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Pediatric Fluids and Electrolytes Katinka Kersten

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Learning Objectives Recognize that fluid and electrolyte homeostasis is different in infants, children and adults Know contents of different fluid compartments in body Know how to estimate maintenance fluid and electrolyte needs Know fluid management for patients with Isonatremic dehydration Hyponatremic dehydration Hypernatremic dehydration Know contents of different intravenous and oral rehydration solutions

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ECF and ICF Body has two fluid compartments Extracellular fluid (ECF) space makes up 1/3 of our body fluids Intracellular fluid (ICF) space makes up 2/3 of our body fluids Extracellular space refers to fluids outside our cells which may be interstitial fluid or plasma or CSF Total body water = 0.6 X weight (kg) for children and adults and 0.78 X weight (kg) for neonates and infants

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Developmental Differences in Children Increased fluid intake and output relative to size. Total body fluid of infants is 20% more than adults Greater surface area relative to size and therefore more water loss through skin Increased metabolic rate Immature kidney function that requires more fluid to excrete waste

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ICF (mEq/L)ECF (mEq/L) Sodium Potassium Chloride Bicarbonate Phosphate Protein7510 ECF and ICF Composition

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Approach to Fluid Calculations 1. Maintenance:Determined by a ‘system’: a. Caloric expenditure method b. Holliday-Segar method c. Surface area method LOW AMOUNT OF ELECTROLYTES IN FLUID 2. Deficit:Determined by acute weight change or clinical estimate HIGH AMOUNT OF ELECTROLYTES IN FLUID 3. Ongoing losses:Determined by measuring

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Basal Metabolism Daily fluid and electrolyte need is related to daily average energy requirement. Daily energy requirement is determined by Resting Energy Expenditure (REE) plus correction factor for activity, fever, trauma, injury and growth. When compared to body weight the Resting Energy Expenditure (REE) is high in the newborn, and lower in adults

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Maintenance Fluid Simplification It’s impossible to know Resting Energy Expenditure and average daily energy needs for different ages and sizes and most people rely on existing tables. Two systems have been proposed to relate maintenance fluid and electrolyte needs to the body weight. Surface area method Holliday-Segar method

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Most widely used method Landmark paper by Holliday and Segar in 1957 Studies done on healthy infants and children Assumes that for each 100 calories metabolized, 100 ml H 2 O will be required (50 ml/100 calories for insensible loss, 67 ml/100 calories for urine and 17 ml/100 calories gained from metabolism) Not suitable for newborns Holliday -Segar Method

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Holliday-Segar FLUID REQUIREMENTS For first 10 kg 100 ml/kg/day (4ml/kg/hr) For second 10 kg 50 ml/kg/day (2ml/kg/hr) Each additional kg 20 ml/kg/day (1ml/kg/hr) ElECTROLYTE REQUIREMENTS Na + 3 mEq/100ml Cl - 4 mEq/100ml K + 2 mEq/100ml

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REPLACEMENT OF DEFICIT

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ECF and ICF Contributions to Loss If losses occur over very short period most of the loss is from ECF If losses occur over long period of time losses are about 50/50 ICF and ECF

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Type PercentSymptoms Very mild<3Thirst may be present Mild3-5Dry mucous membranes and conjunctiva Moderate5-7Sunken eyes, decreased fontanelle Severe7-12Tenting of skin Very severe>12Shock Clinical signs of Dehydration

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Oral Rehydration Therapy Safest way to rehydrate patient is by the enteral route Best to use ORS as this is least hyponatremic. However many patients don’t take this because salty. Pedialyte decent as well and thirdly Gatorate Can not do this in patients with Severe altered mental status Persistent severe vomiting Intestinal obstruction

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Electrolytes in Popular Drinks Electrolytes in Popular Drinks Na (mEq/L)K (mEq/L) Apple juice Coke Gatorade Milk22 36 OJ Pedialyte45 20 WHO ORS90 20

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A 2 year old has a 6-day history of gastroenteritis, poor fluid intake and infrequent urination. On exam you find dryness of the mucous membranes, sunken eyes with mild tenting of the skin. The serum sodium is 137 mEq/L. The weight is 10 kg. You determine the child is suffering from about 10% dehydration. What are the fluid and electrolyte requirements? Isotonic dehydration (Na mEq/L)

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H2O Na K (ml) (mEq) (mEq) Maintenance (Holiday/Segar) Total deficit = 1000 ml Extracellular fluid deficit (50% of total) Intracellular fluid deficit (50% of total) Total Isotonic Dehydration Example

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Hypertonic Dehydration (Na + > 145 mEq/L ) Mortality can be high Often iatrogenic The intravascular volume (extracellular space) is preserved at the expense of the intracellular volume The patient looks better than you would expect based on fluid loss Always assume total fluid deficit of at least 10%

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Free Water Deficit Use 4 ml/kg of body weight for each mEq of Na + above 145 mEq/L as the Free Water Deficit (Serum Na mEq/) x weight x 4 = total amount of free water needed to dilute the serum to get a normal concentration Na + Only correct half of total Free Water Deficit in first 24 hours if Na + < 175 mEq/L For Na + > 175 mEq/L you do not want to correct faster than 1 mEq/L/hr

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Hypertonic Dehydration Example 6-month-old suffering for 3 days from severe diarrhea. Mucous membranes are dry, skin feels doughy and the child is somnolent and lethargic. The serum Na + is 165 mEq/L. The child weighs 5 kg and you assume the fluid deficit is at least 10%. What are the fluid and electrolyte requirements?

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Hypertonic Dehydration Example H2O Na K (ml) (mEq) (mEq) Maintenance (Holiday/Segar) Total deficit = 500 ml ½ of Free Water Deficit {( )x5x4x½} Remainder of deficit {( ) = 300 ml} Extracellular (60%) Intracellular (40%) Total

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Hypotonic Dehydration (Na + < 135 mEq/L) Children with vomiting and diarrhea who have received hypotonic fluids as oral replacement Shock is an early symptom. Physical exam findings usually exaggerate amount of dehydration.

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Additional Na + needed To calculate the Na + Deficit, multiply 0.6 mEq/kg of body weight for each mEq of Na + below 135 mEq/L.

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Hypotonic Dehydration Example A 3-year-old has had diarrhea and vomiting for 1 day. Examination shows sunken eyes and marked tenting of the skin but the child is not in shock. The serum Na + is 120 mEq/L. The weight 14 kg. You estimate the deficit as 7%. What are the fluid and electrolyte requirements for this patient?

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Hypotonic Dehydration Example H2O NaK (ml)(mEq)(mEq) Maintenance (Holliday/Segar) Deficit (7% of 14 kg) Extracellular fluid (80%) Intracellular fluid (20%) Additional sodium {( ) x 0.6 x 14} Total

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NaKClHCO3 Gastric juice Small-intestinal juice Diarrhea Sweat Electrolytes in Body Fluids (mEq/L)

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Fluidcal/L NaK CLHCO3 D5W D10W NS /2 NS D5 1/4 NS LR Alb. 25% <120 Composition of Parenteral Fluids

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