INTENSIVE CARE

Measuring the Differences Between 4 Bubble
CPAP Systems
Chris Campbell
While medical professionals who work in hospital settings
won’t be surprised, some parents might be a little shocked to
learn that in facilities with million-dollar equipment, many use
a “homemade” version of a device designed to help infants with
respiratory distress to breathe spontaneously. 1
The device is called a bubble CPAP, and it’s an affordable type of
CPAP that specifically supports infants. Many hospitals employ
“off-label” bubble CPAP devices concocted out of items found in
their facilities. 4
But use of the “homemade” devices is changing after medical
device makers were granted FDA clearance to market bubble
CPAP devices far more sophisticated than those created in-house
at hospitals.
A group of researchers with the Center for Developmental
Therapeutics, Seattle Children’s Hospital Research Institute,
were curious about how homemade devices and those
manufactured by medical device companies would compare
when tested against each other.
Poli et al had a theory about these devices: “We hypothesized
that there are no differences in the magnitude of oscillations in
lung volume in a preterm neonatal lung model when different
bubble CPAP systems are used.”
After putting four devices through their paces, however, the
researchers concluded something completely different — leading
them to call for more study to learn about the existence of
possible physiologic benefits between different devices.
The Devices
When an infant is suffering with respiratory distress syndrome
(RDS), bubble CPAP is an invaluable device, according to
the study authors: “Unlike CPAP provided by a mechanical
ventilator, bubble CPAP transmits small-amplitude, high
frequency pressure oscillations around the mean airway
pressure. 2 These pressure oscillations are created by gases
bubbling through the air-water interface of the submerged
expiratory tube. Lee et al3 first observed the chest walls of
infants supported by bubble CPAP oscillating at a frequency
similar to high-frequency oscillatory ventilation. Furthermore,
Pillow et al 2 demonstrated that mechanical pressure oscillations
created by bubble CPAP may be more beneficial than ventilator
Chris Campbell is the Senior Editor of Neonatal Intensive Care.
CPAP to aid in lung recruitment and to improve gas exchange in
premature lambs, claiming that oscillations augment ventilation.”
Four different models of bubble CPAP were tested: a “homemade
system that has been described by several investigators 4,6,7 and
three FDA-cleared systems: bubble CPAP system (Fisher &
Paykel Healthcare, Auckland, New Zealand), Babi.Plus bubble
positive airway pressure valve with an n CPAP nasal kit (A
Plus Medical, Carlsbad, California), and WaterPAP (Airways
Development, Kenilworth, New Jersey).”
The four systems were tested on an anatomically realistic
replica with either appropriate or proprietary prongs attached,
according to the authors: “Nasal resistance in the newborn
accounts for nearly half of the total airway resistance. 8 As such,
we designed a realistic replica of the nasal airway modeled
from a computed tomography scan of an infant at 28 weeks of
gestation.” The replica was attached to a Silastic test lung sealed
within a calibrated plethysmograph.
The authors described the homemade device as “a waterfilled
bottle with a corrugated tube submerged within it. The
expiratory limb was stabilized in the water column using a 10-mL
syringe plunger; the CPAP level was determined by the length of
the tube submerged in the water, indicated by tick marks at 1-cm
intervals written on the limb. 7 ”
To measure pressure oscillations: “The nasal prongs were
inserted into a Tygon tubing adapter that was affixed to the nasal
airway model. The adapter formed a tight seal (no leak) between
the nasal model and prongs. All bubble CPAP systems had the
expiratory limb set to a depth of 6 cm.”
The Results
The study authors are upfront in saying that after testing the four
devices, they had to “reject our hypothesis,” going on to say that
“the major finding of this study is that the bubble CPAP systems
provided quantifiable oscillations in DV that may prove to be
clinically meaningful and that the different bubble CPAP systems
studied exhibited differences in the magnitude and frequency of
volume oscillations delivered to a preterm infant lung model.”
The study authors found many deep flaws in the homemade
device: “Although the homemade device is the most costeffective
form of bubble CPAP, it possesses more variability in
its frequency output than the other devices. If employed in the
clinical setting, patients on the homemade device will experience
32 neonatal INTENSIVE CARE Vol. 29 No. 4 • Fall 2016