Page 592 - Clinical Application of Mechanical Ventilation

558 Chapter 17

intrapulmonary shunting, or if the set PEEP is not high enough to overcome criti-
cal opening pressure as indicated when viewing the compliance (pressure volume)
loop. Table 17-7 provides the primary settings for volume-controlled ventilation
using birth weight as a guide.
Once mechanical ventilation is initiated, the ventilator settings are fine-tuned
until appropriate arterial blood gases are achieved. Blood gas measurement can be
achieved by obtaining arterial blood from a peripheral or umbilical artery catheter
(UAC), peripheral artery puncture, or capillary blood from a finger or heel stick.
Under most circumstances, a PaO .50 mm Hg, a PaCO 35 to 45 mm Hg, and
2
2
a pH between 7.3 and 7.45 are acceptable for a UAC sample. An appropriately
-
done capillary sample will roughly correlate with arterial PCO , pH, and HCO ,
3
2
The normal arterial and thus share the same acceptable values. A capillary PO is usually not acceptable
2
blood gases for neonates are as a determinant of oxygenation status and requires the use of a pulse oximeter or
PO 2 .50 mm Hg, a PaCO 2
35 to 45 mm Hg, and a pH transcutaneous PO monitor. Common exceptions to these values are in the case of
2
between 7.3 and 7.45. For chronic lung disease patients such as pulmonary interstitial emphysema in which
capillary samples, a lower PO 2
is acceptable. higher PaCO are acceptable, and patients treated for pulmonary hypertension,
2
where high PO , low PCO , and high pH are used.
2
2
HIGH FREQUENCY VENTILATION (HFV)

Since the explosion of research in neonatal medicine started many years ago, there
is an ongoing search for a better method of ventilation to maintain adequate blood
gas levels without inflicting damage on the premature lung. Several exciting meth-
ods have evolved to address these concerns.
The normally held understanding of ventilation is that the tidal volume must
exceed the amount of physiologic deadspace for alveolar ventilation to occur. Con-
ventional ventilation utilizes this principle by inflating the patient’s lungs with a
tidal volume that exceeds deadspace and inflates the alveoli. Expiration then occurs
by the passive recoil of the thorax and lung.
High frequency ventilation (HFV) is a ventilation technique that delivers small
high frequency ventilation
(HFV): A type of ventilation that tidal volumes at very high frequencies. Early studies involving HFV showed that
uses very high frequencies. It is sub- adequate ventilation occurred even when tidal volumes far below deadspace were
divided into three categories: high
frequency positive pressure ventila- used (Carlo & Chatburn, 1988).
tion (60 to 150 cycles per minute); The major advantage of delivering small tidal volumes is that it can be done at
high frequency jet ventilation (240
to 660 cycles per minute); and high relatively low pressures, greatly reducing the risk of barotrauma. In a recent study,
frequency oscillatory ventilation
(480 to 1,800 cycles per minute). high frequency oscillatory ventilation (HFOV) was compared with conventional
ventilation for pulmonary dysfunction in preterm infants. The outcome resulted
in a reduction in new pulmonary leaks in neonates on HFOV, although there was
high frequency oscillatory no significant difference in mortality rates (Bhuta et al., 2007). Despite the fact
ventilation (HFOV): Ventilation
produced by a piston pump or that HFV offers the advantage of oxygenation and ventilation at a lower risk of
loudspeaker, usually at a frequency barotrauma, it has not been shown to be superior to conventional ventilation, and
between 480 and 1,800/min
its use is often limited to those situations in which conventional ventilation has
failed. It appears to be most useful in treating RDS and pneumonia (Clark, 1994).
It is important to note that although studies regarding the comparison of HFV and

Copyright 2013 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s).
Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.