Fluid Balance
Outline of Talk
• Fluid compartments
• What can go wrong
• Calculating fluid
requirements
• Principles of fluid
replacement
• Scenarios
Where is the Fluid?
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
So for a 75kg person…
• 60% of body weight
is fluid
• 2/3 is intracellular
and 1/3 extracellular
• 2/3 of extracellular is
interstitial and 1/3
intravascular
Intravascular
5 litres
Interstitial
10 litres
Intracellular
30 litres
What is normal fluid intake and
output?
What is normal fluid intake and
output?
Normal intake
2000ml/day
Intravascular
5 litres
Interstitial
10 litres
Intracellular
30 litres
Renal losses
1500ml/day
Insensible losses
500ml/day
What can go Wrong?
What can go wrong?
1. Imbalance between input and
output
Inadequate or
overhydration
Intravascular
5 litres
Interstitial
10 litres
Intracellular
30 litres
XS losses
Vomiting
Diarrhoea
Drains
Fever
Poor Output
Oliguria
What can go wrong?
2. Redistribution
Intravascular
Intravascular
pressure
Capillary
leakage
Plasma oncotic pressure
(hypoalbiminaemia)
Peripheral +/- pulmonary oedema
Interstitial
What can go wrong?
3. Osmolar problems
Interstitial
Hypotonic fluid causes
water to move into
intracellular space
Hypertonic fluid causes
water to move out
of intracellular space
Intracellular
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 litres
2) Correcting any deficits
3) 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?
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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?
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Lung bases
SpO2
Body Weight
Urine Output
Fluid Balance Chart
Serum Biochem
Urine Biochem
Assessment of Volume Status
– are they dry, wet or euvolaemic?
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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 = 40120umol/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 Established ATN
Urine Na <20mmol/l
>40mmol/l
Urine Osm >500mmol/ <350mmol/l
In practice we hardly ever request urine biochem
Assessment of volume status
Hypovolaemic
(dehydrated)
Hypervolaemic
(overloaded)
Assessment of volume status
Hypervolaemic
(overloaded)
Hypovolaemic
(dehydrated)
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Reduced skin turgor
Dry mouth
Tachycardia
Postural fall BP
Poor cap refill
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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 Adult
Water
1.5 - 2.5 litres
Sodium
50 - 100mmol
Potassium 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 Losses
Cardiac Status
Kidney 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?
Plasma
Saline 0.9%
Dextrose 5%
Hartmann’s
Gelofusin
Sodium
mmol/l
Potassium Chloride
mmol/l
mmol/l
136-145
154
0
131
154
3.5-5.2
0
0
5
<0.4
98-105
154
0
111
125
Osmolarity
mosm/l
Other
per litre
280-300
308
278
275
290
Dextrose 50g
Lactate 29mmol
Gelatin 40g
Where does the Fluid Go?
(Volume of Distribution)
Where does the Fluid Go?
(Volume of Distribution)
Saline
Gelofusine Hartmanns Dextrose 5%
Intravascular
5 litres
Interstitial
10 litres
Intracellular
30 litres
Principles of Fluid
Replacement
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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 7090g/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
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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, 50100mmol sodium and 40mmol
potassium
Maintenance IV Fluid for a
Healthy Adult
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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
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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
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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
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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
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BP 80/40mmHg
SEVERE
PR 120/min
SEPSIS
Resp Rate 35
Clinically dry
L Basal Bronchial Breathing
Urea 15.0 with Creatinine 150
Platelets 98 and abnormal clotting
Scenario
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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
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Mr P 70 y day 2 post TURP
Previously well
Increasingly confused and agitated
Called to see him
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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