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?

Intravascular 5 litres Interstitial 10 litres Intracellular 30 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?

Intravascular 5 litres Interstitial 10 litres Intracellular 30 litres Renal losses 1500ml/day Insensible losses 500ml/day Normal intake 2000ml/day What is normal fluid intake and output?

What can go Wrong?

Intravascular 5 litres Interstitial 10 litres Intracellular 30 litres XS losses Vomiting Diarrhoea Drains Fever Poor Output Oliguria 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

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? 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 = umol/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 Adult Water litres Sodium mmol Potassium mmol

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?

Crystalloid Colloid Blood

What Replacement Fluids are Available? Crystalloid Saline 0.9% Hartmanns Dextrose 5%

So What’s in the Fluid?

Sodium mmol/l Potassium mmol/l Chloride mmol/l Osmolarity mosm/l Other per litre Plasma Saline 0.9% Dextrose 5% Hartmann’s Gelofusin < Dextrose 50g Lactate 29mmol Gelatin 40g

Where does the Fluid Go? (Volume of Distribution)

Intravascular 5 litres Interstitial 10 litres Intracellular 30 litres Dextrose 5% Saline Hartmanns Gelofusine 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 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

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

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

Indicated to correct hypovolaemia due to blood loss NB Aggressive correction of anemia in critically ill patients does not improve outcome – target Hb g/l gives same outcomes as target Hb g/l

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 litres water, mmol 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

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

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

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

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

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

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

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

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

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 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 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