Department of Surgery Yong Loo Lin School of Medicine National University of Singapore

1. Department of Surgery Yong Loo Lin School of Medicine National University of Singapore

2. Total Body Water body wt% Total body water% total 60 100 intracellular 40 67 extracellular 20 33 intravas 5 8 interstitial 15 25

3. Composition of Fluids plasma interstitial intracellular Cations Na 140 146 12 K 4 4 150 Ca 5 3 10 Mg 2 1 7 Anions Cl 103 104 3 HCO 24 27 10 SO4 1 1 - HPO4 2 2 116 Protein 16 5 40

4. Control of Volume Kidneys maintain constant volume and composition of body fluids • Filtration and reabsorption of Na • Regulation of water excretion in response to ADH Water is freely diffusible • Movement of certain ions and proteins between compartments restricted

5. Osmoregulation • osmolality 289 mOsm/kg H20 • osmoreceptor cells in paraventricular/ supraoptic nuclei • osmoreceptors control thirst and ADH • small changes in Posm - large response

6. Osmoregulation Excess free water (Posm 280) • thirst inhibited • ADH declines • urine dilutes to Uosm 100

7. Osmoregulation Decreased free water (Posm 295) • thirst increased • ADH increases • urine concentrates to Uosm 1200

8. Volume Control • osmoreceptors - day to day control • baroreceptors - respond to pressure change neural and hormonal efferents hormonal mediators

9. Baroreceptors • Hormonal mediators aldosterone renin ANP dopamine • Hormonal effect ECF  Na and water reabsorption

10. Baroreceptors • Neural mechanism Autonomic nervous system

11. Renin-angiotensin Renin secreted when • drop BP • drop Na delivery to kidney • increased sympathetic tone

12. Renin-Angiotensin

13. Angiotensin II Increases vascular tone • increases catecolamine release • decrease renal blood flow • increases Na reabsorption • stimulates aldosterone release

14. Aldosterone Release stimutlated by • Angiotensin II • increased K • ACTH Effect • Na and water absorption • in distal tubular segments

15. Control of Volume Effective circulating volume • Portion of ECF that perfuses organs • Usually equates to Intravascular volume Third space loss • Abnormal shift of fluid for Intravascular to tissues eg bowel obst, i/o, pancreatitis

16. Normal Water Exchange Avg daily ml Min daily ml Sensibleurine 800-1500 300intestinal up to 10,000 sweat up to litres 500 Insensiblelungs/skin 600-900 600-900 8-10 mls/kg/D -  10%/ o rise in Temp

17. Normal Intake of Water 2000mls - 1300 free water 700 bound to food additional water comes from catabolism

18. Water and Eletrolyte Exchange Surgical patients prone to disruption • nil orally • anaesthesia • trauma • sepsis

19. Fluid and Electrolyte Therapy Surgical patients need • Maintenance volume requirements • On going losses • Volume excess/deficits • Maintenance electrolyte requirements • Electrolyte excess/deficits

21. 1. Maintenance Requirements This includes: insensible urinary stool losses Body weight Fluid required0-10Kg 100ml/kg/dnext 10-20Kg 50 ml/kg/dsubsequent Kg 20ml/kg/d15ml/Kg/d for elderly

22. 70 Kg Man Needs 1st 10kg x 100mls = 1000mls 2nd 10kg x 50mls = 500mls Next 50kg x 20mls= 1000mls TOTAL 2500 mls /d

23. 2. On Going Losses • NG • drains • fistulae • third space losses Concentration is similar to plasma Replace with isotonic fluids

24. 3. Volume Deficit - Acute • vital signs changes • Blood pressure • Heart rate • CVP • tissue changes not obvious • urine output low

25. 3. Volume Deficit - Chronic • Decreased skin turgor • Sunken eyes • Oliguria • Orthostatic hypotension • High BUN/Creatine ratio • HCT increases 6-8 points per litre deficit • Plasma Na may be normal

26. 4. Volume Excess • Over hydration • Mobilisation of third space losses Signs • weight gain • pulmonary edema • peripheral edema • S3 gallop

27. Fluid and Electrolyte Therapy Goal • normal haemodynamic parameters • normal electrolyte concentration Method replace normal maintenance requirements ongoing losses deficits

28. Fluid and Electrolyte Therapy Normal maintenance requirements • use BW formula On going losses • measure all losses in I/O chart • estimate third space losses Deficits • estimate using vital signs • estimate using HCT

29. Fluid and Electrolyte Therapy The best estimate of the volume required is the patients response After therapy started observe • vital signs • Urine output (0.5mls/Kg/hr) • Central venous pressure

30. Maintenance Electrolyte Requirements Na 1-2mEq/Kg/d K 0.5 - 1 mEq/Kg/d • Usually no K given until after urine output is adequate and U/E done. • Always give K with care, in an infusion slowly - never bolus • Ca, PO4, Mg not required for short term

31. Time Frame for Replacement • Usually correct over 24 hours • For ill patients calculate over shorter period and reassess e.g. 1, 2 hours or 3 hours for e op cases • Deficits - correct half the amount over the period and reassess

32. Postoperative Fluid Therapy • Check i/v regime ordered in op form • Assess for deficits by checking I/O chart and vital signs • Maintenance requirements calculated • Usually K not started • Monitor carefully vital signs and urine output

33. Postoperative Fluid Therapy • Urine specific gravity may be used (1.010 - 1.012) • CVP useful in difficult situations (5-15 cm H20) • Body weight measured in special situation e.g. burns

34. Concentration Changes • changes in plasma Na are indicative of abnormal TBW • losses in surgery are usually isotonic • hypoosmolar condition usually caused by replacement with free water

35. Hyponatremia -Usually Excess Free Water • Free water replacement of isotonic losses • Increased ADH secretion • Low intravascular volume states like cirrhosis /low albumin • Excess solute e.g. glucose - intracellular water shifts to ECF

36. Hyponatremia -Usually Excess Free Water • Features - depends on rapidity acute drop below 120 weakness fatigue confusion cramps nausea/vomiting headache/delirium/seizures/coma permanent CNS damage

37. Diagnosis of Hyponatremia • assess circulating volume • exclude hyperosmolar states • check for losses • check for excess free water replacement • In difficult situations measure urine Na (> <20mEq/L)

38. Treatment of Hyponatremia • replace volume deficits in dehydration • restrict free water in overload Na required = [desired Na] - [actual Na] x (TBW) TBW = 0.6xWt Correct half the deficit over 12 hours and reassess

39. Hyperkalaemia • Fatal if undiagnosed • Trauma, burns, septic, acidotic patient • ECG-Peak T, widened QRS, ST depressed • Repeat serum K • Insulin/dextrose, correct acidosis with HCO3, calcium IV infusion, oral calcium resonium, dialysis

40. Hypokalaemia • Depressed neuromuscular function • Dietary, excess loss – vomiting, diuretics • Related to alkalosis • Repeat serum K • Correct primary problem, replace orally or IV

41. Fit pt lap cholecystectomy 1st POD • Na 121 mmol/l (135-145) • K 4.6 mmol/l (3.5-5.0) • Cl 90 mmol/l (98-108) • HCO3 22 mmol/l (23-33) • Urea 3.5 mmol/l (3.0 to 8.0) • Creat 50 umol/l (60 to 120)

42. 60 yr colectomy 1st POD • Na 121 mmol/l (135-145) • K 2.6 mmol/l (3.5-5.0) • Cl 50 mmol/l (98-108) • HCO3 12 mmol/l (23-33) • Urea 1.5 mmol/l (3.0 to 8.0) • Creat 40 umol/l (60 to 120) • HCT 27

43. QUESTIONS ?

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