ventilator management: what does it all mean?

Abstract

Neonatal ventilation has progressed

from a primitive adaptation of adult

ventilatory techniques to its own

science. An understanding of the

fundamental concepts involved is

essential in applying these newer

ventilator modalities to successful care

of the critically ill newborn. A

discussion of pulmonary function and

its application to the newer ventilator

strategies is presented with a historical

approach to the development of the

newer ventilator modalities.

n 2006 Elsevier Inc.

All rights reserved.

Keywords: Ventilation, Neonate,

Pulmonary function

From the Department of Neonatal Medicine,

Pomona Valley Hospital Medical Center, Pomona,

CA; Citrus Valley Medical Center, West Covina, CA;

and Western University Health Sciences, Pomona,

CA.

Address correspondences to Mitchell R. Gold-

stein, MD, FAAP, Department of Neonatal Med-

icine, 1135 South Sunset Ave., Suite # 406, West

Covina, CA 91790.

n 2006 Elsevier Inc. All rights reserved.

1527-3369/06/0602-0137$10.00/0

doi:10.1053/j.nainr.2006.03.003

VentilatorManagement:What Does ItAll Mean?

By Mitchell R. Goldstein, MD, FAAP

The functional differences in the neonatal lung are distinct to the

gestational age of the patient. Term newborn physiology includes a

functional alveolar bed with surfactant function that is not dissimilar to

the adult. The lungs of a 23-week gestation neonate are at a terminal bronchiolar

stage of fetal development in which alveolarization has not yet begun.

Physiologically and structurally, however, the neonate has different needs.

Ventilation must be specifically tailored to the needs of the individual patient.

Conventional mechanical ventilation clearly provides adequate support and

good outcomes for a number of patients but can be the source of barotrauma and

precipitate lung injury in others. Although traditional time-cycled pressure-

limited ventilation has been modified to included strategies to prevent excess

volume generation using newer modes such as Volume Guarantee (VG-Drager),

Pressure Support Ventilation (PSV-Viasys), and Pressure Regulated Volume

Control (PRVC-Maquet), there are still instances where these mechanisms are

insufficient to provide what is needed to prevent lung damage. One must

consider when the baby requires intubation, when conventional mechanical

ventilation should be discontinued, when oscillation becomes necessary, and

when a baby should be extubated.

Noninvasive Ventilation

Early investigations by Gregory and others led to the development of

continuous positive airway pressure (CPAP) for the treatment of respiratory

distress syndrome (RDS).1,2 Continuous positive airway pressure had a major

advantage over previous attempts to ventilate the neonate in that it provided the

necessary pressure to stabilize the airway while limiting the resistance incurred

with the placement of an endotracheal tube. The most challenging part of

delivering CPAP continues to be positioning and maintenance of the CPAP

device. Critics of the use of nasal CPAP (NCPAP) consider it a form of btortureQdespite consistent evidence that it can prevent the occurrence of chronic lung

disease in the most at risk premature populations.3-5 At pressures of 3 to 6 cm

H2O, NCPAP has prevented intubation, excessive periods of ventilation, and

other consequences of chronic ventilation. Nasal CPAP is not a panacea. Rises

in the oxygen requirement and increases in CO2 can indicate developing

atelectasis or excessive work of breathing. These infants may also require

intubation and surfactant where RDS is present. In certain neonatal intensive

care unit environments, NCPAP is much more successful than others.5,6 Recent

studies have demonstrated that the use of CPAP provided through continuous

Newborn and Infant Nursing Reviews, Vol 6, No 2 (June), 2006: pp 79-86 79

Table 1. Pulmonary Function Abbreviations and

Calculations

Vt Tidal volume Volume of air either

exhaled or inhaled

Airway

flow

V Flow of air either exhaled

or inhaled

Airway

pressure

PAW This is determined by

compliance, resistance,

80 Mitchell R. Goldstein

end expiratory ventilator pressure may not be as advan-

tageous as that provided by the bubble devices used in

early studies.7,8 Other devices using humidified high-flow

nasal cannula theoretically simulating CPAP (ie, using a

liter per minute flow without measuring pressure) have not

yet been proven to provide consistent benefit.9 Questions

have been raised about the safety of this mode in the

neonate as well.

tidal volume, and flow rate

VtEXP Expiratory tidal

volume

Volume of air exhaled

VtINSP Inspiratory tidal

volume

Volume of air inhaled

VE Minute ventilation Amount of gas expired over

1 min [RespRate (patient)

� VtEXP (spontaneous)] +

[VentRate �VtEXP (ventilator)]

PTP Transpulmonary

pressure

Pressure exerted on the

lungs to initiate inspiration

PES Esophageal

pressure

Airway pressure exerted on

the esophagus during

inspiration. This will be

diminished when the

endotracheal tube is in

place.

PIP Intrapleural

pressure

Pressure within the pleural

cavity

Kt Time constants Time it takes for pressure to

equilibrate between

proximal airway and

alveoli. Kt = Crs � Rrs

Crs Compliance of the

respiratory system

Elasticity or distensibility

of the lung

Rrs Resistance of the

respiratory system

Capacity of the airway or

lung to resist airflow

KtINSP Inspiratory time

constants

Time to effective delivery

of pressurized gas to level

of alveolus

KtEXP Expiratory time

constants

Time required for alveolus

to empty and recalibrate to

effective PEEP

Pulmonary Function

The newer modes of ventilation are dependent not

only on understanding the basics of bdialingQ in the

numbers but actually being able to read the pulmonary

function scalars and graphics. The ventilator settings

must fit the disease process. An understanding of

pulmonary function is important in any approach to

ventilation.10,11 There are several abbreviations common-

ly used when discussing pulmonary function. Pulmonary

function abbreviations used in this article are defined

in Table 1.

Tidal volume (Vt) monitoring has become a de facto

standard for neonatal ventilation. Inspiratory and expira-

tory tidal volumes should be distinguished. Inspiratory

tidal volume is a gauge of adequacy of spontaneous

ventilation but cannot be used to measure the effective-

ness of mechanical ventilation breaths. Issues of leak and

loss of volume in a compliant ventilator circuit must be

considered carefully. Tidal volume is electronically

integrated from airflow. Airway flow (V) is dependent

on many factors. The physical density of the gas, laminar

nature of the gas flow, and turbulence in the system can

affect the manner in which flow is administered to the

newborn. Airway flow is dependent on the airway

pressure (PAW) delivered over time in producing volume.

Assuming no leak and a noncompliant ventilator circuit,

expiratory tidal volumes are larger than inspiratory tidal

volumes secondary to decompression of the gas, warming

in the tracheobroncheal tree, and humidification (loss of

water). Using different ventilator modalities, VtEXP values

of 2 to 10 mL/kg may be acceptable. Lower values are

common in assisted modes of ventilation and higher tidal

volumes are necessary when only a certain proportion of

breathing is assisted. Particularly, in the premature infant,

5 to 7 mL/kg is considered normal tidal volume.12

Careful monitoring of the Vt along with radiographic

changes can optimize management and minimize over

distention during mechanical ventilation. As the sponta-

neous VtINSP approaches VtEXP of the ventilator, infer-

ences can be made regarding the neonate’s ability to take

over more ventilation and perhaps readiness for extuba-

tion to NCPAP.13

Minute ventilation (VE) is the amount of gas expired

over a minute. This is calculated using VtEXP. Minute

ventilation is defined by:

[RespRate (patient) � VtEXP (spontaneous) + VentRate]� VtEXP (ventilator).

Normal minute ventilation is 250 to 350 mL/kg per

minute. Assist modes of ventilation emphasize the

establishment of normal VE over higher tidal volumes. A

comparison of the contribution of VE from spontaneous

breaths and VE of the mechanical breaths can be useful in

Ventilator Management: What Does It All mean? 81

evaluating the progress of weaning from mechanical

ventilation using the assist modes.

Fig 1. The normal compliance loop in yellow is compared with

decreased compliance loop in blue. This pattern is commonly

seen in RDS. As compliance changes, that is, with surfactan

delivery, the loop will move toward the yellow diagram showing

improved compliance.

Compliance

An understanding of the differences between compli-

ance of the chest wall and the lung is vital to

understanding the principles of mechanical ventilation.

Although no amount of monitoring can substitute for

observation at the bedside, it is critical that there is an

understanding of what exactly is being monitored. There

is a difference between chest wall and total lung

compliance. The overly elastic (compliant) chest wall

can lead the clinician into thinking that the underlying

lung disease is worse than it actually is.14 This, in turn,

can lead to unnecessary ventilation, especially in the

at-risk premature with incomplete ossification of the

chest wall.

Compliance is measured as the lung or tidal volume

over the change in transpulmonary pressure (PTP). Trans-

pulmonary pressure is defined by the difference between

PAW and esophageal pressure (PES) or more accurately

intrapleural pressure (PIP). In the ventilated neonate, this

PES will approach 0 cm. Normal values of compliance

range from 1.3 to 3 mL/cm in neonates.15-22 Lower values

of static compliance have been invariably associated with

extubation failure, whereas high values (z1.3 mL/cm)

were associated with extubation success in 94% of

neonates studied.16 Documentation of an improving

compliance is essential in establishing the appropriate

timing for successful extubation.

Compliance is measured either dynamically or statical-

ly. Static compliance measures the change in pressure as

volume is fixed periodically during decompression.

Dynamic compliance is the slope of the point of end

inspiration and end expiration on the pressure volume

curve. Although it is not truly possible to accurately

describe static changes in pressure with a given volume,

because of its ability to be used continuously in line, there

is less disruption to ventilation. Most conventional

ventilators and conventional pulmonary function monitors

incorporate compliance measures as an enhanced function

set in their newer devices.

Although compliance measures can give a fair

estimation of the adequacy of pulmonary function and

can give a reasonable approximation of the improvement

noted in ventilation after an intervention such as the

administration of surfactant (Fig 1), there are situations

where compliance measurement will not suffice to

complete an understanding of the pathophysiology.

Characteristic of these exceptions to the rule are instances

where the volume displacement of the lung with a given

t

pressure improves beyond its elastic properties and

situations where a worsening compliance fixes the

volume of the lung bregardlessQ of the administered

pressure. Graphically, these situations produce a beaking

of the pressure volume curve with a characteristic bbird’sbeak Q evident in the upper right hand corner of the graph

(Fig 2). Recognition of this pattern is crucial to

avoid unnecessary barotrauma but often cannot be

discerned by measuring tidal volume or compliance

alone.23 In even the most compelling of situations, tidal

volume and compliance can appear normal despite

inordinate pressure administration.

The inspiratory limb and expiratory limb of the

compliance curve differ secondary to changes that have

occurred in the lung resulting in decreased recoil in

expiration. This relationship is referred to as Hooke’s law

and allows ventilation to occur by maintaining volume in

the passively pressurized lung during this phase. If the

lung is allowed to passively deflate, 70% to 80% of the

pressure will be lost within approximately 1 minute. In the

premature infant, with decreased surfactant and concurrent

atelectasis, this process worsens the respiratory symptoms

already seen with RDS.14

Terminal compliance measurement can be used in these

instances to demonstrate where beaking of the pressure

volume curve interferes with the intended ventilation. As

the ratio decreases below 1 and approaches 0, the

excessive pressure is not producing significant volumetric

displacement. Essentially, for the additional pressure cost,

there is no increase in ventilation. A number of the newer

ventilators have incorporated this measure as a guide to

whether the patient is overdistended. This concept may

Fig 2. The upper curve in yellow showed the normal relationship

of volume to pressure. The lower curve in blue shows the

bbeakingQ that is evident with too much pressure. A neonate with

the lower curve without the establishment of adequate ventilation

might be a candidate for high-frequency oscillation.


currently be the most important tool available to clinicians

in avoiding significant barotraumas.23

Resistance

An understanding of resistance is also important to

modern ventilation techniques. An elevated resis-

tance is a major contributor to work of breathing in

neonates. Flow itself may be laminar or turbulent. Laminar

flow is simpler to analyze than turbulent flow. Turbulent

flow occurs with high flow rates, decreases in the diameter

of the airway or endotracheal tube, angulation of the

endotracheal tube in the airway, and/or the normal

branching that occurs in the developing lung.

Total (airway + tissue) respiratory resistance values for

normal neonates range from 20 to 40 cm H2O/L per

second; 50 to 150 cm H2O/L per second is commonly seen

in intubated neonates.24 The increased resistance encoun-

tered during intubation must be taken seriously in the

evaluation of the weaning neonate. Excessively small

endotracheal tubes can worsen the appearance of respira-

tory distress. A less than optimal tube position can produce

dramatic increases in resistance. Higher than necessary

flow rates introduced through the ventilator produce

turbulent flow patterns, higher resistance, and concomitant

increased work of breathing.

Laminar flow is governed by Poiseuille law. Halving

the radius of a tube will increase the resistance by 16

times. With laminar flow, the drop of pressure is related to

the flow rate, and so the bresistanceQ of a tube is inde-

pendent of the flow. Turbulent flow is inherently more

variable because resistance varies with flow. At any given

flow, the pressure change is proportional to the fifth power

of the radius (the Fanning Equation). The implications for

ventilation are clear. The largest possible endotracheal tube

that can be placed bsafely Q should be used. Excessive tube

leak compromises even the best flow compensation

systems, can lead to falsely elevated resistance measure-

ments, and prevent consideration of extubation due to a

falsely elevated work of breathing.

Time Constants

Time constants (Kt) are an important but often

neglected concept and are derived by multiplying

the compliance of the respiratory system (Crs) by the

resistance of the respiratory system (Rrs). This is

expressed as Kt = Crs � Rrs. KtINSP is the time to

effective delivery of the pressurized gas to the level of the

alveolus. KtEXP is the time required for the alveolus to

empty and recalibrate to the effective PEEP. Using a

statistical model and an assumption of uniform lung

compliance, 3*Kt will give a time equivalent at which

point 95% of the alveoli will have equilibrated. Normal

values of Kt are 0.12 to 0.15 seconds. Given a resistance

of 0.1 mL/cm H2O, inspiratory time should generally not

be set longer than 0.36 to 0.45 seconds to minimize the

potential for gas trapping and optimize transmission of

ventilation breaths.25 If the inspiratory time is too short (ie,

less than the time constant), modes of ventilation that

feature breath termination can produce atelectasis and

ventilator failure.

Recoil

As a final step in the approach of modern ventilation

techniques, it is important to understand the different

lung volumes and capacities involved in conventional

ventilation and the normal breathing process. FRC is the

volume of gas in the lung after a normal expiration. The

FRC is determined by the balance between the inward

elastic recoil of the lungs and the outward recoil of the

thoracic cage. FRC decreases with paralysis and anesthe-

sia. FRC for normal infants was measured in one study on

days 1, 2, and 3 and were 2.0 F 0.3, 2.1 F 0.3, and 2.2 F0.3 mL/cm, respectively. For infants with meconium

aspiration, these values were 1.8 F 0.4, 2.3 F 1.1, and

2.2 F 0.6 mL/cm, respectively.22 An FRC that is

inadequate suggests that part of the work of ventilation

is being devoted to open atelectatic areas of lung that do

not have enough pressure during end expiration to prevent

collapse. This relationship can be visualized on a pressure


volume curve. An inspiratory baseline that is flat almost to

the point of end inspiration is suggestive of inadequate

PEEP and FRC that has not been optimized. An FRC that

exceeds normal can also be visualized as an overly flat

compliance curve despite the clinical appearance of

ventilation improvement.26

As discussed earlier, PAW is the mean pressure

measurement in the airway. Whereas spontaneous breaths

incur a negative flow on scalar tracings, ventilator breaths

are associated with a pressure cost of ventilation and thus

a positive scalar tracing. Pressure measurements can be

used to generate compliance and resistance measures,

which can be important in determining the ventilation

modality with the least pressure cost of ventilation.27

Mean airway pressure is the average of PAW throughout

the entire respiratory cycle. This correlates with mechan-

ical breath tidal volume and PEEP level. The upper limit

of Mean PAW is generally 10 to 15 in the conventionally

ventilated neonate.

State of the Science

The concept of modern ventilation for the neonate

distinguishes itself from previous technologies, not

merely in terms of the different modes of ventilation that

are available for the clinician to choose from, but in the

availability of conceptual pulmonary function monitoring

and in vivo testing that was previously only estimated

radiographically and by blood gas analysis. Early attempts

at intermittent positive pressure ventilation (IPPV) were

confounded by an inability to maintain an adequate FRC

and the resultant barotrauma from requisite reexpansion of

atelectatic areas of the lung with each ventilation. Volume

mode ventilation was used in the early stages of the

development of neonatal ventilation. Overly compliant

tubing, excessive circuit leaking, and equipment designed

primarily for the adult market relegated this modality to

the back shelf for generations of neonates. A significant

improvement in technology was the innovation of inter-

mittent mandatory ventilation (IMV). The concept of

continuous PEEP with flow by ventilation not only

minimized the work of breathing but also prevented

significant atelectasis from occurring with the 0 cm PEEP

modus operandi of IPPV.28,29

Even with this improvement, significant lung morbid-

ities continued to occur. Chronic lung disease was

common in the pre-surfactant era. Morbidities such as

pulmonary interstitial emphysema, pneumothorax, and

bronchopulmonary dysplasia were expected consequences

of extended ventilation. Prophylactic chest tube placement

was a real consideration. The concept of breath-to-breath

monitoring was not the expected norm. Pulmonary

function testing was a curiosity that occurred in only the

most sophisticated centers on an intermittent basis. Even

then, the pneumotachographs were adaptations of adult

models. The dead space of these devices could exceed the

lung volume. At issue was the concept that IMV

represented the evolved state of the art. Patient synchro-

nized ventilation was a concept that might be successful in

the adult world with cuffed endotracheal tubes and

minimal expected tube leak. Issues involved in measuring

low flow rates and the difficulty in preventing auto cycling

were paramount with respect to the obstacles faced in

developing these devices.

The initial synchronized ventilators for neonates were

based on impendence and pressure-driven mechanisms

such as the Greysby capsule (a small pressure capsule the

size of a dime that was taped to the chest wall). The

devices were continuous flow, pressure-limited time-

cycled ventilators. The major difference between these

devices and traditional IMV was that a synchrony signal

passing from the pressure capsule could trigger the

generation of a breath from the ventilator. A fixed

inspiratory time was given and the delivered pressure

was determined by the ventilator. The effectiveness of the

synchronization was determined by the placement of the

capsule. Inadvertent motion, seizures, or hiccoughs could

jeopardize the synchrony of ventilation. In the worse case

situation, the ventilation could be delivered 1808 out of

phase, with inhalation synchronized during the expiration

process. The ventilator breath could not be terminated. A

tachypneic baby could attempt to breathe during expira-

tion, resulting in increased work of breathing. Pulmonary

function monitoring was not built into the ventilator.

Adjunct devices were introduced to measure tidal volumes

and generate flow and pressure scalars. Even with the best

possible pulmonary function monitoring, a discerning eye

was necessary to distinguish when appropriate position of

the capsule had been achieved. Flow delivery was

mediated by solenoid valves. The flow signature of these

ventilators were largely square shaped providing that flow

had been set adequately to generate the set pressure limit.

Higher flows were imprudent but did not produce as much

turbulence as might be expected because of this mecha-

nism. An assist control mode was also available but was

inhibited by an inability to adequately terminate breaths.

Stacking of breaths was common in assist control mode

and produced the potential for inadvertent PEEP and

subsequent barotrauma. Studies of this device indicated

improved patient tolerance and suggested that less sedation

was required for patients on this modality of ventilation

but failed to produce a discernable improvement in

outcome measures. Flow synchronization characteristic

of the newer ventilation modalities was limited to a

demand mode, which would allow a predetermined flow


increase during inspiration but did not provide for a

mechanism to terminate the breath.

Newer ventilators use sophisticated pneumotacho-

graphs to measure flow directly at the patient wye.

Relative to older synchronization techniques, flow sens-

ing allowed for better and faster breath tracking and gave

rise to the possibility of enhanced patient control of

ventilation.30,31 Ventilators produced by Viasys, Maquet

(formerly Servo), Drager, and Puritan-Bennett have all

incorporated some of the newer modalities of flow

control. One of the more popularly used is PSV. Unlike

simple time-cycled pressure-limited SIMV, PSV has no

fixed inspiratory time. The PEEP is set along with a level

of pressure support (PS). It is important to remember that

the level of PS is not equivalent to the PIP commonly

seen in the previous generation of ventilators. The peak

pressure is equivalent to the PEEP + PS. The patient

determines the respiratory rate in certain modes and can

terminate breaths with expiratory effort or as a function of

percent of positive pressure in others. Volume guarantee

(VG) is another commonly used mode. Within set

pressure parameters, breath volume is adjusted based on

the changing compliance of the lung. PIP is adjusted

downward bautomatically.Q More sophistication and con-

trol is possible with adjustments to the flow, which can

help establish a decelerating flow pattern, prevent

excessive acceleration in the inspiratory flow pattern,

and prevent inadvertent auto cycling.32,33

Volume or volume-limited ventilation is now practi-

cal. Before the introduction of proximal flow sensing,

volume-targeted ventilation was impractical. Neonatal

endotracheal tubes are uncuffed often resulting in airway

leaks. In previous volume ventilation modalities, predic-

tion of expiratory leaks around the tube was not

possible. Attempts to measure tidal volumes at the valve

inside the ventilator were uncertain because of compli-

ance changes in the ventilator tubing itself. Again

beginning with a set PEEP, the desired tidal volume is

selected (usually 4-6 mL/kg per breath for premature

infants and as much as 8-10 mL/kg per breath for term).

Enhanced computer-automated predictive models of

ventilation have effective leak compensation. Avoidance

of barotrauma may be possible as btoxicQ pressure levels

are not generated.34,35

High-frequency ventilation was introduced to neona-

tology in the late 1970s. The initial high-frequency trials

were less than encouraging. Data suggested that these

devices did not significantly improve ventilatory outcomes

and might increase the risk of intraventricular hemor-

rhage.36 Progress in acceptance of the devices over the

course of the ensuing years occurred with the recognition

that intervention strategies and normalization of lung

expansion were more efficacious than rescue strategies

that relied on the adequacy of an initial conventional

ventilation strategy to avoid the pitfall of barotraumas and

atelectasis inherent in the earlier research.37 Today, this

ventilatory strategy is in wide use. High-frequency

ventilators can be divided into three classes: true oscil-

lators, jet ventilators, and flow interrupters.

In the United States, the Sensormedics 3100A is the

only true oscillator in clinical use. It has FDA indications

for first intent ventilation as well as rescue strategies.

Research conducted by deLemos et al established the

superiority of these devices over conventional IMV

ventilation in the avoidance of barotrauma-based lung

injury.38-41 In the neonatal age group, ventilation is

established by the selection of a mean airway pressure

adequate to produce a satisfactory FRC (chest radiograph

expanded to 9-10 ribs), frequency selection generally

between 8 and 15 Hz (breaths per second), and amplitude

(pressure distance of the breath from the baseline pressure

in inspiration and expiration). Amplitude selection is

generally clinically based on finding a value that will

produce an badequateQ chest wiggle. Although the

inspiratory time can be adjusted, it is usually fixed at

0.33 or 33% of the entire cycle. The active expiratory

mode, which accounts for 66% of the ventilator cycle, is

important in the rapid elimination of CO2.42

The Bunnell Life Pulse High-Frequency bJet Q Ventila-tor provides small high-frequency breaths using passive

instead of active ventilation. Breaths per minute can be set

from 240 to 660. Amplitude is replaced by PIP selection.

Unlike the oscillator, the Jet relies on passive exhalation

for ventilation. In certain circumstances, the Jet may allow

the selection of a lower mean airway pressure and

avoidance of bchokeQ points, which can occur with higher

amplitudes with high-frequency oscillation. The Jet is used

in coordination with conventional ventilators to facilitate

the transition from conventional ventilation. Both high-

frequency and conventional mode ventilation can be active

simultaneously. The Jet has been used extensively for

rescue in the prevention and amelioration of air leak. As a

first intent ventilator, the Jet may offer certain advantages

as well.43,44

Of historical interest is the InfantStar high-frequency

flow interrupter. Although support for this ventilator has

all but been discontinued, the InfantStar is still in

widespread use in many neonatal units. Its main advantage

over other modalities was its flexibility. The ventilator

could be used for nasal CPAP, SIMV ventilation, as well as

high frequency. The oscillatory effect is produced by

solenoid valves interrupting airflow at the preselected rate,

generally between 8 and 14 Hz. Amplitude is adjusted in

the same way as HFOV. The InfantStar does not rely on

an active expiratory phase (similar to the Jet). Compared

with the other devices available, the InfantStar was less


powerful, had fewer features, and had more from

amplitude drift; however, its ease of use established it as

the only high-frequency device in many neonatal intensive

care units until recently.45

Conventional ventilation of the neonate has progressed

in sophistication over the years. From the early makeshift

adaptation of adult ventilators and ventilator strategies,

neonatal ventilation has gradually progressed to a science

of its own. Early volume mode ventilation strategies gave

way to IPPV, which was subsequently supplanted by IMV

mode ventilation. Newer modalities including high fre-

quency ventilation or PSV offer even more possibility for

improved outcomes.46

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