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Fluid Balance

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

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Fluid Balance

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  1. Fluid Balance

  2. Outline of Talk • Fluid compartments • What can go wrong • Calculating fluid requirements • Principles of fluid replacement • Scenarios

  3. Where is the Fluid?

  4. 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

  5. So for a 75kg person… Intravascular 5 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 Interstitial 10 litres Intracellular 30 litres

  6. What is normal fluid intake and output?

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

  8. What can go Wrong?

  9. What can go wrong? 1. Imbalance between input and output XS losses Vomiting Diarrhoea Drains Fever Intravascular 5 litres Inadequate or overhydration Interstitial 10 litres Poor Output Oliguria Intracellular 30 litres

  10. What can go wrong? 2. Redistribution Intravascular Intravascular pressure Capillary leakage Plasma oncotic pressure (hypoalbiminaemia) Peripheral +/- pulmonary oedema Interstitial

  11. 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

  12. Purpose of Fluid Replacement

  13. 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

  14. How to Calculate Daily Fluid Requirements?

  15. How to Calculate Daily Fluid Requirements Requirement = Deficit + Maintenance + Ongoing Losses

  16. Assessment of the Deficit (Volume Status)

  17. 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

  18. Assessment of Volume Status – are they dry, wet or euvolaemic? • Lung bases • SpO2 • Body Weight • Urine Output • Fluid Balance Chart • Serum Biochem • Urine Biochem

  19. Assessment of Volume Status – are they dry, wet or euvolaemic? • Lung bases • SpO2 • Body Weight • Urine Output • Fluid Balance Chart • Serum Biochem • Urine Biochem

  20. Serum Biochem- The Urea:Creatinine Ratio • Normal Blood Urea = • Normal Serum Creatinine = • Normal Urea:Creatinine Ratio =

  21. 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?

  22. 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 secretedby PCT • This leads to U:C ratio >100:1 when dry

  23. Urine Biochemistry Pre-Renal Established ATN >40mmol/l <350mmol/l <20mmol/l >500mmol/ Urine Na Urine Osm In practice we hardly ever request urine biochem

  24. Assessment of volume status Hypovolaemic (dehydrated) Hypervolaemic (overloaded)

  25. Assessment of volume status Hypovolaemic (dehydrated) Hypervolaemic (overloaded) Raised JVP S3 with functional MR Bibasal crackles Periph/sacral oedema Hypertension • Reduced skin turgor • Dry mouth • Tachycardia • Postural fall BP • Poor cap refill

  26. How to Calculate Daily Fluid Requirements Requirement = Deficit + Maintenance + Ongoing Losses

  27. Maintenance Requirements/day in Healthy Adult? Water = Sodium = Potassium =

  28. Maintenance Requirements/day in Healthy Adult Water 1.5 - 2.5 litres Sodium 50 - 100mmol Potassium 40 - 80mmol

  29. How to Calculate Daily Fluid Requirements Requirement = Deficit + Maintenance + Ongoing Losses

  30. 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

  31. 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

  32. Two Other Things it Helps to Know when Judging Fluid Requirements? Deficit Maintenance Ongoing Losses +

  33. Two Other Things it Helps to Know when Judging Fluid Requirements Deficit Maintenance Ongoing Losses Cardiac Status Kidney Function

  34. What Replacement Fluids are Available?

  35. What Replacement Fluids are Available? Crystalloid Colloid Blood

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

  37. So What’s in the Fluid?

  38. 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 136-145 154 0 131 154 98-105 154 0 111 125 280-300 308 278 275 290 3.5-5.2 0 0 5 <0.4 Dextrose 50g Lactate 29mmol Gelatin 40g

  39. Where does the Fluid Go? (Volume of Distribution)

  40. Where does the Fluid Go? (Volume of Distribution) Saline Hartmanns Gelofusine Dextrose 5% Intravascular 5 litres Interstitial 10 litres Intracellular 30 litres

  41. Principles of Fluid Replacement • Saline v Dextrose • Saline v Hartmanns • Crystalloid v Colloid • Blood • Fast v Slow

  42. Saline v Dextrose

  43. 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

  44. Saline v Hartmanns

  45. 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

  46. Crystalloid v Colloid

  47. 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.

  48. Blood

  49. 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

  50. Fast v Slow

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