Which respiratory index is increased in neonates compared with adults?

Which respiratory index is increased in neonates compared with adults?

• A. Tidal volume (mL/kg)
• B. pH
• C. Alveolar ventilation (mL/kg/min)
• D. Functional residual capacity (mL/kg)

Answer: (C)

Neonates must ventilate more air per kilogram to clear the CO2 they produce, because they have a higher metabolic rate and a relatively large dead space compared with their small tidal volumes. The key idea is alveolar ventilation per unit time, which is the air that actually reaches the gas-exchange units. It’s calculated as (tidal volume minus dead space) times the respiratory rate. In newborns, the respiratory rate is much higher, and although tidal volumes per kg are not larger (and dead space makes up a larger fraction of VT), the combination with the high rate means alveolar ventilation per kilogram per minute is increased to meet their CO2 production. That’s why alveolar ventilation per kg per minute is higher in neonates than in adults. Tidal volume per kilogram in neonates is not increased to a notable degree; pH is a separate parameter and functional residual capacity per kilogram is not greater than in adults, so they don’t reflect an increase in this context.

Neonates must ventilate more air per kilogram to clear the CO2 they produce, because they have a higher metabolic rate and a relatively large dead space compared with their small tidal volumes. The key idea is alveolar ventilation per unit time, which is the air that actually reaches the gas-exchange units. It’s calculated as (tidal volume minus dead space) times the respiratory rate. In newborns, the respiratory rate is much higher, and although tidal volumes per kg are not larger (and dead space makes up a larger fraction of VT), the combination with the high rate means alveolar ventilation per kilogram per minute is increased to meet their CO2 production. That’s why alveolar ventilation per kg per minute is higher in neonates than in adults.

Tidal volume per kilogram in neonates is not increased to a notable degree; pH is a separate parameter and functional residual capacity per kilogram is not greater than in adults, so they don’t reflect an increase in this context.