Content uploaded by Samir Gupta
Author content
All content in this area was uploaded by Samir Gupta on May 09, 2016
Content may be subject to copyright.
Review
Continuous positive airway pressure: Physiology and comparison of
devices
Samir Gupta
a
,
*
, Steven M. Donn
b
a
Department of Paediatrics, University Hospital of North Tees and University of Durham, Stockton-on-Tees, UK
b
Department of Pediatrics, Division of NeonatalePerinatal Medicine, C.S. Mott Children's Hospital, University of Michigan Health System, Ann Arbor, MI,
USA
Keywords:
Continuous positive airway pressure (CPAP)
Bubble CPAP
Preterm
Ventilation
Infant Flow
®
driver
Device
summary
Nasal continuous positive airway pressure (CPAP) is increasingly used for respiratory support in preterm
babies at birth and after extubation from mechanical ventilation. Various CPAP devices are available for
use that can be broadly grouped into continuous flow and variable flow. There are potential physiologic
differences between these CPAP systems and the choice of a CPAP device is too often guided by individual
expertise and experience rather than by evidence. When interpreting the evidence clinicians should take
into account the pressure generation sources, nasal interface, and the factors affecting the delivery of
pressure, such as mouth position and respiratory drive. With increasing use of these devices, better
monitoring techniques are required to assess the efficacy and early recognition of babies who are failing
and in need of escalated support.
©2016 Elsevier Ltd. All rights reserved.
1. Introduction
Continuous positive airway pressure (CPAP) is the most
extensively studied non- invasive respiratory support technique in
preterm babies. It has been tested as a primary form of respiratory
support and as continuing support after extubation from me-
chanical ventilation. The rationale for the use of CPAP is to stent
the airways and to maintain functional residual capacity (FRC).
The mechanism of action is multifactorial and includes an in-
crease in the pharyngeal cross-sectional area, improvement in
diaphragmatic activity, enhanced pulmonary compliance, and
decreased airway resistance. The end result is a reduction in the
work of breathing and conservation of surfactant on the alveolar
surface.
CPAP works by delivering continuous distending pressure (CDP)
using an air/oxygen mixture and a device to generate the CDP. The
method of generating nasal CPAP (nCPAP) differs among devices
but may be broadly grouped into two main types: “variable flow”or
“continuous flow.”For example, the Infant Flow
®
driver (IFD) is a
variable-flow device and bubble CPAP (bCPAP) is a continuous-flow
device [1]. In this article we discuss the physiologic effects of CPAP,
factors affecting delivery of CPAP, and the evidence comparing
various types of CPAP devices.
2. Respiratory physiology and CPAP
The full physiologic mechanism by which CPAP improves res-
piratory function in newborns is incompletely understood. During
spontaneous breathing, CPAP augments the driving pressure
required to overcome the elastic, flow-resistive, and inertial prop-
erties of the respiratory system. This is achieved by changes in
intra-pleural pressure normally generated by the respiratory
muscles that help to maintain FRC [2].
The very compliant chest wall and paradoxical inward rib-cage
motion in very premature newborn infants result in lowered FRC
that may result in airway closure, alveolar atelectasis, and ven-
tilationeperfusion mismatch. In response, the infant tries to elevate
the FRC above the relaxation volume by generation of intrinsic end-
expiratory pressure through an increase in the tonic activity of the
diaphragm, a higher than normal respiratory rate, and laryngeal
braking or glottic closure during expiration. Positive pressure
applied to the airway helps to support the infant's own effort to
increase FRC. Physiologic studies suggest that CPAP, by increasing
end-expiratory lung volume, stabilizes the highly compliant chest
wall, thereby improving pulmonary mechanics and thoraco-
abdominal synchrony [3].
*Corresponding author. Address: Research &Development, University Hospital
of North Tees, Stockton-on-Tees, Cleveland TS19 8PE, UK. Tel.: þ44 1642 624232.
E-mail address: Samir.gupta@durham.ac.uk (S. Gupta).
Contents lists available at ScienceDirect
Seminars in Fetal & Neonatal Medicine
journal homepage: www.elsevier.com/locate/siny
http://dx.doi.org/10.1016/j.siny.2016.02.009
1744-165X/©2016 Elsevier Ltd. All rights reserved.
Seminars in Fetal & Neonatal Medicine xxx (2016) 1e8
Please cite this article in press as: Gupta S, Donn SM, Continuous positive airway pressure: Physiology and comparison of devices, Seminars in
Fetal & Neonatal Medicine (2016), http://dx.doi.org/10.1016/j.siny.2016.02.009
The upper airway also plays an important role in the respiratory
mechanics of the premature infant. The increased flexibility of the
epiglottis and the laryngeal cartilage, and the decreased connective
tissue support of the upper airway structures predispose the infant
to partial or complete airway obstruction during regular breathing.
The more cephalad position of the larynx further exacerbates upper
airway resistance. CPAP may produce mechanical splinting of the
upper airway by increasing its cross-sectional area and preventing
collapse of the lateral pharyngeal walls. This, in turn, decreases the
resistance to gas flow (Box 1).
Respiratory inductance plethysmography (RIP) has been used to
study the effects of various CPAP systems by measuring the
thoraco-abdominal synchrony, tidal volume, and FRC. Evidence
from RIP studies suggests that the application of CDP from CPAP
results in increased end-expiratory lung volume. However, RIP has
some limitations, as it does not equate to an absolute level of FRC,
and the validity of the changes in FRC apply only when the body
posture is maintained during measurements. The level of CPAP also
dictates the FRC. Excessive CPAP may be deleterious by increasing
work of breathing, causing a fall in tidal volume, and by producing
adverse cardiovascular effects.
2.1. CPAP and the upper airway
nCPAP of 5 cmH
2
O is effective in abolishing mixed or
obstructive apnea, but has little or no effect on central apnea [4].
Miller et al. studied the manner in which CPAP exerts this selective
effect on apnea accompanied by supraglottic airway obstruction.
They studied 10 infants with a history of apnea at a postconcep-
tional age of 34 ±2 weeks (birth weight 1321 ±310 g) post extu-
bation. The CPAP was applied by nasal mask and pressures were
recorded in the mask, oropharynx and esophagus. nCPAP between
0 and 5 cmH
2
O correlated with the oropharyngeal pressure
(r¼0.94). The supraglottic resistance decreased from 46 ±29 to
17 ±16 cmH
2
O/L/s (P<0.005) during uptitration of CPAP from 0 to
5 cmH
2
O. The decrease in supraglottic resistance was observed
both during inspiration and expiration, accounting for 60% of the
change in total pulmonary resistance at CPAP of 5 cmH
2
O[5]. The
supraglottic airway of apneic infants thus appears to be a potential
site of high resistance during sleep, as simple flexion of the neck
may produce airway obstruction.
2.2. Effect of mouth position
The effect of mouth position on pharyngeal pressure was shown
by DePaoli et al. in preterm infants receiving bubble CPAP (bCPAP)
with the mouth open and closed. They studied 11 infants at a
median postnatal age (interquartile range) of 14 (12e46) days and
at a mean (SD) corrected gestation of 30.6 (1.9) weeks. bCPAP with
binasal Hudson prongs at CPAP 3e8 cmH
2
O was utilized. They re-
ported a mean (95% confidence interval (CI)) pressure fall from
prongs to pharynx of 3.2 (2.6e3.7) cmH
2
O with the mouth open,
and 2.2 (1.6e2.8) cmH
2
O with the mouth closed. The mean differ-
ence in pharyngeal pressure between open and closed mouth po-
sitions was 1.1 (0.7e1.4) cmH
2
O(P<0.05) [6].
2.3. Effect of CPAP on breathing pattern
The high chest wall:lung compliance ratio of premature new-
borns tends to reduce the passive resting volume of the respiratory
system to a level that is close to airway closing volume. The end-
expiratory lung volume of premature newborns is maintained
above passive resting lung volume during active breathing through
the combination of an increased time constant and a high respi-
ratory rate. This is achieved by the persistence of inspiratory muscle
activity during the expiratory phase and adduction of the vocal
cords during expiration, which prolong the time constant of the
respiratory system by decreasing inspiratory resistance. In addition,
the high breathing rate decreases the expiratory time with
incomplete emptying of the lungs. These two mechanisms
dynamically elevate the end-expiratory lung volume [7]. The dy-
namic elevation of FRC occurs when the expiratory time is <3 time
constants.
nCPAP is believed to benefit preterm infants with respiratory
distress. It improves respiratory function by splinting the upper
airway, improving the synchrony of thoracic and abdominal motion
[8], and increasing end-expiratory lung volume [9].
2.4. Effect of different levels of CPAP
Elgellab et al. studied different levels of CPAP (0, 2, 4, 6, and 8
cmH
2
O) to determine its effect on breathing patterns and changes
in lung volumes, using RIP. They observed an increase in end-
expiratory lung volume (EELV) by 2.1 ±0.3 tidal volume (V
t
)as
the CPAP level was increased from 0 to 8 cmH
2
O(P<0.01). Tidal
volume also increased by 43% (P<0.01), and the phase angle
decreased from 76% to 30% (P<0.01) when CPAP was increased
from 0 to 8 cmH
2
O(Fig. 1). They concluded that nCPAP improves
the breathing of premature infants with respiratory failure through
improved thoraco-abdominal synchrony, increased tidal volume,
and a reduced labored breathing index [10].
Magnannent et al. reported a dynamic elevation of FRC with
nCPAP, and the spontaneous volume-preserving expiratory flow-
Box 1
Physiologic effects of continuous positive airway pressure.
Abolition of upper airway occlusion and decrease in up-
per airway resistance
Increased diaphragmatic tone and contractility
Improvement in lung compliance and reduction in airway
resistance
Increased tidal volume of the stiff lung with low functional
residual capacity
Improved ventilation/perfusion and reduction in oxygen
requirement
Conservation of surfactant on alveolar surface and
reduction of alveolar edema
Fig. 1. Lissagous figures and phase angles (degree) at various nasal continuous positive
airway pressure (NCPAP) levels. As the nasal CPAP level increased there was
improvement in rib cage (chest) movement and decrease in phase angle, i.e. thoraco-
abdominal asynchrony. RC, rib cage; AB, abdominal wall. (Adapted from Elgalleb et al.
[10].)
S. Gupta, S.M. Donn / Seminars in Fetal & Neonatal Medicine xxx (2016) 1e82
Please cite this article in press as: Gupta S, Donn SM, Continuous positive airway pressure: Physiology and comparison of devices, Seminars in
Fetal & Neonatal Medicine (2016), http://dx.doi.org/10.1016/j.siny.2016.02.009
braking mechanisms normally present in preterm infants with
respiratory distress were not required during CPAP therapy. This
conclusion was based on the decreased phase angle changes be-
tween the abdominal and thoracic compartments and increased
tidal volume during nCPAP [11].
As there is a direct relationship between the nCPAP the EELV, a
theoretical risk of overdistension exists in preterm infants at higher
CPAP levels. If high nCPAP levels result in hyperinflation of the lung,
this may have deleterious effects by causing a decrease in compli-
ance, thoraco-abdominal asynchrony, and placing the diaphragm at
a mechanical disadvantage. Interestingly, in the study by Elgalleb
et al. [10] using IFD CPAP, one infant exhibited worsening respira-
tory failure at a CPAP of 8 cmH
2
O. This raises the question of what is
the optimum nCPAP level and suggests variability between
continuous and variable flow devices.
The outcome of different levels of CPAP in clinical situations
depends not only upon the type of CPAP used, but also upon the
severity of underlying lung disease [12].
3. Methods of generating CPAP
CPAP is derived from either continuous or variable gas flow.
Continuous-flow CPAP consists of gas flow directed against the
resistance of the expiratory limb of the breathing circuit. Ventilator-
derived CPAP and bubble or water-seal CPAP are examples of
continuous-flow devices. In variable-flow CPAP, pressure is gener-
ated at the airway proximal to the infant's nares and uses the
Bernoulli effect to alter the gas flow to maintain constant pressure.
3.1. Variable-flow CPAP
3.1.1. Infant Flow Driver (IFD)
The Infant Flow CPAP system™(Electro Medical Equipment Ltd,
Brighton, UK; Infant Flow
®
SiPAP System, CareFusion
®
, San Diego,
USA) is an example of variable-flow CPAP. It uses a dedicated flow
driver and gas generator with a fluidic-flip mechanism to deliver
variable flow (Fig. 2). The principle of IFD CPAP is the Bernoulli
effect, which directs gas flow towards each naris, and the Coanda
effect to cause the inspiratory flow to flip and exit the generator
chamber via the expiratory limb. This may assist spontaneous
breathing and reduce the work of breathing by decreasing expira-
tory resistance and maintaining stable airway pressure throughout
respiration [13]. CPAP may be delivered with binasal prongs or a
nasal mask.
3.1.2. Benveniste gas-jet valve CPAP
This is an alternative variable-flow system. The device consists
of two coaxially positioned tubes connected by a ring. It works via
the Venturi principle to generate pressure. It is connected to a
blended gas source and then to the patient via nasal prongs,
generating variable-flow CPAP [14].
3.2. Continuous-flow CPAP
3.2.1. Bubble CPAP
Underwater or bCPAP or water-seal CPAP is a continuous-flow
system. It was first described in 1914 and has been in use since
the early 1970s (Fig. 3)[15]. Blended gas is heated and humidified
and delivered to the infant through a secured low-resistance nasal-
prong cannula. The distal end of the expiratory tubing is submersed
and the CPAP generated is equal to the depth of submersion of the
expiratory limb. Chest vibrations produced by bCPAP may
contribute to gas exchange [16].
3.2.2. Ventilator-derived CPAP (conventional CPAP)
Ventilator-derived CPAP is another way of providing continuous
flow CPAP. The CPAP is increased or decreased, in general, by
varying the ventilator's expiratory orifice size. The exhalation valve
works in conjunction with other controls, such as flow and pres-
sure, to maintain the desired CPAP.
3.2.3. CPAP interface
The interfaces currently used for the delivery of nCPAP include
single and binasal prongs in short (6e15 mm) and long
(40e90 mm) versions. Short binasal prongs include Hudson,
Argyle, INCA, and those used with IFD and Bubble CPAP (Fisher &
Paykel, Auckland, New Zealand), and examples of long CPAP prongs
are nasopharyngeal tubes, endotracheal tubes, and Duotube.
In addition, nasal masks are available for use with CPAP systems.
The older CPAP interfaces such as endotracheal tubes, head
chambers (head boxes), face chambers, and full face masks are now
obsolete. Nasal cannulas are also used to deliver air/oxygen and at
high flows can provide CDP.
Evidence comparing nasal interfaces is sparse. Davis et al.
compared binasal short Hudson prongs with a single long prong
(Portex size: 2.5 or 3.0 mm, inserted to 2.5 cm). They randomized
87 infants before extubation to one of the two CPAP interfaces
connected to the ventilator to provide nasal CPAP. This trial was
stopped early before achieving the target sample size of 130.
There was a significantly lower incidence of respiratory failure
within seven days post extubation with short binasal prong use,
but no differences in other outcomes [17]. Roukema et al. also
compared short binasal prongs with nasopharyngeal prongs and
reported a lower rate of reintubation with the use of short prongs
[18]. This trial used different CPAP devices, thus making the
interpretation difficult. In the trial by Mazzela et al., short binasal
Fig. 2. Infant Flow Driver pressure generator. The variable-flow generator uses the Bernoulli principle via injector jets directed toward each naris; Venturi action allows the infant to
draw additional gas flow through the injector jets from either the gas supply or exhalation tube reservoir. The dual-jet variable flow generator utilizes fluidic technology to deliver a
constant continuous positive airway pressure.
S. Gupta, S.M. Donn / Seminars in Fetal & Neonatal Medicine xxx (2016) 1e83
Please cite this article in press as: Gupta S, Donn SM, Continuous positive airway pressure: Physiology and comparison of devices, Seminars in
Fetal & Neonatal Medicine (2016), http://dx.doi.org/10.1016/j.siny.2016.02.009
prongs and nasopharyngeal prongs were used, but the outcomes
were not assessed beyond 48 h, and again the CPAP devices were
different [19]. In the meta-analysis of the studies, De Paoli et al.
concluded that short binasal prongs are more effective in
reducing the rate of reintubation [20]. Another trial compared
nasal prongs and nasal masks for delivering IFD CPAP in 120
babies <31 weeks of gestation. Mask nCPAP was more effective
than nasal prong CPAP for preventing intubation within 72 h of
starting therapy [21].
The pressure fall through various CPAP devices may differ ac-
cording to the design, length, and the physical principle used for
CPAP generation. De Paoli et al. compared resistances of different
devices in vitro for delivery of nCPAP in neonates. They studied
different devices at a flow of 4e8 L/min, and measured the resul-
tant fall in pressure using a calibrated pressure transducer. They
concluded that devices with short binasal prongs had the lowest
resistance to flow, and suggested that a large variation in pressure
could occur in the clinical setting [22].
4. Effect of bubbling on CPAP
The gas flow rate during bCPAP has been observed to affect the
degree of bubbling. Bubbling may enhance gas exchange by deliv-
ering low-amplitude, high-frequency oscillations to the lungs.
Lee et al. observed vibrations of the chest secondary to vigorous
bubbling while babies were receiving bCPAP. They tested this in a
crossover design in 10 preterm babies ready for extubation to
determine whether bCPAP results in better gas exchange than
ventilator-derived CPAP. They measured tidal volume, minute vol-
ume, respiratory rate, pulse oximetry, and transcutaneous carbon
dioxide. They reported a 39% reduction in minute volume
(P<0.001) and a 7% reduction in respiratory rate (P¼0.004) with
no change in oxygenation or ventilation. They concluded that the
chest vibrations produced by bCPAP might have contributed to gas
exchange [16]. This study has been widely cited, but was done in
the group of babies who had recovered from acute lung disease
nearing extubation and in larger babies with a mean corrected
gestational age of 30.7 ±1.8 weeks and mean weight of
1350 ±390 g. In addition, there appears to be an arithmetic error in
the calculation of minute ventilation, inadvertently favoring
ventilator-derived CPAP.
Morley et al. further studied the physiologic effects of bubble
CPAP. They enrolled 26 babies at a median gestational age of 27
weeks (range 24e32) and a birth weight of 1033 g (range
604e1980). The nCPAP was used at 6 cmH
2
O (range 5e9). The
baseline gas-flow rate was kept at 6 L/min (range 5e9), and the
inspired oxygen at 0.21 (range 0.21e0.30). The median (inter-
quartile range) pressure amplitude was 2.7 cmH
2
O (2.5e4.0) for
slow bubbling (at 3 L/min) and 6 cmH
2
O (4.6e7.1) for vigorous,
high-amplitude bubbling (at 6 L/min). They also reported slightly
lower (effective CPAP) pressure with slow bubbling compared to
vigorous (5.28 vs 5.98 cmH
2
O; P<0.001). They did not observe any
effect of bubbling on transcutaneous carbon dioxide, oxygen satu-
ration, respiratory rate, or minute ventilation [23].
Pillow and Travadi hypothesized that superimposing noise on
the underlying constant pressure in bCPAP may promote lung
volume recruitment and reduce intrinsic work of breathing. In an
in-vitro model, they examined how lung compliance and applied
flow altered the frequency and magnitude of the oscillatory
component of bCPAP. They concluded that in a closed system,
increasing flow increased both the mean pressure and the range of
pressure oscillations, whereas decreasing compliance increased the
frequency and magnitude of the transmitted oscillations. They
suggested that the use of bCPAP in a poorly compliant lung may
promote lung volume recruitment through stochastic resonance
and augment the efficiency of gas mixing [24]. This study has
limitations of an in-vitro model with no leak and the amplitude of
transmitted oscillations may be greater than that observed in a
clinical situation. However, some reports of visible chest vibrations
have been reported in vivo with bCPAP.
In another study, Pillow et al. compared constant-pressure CPAP
with bCPAP in a lamb model. They hypothesized that bCPAP en-
hances volume recruitment in the newborn preterm lung. They
compared various physiologic parameters among three study
groups in 32 lambs; bCPAP at 8 L/min flow (n¼10), constant-
pressure CPAP (n¼12), and bCPAP at a flow of 12 L/min (n¼10).
Flow did not influence 3 h outcomes in the bCPAP groups. The
bubble technique was also associated with a higher PaO
2
, oxygen
uptake, and area under the flow-volume curve, and a decreased
alveolar protein, respiratory quotient, PaCO
2
, and ventilation ho-
mogeneity compared to the constant-pressure group. They
concluded that bCPAP promotes airway patency and may offer
protection against lung injury [25].
Kahn et al. compared delivered to intended intra-prong, prox-
imal-airway, and distal-airway pressures using ventilator CPAP and
bCPAP devices. They repeated measurements at five flow rates (4, 6,
Fig. 3. Continuous-flow positive airway pressure (CPAP) system. ETT, endotracheal tube.
S. Gupta, S.M. Donn / Seminars in Fetal & Neonatal Medicine xxx (2016) 1e84
Please cite this article in press as: Gupta S, Donn SM, Continuous positive airway pressure: Physiology and comparison of devices, Seminars in
Fetal & Neonatal Medicine (2016), http://dx.doi.org/10.1016/j.siny.2016.02.009
8, 10, and 12 L/min) and three nasal CPAP pressure levels (4, 6, and 8
cmH
2
O) under no, small, and large leak conditions. The authors
concluded that the self-adjusting capability of ventilators allows
closely matched actual versus intended ventilator CPAP levels. For
bCPAP, at the range of flows used clinically, there were higher intra-
prong and intra-airway bCPAP pressures at increasing flows than
operator-intended levels, even when an appreciable leak was pre-
sent [26].
The conflicting results discussed above highlight the need for
standardization of clinical practices. These pressure, flow, and
bubbling dynamics are very complex, and the in-vivo delivery of
CPAP is dependent upon many other factors, including the severity
of lung disease and the individual patientedevice interaction.
5. Work of breathing and choice of CPAP
Although the initial use of nasal CPAP in preterm infants utilized
the continuous-flow underwater device promoted by Gregory et al.
in 1971 [15], there has been a wide variation in the choice of de-
vices, especially since the introduction of variable flow first
described by Moa et al. in 1988 [13].
Although the advantages of nCPAP on decreasing the work of
breathing are well established, efforts to optimize CPAP delivery
continue. Recent studies compared the work of breathing using
variable versus continuous flow CPAP. The initial study of Moa et al.
on a lung model claimed that despite a virtually constant pressure
within the traditional CPAP system, variations in mean airway
pressure and external workload were considerably less with the
variable-flow device, which was also reported to be less sensitive to
airway leakage [13].
Klausner et al. compared work of breathing between a variable
and continuous flow device. They observed an imposed work of
breathing with IFD CPAP of 0.135 mJ/breath (95% C ±0.004)
compared to 0.510 mJ/breath (95% CI ±0.004) with conventional
CPAP (difference P<0.01) and concluded that imposed work of
breathing with variable flow was approximately one-fourth that of
the continuous-flow system [27].
6. Studies comparing variable-flow and continuous-flow
devices
Multiple studies compared variable and continuous flow de-
vices, albeit with different nasal interfaces. Measurements reported
in these studies included changes in lung volume, thoraco-
abdominal synchrony, resistance to breathing, and changes in
pleural pressure measured with an esophageal balloon. Together,
these studies reported advantages of the variable-flow device over
the continuous-flow device at varying CPAP levels of 0, 4, 6, and 8
cmH
2
O water.
Courtney et al. compared three CPAP devices: continuous-flow
nCPAP via prongs, continuous nCPAP via modified nasal cannula,
and variable-flow nCPAP. The continuous-flow CPAP was generated
using the CPAP mode on a conventional ventilator. The study was
carried out in 32 premature infants with mild respiratory failure at
a mean gestational age of 29 weeks, and the age at study was 13
days. After initial lung recruitment at 8 cmH
2
O, they tested the
breathing parameters at 8, 6, and 4 cm and compared with
0 cmH
2
O CPAP. Lung recruitment was better with the variable-flow
device than with both the continuous flow devices. The breathing
synchrony obtained with the continuous flow was similar to that
with variable flow. They suggested that better lung recruitment
with the variable-flow system could have resulted from decreased
variability of the mean airway pressure as reported by Moa et al.
[13] and Klausner et al. [27]. These differences could also be
affected by the variations in the flow rates and the nasal interfaces.
They also observed comparable lung volume recruitment with
continuous flow and a modified nasal cannula compared to
continuous-flow nasal prongs, but this was at the cost of higher
thoraco-abdominal asynchrony, higher respiratory rates and higher
FiO
2
requirements. They discouraged the use of nasal cannula CPAP
[9].
In another study by Pandit et al., constant flow nCPAP was
delivered by connecting INCA nasal prongs to an infant ventilator
set on the CPAP mode, and compared to variable flow nCPAP using
the Aladdin/IFD CPAP. They evaluated the work of breathing be-
tween the two systems using a crossover design at CPAP of 0, 4, 6,
and 8 cmH
2
O in 24 preterm infants with mild respiratory distress
born at a mean gestation of 28 weeks and at a mean postnatal age of
14 days. They calculated the inspiratory work of breathing and lung
compliance using esophageal pressure measurements and stan-
dardized the results by dividing work of breathing by tidal volume.
They reported decreased work of breathing at all CPAP levels with
the variable-flow device, the greatest reduction being ata CPAP of 4
cmH
2
O. Lung compliance increased with variable flow and
decreased with continuous flow, except at 8 cmH
2
O when
compliance decreased with variable flow and increased with
continuous flow. The findings of this study, however, cannot be
extrapolated to infants with moderate-to-severe lung disease
requiring higher pressure [28].
Courtney et al. compared two variable-flow nasal CPAP devices:
Infant Flow™(EME, Brighton, UK) and Arabella
®
(Hamilton Medi-
cal™, USA). They assessed lung recruitment and work of breathing
between the two devices in very low birth weight babies requiring
nasal CPAP. In 18 infants at a mean (SD) birth weight of 1107 (218) g
and a gestational age of 27.9 (2.0) weeks, there were no differences
in lung volume recruitment at any nCPAP level (P¼0.943), inspi-
ratory work of breathing (P¼0.468), or resistive work of breathing
(P¼0.610) between devices [29].
The investigators also compared the work of breathing using
bCPAP with Hudson prongs versus variable-flow nCPAP using the
Viasys (CareFusion) system. They studied seven very low birth
weight infants with mild respiratory distress on each device at a
mean (SD) age of 8 (8.7) days. They reported a significantly lower
inspiratory and resistive work of breathing with variable-flow CPAP
at 6 and 4 cmH
2
O pressure [30].
As many of the previously reported studies advocated the use
of a ventilator to deliver continuous-flow nasal CPAP, the study by
Lipsten et al. compared work of breathing and breathing asyn-
chrony during bCPAP versus variable-flow nCPAP in 18 premature
infants with a mean gestation of 28 weeks and a birth weight of
1042 g at a mean postnatal age of 9.4 days. Their findings were
consistent with the previously reported studies, showing an
increased respiratory rate, phase angle, and resistive work of
breathing with bCPAP. Interestingly, the inspiratory work of
breathing, minute ventilation, and tidal volume were similar be-
tween the two groups. They explained the observed differences in
resistive work of breathing and asynchrony as relevant during
expiration only, not during inspiration. The total work of
breathing with bCPAP was also not as markedly increased as re-
ported in the other studies with continuous flow, ventilator-
derived CPAP. They speculated that bCPAP may provide an
advantage [31].
Kahn et al. compared the work of breathing between bCPAP and
ventilator-derived CPAP. They studied 10 preterm babies with mild
respiratory distress at a mean gestation of 28.8 ±1.9 weeks and a
postnatal age of 11 ±7 days. Each infant was studied on both de-
vices in a randomized crossover design and the nCPAP pressure was
varied as 3, 5, 7, 4, and 2 cm H
2
O (in that order). They observed
identical intra-prong pressures and similar inspiratory work of
breathing between the two devices. They concluded that when
S. Gupta, S.M. Donn / Seminars in Fetal & Neonatal Medicine xxx (2016) 1e85
Please cite this article in press as: Gupta S, Donn SM, Continuous positive airway pressure: Physiology and comparison of devices, Seminars in
Fetal & Neonatal Medicine (2016), http://dx.doi.org/10.1016/j.siny.2016.02.009
intra-prong pressures were controlled, the inspiratory work of
breathing was no different between the devices [26].
The available data on the work of breathing and the choice of
nCPAP device address the important issue of the intended and the
actual airway-distending pressure. The data also highlight the dif-
ferences in the inspiratory and resistive work of breathing across
the available devices. It is important to recognize these differences,
but it will be more pertinent to relate these findings to clinically
relevant outcomes in clinical trials.
6.1. Cardiovascular effects of CPAP
There are limited data on the hemodynamic effects of CPAP in
preterm newborns. An animal study by Adams et al. reported the
hemodynamic effects produced by CPAP and continuous negative
extrathoracic pressure (CNEP). CPAP and CNEP of 4 and 8 cmH
2
O
were compared in eight normal, spontaneously breathing piglets.
Arterial blood gases and hemodynamic measurements were ob-
tained before and during CPAP and CNEP. At 8 cmH
2
O, CPAP and
CNEP produced significant increases (P<0.01) in PaO
2
from
baseline. No significant changes occurred in PaCO
2
or cardiac
index, except during CPAP of 8 cmH
2
O, the PaCO
2
increased
significantly (P<0.05), and cardiac index decreased (P<0.05).
During CPAP of 4 cmH
2
O, there were significant increases in
mean right atrial pressure (P
ra
), left ventricular end-diastolic
pressure (LVEDP), and mean pulmonary artery pressure (P
pa
).
CPAP of 8 cmH
2
O produced marked increases in P
ra
, LVEDP, and P
pa
[32].
7. Comparison of CPAP devices
nCPAP has been used immediately after birth for the manage-
ment of RDS and after extubation for providing respiratory support
to preterm babies. Investigators have compared ventilator-derived
CPAP, bCPAP, and IFD CPAP in observational studies and clinical
trials.
7.1. Cohort and observational studies
The cohort study by Narendran et al. incorporated the intro-
duction of bCPAP in one hospital and conventional nCPAP at
another for the management of preterm babies with RDS (birth
weights 401e1000 g). The data were collected on all extremely low
birth weight babies and compared to historical controls and be-
tween the hospitals. They reported a reduction in delivery room
intubations with the use of both bCPAP and conventional nCPAP
compared to historical controls (P<0.001). There was also a sig-
nificant reduction in the use of postnatal steroids with bCPAP, but
not with conventional nCPAP (P<0.001), and a trend towards a
reduction in chronic lung disease with bCPAP [33].
In an observational study from Canada, Pelligra et al. reported a
comparison of two time-periods; the first used ventilator-derived
CPAP with a nasopharyngeal tube, and the second used bCPAP.
Data from 821 babies <32 weeks (397 babies in period 1, and 424
babies in period 2) were analyzed. There was a significant
reduction in the use of exogenous surfactant, postnatal steroids,
and in the duration of mechanical ventilation with the use of
bCPAP [34].
In another observational study, Massaro et al. collected data on
36 preterm babies <2000 g who were solely managed on nCPAP
over a period of 16 months. They grouped the babies into those
who received bCPAP support and those who received ventilator-
derived CPAP at the same pressures. The groups were demo-
graphically equivalent. The authors reported no differences in the
duration of nCPAP support and other clinical outcomes, except
that babies managed on bCPAP required oxygen for a shorter
duration [35].
Although these observational studies suggest advantages with
bCPAP, the heterogeneity of the data warrants further evidence
from well-designed randomized trials. There were no observational
studies comparing IFD CPAP and continuous-flow CPAP devices.
7.2. Randomized trials
7.2.1. Randomized controlled trials at birth
Mazzela et al. compared IFD CPAP with binasal prongs and
bCPAP through a single nasopharyngeal prong. They randomized
36 preterm infants <36 weeks of gestation at <12 h of age to receive
one of the CPAP modes. They reported a significant beneficial effect
on both oxygen requirement and respiratory rate (P<0.0001) with
IFD CPAP, compared to bCPAP, and a trend towards a decreased
need for mechanical ventilation. This study, however, was limited
by a small sample size and the use of different nasal interfaces [19].
McEvoy et al. randomized 53 spontaneously breathing preterm
babies between 25 and 32 weeks of gestation to receive either
bCPAP or ventilator-derived CPAP using Hudson prongs after initial
stabilization. The respiratory measurements (FRC and compliance)
and CPAP failure through seven days were compared. They
observed no differences in the respiratory measurements, CPAP
failures, surfactant use, days on CPAP, and oxygen need and BPD at
36 weeks between groups [36].
Tagare et al. compared the efficacy and safety of bCPAP with
ventilator-derived CPAP in preterm neonates with respiratory
distress. Preterm neonates with a SilvermaneAnderson score 4
and oxygen requirement >30% within first 6 h of life were randomly
allocated to bCPAP or ventilator-derived CPAP and the proportion of
neonates succeeding was compared. In all, 47 of 57 (82.5%) neo-
nates receiving bCPAP and 36 of 57 (63.2%) receiving ventilator-
derived CPAP did not require mechanical ventilation (P¼0.03),
suggesting superiority of bCPAP for managing preterm neonates
with early onset respiratory distress [37].
Mazmanyan et al. randomized 125 infants <37 weeks of gesta-
tion to bCPAP or IFD CPAP after stabilization at birth in a resource-
limited setting. bCPAP was equivalent to IFD CPAP in the total
number of days needing CPAP within a margin of 2 days. The me-
dian days (range) for the primary outcome (days on CPAP) were 0.8
days (0.04e17.5) on bCPAP, and 0.5 days (0.04e5.3) on IFD CPAP
[38]. It is difficult to determine whether study infants required
CPAP support or were put on CPAP as part of the trial, as the
duration of support is less than a day in both study arms. The results
of this trial should be interpreted with caution in extremely and
moderately premature babies, as the studygroup was more mature,
but it is a reassuring finding for a population of larger babies in a
developing country [38].
The trial by Bhatti et al. compared Jet-CPAP (variable flow) and
bCPAP in 170 preterm newborns <34 weeks of gestation with res-
piratory distress within 6 h of birth. CPAP failure rates within 72 h
were similar in infants who received Jet-CPAP and in those who
received bCPAP (29% versus 21%; relative risk 1.4 (95% CI 0.8e2.3),
P¼0.25). Mean (95% CI) time to CPAP failure was 59 h (54e64) in
the Jet-CPAP group compared to 65 h (62e68) in the bCPAP group.
In this well-designed trial, no difference was reported between the
two study devices; however, the investigators did not stratify ba-
bies by severity of respiratory illness or gestational age [39].
7.2.2. Randomized trials after extubation
The initial studies compared IFD CPAP with ventilator-derived
CPAP, using either binasal prongs or nasopharyngeal prongs with
ventilator-derived CPAP.
S. Gupta, S.M. Donn / Seminars in Fetal & Neonatal Medicine xxx (2016) 1e86
Please cite this article in press as: Gupta S, Donn SM, Continuous positive airway pressure: Physiology and comparison of devices, Seminars in
Fetal & Neonatal Medicine (2016), http://dx.doi.org/10.1016/j.siny.2016.02.009
Sun et al. randomized 73 premature babies >30 weeks of
gestation and birth weight >1250 g to IFD CPAP or ventilator-
derived CPAP with binasal prongs. They reported that 19/35 (54%)
babies receiving ventilator-derived CPAP met failure criteria versus
6/38 (16%) on IFD CPAP (P<0.001). The results favored IFD CPAP
over ventilator-derived CPAP in this population [40]. Stefanescu
et al. randomized 162 extremely low birth weight infants after
extubation from mechanical ventilation to receive either IFD CPAP
or conventional CPAP through a ventilator using INCA prongs. The
primary outcome for this study was the need for reintubation in the
first seven days after extubation. The investigators found no dif-
ference in the extubation success rate between the two study
groups [41].
The trials by Sun et al. and Stefanescu et al. did not stratify ba-
bies by duration of ventilation. The demographic differences in the
trials also make it difficult to draw concrete conclusions but the
results suggest that IFD CPAP is either superior to or has similar
efficacy to ventilator-derived CPAP when used after extubation.
Roukema et al. randomized 93 very low birth weight infants to
IFD CPAP or nasopharyngeal CPAP. In their trial, 27/45 (60%) failed
extubation on nasopharyngeal CPAP versus 18/48 (38%) on IFD
CPAP (P¼0.0006). These results should be interpreted with
caution, as there is heterogeneity in the nasal interface used in the
study. They used short binasal prongs with IFD CPAP but a naso-
pharyngeal prong for the delivery of ventilator-derived CPAP [18].
De Paoli et al. stressed in their meta-analysis that a comparable
nasal interface is needed to allow comparison of CPAP pressure
generation systems in randomized trials, and thus the results of
Roukema et al. have limited usefulness [20].
In a subsequent trial Gupta et al. randomized 140 preterm in-
fants 24e29 weeks of gestation or 600e1500 g at birth to receive
bCPAP or IFD CPAP at the first attempt at extubation [42]. Infants
were stratified according to duration of initial ventilation (14
days or >14 days). Babies were extubated when they passed a
minute ventilation test used to assess objectively readiness for
extubation [43]. The primary outcome of the study was the need
for reintubation within 72 h. If an infant required reintubation,
then the same CPAP device to which the infant was initially ran-
domized was used at subsequent extubation until the infant was
no longer requiring respiratory support. Although there was no
statistically significant difference in extubation failure rates (16.9%
on bCPAP, 27.5% on IFD CPAP), the median duration of CPAP sup-
port was 50% shorter in the infants on bCPAP (median 2 days, 95%
CI 1e3) compared to IFD CPAP (4 days, 95% CI 2e6) (P¼0.031). In
infants ventilated for 14 days (n¼127), the extubation failure
rate was significantly lower with bCPAP (14.1%; 9/64) compared to
IFD CPAP (28.6%l 18/63) (P¼0.046) [42].
This well-designed clinical trial suggests the superiority of post-
extubation bCPAP over IFD CPAP in preterm babies at <30 weeks
who are initially ventilated for <2 weeks. In this trial, similar nasal
interfaces were used, stratification by duration of ventilation was
performed, a similar weaning approach was utilized, and enroll-
ment occurred after an objective assessment for readiness for
extubation.
8. Nasal septal injury
Nasal septal injury is recognized as an important complication
of nCPAP therapy. It may cause destruction of the nasal septum
requiring surgery. The success or failure of a CPAP device depends
to a large extent upon the nasal interface, the experience of the
staff, and the ease of use. Among very low birth weight babies, the
incidence of significant nasal trauma with the use of nasal prongs
has been reported to be 35% with a mean age of onsetof 8 days [44].
In study by Gupta et al. [42], a prospectively validated nasal scoring
was used for all babies. In the study population, nine babies (17%)
on IFD CPAP and 13 babies (25%) on bCPAP developed nasal septal
injury (defined as indentation of the septum with or without skin
breakdown). Moreover, the median age at nasal injury was 14 days
in this study [45]. The lower incidence and higher age at onset
could relate to better nursing practices and/or the use of Cannu-
laide
®
and Lyofoam
®
dressings between the prongs and the nose.
Although the incidence of nasal injury with nasal mask and nasal
prong on IFD CPAP has been reported to be similar [44], all babies
with nasal septum injuries in Gupta et al.’s study were managed
with a nasal mask using IFD CPAP [45]. In a cross-sectional study by
Jatana et al. nasal complications were reported in 12 of the 91 pa-
tients (13.2%) with at least seven days of nasal CPAP exposure,
whereas no complications were seen in the nine patients with nasal
cannula use alone [46]. The nasal cannula interface is used with a
humidified high-flow system and fewer nasal injuries are reported
with its use. These differences need to be studied further in well-
designed trials.
9. Conclusion
There seems to be only a slight difference between continuous-
or variable-flow CPAP devices but there is a trend in favor of bCPAP
for post-extubation support, especially in babies ventilated for 2
weeks. The nasal interface is important for optimal delivery of
pressure and CPAP delivery, while limiting untoward effects, which
also requires close monitoring and good nursing care. With
increasing use of CPAP devices it is important that units use the
evidence to select an appropriate CPAP device and minimize
complications.
Conflict of interest statement
None declared.
Funding sources
None.
Practice points
CPAP devices are either continuous-flow or variable-flow
systems.
Efficacy of CPAP depends on CPAP generation, the nasal
interface, and good nursing care.
Currently available CPAP devices have comparable effi-
cacy when used for respiratory support after birth.
In babies ventilated for less than two weeks, bubble CPAP
seems to reduce extubation failures.
Research directions
Better respiratory monitoring techniques to detect early
decompensation on CPAP.
Optimum CPAP pressure during acute and recovery
phases of RDS.
Effect of different levels of CPAP on hemodynamics.
Techniques for minimizing nasal injury on CPAP.
S. Gupta, S.M. Donn / Seminars in Fetal & Neonatal Medicine xxx (2016) 1e87
Please cite this article in press as: Gupta S, Donn SM, Continuous positive airway pressure: Physiology and comparison of devices, Seminars in
Fetal & Neonatal Medicine (2016), http://dx.doi.org/10.1016/j.siny.2016.02.009
References
[1] Courtney SE, Barrington KJ. Continuous positive airway pressure and nonin-
vasive ventilation. Clin Perinatol 2007;34:73e92.
[2] Bhutani VK. Development of respiratory system. 2nd ed. Philadelphia: Mosby/
Elsevier; 2006.
[3] Hammer J. Nasal CPAP in preterm infants edoes it work and how? Intensive
Care Med 2001;27:1689e91.
[4] Miller MJ, Carlo WA, Martin RJ. Continuous positive airway pressure selec-
tively reduces obstructive apnea in preterm infants. J Pediatr 1985;106:91e4.
[5] Miller MJ, DiFiore JM, Strohl KP, Martin RJ. Effects of nasal CPAP on supra-
glottic and total pulmonary resistance in preterm infants. J Appl Physiol
1990;68:141e6.
[6] De Paoli AG, Lau R, Davis PG, Morley CJ. Pharyngeal pressure in preterm in-
fants receiving nasal continuous positive airway pressure. Archs Dis Child
Fetal Neonatal Ed 2005;90:F79e81.
[7] Griffiths GB, Noworaj A, Mortola JP. End-expiratory level and breathing
pattern in the newborn. J Appl Physiol 1983;55(1 Pt 1):243e9.
[8] Locke R, Greenspan JS, Shaffer TH, Rubenstein SD, Wolfson MR. Effect of nasal
CPAP on thoracoabdominal motion in neonates with respiratory insufficiency.
Pediatr Pulmonol 1991;11:259e64.
[9] Courtney SE, Pyon KH, Saslow JG, Arnold GK, Pandit PB, Habib RH. Lung
recruitment and breathing pattern during variable versus continuous flow
nasal continuous positive airway pressure in premature infants: an evaluation
of three devices. Pediatrics 2001;107:304e8.
[10] Elgellab A, Riou Y, Abbazine A, Truffert P, Matran R, Lequien P, et al. Effects of
nasal continuous positive airway pressure NCPAP on breathing pattern in
spontaneously breathing premature newborn infants. Intensive Care Med
2001;27:1782e7.
[11] Magnenant E, Rakza T, Riou Y, Elgellab A, Matran R, Lequien P, et al. Dynamic
behavior of respiratory system during nasal continuous positive airway
pressure in spontaneously breathing premature newborn infants. Pediatr
Pulmonol 2004;37:485e91.
[12] Mulrooney N, Champion Z, Moss TJ, Nitsos I, Ikegami M, Jobe AH. Surfactant
and physiologic responses of preterm lambs to continuous positive airway
pressure. Am J Resp Crit Care Med 2005;171:488e93.
[13] Moa G, Nilsson K, Zetterstrom H, Jonsson LO. A new device for administration
of nasal continuous positive airway pressure in the newborn: an experimental
study. Crit Care Med 1988;16:1238e42.
[14] Benveniste D, Pedersen JE. A valve substitute with no moving parts, for arti-
ficial ventilation in newborn and small infants. Br J Anaesth 1968;40:464e70.
[15] Gregory GA, Kitterman JA, Phibbs RH, Tooley WH, Hamilton WK. Treatment of
the idiopathic respiratory-distress syndrome with continuous positive airway
pressure. N Engl J Med 1971;284:1333e40.
[16] Lee KS, Dunn MS, Fenwick M, Shennan AT. A comparison of underwater
bubble continuous positive airway pressure with ventilator-derived contin-
uous positive airway pressure in premature neonates ready for extubation.
Biol Neonate 1998;73:69e75.
[17] Davis P, Davies M, Faber B. A randomised controlled trial of two methods of
delivering nasal continuous positive airway pressure after extubation to in-
fants weighing less than 1000 g: binasal Hudson versus single nasal prongs.
Archs Dis Child Fetal Neonatal Ed 2001;85:F82e5.
[18] Roukema H, O'Brian K, Nesbitt K. A crossover trial of Infant Flow (IF)
continuous positive airway pressure (CPAP) versus nasopharyngeal (NP) CPAP
in the extubation of babies 1250 grams birth weight [abstract 1874]. Pediatr
Res 1999;45:318A.
[19] Mazzella M, Bellini C, Calevo MG, Campone F, Massocco D, Mezzano P, et al.
A randomised control study comparing the Infant Flow Driver with nasal
continuous positive airway pressure in preterm infants. Archs Dis Child Fetal
Neonatal Ed 2001;85:F86e90.
[20] De Paoli AG, Davis PG, Faber B, Morley CJ. Devices and pressure sources for
administration of nasal continuous positive airway pressure (NCPAP) in pre-
term neonates. Cochrane Database Syst Rev 2008;(1):CD002977.
[21] Kieran EA, Twomey AR, Molloy EJ, Murphy JF, O'Donnell CP. Randomized trial
of prongs or mask for nasal continuous positive airway pressure in preterm
infants. Pediatrics 2012;130:e1170e6.
[22] De Paoli AG, Morley CJ, Davis PG, Lau R, Hingeley E. In vitro comparison of
nasal continuous positive airway pressure devices for neonates. Archs Dis
Child Fetal Neonatal Ed 2002;87:F42e5.
[23] Morley CJ, Lau R, De PA, Davis PG. Nasal continuous positive airway pressure:
does bubbling improve gas exchange? Archs Dis Child Fetal Neonatal Ed
2005;90:F343e4.
[24] Pillow JJ, Travadi JN. Bubble CPAP: is the noise important? An in vitro study.
Pediatr Res 2005;57:826e30.
[25] Pillow JJ, Hillman N, Moss TJ, Polglase G, Bold G, Beaumont C, et al. Bubble
continuous positive airway pressure enhances lung volume and gas exchange
in preterm lambs. Am J Respir Crit Care Med 2007;176:63e9.
[26] Kahn DJ, Courtney SE, Steele AM, Habib RH. Unpredictability of delivered
bubble nasal continuous positive airway pressure role of bias flow magnitude
and nares-prong air leaks. Pediatr Res 2007;62:343e7.
[27] Klausner JF, Lee AY, Hutchison AA. Decreased imposed work with a new nasal
continuous positive airway pressure device. Pediatr Pulmonol 1996;22:
188e94.
[28] Pandit PB, Courtney SE, Pyon KH, Saslow JG, Habib RH. Work of breathing
during constant- and variable-flow nasal continuous positive airway pressure
in preterm neonates. Pediatrics 2001;108:682e5.
[29] Courtney SE, Aghai ZH, Saslow JG, Pyon KH, Habib RH. Changes in lung volume
and work of breathing: a comparison of two variable-flow nasal continuous
positive airway pressure devices in very low birth weight infants. Pediatr
Pulmonol 2003;36:248e52.
[30] Courtney SE, Aghai ZH, Saslow JG, Pyon KH, Habib RH. Work of breathing
(WOB) during nasal continuous positive airway pressure (NCPAP): a pilot
study of bubble vs. variable-flow (VF) NCPAP. PAS 2003;53:2039.
[31] Liptsen E, Aghai ZH, Pyon KH, Saslow JG, Nakhla T, Long J, et al. Work of
breathing during nasal continuous positive airway pressure in preterm in-
fants: a comparison of bubble vs variable-flow devices. J Perinatol 2005;25:
453e8.
[32] Adams JA, Osiovich H, Goldberg RN, Suguihara C, Bancalari E. Hemodynamic
effects of continuous negative extrath oracic pressure and continuous posi-
tive airway pressure in piglets with normal lungs. Biol Neonate 1992;62:
69e75.
[33] Narendran V, Donovan EF, Hoath SB, Warner BB, Streichen JJ, Jobe AH. Com-
parison between early bubble CPAP and conventional CPAP in reducing the
incidence of chronic lung disease. PAS 2002;51:1960.
[34] Pelligra P, Abdellatif MA, Lee SK. Comparison of clinical outcomes between
two modes of CPAP delivery: underwater bubble versus conventional venti-
lator-derived. E-PAS 2006;59:475.
[35] Massaro AN, Abdel-Haq I, Aly HZ. Underwater seal bubble CPAP versus
ventilator-derived CPAP: does mode of delivery make a difference in clinical
outcome? PAS 2005;57:2053.
[36] McEvoy CT, Colaizy T, Crichton C, Frietag B, Gilhooly J, Pillers DM, et al.
Randomized trial of early bubble continuous positive airway pressure (BCPAP)
versus conventional CPAP (CCPAP): effect on pulmonary function in preterm
infants. PAS 2004;55:2988.
[37] Tagare A, Kadam S, Vaidya U, Pandit A, Patole S. Bubble CPAP versus ventilator
CPAP in preterm neonates with early onset respiratory distress ea ran-
domized controlled trial. J Trop Pediatr 2013;59:113e9.
[38] Mazmanyan P, Mellor K, Dore CJ, Modi N. A randomised controlled trial of
flow driver and bubble continuous positive airway pressure in preterm in-
fants in a resource-limited setting. Archs Dis Child Fetal Neonatal Ed
2016;101:16e20.
[39] Bhatti A, Khan J, Murki S, Sundaram V, Saini SS, Kumar P. Nasal Jet-CPAP
(variable flow) versus bubble-CPAP in preterm infants with respiratory
distress: an open label, randomized controlled trial. J Perinatol 2015;35:
935e40.
[40] Sun SC, Tien HC, Banabas S. Randomised controlled trial of two methods of
nasal CPAP (NCPAP): flow driver vs conventional CPAP [abstract 1898].
Pediatr Res 1999;45:322A.
[41] Stefanescu BM, Murphy WP, Hansell BJ, Fuloria M, Morgan TM, Aschner JL.
A randomized, controlled trial comparing two different continuous positive
airway pressure systems for the successful extubation of extremely low birth
weight infants. Pediatrics 2003;112:1031e8.
[42] Gupta N, Saini SS, Murki S, Kumar P, Deorari A. Continuous positive airway
pressure in preterm neonates: an update of current evidence and implications
for developing countries. Indian Pediatr 2015;52:319e28.
[43] Wilson Jr BJ, Becker MA, Linton ME, Donn SM. Spontaneous minute ventilation
predicts readiness for extubation in mechanically ventilated preterm infants.
J Perinatol 1998;18(6Pt 1):436e9.
[44] Yong SC, Chen SJ, Boo NY. Incidence of nasal trauma associated with nasal
prong versus nasal mask during continuous positive airway pressure treat-
ment in very low birthweight infants: a randomised control study. Archs Dis
Child Fetal Neonatal Ed 2005;90:F480e3.
[45] Alsop L, Cook J, Gupta S. Nasal injuries in preterm infants: comparison of the
infant flow driver to bubble CPAP. PAS 2008. 4456.4.
[46] Jatana KR, Oplatek A, Stein M, Phillips G, Kang DR, Elmaraghy CA. Effects of
nasal continuous positive airway pressure and cannula use in the neonatal
intensive care unit setting. Arch Otolaryngol Head Neck Surg 2010;136:
287e91.
S. Gupta, S.M. Donn / Seminars in Fetal & Neonatal Medicine xxx (2016) 1e88
Please cite this article in press as: Gupta S, Donn SM, Continuous positive airway pressure: Physiology and comparison of devices, Seminars in
Fetal & Neonatal Medicine (2016), http://dx.doi.org/10.1016/j.siny.2016.02.009
