Matching Ventilatory Support Strategies
to Respiratory Pathophysiology
Anne Greenough, MDa,*,
Steven M. Donn, MDb
aDivision of Asthma, Allergy and Lung Biology, King’s College London,
Children Nationwide Regional Neonatal Intensive Care Centre,
4th Floor, Golden Jubilee Wing, King’s College Hospital,
London SE5 9PJ, UK
bDepartment of Pediatrics, Division of Neonatal–Perinatal Medicine,
C.S. Mott Children’s Hospital, University of Michigan Health System,
1500 E. Medical Center Drive, Ann Arbor,
MI 48109-0254, USA
During the last two decades, new respiratory techniques have become
available to support the neonate. Although these have been actively
researched, many studies have only included prematurely born infants
who have acute respiratory distress. The newborn can suffer from various
diseases, each with a different pathophysiology and impact on lung function.
A term infant who has meconium aspiration syndrome may have over-
distended lungs with high airway resistance, whereas the surfactant-deficient
lungs of prematurely born infants are atelectatic and noncompliant. Thus,
the concept of ‘‘one size fits all’’ can no longer be an appropriate manage-
ment strategy, and the results of studies examining the efficacy of respiratory
support modes that have included only one type of lung disorder may not be
generalized to others.
In this review, the authors discuss respiratory strategies according to
pathophysiology and critically evaluate the evidence, because many of the
studies undertaken have lacked suitable or indeed any comparator controls,
and other randomized trials have been too small to robustly test a clinically
AG has received research grants and/or support to attend meetings from SLE Systems
UK, Draeger Medical, and F. Stephan Biomedical.
* Corresponding author.
E-mail address: email@example.com (A. Greenough).
0095-5108/07/$ - see front matter ? 2007 Elsevier Inc. All rights reserved.
Clin Perinatol 34 (2007) 35–53
Time-cycled, pressure-limited ventilation
Time-cycled, pressure-limited ventilation (intermittent positive pressure
ventilation [IPPV]) has been the most frequently used mode for the
newborn. During IPPV, inflations can be delivered at rates of 30 to 120 bpm;
when rates of 60 bpm or more are used, this is termed high-frequency
positive pressure ventilation (HFPPV). Inspiratory times between 0.3 and
0.5 seconds with a longer expiratory than inspiratory time (giving a physi-
ologic inspiratory/expiratory ratio) are generally used, because these are
similar to spontaneous respiratory times in the preterm infant and more
likely to promote a synchronous interaction and improved gas exchange
[1,2]. If, however, the infant has severe disease, an inspiratory time longer
than the expiratory time is sometimes used (reversed inspiratory/expiratory
ratio) to increase mean airway pressure (MAP) and oxygenation. Positive
end expiratory pressures (PEEP) of 3 to 6 cmH2O are generally employed,
but if the infant has severe disease, the PEEP can be raised as high as
12 cmH2O, again to increase MAP. The relative effectiveness of these
variations, except for comparing different rates (see later discussion),
have usually only been tested in physiologic studies with gas exchange
as the outcome.
Patient-triggered ventilation was reintroduced into neonatal intensive
care in the 1980s, initially as assist/control (A/C) (inflations triggered by ev-
ery spontaneous breath that exceed the critical trigger threshold) and syn-
chronized intermittent mandatory ventilation (SIMV) (only the preset
number of inflations are triggered regardless of the infant’s spontaneous re-
spiratory rate). Newer triggered modes, such as pressure support ventilation
(PSV) and proportional assist ventilation (PAV), are now available. During
PSV, not only the initiation (as with A/C and SIMV), but also the termina-
tion of ventilator inflation are determined by the infant’s spontaneous respi-
ratory efforts by using airway flow changes as an expiratory trigger. Inflation
is terminated when the inspiratory flow level reaches a certain percentage of
peak flow. For example, in PSV mode of the Draeger Babylog 8000 (Draeger
Medical, Luebeck, Germany), inflation is terminated when the flow is re-
duced to 15% of the maximum inspiratory flow, whereas PSV termination
criteria used with the VIP BIRD (Bird Products, Palm Springs, California)
are 5% to 25%, depending on the delivered tidal volume. This is referred
to as flow cycling. During PAV, the applied pressure is servo-controlled
throughout each spontaneous breath, and the frequency, timing, and rate
of lung inflation are controlled by the patient. The applied pressure increases
in proportion to the tidal volume and inspiratory flow generated by the pa-
tient. This can be enhanced to reduce the work of breathing .
GREENOUGH & DONN
volume; this ventilator modality will subsequently be referred to as volume-
changes in the infant’s respiratory compliance and/or efforts; this is achieved
by servo-controlled adjustments in the inflating pressure. The adjustments in
inflating pressure are made in response to differences in the preset and either
the exhaled or inhaled volume. There are different forms of VTV . During
volume-controlled or volume-support ventilation, the desired tidal volume is
selected and the duration of inflation depends on the time taken for the vol-
ume to be delivered, which is adjusted by changes in the inspiratory flow
rate. During Volume guarantee (Draeger Medical, Luebeck, Germany) ven-
tilation, a preset expiratory tidal volume is selected, but the preset inspiratory
time determines the duration of inflation, and the maximum pressure set by
the clinician limits the maximum peak inflation pressure. The desired tidal
volume, however, will not be delivered if the preset peak inspiratory pressure
ventilation, during which the pressure support for any inflation is aborted if
the measured inspired tidal volume exceeds a preset upper limit. During vol-
ume-controlled inflation, there is breath-by-breath servo-controlled flow,
which is constant during inspiration so that the required volume is delivered
over the set inspiratory time. Ventilator manufactures have used different
strategiesto achieve VTV.The SLE 5000(Specialised LaboratoryEquipment
Ltd., UK) and Bear Cub 750 psv (Viasys Healthcare, Palm Springs, Califor-
nia) deliver targeted tidal or volume-limited ventilation, the Draeger Babylog
8000 delivers volume guarantee ventilation, the VIP BIRD and Avea (Viasys
Healthcare, Palm Springs, California) deliver volume-controlled (or volume-
support) ventilation and the Stephanie paediatric ventilator (F. Stephan Bio-
volume guarantee (VG) levels between 4 and 6 mL/kg have been used, but
there is evidence to suggest that the VG level used may be critical to efficacy.
In one study , a VG level of 4 mL/kg with SIMV in the first 48 hours after
of the time. It seems likely that 6 mL/kg may be the most appropriate level. A
level of 6 but not 4.5 mL/kg reduced the duration of hypoxemic episodes
during SIMV in one study , and in another trial, 6 mL/kg compared with
4 or 5 mL/kg was associated with the lowest work of breathing . Both
VTV and VG are described in more detail in other articles in this issue.
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