• причины и симптомы;
• лечение и регидратация;
• расчёт дефицита жидкости;
• что-то другое.

• causes and symptoms
• treatment and rehydration
• fluid deficit calculation
• something else

1. What is happening

• Water is lost in excess of solute, so the fluid lost is hypotonic. Water moves from cells into the extracellular fluid, which partly protects the circulation. Signs of dehydration are therefore milder than the water loss would suggest, and severe loss can be missed. - Brenner and Rector's The Kidney, p. 3144-3145
• In infants, weight losses of 5%, 10% and 15% correspond to mild, moderate and severe dehydration. - Brenner and Rector's The Kidney, p. 3145
• The classic neonatal cause is insufficient lactation in an exclusively breastfed baby, usually a firstborn. These infants typically present at 10 to 21 days. Sodium has been reported as high as 188 mmol/L. The extent of dehydration is often missed until it is severe. - Brenner and Rector's The Kidney, p. 3145
• Other causes are diarrhea, high insensible losses and high sodium intake. Nephrogenic diabetes insipidus is a later cause.
• Features include irritability, a high-pitched cry, lethargy, fever, jaundice, seizures, oliguria and shock. Metabolic acidosis is common, and a bicarbonate below 17 mmol/L suggests moderate to severe hypovolemia. - Brenner and Rector's The Kidney, p. 3145

• Hypovolemia lowers GFR and distal delivery of sodium and water, so less potassium is excreted. Neonates are especially prone to this.
• Acidosis and hyperosmolality move potassium out of cells.
• Many "hyperkalemia" results are spurious. In infants, a high potassium is most often hemolysis from phlebotomy. Even so, do not assume it is false: repeat the sample, examine the child, obtain an ECG and monitor. - Tintinalli's Emergency Medicine, Hyperkalemia section
• Hemolysis is present in about 4% of laboratory samples, and nearly half of those come from newborns. - Barash, Cullen, and Stoelting's Clinical Anesthesia, Table 16-21
• If the hyperkalemia is real, look for acute kidney injury. Also consider adrenal insufficiency or congenital adrenal hyperplasia, although that usually causes hyponatremia rather than hypernatremia.

2. Management

• Check airway, breathing and circulation, and get a true current weight. Compare it with the birth weight.
• Obtain an ECG and monitor the heart rhythm.
• Send sodium, potassium, glucose, bicarbonate, urea and creatinine, and a blood gas. Use a free-flowing, non-hemolyzed sample for potassium.
• Check blood glucose.

• Give isotonic saline even though sodium is high. A hypovolemic child needs 0.9% saline regardless of the sodium value. - Medscape pediatric hypernatremia review
• The Harriet Lane bolus is 20 mL/kg of normal saline. A neonatal case report used 10 mL/kg over 20 minutes. Repeat as needed for hemodynamic stability.
• If sodium is above 175 mEq/L, a plain saline bolus may drop sodium too fast. The Harriet Lane approach is to run normal saline and 3% saline together, giving a bolus fluid with sodium no more than 15 mEq/L below the patient's serum sodium. - The Harriet Lane Handbook, Box 11.7
  • Example: 3 kg neonate, sodium 185 mEq/L. The target bolus sodium is 170 mEq/L, which needs about 47 mL of 3% saline per litre of normal saline. A 60 mL normal saline bolus therefore gets about 2.8 mL of 3% saline.

• If there are ECG changes or arrhythmia, give 10% calcium gluconate 100 mg/kg (1 mL/kg) IV, and sodium bicarbonate 1 mEq/kg. - Tintinalli's Emergency Medicine, Hyperkalemia section
  • This applies to infants and children, and I did not find a neonate-specific dose in the library. Use your neonatal unit's protocol or formulary for exact doses.
• Tintinalli advises against insulin with glucose for hyperkalemia in infants because of the risk of profound hypoglycemia. Many neonatal units do use insulin with dextrose under close glucose monitoring, so follow your local protocol.
• Albuterol (salbutamol) is another way to shift potassium. Rosen's pediatric AKI dosing is 0.5 g/kg dextrose with 0.1 units/kg insulin, plus albuterol and bicarbonate. - ROSEN's Emergency Medicine, Management section
• Do not add potassium to fluids until urine output is established and the potassium is known. Treat the underlying hypovolemia and acidosis.
• If hyperkalemia persists with oliguric renal failure, involve nephrology early.
• From my own knowledge, not the library: sodium polystyrene is generally avoided in neonates because of the risk of bowel injury.

• The aim is to lower serum sodium by no more than 10 mEq/24 h, correcting the free water deficit over 48 hours. - The Harriet Lane Handbook, Section 11.B
• Other sources cite 10 to 12 mEq/L per day, or 0.5 mEq/L per hour, over 48 to 72 hours, and say the more severe the case, the slower the correction. - Medscape pediatric hypernatremia review; Cureus case report on a breastfed neonate; Journal of Neonatology retrospective study
• The Harriet Lane notes an exception: witnessed onset over hours can be corrected faster, because the brain has not yet generated idiogenic osmoles. - The Harriet Lane Handbook, Section 11.B
• An expert-opinion starting fluid is D5 ½ NS, and the Harriet Lane then calculates the exact sodium content (formulas below).

• Free water deficit (mL) = TBW (mL) × [1 − desired Na / serum Na].
• Solute fluid deficit = fluid deficit − free water deficit.
• Sodium required (mEq) = (solute fluid deficit + maintenance volume) × 14 mEq/100 mL.
• Fluid sodium (mEq/L) = sodium required ÷ (fluid deficit + maintenance volume, in litres).
• The Harriet Lane worked example is a 15 kg child with 10% dehydration and sodium 155. It gives about 115 mL/h in total and fluid of about 110 mEq/L sodium.
• A quick check is the change in serum sodium per litre of infusate = (infusate Na + K − serum Na) ÷ (TBW + 1).

• If the baby is not in shock, rehydration can be given enterally with breast milk or formula. - Journal of Neonatology retrospective study
• Check sodium every 2 to 4 hours at first. Also monitor potassium, glucose, bicarbonate, urine output and neurological status.
• If sodium is falling faster than 0.5 mEq/L per hour, slow the rate of fluid.
• Seizures during correction suggest cerebral edema from correcting too fast. The usual treatment is a small bolus of 3% saline, per local protocol.
• Hypernatremia also carries a risk of subdural hematoma and cerebral venous thrombosis, from brain shrinkage. - ROSEN's Emergency Medicine, Chapter 167
• Prevention matters: follow weight and feeding closely in the first 2 to 3 weeks and support first-time mothers. - Brenner and Rector's The Kidney, p. 3145

3. Recent evidence check