Fluids And Electrolytes

Fluids and electrolytes

Maintenance: Can be calculated from caloric expenditures Maintenance water requirements: Determined by water lost from feces and urine and insensible losses (ie, losses through the lung and skin) Fecal losses are minimal 100 ml for each 100 Kcal expended may be used when calculating insensible and renal water losses

Na+ lost daily in the urine: 2-3 meq/kg K+ lost daily in the urine: 1-2 meq/kg Maintenance done as following: •0 – 10 Kg: 100 ml/kg •11 – 20 kg: 1000 ml + 50 ml/kg for each kg > 10 kg •>20 kg: 1500 ml + 20 ml/kg for each kg > 20 kg

Plasma Osmolality mOsm/kg = 2 (Na, meq/l) + glucose, mg/dl + BUN, mg/dl 18 2.8

•Isonatremic (isotonic ): Na is 130 – 150 meq/l with proportional losses of fluid and electrolytes from the extracellular space •Hyponatremia (hypotonic): Na < 130 meq/l; lose more Na than water •Hypernatremic (hypertonic): Na >150 meq/l; lose more water •Deficit from extracellular and intracellular fluid compartments

History Physical exam Lab tests Degree of dehydration: Mild Moderate Infants 5% 10% Adolescents 3% 6%

Severe 15% 9%

Assessment of degree of dehydration: Mild

Moderate

Severe

•Isotonic fluids such as normal saline or lactated Ringer’s should be used for volume resuscitation •Oral rehydrating solutions (ORS) •WHO ORS •Successful in mild to moderated dehydration

Composition of WHO oral rehydration solution

Advantages of 2002 formula have been quoted as: - lower osmolality allows quicker absorption of fluids - less chances of hypernatremia - more stability of reconstituted solution - decreased number of hospitalizations - less cost of manufacturing

Typical Electrolyte Compositions of Various Body Fluids  

Diarrhea Gastric Small intestine

Na+ (mEq/L)   10–90 20–80 100–140

K+ (mEq/L)   10–80 5–20 5–15

HCO3– (mEq/L)   40 0 40

Ileostomy

45–135

3–15

40

Estimated Water and Electrolyte Deficits in Dehydration (Moderate to Severe) Type of H2O Dehydration (mL/kg)  

Na+ K+ Cl– and HCO3– (mEq/kg) (mEq/kg) (mEq/kg)      

Isotonic

100–150

8–10

8–10

16–20

Hypotonic

50–100

10–14

10–14

20–28

Hypertonic

120–180

2–5

2–5

4–10

Therapy Re-evaluate Total volume = Deficit + Maintenance + Ongoing losses When the child presents in hopovolemic shock, rapid volume expansion is needed

Therapy (Contd…) Intavenous bolus of 20 ml/kg of isotonic fluid given After the bolus, patient reassessed , and second bolus of isotonic solution may be given Subsequent therapy should be aimed at correcting the factors contributing to the hypovolumic shock

Therapy Isotnatremic dehydration Deficit should be replaced over 8 – 24 h Hyponatremic dehydration Deficit should be replaced over 8 – 24 h Severe hyponatremic dehydration, Na may be given as a 3% Nacl solution Amount of Na (meq) that can be given as 3% = (Desired Na – current Na) X Body weight in Kg X 0.6

Hypertonic dehydration: •Deficit should be replaced over 48 h •Prevents fluid shifts into the cells •A rapid decrease in serum Na decreases serum osmolality faster than intracellular osmolality, and fluid goes into the cells, resulting in edema •Na should be lowered no faster than 10 meq/l/d