Page 587 - Clinical Application of Mechanical Ventilation

Neonatal Mechanical Ventilation 553

respiratory acidosis (pH less than 7.20), or unsatisfactory PaO on .50% of oxy-
2
gen with N-CPAP, intubation and surfactant therapy should be considered.

BASIC PRINCIPLES OF NEONATAL VENTILATION

The primary mode of neonatal mechanical ventilation is pressure-controlled venti-
lation. The ventilator generates a sufficient flow and delivers variable tidal volumes
by the preset pressure. Alternatively, ventilation can be achieved by using a preset
volume (volume-controlled ventilation).

Pressure-Controlled Ventilation

In pressure-controlled ventilation, a preset peak inspiratory pressure (PIP) is used
pressure-controlled ventilation:
A preset pressure is used to deliver to deliver the volume. Thus, pressure is constant and volume is variable, depending on
tidal volumes; the delivered volumes the compliance and airflow resistance characteristics of the infant. A decreasing com-
are variable.
pliance or an increasing airflow resistance requires a higher pressure to maintain the
same tidal volume. With the use of pressure-controlled ventilation, frequency would
more likely be adjusted to maintain minute ventilation, since the strategy of setting a
PIP is to protect the lung from excessive airway pressures. As the patient’s condition
improves (increased compliance or decreased airflow resistance), the pressure must be
Following surfactant decreased to avoid excessive volume and pressure. An example of this observation is
replacement, the PIP must
be monitored and reduced the successful therapeutic response to surfactant replacement. The lung compliance
accordingly to avoid overex-
pansion of the lungs. of the infant increases dramatically and rapidly soon after surfactant administration.
The PIP must be reduced accordingly to avoid overexpansion of the lungs.

Volume-Controlled Ventilation

Volume-controlled ventilation has gained popularity because the volume is preset
volume-controlled ventilation:
A desired tidal volume is preset; using variable pressures. This strategy reduces the incidence of overexpansion of
the pressure needed to deliver the the lungs. For extremely low-birth-weight infants, some ventilators (e.g., Drager
volume is variable.
Babylog) can provide a tidal volume as low as 2 mL. This is an important feature
when trying to maintain a range of 3–7 mL/kg for extremely low-birth-weight
infants (e.g., as low as 500 g birth weight). Typically, an initial tidal volume of
5 mL/kg is used to ventilate these infants, and the volume may be titrated up or
down to meet the infant’s needs. It is important to note that although volume
remains constant, pressure will vary, which may result in excess pressures being
delivered to the infant as a result of a decrease in compliance or increase in airway
resistance. Careful setting of peak pressure alarms will aid in preventing excessive
pressures being delivered in volume-controlled ventilation.

Ventilator Circuits and Humidifiers

During mechanical ventilation, some of the ventilator volume is “lost” within the
circuit and humidifier and is not delivered to the patient. This wasted volume is

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