l
Potassiummmol/l
Chloridemmol/l
Osmolaritymosm/l
Otherper litre
PlasmaSaline 0.9%Dextrose 5%Hartmann’sGelofusin
136-1451540131154
3.5-5.2005<0.4
98-1051540111125
280-300308278275290
Dextrose 50gLactate 29mmolGelatin 40g
Where does the Fluid Go? (Volume of Distribution)
Intravascular5 litres
Interstitial10 litres
Intracellular30 litres
Dextrose 5%SalineHartmannsGelofusine
Where does the Fluid Go? (Volume of Distribution)
Principles of Fluid Replacement
• Saline v Dextrose• Saline v Hartmanns• Crystalloid v Colloid• Blood• Fast v Slow
Saline v Dextrose
Saline v Dextrose• Saline more effective than dextrose
for fluid resuscitation because sodium content restricts distribution
to extracellular space. Dextrose loses osmotic effect of glucose as it is
metabolised and so moves into intracellular sace
Saline v Hartmanns
Saline v Hartmanns• Both used to expand the intravascular space and
both distributed throughout the interstitial space• Saline preferred if hypochloraemic. Large volumes
may cause hyperchloraemic acidosis• Hartmanns is the more physiological of the two.
Only clear contraindications are tight brains (risk of cerebral oedema) and hyponatraemia (because not enough sodium). Risks of lactic acidosis and hyperkalaemia are probably exaggerated
Crystalloid v Colloid
Crystalloid v Colloid• Colloid better at expanding intravascular
space (1 litre gelofusine equiv 2 litres saline) and probably preferred as initial
volume expander in haemorrhagic shock while waiting for blood. Otherwise no
clear indication to give one over the other.
Blood
Blood• Indicated to correct hypovolaemia
due to blood loss• NB Aggressive correction of anemia
in critically ill patients does not improve outcome – target Hb 70-
90g/l gives same outcomes as target Hb 100-120g/l
Fast v Slow
Fast v Slow• Aim is to give as much as required in order to
restore circulating blood volume, and by implication tissue perfusion, as quickly as possible
• NB 4 hourly bags usually run 5 hourly and then only deliver 100ml/hr, ie < 1/3 of a can of coke per hour.
• Remember to choose the correct venflon
Choose the Correct Venflon
Scenarios• Maintenance IV Fluid• Pre-op fluids• Septic shock• Massive blood loss from trauma• AKI but not shocked• Post obstructive diuresis/recovery from ATN• Cardiorenal Failure• Diagnosis of hypovolaemia in doubt• XS losses from vomiting• XS losses from diarrhoea
Prescribe Maintenance IV Fluid for a
healthy adult to give 1.5-2.5 litres water, 50-
100mmol sodium and 40mmol potassium
Maintenance IV Fluid for a Healthy Adult
• Dextrose 5% + 20mmol K• Dextrose 5%• Saline N + 20mmol K• Dextrose 5%
Rx 6 hourly to give 2 litres water, how much sodium and 40mmol K?
Maintenance IV Fluid for a Healthy Adult
• Dextrose 5% + 20mmol K• Dextrose 5%• Saline N + 20mmol K• Dextrose 5%
Rx 6 hourly to give 2 litres water, 77mmol sodium and 40mmol K
Pre-Op Fluids
Pre-Op Fluids
• Clear fluids and calorific drinks can safely be given until 2 hours before GA
• If bowel prep given (and it isnt always) then fluid replacement will be required
• People with diabetes will require variable rate insulin infusion (previously known as
sliding scale)
Septic Shock
Septic Shock• Rx Saline, Hartmann’s or Gelofusine
(probably doesn’t matter which) 20ml/kg as quickly as possible
• Vasoconstrictor inotropes such as Noradrenaline also often required
• NB Fluids are an important part of a package of measures (the Sepsis Six) required to treat
septic shock effectively
Massive Blood Loss from Trauma
Massive Blood Loss from Trauma
• Rx Gelofusine 20ml/kg fast until blood products arrive. Use O neg blood if delay
rather than more gelofusin• NB there is no absolute indication to give
Gelofusine here though it will expand the intravascular space for longer than an
equivalent volume of saline
Minimum Volume Resuscitation
• Better to restore a recordable BP than a normal BP. For example in AAA where unable to control bleeding if you fill to achieve a normal intravascular volume then patient more likely to continue bleeding. Also no clotting factors in gelofusine or crystalloid. So Rx gelofusine 20ml/kg then O neg blood if cross match blood still unavailable
AKI but not shocked
AKI but not shocked• Rx Saline or Hartmann’s
- in the absence of any signs of fluid overload the default should be 1 litre in one hour, 1 litre in 2
hours, 1 litre in 4 hours then review• Decision on whether Saline or Hartmann’s will be
determined to an extent by the serum K and the likelihood it might rise further
Post Obstructive Diuresis/ Recovery from ATN
Post Obstructive Diuresis/ Recovery from ATN
• Recovery from obstruction/ATN usually characterised by polyuria of up to 5 litres poor quality urine daily, preceding the fall in urea and creatinine
• ‘500mls plus previous days output’ doesn’t work because patients will start mobilising the XS interstitial fluid they have accumulated during acute illness
• eg if passing 5 litres/day try 4.5 litres intake while checking U&E daily. If both U and C falling proportionately then prescription probably ok.
Cardiorenal Failure
Cardiorenal Failure• Rx trial of frusemide IV with salt and water restriction
if cardiac failure predominates, recognising that worsening kidney function may be the price you have to pay in order to keep lungs free of fluid
• Rx cautious trial of fluid if renal failure predominates, recognising that peripheral oedema may be an acceptable compromise in the trade off between heart and kidneys
• This is usually tricky requiring senior help and sometimes dialysis
Diagnosis of Hypovolaemia in Doubt
Diagnosis of Hypovolaemia in Doubt
• Rx bolus of 250mls N Saline or Gelofusin over 5-10 mins (ie squeezed in) with measurement of HR, BP, Cap
Refill, CVP if monitored, before and 15 mins after infusion. If vital signs
improve then further bolus likely to be required
XS losses from Vomiting
XS losses from Vomiting
• Rx Saline 0.9% or Hartmann’s and appropriate K supps with maintenance
Dextrose 5% • Vomit contains mainly HCl so patients
likely to be hypochloraemic. If so then Hartmann’s doesn’t contain enough
chloride
XS losses from Diarrhoea
XS losses from Diarrhoea
• Rx Hartmann’s and appropriate K supps with maintenance Dextrose 5%
• Diarrhoea doesn’t contain chloride so risk of hyperchloraemia with Saline
• Same advice applies for ileostomy, small bowel fistula, ileus, bowel obstruction
Summary• To be written!
Question 1
• You are called to the receiving ward to write up more iv fluids for Mrs S age 65. She is currently nil by mouth and is now awaiting a second day for (delayed) endoscopy after a small nonhaemodynamically significant haematemesis.
• Well with no other PMH; MEWS 0• Hb unchanged at 12.5. U+E all n range
• What will you prescribe?
Typical Maintenance Fluids
• How much and how fast?
• 2L• 6 hourly 500 ml bags• 2:1 dextrose:saline 40-60 mmol K
Example Typical Maintenance Fluids
• 500 ml 5% dextrose 6 hours 20 mmol KCl• 500 ml 5% dextrose 6 hours• 500 ml N saline 6 hours 20 mmol KCl• 500 mls 5% dextrose
Who gets maintenance fluids?
• Patient with normal renal function with upset in normal water intake eg pre-operatively
• Do not already have upset in water or electrolyte balance
• Special circumstances need greater individualised care
Question 2
• You are asked to write up fluids for a 60 year old man who has diarrhoea. Nurses concerned “looks a bit dry.” U+E checked previous day were N.
• Weight is 70 kg– BP 120/70 mmHg– PR 80/min– Mucous Membranes dry. Skin turgor seems normal and
CRT 2 secs. Chest Clear.– Oral intake minimal with faecal output of 1000 ml a day– Urine output 100 ml in the last 3 hours. Managed 1200
yesterday
• What will you prescribe?
Prescription-suggestion
• 1 L NaCL 0.9% - 4hrs • 500 ml Dextrose 5 % - 4 hrs + 20mmol KCL
• 500 ml Dextrose 5 % - 4hrs • 500 ml NaCL 0.9% - 4hrs + 20 mmol KCL
• 500 ml Dextrose 5% - 4hrs• 500ml Dextrose 5 % + 20 mmol KCL -4hrs
Total in 24 hours = 3. 5 L
CHECK U/Es and Reassess
Question 3
• You are with your senior assessing a new admission. Mrs D aged 50 has Crohns Disease and has not been very well for 5 days.
• She has been passing large volumes of liquid stool into her colostomy bag and has had a very poor oral intake of fluids.
• Poor urine volumes
Question 3 cont
• Mucous membranes dry, reduced skin turgour eyes sunken
• CRT 4 secs• P 86 BP 105/70• Urea 17 creat 128
• Senior says she is severely dehydrated and wants you to write up appropriate fluid
What would be an appropriate regime for the severely dehydrated
patient?
• 1L saline 1 hour• 1L 2 hours• 1L 4 hours
Question 4
You are asked to see a 60 year old male who is 2 days post laparotomy who has stopped passing urine
• Let’s consider if it was oliguria?
Question 5
• A 30 year old lady attends AMU with a 3 day history of cough, breathlessness and temp 39. On arrival she has
BP 80/40mmHg PR 120/min Resp Rate 35 Clinically dry L Basal Bronchial Breathing Urea 15.0 with Creatinine 150 Platelets 98 and abnormal clotting
SEVERE SEPSIS
Scenario
• Mrs N 85 y resident nursing home• Less well for 1 week• Poor oral intake and intermittant diarrhoea• This morning, staff of nursing home difficulty waking her• Sleepy and confused
• PMH angina osteoporosis R # NOF 2008 hemi-arthroplasty
• DH aspirin 75 mg alendronate 70 mg weekly paracetamol prn
• GCS E3 M6 V4 looks very dry p 80 BP 120/70 T 37 O2 sats
• Reduced skin turgor• No JVP
• No localising signs, no neck stiffness
• Little else to find despite full examination of CVS, RS, GIS and CNS
• Differential?
• Vascular event? Head injury?• Infection – respiratory, UTI, GI source ?• meningitis??• Bowel infarction?
• Investigations – Na 165 mmol/L• HYPERNATRAEMIA
scenario
• Mr P 70 y day 2 post TURP• Previously well• Increasingly confused and agitated• Called to see him
• What goes through your mind?• Drug effect – new or withdrawal?• Infection?• Hypoxic – PTE, pneumonia• “Silent” MI• Glucose?
Na 121 mmol/L
previous U+E pre-op N 141mmol/L
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