- Home
- Medical books
- Pediatric pathology
- New-born fluid and electrolyte balance
New-born fluid and electrolyte balance
The newborn baby is largely water (775% term, 785% at 26/40).
New-born fluid and electrolyte balance
Normal
- The newborn baby is largely water (775% term, 785% at 26/40).
- There is a large extracellular compartment (65% of body weight at 26/40 compared to 40% by term, 20% in adult).
- There is a rapid loss of extracellular fluid after birth.
- Decreased pulmonary vascular resistance increases blood flow to left atrium, thereby inducing increased Atrial Natriuretic Peptide release (i GFR/d Na+reabsorbtion/ ‘fall’ renin-angiotensin-aldosterone system).
- Physiological increased urine output at 712–24hr after birth.
- Na/K ATPase activity is low at birth but increases steadily (Na/K ATPase is responsible for reabsorbing Na+ from the renal tubular lumen, in turn creating a gradient to allow reabsorption of Glucose, Na+and amino acids. Immature infants have lower enzyme activity.
Preterm babies have
- A variable ability to excrete a sodium load.
- An excellent ability to deal with water load.
- Modulated by ADH (osmo and baroreceptors).
- A tendency to lose sodium in urine over the first weeks as the increased glomerular filtration rate (GFR) exceeds the ability to resorb Na+.
- A high transepidermal water loss (TEWL). Evaporation from immature skin, <28/40. To reduce nurse in an incubator with 80% humidity
- Respiration related water losses (ventilated and spontaneously breathing infants) can be countered with warm-humidified gases.
- Sick infants (e.g. respiratory distress syndrome (RDS)) will have delayed dieresis;
- giving additional Na+will further delay diuresis and may worsen outcome;
- attempts to induce diuresis (e.g. with Furosemide) unlikely to be helpful.
Postnatal weight loss
- Weight loss after birth is normal;
o up to 10 % in well term infants over the first week of life;
o greater in preterm/VLBW.
- Rising sodium suggests dehydration (term and preterm infants).
- Failure to lose weight may suggest fluid retention/overload.
- Infants with >10% weight loss require further assessment of feeding;
o risk of hypernatraemic dehydration;
o usually breast-fed infants with unrecognized poor feeding;
o weigh all babies day 3 (some suggest day 5);
o check U&E if weight loss >12%;
o support the mother with breast expressing/top-up feeds;
- may require admission/NG feeds/IV fluids
Specific disturbances
Hyponatraemia
- Na+< 130mmol/L.
- Causes:
o water overload (most common in first-week);
o maternal fluid overload;
o iatrogenic;
o sick infant (e.g. birth asphyxia, sepsis);
o excess renal loss (common ‘late’ cause in preterm infants);
o GI loss, e.g. diarrhoea, NG aspirates, high output stoma;
o drainage of ascites/CSF;
o other (e.g. hypoadrenalism of any cause, Bartter syndrome/Fanconi syndrome).
- Symptoms: irritability, apnoeas, seizures.
- Treatment: dependent on underlying cause (e.g. fluid restriction/ Na+supplementation)
- Take care as too rapid correction can cause neurological damage.
Hypernatraemia
- Risk of seizures if Na+>150mmol/L.
- Causes: water depletion (usual), excess Na+administration (unusual as normally retain water also).
- Two major at-risk groups:
o extreme preterm infants in first days of life (excess water losses, e.g. TEWL);
o breast-fed infants with poor intake.
- Treatment: increase fluid intake (caution with rapid correction).
Hypokalaemia
- K+ <2.5mmol/L—causes:
o excess losses (diarrhoea, vomiting, NG aspirate, stoma, renal/ diuretics);
o inadequate intake (failure to recognize daily requirement, e.g. TPN).
- Correct with supplementation (IV or enteral):
o caution with enteral if GI disturbance;
o extreme caution with IV infusion as the risk of heart arrhythmia.
Hyperkalaemia
- K+>7.5mmol/L OR >6.5mmol/L and ECG changes.
- Causes: Failure of K+excretion, e.g. renal failure.
- Treatments:
o myocardial stabilization: calcium gluconate;
o elimination: calcium resonium, dialysis;
- re-distribution: salbutamol, insulin.