Specific features of children's homeostasis:

body fluids compartments, electrolytes and

fluid balance, interpretation of acid-base

disturbances

Assoc.Prof. Virginija Zilinskaite,MD,PhD

Vilnius

2017

Various conditions may cause fluid, electrolyte and acid-base imbalances.

Most i ala es result fro a o ditio s that disrupts the ody’s regulatory mechanism or the treatment implemented to correct the condition

Body fluids compartments

Body fluids compartments

Premat.

newborn

Newb

orn

1 y. 3 y. Adult

Body weight (kg) 1,5 3 10 15 70

Body surface (m2) 0,15 0,2 0,5 0,6 1,7

Total body water (TBW %) 80 78 65 60 60

Extracellular fluid (ECV %) 50 45 25 20 20

Intracellular fluid (ICV %) 30 33 40 40 40

V.Žili skaitė, 7

Fluid and electrolyte balance in children

• A proportionately greater amount of body water

• A proportionately greater extracellular fluid, labile water

Fluid and electrolyte balance

• Compared to adults, children are at greater risk for fluid and electrolyte imbalance – A proportionately greater amount of body water and a greater

body surface and a higher percentage of total body water

– Require more fluid intake and subsequently excrete more fluid

– A greater potential for fluid loss via the gastrointestinal tract and skin

– An increased incidence of fever, upper respiratory infections, gastroenteritis

– A greater metabolic rate

– Kidneys that have a decreased ability to concentrate urine

– Increased risk for development hypernatremia based on their inability to verbalize thirst

Electrolytes

• Chemically, electrolytes are substances that become ions in

solution and acquire the capacity to conduct electricity

• Essential for normal function of the cells and organs

• Sodium, potassium, chloride and bicarbonate

Electrolytes • Sodium Na+

– 135 to 145 mEq/l (mmol/l)

– Major positive ion in fluid outside the cells

– Regulates the total amount of water in the body and the transmission of into

and out of cells

• Potassium (K+)

– 3,5 to 5,0 mEq/L (mmol/L)

– Major positive ion found inside the cells

– Regulation of the heartbeat and function of the muscles

• Chloride (Cl-)

– 98 to 108 mmol/L

– Major anion (negatively charged ion) found outside the cells and in the blood

– Helping the body maintain a normal balance of fluids

• Bicarbonate (HCO3-)

– 21 to 25 mmol/L

– Acts a buffer to maintain the normal level of pH in the blood and other fluids in the body

– Measured to monitor the acidity of the blood and body fluids

Osmolality vs osmolarity

Normal value = 275-295 mOsm/L

Measurement values • 1 mol = molecular weight in grams

• 1 mmol. = 1/1000 mol. (does not depend on valentia)

– glucose - m.w. 180, 180 mg = 1 mmol

• mosm. - does not depend on valentia or molecular weight , this is the

number of particles in the solution

• glucose, urea - 1 mmol = 1 mosm (does not dissociate)

– 1 mmol NaCl = 2 mosm

• mosm/l = mg/l : molecular weight x number of particles

• 9g NaCl/l = 9000mg/l : m.w.58,5 x 2 = 308 mosm/l

– 9g gluc/l = 9000mg/l : m.w.180 x 1 = 50 mosm/l

• mekv./l - depend on valentia

– Na+ - 1 mmol/l = 1 mekv/l = 1 mosm/l

– Mg++ - 1 mmol/l = 2 mekv/l = 1 mosm/l

V.Žili skaitė, 7

Body fluid Osmolality

Osmolality: clinical point

ADH disturbances

• Syndrome of inappropriate ADH ( )

secretion

– Normovolemic hyponatremia with oliguria

– unproduction of ADH

– Normo or hypovolemic hypernatremia with

hypotonic polyuria

Diabetes insipidus

ECG changes

Hyperkalemia

Pediatric Clinical Dehydration Scale (CDS)

Symptoms of water disorders in different

body water compartments

V.Žili skaitė, 7

Deficit

IVF Hypovolemia: tachycardia,

mental status, skin

perfusion, diuresis

IstF Impaired skin elasticity

and turgor

Thirst, CNS deterioration,

seizure, coma

Excess

IVF Hypervolemia: acute cardiac

failure, dyspnea, crackles in

lungs

IstF Edema

Headache, nausea,

vomiting, CNS

deterioration, seizure, coma

Fluid and electrolytes imbalance

• Evaluate:

– Loss mechanism

– Signs of dehydration

– Laboratory tests (acid-base state, electrolytes)

• Choose correction:

– Oral rehydration

– IV rehydration

Standard format of writing an ABG

pH < 7.35 – acidemia, pH > 7.45 - alkalemia

HCO3- + H+ CO2 + H2

A simple method for evaluating acid-base disorders

Respiratory acidosis: Symptoms and causes

Respiratory alkalosis: Symptoms and causes

Metabolic acidosis: Symptoms and causes

Metabolic alkalosis: Symptoms and causes

Blood Gas Differentialiser

Anion gap

• Cations = Na + unmeasured cations UC (Mg, Ca, K) 11 mekv/l

• Anions = Cl + HCO3 + unmeasured anions UA (SO4, PO4) 23 mekv/l

• Na + UC = Cl + HCO3 + UA

• Na - (Cl+HCO3) = UA - UC = 23mekv/l - 11mekv/l = 12 mekv/l anion gap