Basic Fluid Management …with references to the Harriet Lane (because you have it with you)

1. Basic Fluid Management…with references to the Harriet Lane(because you have it with you) Julie Story Byerley, MD, MPH

2. Why does fluid management matter? • It’s basic pediatrics. • Pediatricians are supposed to be the experts of fluid management. • It matters to just about every inpatient. • Fluid is often extremely effective therapy. • Incorrect fluid management can seriously hurt patients. • It’s not always as simple as you might think – but you can make it simple.

3. Outline • Maintenance requirements • Management of dehydration • Normonatremic • Hyponatremic • Hypernatremic • A few little pearls

4. Maintenance requirementsChapter 10, Harriet Lane, p. 233 • The two functions of maintenance fluids include • Solute excretion in urine • Heat dissipation through insensible losses of water • Insensible losses are about 2/3 skin and 1/3 lungs • Each can be considered as about 50% when maintenance needs are exactly met and urine concentration is 1.010 • The kidneys are usually smart – insensible losses come first (less adjustable) and the kidneys can then adjust how much water is in the urine

5. Maintenance Requirements • Caloric Expenditure Method • Holliday-Segar Method • Body Surface Area Method • Remember that maintenance requirements are over about 24 hours, and don’t have to be given evenly divided over each hour

6. Caloric Expenditure Method • Water and electrolyte needs parallel caloric needs • Caloric needs depend on activity • For each 100 kcals, • 100-120 cc water, • 2-4 MEq Na, and • 2-3 MEq K are needed

7. Average Caloric NeedsSee page 436 in Harriet Lane (table 20-1) • At normal activity • Infants approx. 100 kcal/kg/d • 4-6yo approx. 90 kcal/kg/d • 7-10yo approx. 70 kcal/kg/d • Teens approx. 50 kcal/kg/d • Caloric needs are based on resting energy expenditure and activity • Resting energy expenditure (REE) is based on size • Energy needs increase with injury, fever, growth, etc. • See p. 435 in Harriet Lane • REE (Resting Energy Expenditure) + REE X (Mtn + Injury + Activity + Growth) • Don’t memorize it, just get the concept

8. Example, Caloric Expenditure Method • 10 yo boy with injuries and fever, 30kg • = REE + REE x (Mtn + Activ + Fever + Inj + Growth) • = 40 + 40 x(0.2 + 0.1 + 0.13 + 0.4 + 0.5) • = 40 + 40 x(1.33) • = 93 kcal/kg/d = 2790 kcal/d • Therefore, he needs 2790 cc water per day • water needs parallel caloric needs • 3 MEq Na/(100 kcals) = 84 MEq Na total per day • 2 MEq K/(100 kcals) = 56 MEq K total per day

9. The Math – what fluid? • D5 is standard • 2790 cc of D5 has only 474 kcals • only 16 kcal/kg/d • people are malnourished when they only receive IVF! • 84 MEq Na/ 2790 cc = X / 1000; X = 30 • Quarter NS = 38.5 MEq Na/L • 56 MEq K/ 2790 cc = Y / 1000; Y = 20 • Try D5 quarter NS with 20 KCl at 116 cc/hour • More fluid than using the 4:2:1 rule (70cc/h); necessary because of injuries and fever

10. Holliday-Segar Method • Estimates caloric and fluid needs from weight alone • Can over-estimate fluid needs for infants and under-estimate fluid needs in fever and injury • Method we tend to use most commonly • 4,2,1 rule

11. Holliday-Segar Method

12. Holliday-Segar Method • Electrolyte Requirements • Na – 3 MEq per 100 cc water • K - 2 MEq per 100 cc water • Example, 25 kg kid, 1600 cc/d • 48 Meq Na, 32 Meq K • 48/1600 = X/1000; X = 30 • (Remember that quarter NS has 38.5 MEq/L Na) • 32/1600 = Y/ 1000; Y= 20 • D5 quarter NS with 20 MEq/L KCl (as Cl is your anion to fill with)

13. Sodium • Since the ratio of electrolytes needed to amount of water does not change, the Na concentration in MIVF does not need to change based on weight • Often people use D5 ¼ NS for small babies and D5 1/2 NS for bigger kids and adults • This can give adults more sodium than needed • This error is based on the fact that fluid needs decrease as size increases • Na should be calculated based on kcals, (therefore cc’s not kg) • We decrease water needs as weight increases (the 4,2,1 rule), but we tend to calculate Na needs as 3 MEq per kg per day. Na needs are not linear. They should decrease like water needs do. • Many argue that D5 ¼ NS with 20 K is an appropriate maintenance fluid for all people.

14. Body Surface Area Method • Method not used as frequently, but often taught in nephrology • More difficult to use with small children • To calculate the BSA you need to know height • Maintenance requirements are about 1500 ml/m2/day

15. Dehydration

16. Background • Dehydration complicates many acute illnesses • Accurate assessment is important • Consequences of under-estimation • Consequences of over-estimation • Practice guidelines for evaluation and management

17. Dehydration • Initial resuscitation • Determining deficit • Adding in maintenance • Ongoing losses (don’t forget!)

18. Estimating degree of dehydration…traditional teaching • Recent weight changes • Physical exam findings

19. Caveats…traditional teaching • The previous chart applies to babies. For adults it should be scaled back to 3%, 6%, and 9%. • Older kids show symptoms at a lower % dehydration • Hyponatremic dehydration looks worse clinically – exaggerated hemodynamic instability • Hypernatremic dehydration looks better clinically – circulation maintained at the expense of intracellular volume

20. Systematic Review of the Published Data on History, PE, and Labs in Dehydration Mike Steiner, Darren DeWalt, Julie Byerley, 2002-3

21. Historical Factors • Previous visit to PCP, or previous trial of clears provided minimal but some increase in the likelihood of dehydration • Physical exam signs less helpful than previously taught

22. Delayed Capillary Refill • Limitations: • Inter-rater agreement only slight to fair • Kappa 0.01-0.35 • Site of application, lighting and ambient temperature

23. Abnormal Skin Turgor • Limitations: • Inter-rater agreement fair to moderate • Kappa 0.36-0.55 • Hypernatremia increases false negatives

24. Abnormal Respirations • Limitations: • Inter-rater agreement of only chance to fair • Kappa –0.04 to 0.40 • Varying measurements and definitions

25. Less Useful Signs

26. Combinations of Signs • Vega evaluated the standard dehydration table • ‘Severe’ classification • LR 3.4 for 5% dehydration • ‘Mild or ‘Moderate’ classification • No increase in likelihood of dehydration • Gorelick found an LR of 4.9 when 3/10 signs of dehydration present

27. Results: Laboratory Tests • BUN • Study of hospitalized patients with gastroenteritis • BUN >45, specificity: 1.00, LR positive of 46.1 • BUN cutoffs of 8, 18, and 27 yielded mixed results in four other studies • Acidosis • One study found no statistical increase in likelihood • Four studies found significant positive LRs between 1.5 and 3.5

28. Discussion • Poor to moderate inter-observer agreement • History and parental report have limited value • Best individual tests • Prolonged capillary refill • Abnormal skin turgor • Abnormal respirations • Groups of positive signs are helpful • Extremely abnormal lab tests are helpful

29. Implications • Focus on symptoms and signs with proven utility • Ability to estimate exact degree of dehydration is limited • Support change to ‘none, some, or severe’ classification scheme

30. Oral Rehydration • Recommended by the AAP, WHO, and CDC • Appropriate for mild-moderate (some) dehydration • Goal is 50-100 cc/kg over 4 hours for mild-moderate dehydration • 5 cc every 1-2 minutes • Solution containing 40-60 MEq/L Na

31. The Fluid Used Matters

32. Fluid Management in Shock • Initial boluses of 20 cc/kg over 30 min • 20 cc/kg is 2% of body weight – therefore it should take a 10% dehydrated baby to only 8% dry • One bolus is not enough when someone is 15% dry • Use isotonic solutions (NS, LR) • Consider blood, other fluids and/or pressors in special circumstances • Trauma or blood loss • Nephrotic syndrome • Septic and cardiogenic shock

33. Fluid Composition

34. Rehydration • First resuscitate out of shock – restore perfusion • Calculate maintenance, including ongoing losses, and deficit • Run maintenance as usual • Replace ongoing losses • Typical is to replace deficit over 24 hours • Half in first 8 hours • Other half over 16 hours

35. Where the dehydration comes from…traditional teaching • In a brief duration of illness (<3 days), 80% of the deficit is typically from the ECF • More than 3 days of illness and the deficit from the ICF increases to about 40% (therefore 60% from ECF) • This matters because ECF contains a lot of sodium (135-145 mEq), and intracellular fluid contains a lot of potassium (150MEq) • But remember…“No walls, no sparks”

36. Example Calculations, normal Na(See table 10-7 in Harriet Lane on page 237.) 7 kg infant with 10% dehydration that accumulated over >3d.

37. First 8 hours • MIVF for 8 hours plus 50% of the deficit • 583/8=73 cc/h; 38/0.583=65MEqNa/L = 0.42NS (65/154); 26/0.583=45MEqK/L • Roughly D5halfNS plus 40 KCl at 75 cc/h

38. Next 16 hours • MIVF for 16 hours plus other 50% of the deficit • 817/16=51 cc/h; 44/0.817=54MEqNa/L = 0.35NS (54/154); 30/0.817=37MEqK/L • Roughly D5halfNS plus 40 KCl at 50 cc/h

39. Simplified – what fluid, normal Na (Roberts’ method) • Usually after boluses with NS or LR, D5halfNS is an appropriate rehydration fluid • After urine output is assured, give K as 20 MEq/L • That is usually safe • Often you don’t need to fully replete K losses acutely • Watch the rate of fluids regarding K and don’t give more than 1 MEq/kg/h

40. Simplified – what rate (Roberts’ method) • If a child is 10% dehydrated - • Give a 20 cc/kg bolus of NS • Restores hydration 2% • Next give 10 cc/kg/h of D5halfNS with 20 KCl for 8 hours • Restores hydration 8% • Next give 1.5 times MIVF using D5quarterNS with 20KCL for 16 hours • That day’s maintenance

41. Example, the Robert’s method • 7kg child with 10% dehydration • Bolus of 140 cc NS • 70 cc/h of D5halfNS with 20 KCL for 8 hours, then • 40 cc/h of D5quarterNS with 20 KCL for 16 hours

42. Hyponatremia Always measure the sodium. Hyponatremic patients look more dehydrated than they probably are.

43. Example calculation, hyponatremia (7kg with 10% dehydration, Na 115, >3 d duration)Table 10-8 on p. 238 • Fluid deficit – same as before • 10% of 7 kg=700 ml total fluid deficit • 60% from ECF, 40% from ICF • Na deficit (from dehydration) – same as before • ECF Na x 60% of total fluid deficit • 145 mEq/L x .6 x .7L = 61mE • ExcessNa deficit (because hyponatremic) • (Desired Na – Actual Na) x distribution factor x wt • (CD-CA) x fD x weight • (135-115)MEq/L x 0.6L/kg x 7kg = 84 mEq Na • Replace excess Na deficit over 24 hours • Replace Na faster if symptomatic

44. K deficit (same as before) • ICF K x 40% of total fluid deficit • 150mEq/L x 0.4 x 0.7L=42 mEq • Make a table!

45. First 8 hours, hyponatremia • MIVF for 8 hours plus 50% of the deficit • 583/8=73 cc/h; 80/0.583=137MEqNa/L = 0.89NS (137/154); 26/0.583=45MEqK/L • Roughly D5halfNS plus 40 KCl at 75 cc/h

46. Next 16 hours, hyponatremia • MIVF for 16 hours plus other 50% of the deficit • 817/16=51 cc/h; 86/0.817=105MEqNa/L = 0.68NS (105/154); 30/0.817=37MEqK/L • Roughly D5halfNS plus 40 KCl at 50 cc/h

47. Practical Interpretation, Hyponatremia • In adults, rapid correction of hyponatremia may be associated with central pontine myelinoysis. • Correct the Na fast only if the patient is symptomatic (seizing or particularly irritable) • For asymptomatic patients, the goal should be to increase the Na no faster than 1 MEq/L per hour • Start with NS boluses and then D5NS or D5halfNS • Follow Na carefully

48. Hypernatremia Always measure the sodium

49. Hypernatremia • In hypernatremia, rehydrate more slowly to avoid fluid shifts that could cause cerebral edema or intracranial bleeding • Remember that the hypernatremic patient doesn’t always look as dry as they are because the intravascular volume is protected • The hypernatremic dehydrated patient is still sodium depleted, but in addition has lost free water • Free water losses must be calculated and subtracted from total deficit to calculate the solute deficit

50. Example calculation, hypernatremia (7kg with 10% dehydration, Na 155, >3 d duration)Table 10-9 on p. 239 • Same fluid deficit, maintenance fluid and electrolytes as before, in isotonic dehydration example • FW deficit =(measured Na – ideal Na)x 4cc/kg x wt • FW def = (155-145) x 4 x 7 = 280 cc • Replace free water deficit evenly over 48 h • Give only half of FW deficit in first day • Drop Na less than 15 MEq/L/day • Follow lytes closely – every 4 hours at first • Subtract the free water deficit from the total deficit to determine Na deficit