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Pins and Needles: Fluids

Rob Fleming Specialty Doctor – Anaesthetics 22/07/2014. Pins and Needles: Fluids. Robert.Fleming@doctors.org.uk. Introduction. Why is it important? Basic science Body fluid compartments Barriers to fluid movement Commonly used fluids Assessing fluid status Prescribing: the 5 Rs

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Pins and Needles: Fluids

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  1. Rob Fleming Specialty Doctor – Anaesthetics 22/07/2014 Pins and Needles: Fluids Robert.Fleming@doctors.org.uk

  2. Introduction • Why is it important? • Basic science • Body fluid compartments • Barriers to fluid movement • Commonly used fluids • Assessing fluid status • Prescribing: the 5 Rs • Summary

  3. Why is it important? • Fluid management not (very) complicated, but is often done badly • Inappropriate fluid management can lead to: • Hypoperfusion, renal failure, shock (too little) • LVF, pulmonary oedema (too much) • Electrolyte abnormalities ( /  Na+, K+, Cl-), peripheral oedema (wrong fluid) • Good fluid management reduces both morbidity and mortality

  4. Body fluid compartments • Water is a large fraction of total body weight: • Adult men: 60% • Adult women 55% • Neonates: 75 - 80% • Total body water: 40L in a 70kg male • Extracellular (ECF) 1/3 – 15L • Intracellular (ICF) 2/3 – 25L

  5. Extracellular fluid (ECF) • Interstitial 80% – 12L • Plasma 20% – 3L • “Transcellular” / special extracellular fluids: CSF, lymph etc. – <1L

  6. Barriers • Water and electrolytes enter the body via the plasma: • absorption from the gut • IV administration • To enter most body cells, water and electrolytes must pass: Plasma -> Interstitium -> Cell cytoplasm • The water will always follow the solutes

  7. Barriers: Plasma -> Interstitium • Capillary wall: • allows passage of water, electrolytes • prevents passage of plasma proteins (in health)

  8. Barriers: Interstitium -> Cell • Cell membrane: • Permeable to water • Selectively permeable to electrolytes

  9. Composition of fluid compartments

  10. Medical Fluids • Crystalloids • Colloids

  11. Crystalloids • Electrolyte / small molecule solutions • 0.9% NaCl (“normal” saline) • 5% glucose • 4% glucose, 0.18% saline (“dextrose” saline) • Compound sodium lactate (Hartmann’s) • Hypertonic saline • Glucose 10% / 20% / 50% • 5% glucose, 0.45% saline

  12. Crystalloids

  13. Colloids • Large chain protein / starch molecules in an electrolyte solution • Starches – Voluven, Hemohes, Volulyte, ...withdrawn June 2013 by MHRA • Gelatins – Gelofusine / Geloplasma, ...lack of good quality evidence • Blood products / Human Albumin Solution

  14. Assessing fluid status • History: • Thirst • Abnormal losses: Sweating, Vomiting / diarrhoea, Haemorrhage, Sepsis / SIRS / post-operatively • Comorbidities, medications • Examination: • Pulse, blood pressure, capillary refill and jugular venous pressure (JVP) – current / trends • Pulmonary or peripheral oedema • Postural hypotension • Dry mucous membranes, loss of skin turgor

  15. Assessing fluid status • Monitoring (current / trends): • National Early Warning Scoring (NEWS) • Fluid balance charts • Weight • Investigations: • Urea, creatinine and electrolytes (U&Es) • Full blood count (FBC)

  16. NICE guidelines: the 5 Rs • Resuscitation • Routine maintenance • Replacement & Redistribution • Reassessment

  17. Fluid Resuscitation • Cardiac output is partially dependent on venous return: Frank – Starling law of the heart

  18. Fluid Resuscitation • Is the patient hypovolaemic?: • systolic blood pressure is less than 100 mmHg • heart rate > 90 beats / min • capillary refill > 2 seconds or cold peripheries • respiratory rate > 20 breaths / min • National Early Warning Score (NEWS) ≥ 5 • ABCDE approach, call for help • Identify cause and treat it • Fluid bolus (challenge) of 500ml 0.9% NaCL or CSL • Reassess and repeat as needed

  19. Routine Maintenance Fluids • Fluid and electrolytes are lost daily in: • Faeces (100ml/day) • Urine (1500ml/day) • “Insensible” evaporative losses (500 – 1000ml/day) • Routine maintenance fluids alone are indicated only where there is: • No abnormal fluid loss • No abnormal redistribution

  20. Routine Maintenance Fluids • To maintain homeostasis water and electrolytes must be replaced at a minimum rate of.... • Water 25 – 30 ml/kg/day (2 - 2.5 L in a 70kg male) • Na+ 1 (– 1.5) mmol/kg/day (70 – 100 mmol) • K+ (0.7 –) 1 mmol/kg/day (50 – 70 mmol) • Cl- 1 (– 2) mmol/kg/day (100 – 140mmol) • 50 – 100 g/day glucose ....IN HEALTH!

  21. Routine Maintenance Fluids • This equates roughly to: • either 1L 0.9% NaCl and 1 - 2L 5% glucose • or 2 – 3L of 0.18% NaCl in 4% Glucose ...with 60 mmolkCl added to either of the above • Remember, this is the minimum requirements of an otherwise well 70kg man • In the majority of cases, fluid prescribing is also replacing fluid loss / redistribution

  22. Replacement and Redistribution • Abnormal losses: • Gut: • Vomiting • Diarrhoea • Stomas/ fistulae/ drains • Sweating / pyrexia • Polyuria ( e.g. DI) • Hyperventilation • Haemorrhage

  23. Replacement and Redistribution • Redistribution • Stress response: • Activation of renin-angiotensin-aldosterone system • -> Sodium and water retention • Increased secretion of cortisol and catecholamines • Reduced secretion of insulin • -> Hyperglycaemia • Increased capillary permeability leads to increased interstitial volume (SIRS / sepsis / post-operatively)

  24. Replacement and Redistribution • Fluid prescribing should attempt to meet losses in both volume and electrolyte composition • Seek expert help if patients have complex fluid / electrolyte requirements: • gross oedema • severe sepsis • severe hyponatraemia or hypernatraemia • renal, liver and/or cardiac impairment • post-operative fluid retention and redistribution • malnutrition / refeeding

  25. Reassessment • All patients continuing to receive IV fluids need regular monitoring: • Fluid balance and U&Es daily • Weight measurement twice weekly • Patients receiving IV fluids for replacement or redistribution problems may need more frequent monitoring • Patients on longer-term IV fluid therapy whose condition is stable may be monitored less frequently • Always reassess!

  26. Reassessment • Urinary sodium measurement may be helpful in patients with high-volume GI losses • Urinary sodium < 30 mmol/l indicates total body sodium depletion • Urinary sodium may also indicate the cause of hyponatraemia, and guide a negative sodium balance in patients with oedema • If patients have received IV fluids containing high chloride concentrations, monitor serum chloride concentration daily to prevent hyperchloraemic acidosis

  27. Summary and hints • Fluid management is not (very) complicated • Estimate fluid status based on history, examination and investigations • Is this maintenance? • What are you replacing?? • Does the patient need resuscitation??? • Always reassess! • Any patient receiving IV fluids should have their U&Es checked daily • Stop IV fluids as soon as possible

  28. Questions ?

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