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