Paediatric Anaesthesia
PHYSIOLOGY IN THE NEONATE
TABLE 36.1
Lung Mechanics of the Neonate Compared with the Adult
Neonate | Adult | |
Compliance (mL cmH2O−1) | 5 | 100 |
Resistance (cmH2O L−1 s−1) | 30 | 2 |
Time constant (s) | 0.5 | 1.3 |
Respiratory rate (breath min−1) | 32 | 15 |
TABLE 36.2
Respiratory Variables in the Neonate
Tidal volume (V) | 7 mL kg−1 |
Dead space (VD) | (VT) × 0.3 mL |
Respiratory rate | 32 breath min−1 |
Cardiovascular System
Fluid Therapy
An intravenous infusion delivering maintenance fluids should be in place for all neonates requiring surgery. Maintenance fluid requirements increase over the first few days of life (Tables 36.5, 36.6). The normal infant requires of the order of 3–5 mmol kg−1 of sodium and an equivalent amount of potassium per day to maintain normal serum electrolyte concentrations. The ability of the infant’s kidneys to eliminate excess sodium is limited. Exceeding this amount in the absence of loss results in hypernatraemia and its sequelae. Infants undergoing any procedure more than the briefest should also have their calorific needs addressed. This may be achieved by including glucose-containing fluids in the regimen; failure to do so results in hypoglycaemia and ketosis. This may occur rapidly because of the limited glycogen stores and high metabolic rate of the infant.
TABLE 36.5
Fluid Requirements in the First Week of Life
Day | Rate (mL kg−1 Day−1) |
1 | 0 |
2, 3 | 50 |
4, 5 | 75 |
6 | 100 |
7 | 120 |
TABLE 36.6
Maintenance Fluid Requirements
Weight (kg) | Rate (mL kg−1 Day−1) |
Up to 10 kg | 100 |
10–20 kg | 1000 + 50 × [weight (kg) – 10] mL |
20–30 kg | 1500 + 25 × [weight (kg) – 20] mL |