Salty Solutions or Salty Problems? Outline. Outline 29/04/2013

Transcription

1 Salty Solutions or Salty Problems? 18 th October 2012 Richard Seigne Anaesthetist 1

2 - Non fluid 40% T o t a l b o d y f l u i d 60% NaCl NaCl Intra-cellular fluid 2/3 KCl Interstitial fluid 3/4 of ECF Plasma 1/4 of ECF Extra-cellular fluid 1/3 - Water 70kg person 42L water Water required/24hr L or 25-35ml/kg/day (2L/24hr = 83ml/hr) Lymph - 1-2L Gut - 8-9L Kidneys - 180L Capillaries - 80,000L Water Flow 2

3 Sodium (Na) Maintains plasma volume & therefore blood pressure (osmosis) Propagates nerve impulses low sodium neurological symptoms Sodium 70 (50-100) mmol (1mmol/kg/day) or 0.5-1g, NaCl 1-2.5g per 24hr Salt - maximum advised 6g/day, average Kiwi 9g! Daily Obligatory Water Loss Insensible loss: 800 mls respiratory, skin Minimal sweat loss: 100 mls Faecal loss: 200 mls Minimal urine vol to excrete solute load: 500 mls Total: 1,600 mls Water from metabolism 400mls 3

4 Fluid replacement Maintenance (obligatory loss) - water Fluid loss (salt & water) - blood - gut losses (visible and invisible) - excessive sweat and respiratory Third space IV salt solutions saved lives from 1830s cholera Used for surgical patients late 1800s Lots of IV fluid is good....but maybe not as good as we thought 4

5 1 Pre-operative hypovolaemia 2 Large intra-operative insensible losses 5

6 3 Third space losses requiring generous substitution 4 Hypervolaemia is harmless - the kidneys regulate the overload glycocalyx damage 5 Urine output must always be 0.5-1ml/kg/hr 6

7 6 Maintenance Replacement Resuscitation they re all just IV fluids Hmmmm Too little fluid shock, renal failure & death Too much fluid renal & lung failure, shock & death Fluid therapy may be more difficult than you think How much is the right amount? 7

8 of salt and water We are? % water 1/3 water is? 2/3 water is? 60% - 42L 70kg person Extracellular Intracellular Extracellular interstitial water and plasma NaCl mostly? KCl mostly? Extracellular Intracellular Non fluid 40% T o t a l b o d y f l u i d 60% NaCl NaCl Intra-cellular fluid 2/3 KCl Interstitial fluid 3/4 of ECF Plasma 1/4 of ECF Extra-cellular fluid 1/3 Salt and water hand in glove Osmosis semi permeable membrane Osmostic pressure Oncotic pressure 8

9 Control of salt and water Sodium content influences water content especially plasma volume (osmosis) Kidney s are crucial Control primarily by osmoreceptors - ADH Poor ability to excrete extra salt Excreting Salt 9

10 Peri-operative control of salt and water Salt (NaCl) and water retention - renal blood flow less filtering (180L/day) - kidney s ability to concentrate & dilute urine - secretion ADH, cortisol, aldosteone - excessive chloride renal function Oliguria Peri-operative control of salt and water Excessive sodium results in oedema & weight gain - impaired tissue oxygen transport - impaired gut function, nausea - poor wound healing (inc anastomosis) - delay in enteral uptake - worsens capillary leak more IV fluid given Peri-operative control of salt and water ADH Retention of water risk of hyponatraemia <120mmol severe Elderly and children Symptoms Neurological nausea, poor appetite, headache, lethargy, restless, agitation, confusion, fits, coma 10

11 Salty Solutions Plasma Normal 0.9% Saline (NS) Hartmann s Solution or Compound Solution of Lactate (CSL) 4% Dextrose 0.18% Saline D4S Hydroxyethyl Starch (HES) 6% (Voluven) 5% Dextrose 11

12 Salty Solutions Solution Sodium mmol/l Chloride mmol/l Plasma Normal Saline CSL D4S HES (Voluven) D5W 0 0 Body 40% T o t a l b o d y f l u i d Intra-cellular fluid 2/3 KCl NaCl Interstitial fluid 3/4 of ECF NaCl Plasma 1/4 of ECF Extra-cellular fluid 1/3 60% Salty Solutions where do they go? ICF E C F ISF Plasma 12

13 Salty Solutions where do they go? 0.9% N Saline (154) CSL (131) ICF E C F ISF Plasma Salty Solutions where do they go? D5W D5W D5W ICF E C F ISF Plasma Salty Solutions where do they go? D4S (31) D4S (31) D4S (31) D4S is ICF E C F ISF Plasma Effectively 80% D5W 20% NS 13

14 Salty Solutions where do they go? Colloid (154) Blood (154) ICF E C F ISF Plasma Salty Solutions where do they go? In reality not where the text book says! Crystalloid : Colloid 3 : 1 1.5: 1 ICF E C F ISF Plasma 14

15 Strange Goings On Rate of fluid administration may influence where it goes Hypervolaemia creates more oedema (prophylactic, rapid administration) Greater weight gain - greater mortality (association) Starling s equation too simplistic? Avoid prolonged fasting pre-operative drinks Avoid hypovolaemia & hypervolaemia Oral fluid and remove IV fluids Watch for hyponatraemia - elderly children 15

16 ? Accept a degree of post-operative oliguria Early enteral fluid and food Pre-post operative weights? Diuretics Fluid therapy is poorly understood Water and salt retention are an adaptive response to trauma & surgery Sodium excretion is inefficient sodium retains water oedema Elderly and children are vulnerable to hyponatraemia Enteral intake is best when possible 16

17 ? 17