Fig. 1
Relative body fluid compartments by age. As children grow, the relative size of body fluid compartments change. ECF extracellular fluid, ICF intracellular fluid (Source: Christopher Coppola)
2.
Urine output:
(a)
Measurement of hourly urine output is essential in critically ill children.
(b)
Catheterization of small infants, especially the male is fraught with complication and should only be undertaken by experienced personnel.
(c)
In order to excrete adequate solute load, the following are approximations of adequate hourly urine output:
(i)
Infant ~ 2 mL/kg.
(ii)
Child ~ 1 mL/kg.
(iii)
Adolescent ~ 0.5 mL/kg.
(d)
These are only approximate volumes and are certainly an underestimate in the critically ill child.
(e)
Other signs of adequate perfusion include capillary refill, skin temperature, heart rate, level of consciousness and fontanel examination in the infant.
3.
Fluid requirements: “4 -2 -1 rule”.
(a)
4 mL/kg/h for the first 10 kg of dry body weight.
(b)
2 mL/kg/h for the next 10 kg of dry body weight.
(c)
1 mL/kg/h for each additional kg of dry body weight.
(d)
Example: A 20 kg child will need approximately 60 mL/h of maintenance fluid.
(e)
This is only an estimate and may require frequent adjustment depending on urine output, heart rate and other signs of perfusion.
4.
Insensible water loss:
(a)
Respiratory: May be mitigated by humidifying inspired gases in those children who require mechanical ventilation.
(b)
Skin.
(i)
Especially significant in premature infants.
(ii)
Mitigated by wrapping extremities, humidified incubators.
5.
Common electrolyte anomalies:
6.
Sodium (Na): Newborn requires approximately 2 mEq/kg/day.
(a)
Hyponatremia.
(i)
Most common electrolyte abnormality in surgical patients.
(ii)
Usually indicates hypo-osmolality and excess extracellular water.
(iii)
Symptoms are CNS related and include headache, nausea, lethargy, hallucinations and coma.
(iv)
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Common Causes in children:
1.
Excess ADH secretion in postoperative period.
2.
Bowel obstruction.
3.
Peritonitis.
4.
Renal impairment.
5.
Hypotonic intravenous fluid administration.
