Pediatric Fluids and Electrolytes Katinka Kersten

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 contents of different intravenous and oral rehydration solutions Know fluid management for patients with Isonatremic dehydration Hyponatremic dehydration Hypernatremic dehydration

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

Developmental Differences in Children 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

ECF and ICF Composition ICF (mEq/L) ECF (mEq/L) Sodium 20 135-145 Potassium 150 3-5 Chloride --- 98-110 Bicarbonate 10 20-25 Phosphate 110-115 5 Protein 75 10

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

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

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

Holliday Segar Method Most widely used method in pediatrics to estimate maintenance fluid need Landmark paper by Drs. Holliday and Segar in 1957 Studies done on healthy infants and children Assumes that for each 100 calories metabolized, 100 ml H2O 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 FLUID REQUIREMENTS ElECTROLYTE 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

Replacement of Deficit

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

Clinical Signs of Dehydration Type Percent Symptoms Very mild <3 Thirst may be present Mild 3-5 Dry mucous membranes and conjunctiva Moderate 5-7 Sunken eyes, decreased fontanelle Severe 7-12 Tenting of skin Very severe >12 Shock

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

Electrolytes in Popular Drinks Na (mEq/L) K (mEq/L) Apple juice 0.4 26 Coke 4.3 0.1 Gatorade 21 2.5 Milk 22 36 OJ 0.2 49 Pedialyte 45 20 WHO ORS 90 20

Electrolytes in Body Fluids Na K Cl HCO3 Gastric juice 140 15 155 0 Small-intestinal juice 140 15 155 40 Diarrhea 40 40 40 40 Sweat 70 15 60 0

Composition of Parenteral Fluids Fluid cal/L Na K CL HCO3 D5W 170 0 0 D10W 340 0 0 NS 0 154 154 1/2 NS 0 77 77 D5 1/4 NS 170 34 34 LR 0 130 4 109 28 Alb. 25% 1000 100-160 <120

Isotonic Dehydration (Na 135-`45 mEq/L) 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 H2O Na K (ml) (mEq) (mEq) Maintenance (Holiday/Segar) Total deficit = 1000 ml Extracellular fluid deficit (50% of total) Intracellular fluid deficit Total 1000 30 20 500 70 500 75 2000 100 95

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%

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+ -145 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

Hypertonic Dehydration 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?

Hypertonic Dehydration H2O Na K (ml) (mEq) (mEq) Maintenance (Holiday/Segar) Total deficit = 500 ml ½ of Free Water Deficit {(165-145)x5x4x½} Remainder of deficit {(500-200) = 300 ml} Extracellular (60%) Intracellular (40%) Total 500 15 10 200 180 25 120 18 1000 40 28

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.

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.

Hypotonic Dehydration 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?

Hypotonic Dehydration H2O Na K (ml) (mEq) (mEq) Maintenance (Holliday/Segar) Deficit (7% of 14 kg) Extracellular fluid (80%) Intracellular fluid (20%) Additional sodium {(135-120) x 0.6 x 14} Total 1200 36 24 800 112 200 30 126 2200 274 54