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FLUIDS

FLUIDS. Aims. Understanding of human water and sodium homeostasis Develop fluid management skills. Learning Objectives / Plan. Why this is important? Body fluid compartments Water and sodium homeostasis Normally In disease states Intravenous fluids Cases / scenarios. Intravenous Fluids.

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FLUIDS

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  1. FLUIDS

  2. Aims Understanding of human water and sodium homeostasis Develop fluid management skills

  3. Learning Objectives / Plan • Why this is important? • Body fluid compartments • Water and sodium homeostasis • Normally • In disease states • Intravenous fluids • Cases / scenarios

  4. Intravenous Fluids • 1830s • cholera epidemic • Late 19th Century • surgical patients • Now • Routine • ……too routine?

  5. Problems(first reported as early as 1911) Too much given Wrong stuff Or Not enough given • Estimated 8315 excess deaths / year USA due to iatrogenic pulmonary oedema • ?number with renal failure / underperfusion • easier to see and treat

  6. Reasons • Poor understanding of normal and perioperative Na and water physiology • <50% know Na content of NaCl 0.9% • Fluid balance charts • infrequently checked • Infrequently correct • Perioperative patients frequently (in only the first few days) • 7000ml positive fluid balance • 700mmol positive Na balance • Poor understanding of the effect of • Age • Comorbidity • Medications

  7. Case 1 55 year old female 50kgASA IElective Total Abdominal HysterectomyFasted from midnight Prescribe an IV fluid regimen for the next 24 hours

  8. Case 2 80 year old maleDx Subacute Bowel Obstruction Booked for acute theatre list following a.m.Pulse rate 120 bpm; BP 90/60; Urine output 15ml/hr

  9. Definitions • Solute – a dissolved substance e.g. glucose • Solvent – a liquid which is able dissolve a solute to form a solution e.g. water • Semipermeable membrane – freely permeable to the solvent but not the solute • Diffusion - movement of solute down concentration gradient • Osmosis - movement of water from less concentrated solution to a more concentrated solution • Osmotic pressure is proportional to the number of particles in solution • Concentration of osmotically active particles in the solution = osmolarity (unit = milliosmoles)

  10. Fluid Compartments • Intracellular • Proteins • Extracellular • Sodium • Volume of ECF directly dependent upon total body Na • Na virtually confined to ECF • Water intake and losses regulated to hold concentration of sodium in ECF constant • Blood • Plasma proteins

  11. Sodium-Potassium Pump

  12. Body Compartments

  13. Water Water loss increased ECF osmolarity Stimulates hypothalamic thirst centre osmoreceptors ADH release Increased water reabsorption at renal tubules Na Baroreceptors and sympathetic system regulate Renin-Angiotensin System Low BP, reduced ‘stretch’ renin angiotensin 2 aldosterone sodium reabsorption (Natriuretic hormones) inhibit sodium pump increased sodium excretion Water and Na Homeostasis in Health

  14. Daily requirements Water 30 - 40ml/kg Energy 30 – 40kcal/kg Nitrogen 0.2g/kg Sodium 1-2mmol/kg Potassium 1mmol/kg Chloride 1.5mmol/kg Phosphate 0.2-0.5mmol/kg Calcium 0.1-0.2mmol/kg Magnesium 0.1-0.2mmol/kg

  15. Water Non-physiological ADH release Water retention Hyponatraemia Na Renin release Etc Sodium (and water) retention Fluid overload Water and Na Homeostasisillness / injury / starvation • Pain and sympathetic stimulation • Inflammatory mediators • Normal mechanisms overridden

  16. Intravenous Fluids • Crystalloids • NaCl • Dextrose • DexSal • Hartmann’s / Ringer’s • Colloids • Gelofusin • Voluven • Volulyte • Others • Blood • Albumin (HAS)

  17. Crystalloid • Water soluble crystalline substance capable of diffusion through a semi-permeable membrane • Can equilibrate across membrane • NaCl • Dextrose 5% • DexSal • Hartmann’s / Ringer’s

  18. Crystalloid • Can infuse rapidly in large volumes • Readily available • Cheap • But • Equilibrate with large fluid compartments • Short duration in circulation • Risk of over-infusion, pulmonary oedema

  19. 0.9% NaCl‘Normal’ Saline • 9g of NaCl per litre of water • 154 mmol/l sodium • 154 mmol/l chloride • Osmolarity 308mosm/l • pH 5 • Distributes to ECFV : • 25% intravascular; 75% interstitial • After 20 minutes only 50% in ECF • 4.7L=> 1L increase in plasma volume

  20. Would 0.9% NaCl get past ethics committees? • Feel rotten • Abdominal pain • Nausea • Non-physiological • Normal people can’t handle the load • Hyperchloraemic acidosis • Normal anion gap metabolic acidosis • [Na+] + [K+]) – ([Cl-] + [HCO3-] • High Cl, low Bc • Cl inhibits Na excretion • Lowers GFR • Vasoconstriction

  21. Hartmann’s or Ringer’s Compound Sodium Lactate (HCSL) • Na+ 131 • Cl- 111 • K+ 5 • Ca++ 2 • Lactate 29 • Osmolarity 279 • pH 6.5 • Similar distribution to 0.9% NaCl i.e. to ECFV • 4.7L => 1L increase in PV • Lactate ~ Bicarbonate thanks to liver

  22. 5% Dextrose • 50g dextrose per litre • Glucose taken up by cells • Equivalent to giving free water • Fluid rapidly lost from intravascular compartment • Distributes throughout total body water • 2/3 intracellular; 1/3 extracellular • <10% intravascular • 14L to increase PV by 1L • hyponatraemia • Calorific value approx. 200 kcal

  23. 4% Dextrose/ 0.18% NaCl(DexSaline) • 40g dextrose = 160 kcal • 30 mmol/l Na+; • 30 mmol/l Cl- • Similar distribution to 5% dextrose • Free water • Haemodilution • Hyponatraemia

  24. Constituents of Crystalloids

  25. Colloids • a suspension of finely divided osmotically active particles in a continuous medium Gelofusin Voluven Volulyte Albumin Blood

  26. Colloids • Fluid stays in circulation • If capillary permeability normal • More effective in resuscitation theoretically (but not evidence based) • All contain NaCl • risk of hyperchloraemic acidosis • Volulyte is different • Watch this space • Remember! • No oxygen carrying capacity

  27. GelatinsGelofusin, Haemaccel, Volplex • Contain modified gelatin in NaCl • Plasma half-life only 2-3 hours • Leaks • Average MW 30-35 kDa • Metabolised • Small risk of allergic reactions (1/13000)

  28. Starches Voluven • Hydroxyethylstarch (HES) in NaCl • Variety of different brands • Wide range of MW and concentrations • Molecular substitutions • Voluven • mean MW 130 kDa • Intravascular t1/2 24 hours • 90% eliminated in 40 days • Adverse effects • Pruritis • Coagulopathy (max 50ml/kg/day) • Hyper-oncotic state • acute kidney injury • Allergy 1/16000

  29. AlbuminHAS = Human Albumin Solution • Pooled human plasma • MW 69kDa • Two strengths • 5% iso-oncotic • 20% hyper-oncotic • Stays within intravascular space • Unless capillary permeability abnormal • Intra-vascular t1/2 ~ 24 hours theoretically • Initial 70% increase in intravascular volume • Effect only lasts 1-2hours • Natural turnover

  30. Properties of Colloids

  31. Volulyte HES (like Voluven) in a balanced electrolyte solution (like Hartmann’s) • Na 137 • K 4 • Ca 1.5 • Cl 110 • Acetate 34 • Significantly lower chloride levels • Minimise hyperchloraemic acidosis

  32. Body Compartments

  33. Clinical Fluid Management Options are: copy what went before or prescribe a logical regimen

  34. Clinical Fluid Management • Individualise • Assess • Replace deficit • Maintenance • Replace ongoing losses

  35. Case 1 55 year old female 50kgASA IElective Total Abdominal HysterectomyFasted from midnight Prescribe an IV fluid regimen for the next 24 hours

  36. How about? Saline 0.9% 1000mL Dextrose 5% 1000mL Dextrose 5% 1000mL Over a day, each bag 8hrly

  37. This gives • 153 mmol Na • 3000 ml Water • 0 mmol K

  38. Requirements • Water 40ml/kg/day 2000ml • Na 1.5 mmol/kg/day 75mmol • K 1 mmol/kg/day 50mmol

  39. Better choice • DexSaline + 20mmol K 1000ml • DexSaline + 20mmol K 1000ml • Gives; • 60mmol Na, 40mmol K, 2000ml Water

  40. Or • Hartmanns CSL 500ml • Dextrose 5% 500ml + 10mmol K • Dextrose 5% 1000ml + 20mmol K • Gives; • 65mmol Na, 32.5mmol K, 2000ml Water • Less Cl too

  41. Case 2 • 80 year old male, 70kg • Constipation, vomiting, abdo pain • Dx Subacute Bowel Obstruction • Booked for acute theatre list following a.m. • Pulse 120 bpm; BP 90/60; Urine output 15ml/hr

  42. Clinical Fluid Management • Individualise • Assess • Replace deficit • Maintenance • Replace ongoing losses

  43. Assessment of Fluid Status • History • How long starved? • How much lost? • Ongoing losses • Examination • Dry mucous membranes • Loss of skin turgor • Oliguria • Hypotension • Tachycardia • Decreased JVP / CVP

  44. Assessment of Fluid Deficit • Mild • Loss of 4% body weight • Loss of skin turgor • Dry mucus membranes • Moderate • 5-8% body weight • Oliguria • Tachycardia • Hypotension • Severe • >8% body weight • Profound oliguria • CVS collapse

  45. The Fluid Challenge • Large bore intravenous cannula • Preferably in a proximal site – antecubital fossa • Preferably colloid (preferably a starch) • 250-500ml stat bolus • Observe for clinical response • BP • UO • JVP / CVP

  46. Plan • Replace Deficit • Colloid boluses according to clinical response • Maintenance • 70kg and old: • 100mmol Na, 60mmol K, 2500ml Water • Replace Ongoing Losses • Replace like-with-like according to nasogastric aspirate • ?what to use

  47. Constituents of GI Fluids

  48. Abnormal Fluid Losses Common in surgical patient • Gut • NG suction / Vomiting • Bowel obstruction • Bowel prep • Skin/Lungs • Increased losses with hyperventilation • Fever • losses increase by 12% per oC rise • Burns • Loss proportional to %age burn • Urine • hyperglycaemia • diuretics

  49. Imbalances: Fluid Depletion • Decreased intake • Elderly • Dysphagia • Unconsciousness • Fasting /Nil by mouth • The Third Space

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