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CPAP Devices for Emergency Prehospital Use: A Bench Study
Claudia Brusasco MD, Francesco Corradi MD PhD, Alessandra De Ferrari MD, Lorenzo Ball MD,
Robert M Kacmarek PhD RRT FAARC, and Paolo Pelosi MD
BACKGROUND: CPAP is frequently used in prehospital and emergency settings. An air-flow
output minimum of 60 L/min and a constant positive pressure are 2 important features for a
successful CPAP device. Unlike hospital CPAP devices, which require electricity, CPAP devices for
ambulance use need only an oxygen source to function. The aim of the study was to evaluate and
compare on a bench model the performance of 3 orofacial mask devices (Ventumask, EasyVent, and
Boussignac CPAP system) and 2 helmets (Ventukit and EVE Coulisse) used to apply CPAP in the
prehospital setting. METHODS: A static test evaluated air-flow output, positive pressure applied,
and F
IO
2
delivered by each device. A dynamic test assessed airway pressure stability during simu-
lated ventilation. Efficiency of devices was compared based on oxygen flow needed to generate a
minimum air flow of 60 L/min at each CPAP setting. RESULTS: The EasyVent and EVE Coulisse
devices delivered significantly higher mean air-flow outputs compared with the Ventumask and
Ventukit under all CPAP conditions tested. The Boussignac CPAP system never reached an air-flow
output of 60 L/min. The EasyVent had significantly lower pressure excursion than the Ventumask
at all CPAP levels, and the EVE Coulisse had lower pressure excursion than the Ventukit at 5, 15,
and 20 cm H
2
O, whereas at 10 cm H
2
O, no significant difference was observed between the 2
devices. Estimated oxygen consumption was lower for the EasyVent and EVE Coulisse compared
with the Ventumask and Ventukit. CONCLUSIONS: Air-flow output, pressure applied, F
IO
2
de-
livered, device oxygen consumption, and ability to maintain air flow at 60 L/min differed signifi-
cantly among the CPAP devices tested. Only the EasyVent and EVE Coulisse achieved the required
minimum level of air-flow output needed to ensure an effective therapy under all CPAP conditions.
Key words: noninvasive CPAP; emergency department; ambulance; cardiogenic pulmonary edema;
helmet CPAP; Boussignac; acute respiratory failure. [Respir Care 0;0(0):1–•. © 0 Daedalus Enterprises]
Introduction
Noninvasive ventilation (NIV) reduces the need for en-
dotracheal intubation, the occurrence of nosocomial infec-
tions, and both morbidity and mortality associated with
respiratory failure.
1-5
The benefits of NIV are greater if
started early, thus constituting the rationale for the increas-
ing use of NIV in prehospital and emergency department
settings.
6-8
Because of its ease of use and the small size of
commercially available devices, CPAP is the most com-
monly used NIV technique in these settings.
5,9
The bene-
fits of CPAP have been extensively described in the treat-
ment of acute cardiogenic pulmonary edema
10-12
and acute
Drs Brusasco, De Ferrari, Ball, and Pelosi are affiliated with the Dipar-
timento di Scienze Chirurgiche e Diagnostiche Integrate, Sezione Anes-
tesia e Rianimazione, Universita` degli Studi di Genova, Genova, Italy.
Drs De Ferrari, Ball, and Pelosi are also affiliated with the Istituto di
Ricovero e Cura a Carattere Scientifico (IRCCS) Azienda Ospedaliera
Universitaria San Martino-Istituto Scientifico Tumori, Genova, Italy. Dr
Corradi is affiliated with the SC Anestesia e Rianimazione, EO Os-
pedali Galliera, Genova, Italy. Dr Kacmarek is affiliated with the
Department of Anesthesiology and Critical Care and the Department
of Respiratory Care, Massachusetts General Hospital, Boston,
Massachusetts.
Dr Kacmarek has disclosed relationships with Covidien and Venner Med-
ical. The other authors has disclosed no conflicts of interest.
Correspondence: Claudia Brusasco MD, Dipartimento di Scienze Chiru-
rgiche e Diagnostiche Integrate, Sezione Anestesia e Rianimazione, Uni-
versita` degli Studi di Genova, Largo Rosanna Benzi 8, 16132 Genova,
Italy. E-mail: claudia.brusasco@gmail.com.
DOI: 10.4187/respcare.04134
RESPIRATORY CARE •●●VOL ●NO●1
RESPIRATORY CARE Paper in Press. Published on September 29, 2015 as DOI: 10.4187/respcare.04134
Copyright (C) 2015 Daedalus Enterprises ePub ahead of print papers have been peer-reviewed, accepted for publication, copy edited
and proofread. However, this version may differ from the final published version in the online and print editions of RESPIRATORY CARE
respiratory failure
13-15
and include opening collapsed al-
veoli, preserving patency of already open-lung units, im-
proving gas exchange, reducing patient’s work of breath-
ing,
16
and increasing cardiac performance by a reduction
in venous return and left-ventricular afterload.
17-19
CPAP
can be delivered with masks or helmets.
For successful CPAP treatment, CPAP devices must
deliver sufficiently high air flow to maintain airway pres-
sure throughout the breathing cycle. Because conditions
such as tachypnea, high minute ventilation, or large tidal
volumes can increase inspiratory flows, air flow delivered
by CPAP devices should always be higher than the pa-
tient’s peak inspiratory flow to ensure positive airway pres-
sure during the entire breathing cycle. A minimum of 60
L/min is generally considered sufficient to guarantee a
constant CPAP level under most degrees of patient in-
spiratory demand,
20
although higher flows might be re-
quired in severe respiratory distress at high breathing
frequency, large tidal volumes, and high minute ventila-
tion.
20,21
Delivered F
IO
2
is dependent upon the amount of
air entrained during the operation of the device and the
patient’s inspiratory demand. If the device entrains a large
volume of room air, the maximum F
IO
2
will be limited. In
addition, the more that the patient’s inspiratory demand
exceeds the total air-flow output of the device, the lower
the F
IO
2
will be because additional room air must be en-
trained to meet the patient’s demand for inspiratory flow.
The aim of this study was to evaluate and compare the
intrinsic capabilities of 5 commercially available CPAP
devices in prehospital and emergency settings. The per-
formance of each device was evaluated in terms of effec-
tiveness (air-flow output, pressure, and F
IO
2
) and efficiency
(oxygen consumption by the device).
Methods
Devices
Five commercially available devices for delivery of non-
invasive CPAP in prehospital settings were studied (Fig.
1): 3 orofacial mask devices (Ventumask [StarMed, Mi-
randola, Italy], EasyVent [Dimar, Mirandola, Italy], and
Boussignac CPAP system [Vygon, E
´couen, France]) and 2
helmet-type devices (Ventukit [StarMed] and EVE Cou-
lisse [Dimar]). All of these devices require only an oxygen
source to generate CPAP, thus making them useful on
ambulances.
The Ventumask, EasyVent, Ventukit, and EVE Coulisse
devices use the Venturi effect to entrain room air and
generate a high gas output flow and an adjustable mechan-
ical CPAP valve to set the desired positive pressure. A
supplementary oxygen source located downstream from
the air-entrainment valve can be connected to increase
F
IO
2
. Tables provided by the manufacturers indicate, for
each level of CPAP, the oxygen flows needed to provide
a specific total air flow and F
IO
2
with a maximum use of 15
L/min oxygen.
The Boussignac CPAP system uses the virtual Boussig-
nac valve,consisting of a small cylinder with 4 micro-
channels: when receiving oxygen flow from a source, tur-
bulence is generated inside the cylinder itself, resulting in
a positive pressure. The performance of the Boussignac
CPAP system depends only on the delivered oxygen flow:
F
IO
2
and positive pressure cannot be set by the operator
because both are a result of the oxygen flow setting re-
quired to power the device and the amount of air the
patient inhales above that delivered by the device. This
device does not incorporate an air-entrainment Venturi
system.
The Ventukit and EVE Coulisse are 2 transparent, latex-
free, polyvinylchloride hoods joined by a metal ring to soft
polyvinylchloride collars to form helmets. These devices
have an internal gas volume of 17 L. Both helmets include
an air-entrainment system utilizing the Venturi effect and
an adjustable CPAP valve. The Ventukit helmet has a plug
to reduce the noise generated by the device at the exit
point of the flow generated by the air-entrainment Venturi
system exerting 6 cm H
2
O per 50 L/min resistance to gas
flow.
QUICK LOOK
Current knowledge
CPAP is frequently used in prehospital and emergency
settings. A minimum flow output of 60 L/min and a
constant positive pressure are 2 important features of a
successful CPAP device. CPAP devices for ambulances
typically need only an oxygen source to function. In-
spired oxygen can be altered by air entrainment, which
also increases total flow. Prehospital use of CPAP for
cardiogenic pulmonary edema is associated with im-
proved clinical outcomes.
What this paper contributes to our knowledge
In a bench study of 5 CPAP devices, there were con-
siderable differences in performance among the devices
tested. The EasyVent and EVE Coulisse achieved the
best overall performance in terms of effectiveness and
efficiency; the Ventumask and Ventukit presented more
limited air-flow outputs at lower positive pressures; and
the Boussignac CPAP system delivered low total air-
flow outputs, low positive pressures, and high non-
adjustable F
IO
2
. Clinicians and prehospital caregivers
should be aware of specific device performance char-
acteristics to optimize effective application of CPAP in
prehospital and emergency settings.
CPAP IN EMERGENCY SETTINGS
2RESPIRATORY CARE •●●VOL ●NO●
RESPIRATORY CARE Paper in Press. Published on September 29, 2015 as DOI: 10.4187/respcare.04134
Copyright (C) 2015 Daedalus Enterprises ePub ahead of print papers have been peer-reviewed, accepted for publication, copy edited
and proofread. However, this version may differ from the final published version in the online and print editions of RESPIRATORY CARE
Comparisons were performed between masks and be-
tween helmets because the devices from the same manu-
facturer (Ventumask/Ventukit and EasyVent/EVE Cou-
lisse) use the same air-entrainment system and the
difference between devices is the interfaces (mask or hel-
mets). Moreover, the choice to use a mask or a helmet is
strictly clinical, based on the patient’s adherence or ex-
pected duration of needed assistance.
Experimental Setting
Figure 2 shows the in vitro circuit used to evaluate the
performance of each device in terms of flow, generated
pressure, and delivered F
IO
2
. A flow meter (ICU-Lab,
KleisTEK, Bari, Italy) measuring air flow generated by the
CPAP device was positioned downstream from each CPAP
device’s air-entrainment valve, as well as a rapid-response
oxygen analyzer (MaxO
2
⫹
AE, Maxtec, Salt Lake City,
Utah) and a manometer.
The Ventumask, EasyVent, Ventukit, and EVE Coulisse
devices were evaluated without CPAP and at 4 levels of
CPAP (5, 10, 15, and 20 cm H
2
O) set with each device’s
adjustable valve. For each CPAP valve level, the devices
were tested at oxygen source flows of 5–15 L/min in 1
L/min increments, and generated pressure, air flow, and
F
IO
2
were measured. The Boussignac CPAP system was
evaluated for delivered air flow, F
IO
2
, and pressure starting
at 5 L/min oxygen up to 30 L/min, as recommended by the
manufacturer, in 1 L/min increments from 5 to 15 L/min
and then in 5 L/min steps to 30 L/min.
Each device was evaluated during simulated spontane-
ous breathing using a lung model. Airway pressure stabil-
ity throughout the breathing cycle, estimated by calculat-
ing the mean of the pressure excursion inside the device
chamber (maximum pressure-minimum
pressure⫽excursion pressure), was used as an indirect in-
dex of work of breathing. As shown in Figure 2, a pneu-
matic lung simulator (Dimar) generating a mildly tachy-
pneic sinusoidal flow pattern (tidal volume 500 mL,
inspiratory time 0.8 s, expiratory time 1.6 s, breathing
frequency 25 breaths/min) was directly connected to each
device. A pneumotachograph and pressure transducer (ICU-
Lab) were positioned between devices and the pneumatic
lung simulator, and each device was tested during 60 s of
uninterrupted simulated breathing. Air-entrainment devices
were evaluated by delivering increasing levels of oxygen
flow from 5 to 15 L/min in 1 L/min increments and then
from 15 to 30 L/min in 5 L/min increments and at 4
different CPAP levels (5, 10, 15, and 20 cm H
2
O), set with
each device’s adjustable CPAP valve. The Boussignac
CPAP system was tested by delivering an increasing flow
of oxygen from 5 to 30 L/min. For all devices, pressure
excursion was calculated as mean of the pressure excur-
sion over the 25 ventilatory cycles occurring during the
recording time.
In addition, device oxygen consumption or rather oxy-
gen inflow requirement was calculated from an oxygen
tank (volume of 7 L) fully charged at 200 bar for a total
1,400 L of oxygen. The oxygen flow needed to generate a
minimum air-flow output of 60 L/min was used to esti-
mate efficiency in total minutes of run time. All experi-
ments were carried out by the same researcher (CB).
Statistical Analysis
Data are expressed as mean ⫾SD. All statistical anal-
yses were performed using SPSS 21 (IBM, Armonk, New
York), and significance was considered to be P⬍.05. All
data were analyzed by averaging measurements on 3 dif-
ferent devices of each evaluated model.
Gas Output Flow Generation Performances
The total gas output flow obtainable with the different
devices was compared by 2-way analysis of variance, with
input flow and device as factors. The relationship between
oxygen input flow and generated air-flow outputs of each
device was tested by linear regression analysis.
Fig. 1. The 5 tested devices. A: Boussignac CPAP system; B:
EasyVent; C: Ventumask; D: Ventukit; E: EVE Coulisse.
CPAP IN EMERGENCY SETTINGS
RESPIRATORY CARE •●●VOL ●NO●3
RESPIRATORY CARE Paper in Press. Published on September 29, 2015 as DOI: 10.4187/respcare.04134
Copyright (C) 2015 Daedalus Enterprises ePub ahead of print papers have been peer-reviewed, accepted for publication, copy edited
and proofread. However, this version may differ from the final published version in the online and print editions of RESPIRATORY CARE
Static Test
Masks and helmets were analyzed separately. The gen-
erated flows and F
IO
2
of devices, at a fixed oxygen input
flow of 15 L/min, were compared by 2-way analysis of
variance, with CPAP level and device as factors. Differ-
ences between devices at a given CPAP level were tested
post hoc, and Pvalues of multiple comparisons were cor-
rected using the Bonferroni correction.
Dynamic Test
Masks and helmets were analyzed separately. Normality
of distributions was assessed by the D’Agostino-Pearson
omnibus test, and correlations were assessed by Pearson R
or Spearman’s rho, accordingly. Pressure excursions of
masks and helmets were compared by 2-way analysis of
variance, with CPAP level and device as factors. Differ-
ences between devices at a given CPAP level were tested
post hoc, and Pvalues of multiple comparisons were cor-
rected using the Bonferroni correction.
Results
Gas Output Flow Generation Performances
The gas output flow of each device without a CPAP
valve was linearly related to the oxygen input flow (Fig.
3), and the results of linear regression are reported in Table
1. The EasyVent (83 ⫾27 L/min) and EVE Coulisse
(78 ⫾28 L/min) produced a greater air-flow output than
the Ventumask (49 ⫾20 L/min), Boussignac CPAP sys-
tem (10 ⫾4 L/min), and Ventukit (45 ⫾10 L/min) at all
oxygen input flows (P⬍.001 for comparisons between all
pairs of devices, except EasyVent vs EVE Coulisse at an
input flow of 14 L/min, P⬎.99).
Fig. 2. Illustration of the in vitro circuit used to evaluate the performance of each device in terms of flow, generated pressure, and delivered
F
IO
2.
Fig. 3. Air-flow outputs generated by each device at different oxygen flows from 5 to 15 L/min in 1 L/min increments without any CPAP valve.
CPAP IN EMERGENCY SETTINGS
4RESPIRATORY CARE •●●VOL ●NO●
RESPIRATORY CARE Paper in Press. Published on September 29, 2015 as DOI: 10.4187/respcare.04134
Copyright (C) 2015 Daedalus Enterprises ePub ahead of print papers have been peer-reviewed, accepted for publication, copy edited
and proofread. However, this version may differ from the final published version in the online and print editions of RESPIRATORY CARE
Static Test
Masks. Considering the architectural differences between
the Boussignac CPAP system and the other 4 devices (in
particular, the inability to preset a positive pressure and
F
IO
2
), an initial separate characterization was performed
(Fig. 4). The maximum positive pressure achieved with
the Boussignac CPAP system was 9 cm H
2
O at an oxygen
input flow of 30 L/min; therefore, no direct comparison
with other mask devices could be performed at CPAP
levels of 10, 15, and 20 cm H
2
O.
At a CPAP of 5 cm H
2
O, the EasyVent generated a
higher output flow than the Ventumask and Boussignac
(120, 75, and 15 L/min, respectively; P⬍.001 for all
pairwise comparisons), with a lower F
IO
2
(31, 37, and 58%,
P⬍.001 for all comparisons). At a CPAP of 10 cm H
2
O,
the EasyVent generated a higher output flow than the Ven-
tumask (118 vs 70 L/min, P⬍.001), with a lower F
IO
2
(30% vs 40%, P⬍.001). At a CPAP of 15 cm H
2
O, the
EasyVent generated a higher output flow than Ventumask
(100 vs 72 L/min, P⬍.001), with a lower F
IO
2
(33% vs
42%, P⬍.001). At a CPAP of 20 cm H
2
O, the EasyVent
generated a higher output flow than the Ventumask (90 vs
40 L/min, P⬍.001), with a lower F
IO
2
(35% vs 55%, P⬍
.001).
Helmets. At a CPAP of 5 cm H
2
O, the EVE Coulisse
generated a higher output flow than the Ventukit (120 vs
60 L/min, P⬍.001), with a lower F
IO
2
(31% vs 41%, P⬍
.001). At a CPAP of 10 cm H
2
O, the EVE Coulisse gen-
erated a higher output flow than the Ventukit (112 vs 46
L/min, P⬍.001), with a lower F
IO
2
(30% vs 47%, P⬍
.001). At a CPAP of 15 cm H
2
O, the EVE Coulisse gen-
erated a higher output flow than the Ventukit (95 vs 35
L/min, P⬍.001), with a lower F
IO
2
(32% vs 54%, P⬍
.001). At a CPAP of 20 cm H
2
O, the EVE Coulisse gen-
erated a higher output flow than the Ventukit (80 vs 20
L/min, P⬍.001), with a lower F
IO
2
(34% vs 80%, P⬍
.001).
A comparison of the overall efficiency of all devices
with the static test is illustrated in Figures 4 and 5. All
CPAP devices showed a reduction of air-flow output and
an increase in F
IO
2
as the CPAP level was increased.
Dynamic Test
Because the Boussignac CPAP system never reached a
minimum air-flow output of 60 L/min, it was considered
not to be comparable with the other devices and was not
included in the dynamic bench test. Normality assumption
for pressure excursion distribution was rejected for both
masks and helmets, with P⬍.001. The dynamic bench
test showed a significant negative correlation between the
gas flow generated by the CPAP devices and the pressure
excursion inside the device for both masks (rho ⫽⫺0.86,
P⫽.01) and helmets (rho ⫽⫺0.79, P⫽.03). For both
air-entrainment masks and helmets, a steep decrease in
pressure excursion was observed when the delivered flow
reached the threshold of 60 L/min (Fig. 6). Absolute val-
ues of pressure excursion were lower in helmets due to
their high internal volume.
The EasyVent had significantly lower pressure excur-
sion than the Ventumask at all CPAP levels (P⬍.001),
and the EVE Coulisse had lower pressure excursion than
the Ventukit at 5 cm H
2
O(P⬍.001), 15 cm H
2
O(P⫽
.02), and 20 cm H
2
O(P⬍.001), whereas at 10 cm H
2
O,
no significant difference was observed between the 2 de-
vices (P⬎.99). The results of the dynamic test are illus-
trated in Figure 7. The efficiency of devices in terms of
oxygen consumption needed to achieve the output flow
threshold of 60 L/min at a given CPAP level are reported
in Table 2.
Discussion
The major findings of this study are: (1) different de-
vices for noninvasive CPAP varied significantly in their
Table 1. Output Flow Generation Performance of Each Tested
Device
Device Slope (95% CI) Intercept (95% CI) r
2
Boussignac system 0.7–0.9 0.8–3.1 0.97
Ventumask 5.9–6.4 ⫺14.5 to ⫺9.8 ⬎0.99
EasyVent 4.8–11.0 7.3–8.8 0.98
Ventukit 4.2–5.3 ⫺18.7 to ⫺5.3 0.99
EVE Coulisse 7.9–9.0 ⫺11.8 to ⫺0.5 ⬎0.99
Results of linear regression of output flow versus input flow are reported.
Fig. 4. Performances of the CPAP Boussignac system. The X axis
represents CPAP values. The left Y axis represents air-flow out-
puts, and the right Y axis represents F
IO
2generated at different
oxygen flows from 5 to 30 L/min. Point labels are input flows
(L/min). With the Boussignac CPAP system, output flows were
slightly lower than input flows, possibly due to oxygen leakage
through the virtual valve.
CPAP IN EMERGENCY SETTINGS
RESPIRATORY CARE •●●VOL ●NO●5
RESPIRATORY CARE Paper in Press. Published on September 29, 2015 as DOI: 10.4187/respcare.04134
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and proofread. However, this version may differ from the final published version in the online and print editions of RESPIRATORY CARE
ability to deliver high air flow and F
IO
2
and to minimize
pressure excursion. (2) The Boussignac CPAP system de-
livered lower total air flows and higher F
IO
2
than air-en-
trainment devices, with pressure and F
IO
2
not indepen-
dently adjustable. (3) Of the air-entrainment devices, the
EasyVent and EVE Coulisse were both more effective and
efficient than Ventumask and Ventukit.
In this study, 5 CPAP devices commercially available
for prehospital and emergency department use were eval-
uated: 3 facial masks and 2 helmets. All of these devices
are easily usable during ambulance transport because none
require electrical power, but only an oxygen source, mak-
ing them ideal devices for prehospital emergency settings.
Four of these devices use the jet air-entrainment principle
to entrain room air, increasing the total air flow delivered
to the patient, and adjustable CPAP valves to provide CPAP.
The Boussignac CPAP system does not entrain ambient
air: the virtual Boussignac valve is designed only to es-
tablish a positive pressure.
Over the past decade, the Boussignac CPAP system has
been used frequently in emergency settings because it is
extremely easy to apply and does not require presettings
by the operator other than oxygen flow, making it conve-
nient for use by paramedical personnel on ambulances.
22-24
We presume that the success of the Boussignac CPAP
system is a result of these characteristics and the fact that
it delivers a high F
IO
2
. However, it does not maintain suf-
ficient air flow to prevent entrainment of ambient air by
the patient, affecting both the effective positive pressure
applied and F
IO
2
delivered. The positive pressure gener-
ated by the virtual valve reached a maximum of 9 cm H
2
O
when driven by 30 L/min oxygen. Because the virtual
valve is in open communication with the external environ-
ment, the oxygen concentration is lowered by dilution by
ambient air inspiration, and a drop in airway pressure at
high minute ventilation has been observed.
25
Moreover,
with each breath, depending on the patient’s respiratory
pattern and strength, a negative pressure will be generated
during inspiration, and a reversal of flow through the vir-
tual valve will occur during expiration, thus altering the
positive pressure generated by the system and therefore
not establishing CPAP.
Of the mask-based devices, the EasyVent demonstrated
greater efficiency than the Ventumask at the same CPAP
and oxygen settings and generated greater air-flow outputs
and lower F
IO
2
. The EasyVent generated high air-flow out-
put even with a CPAP of 20 cm H
2
O, always remaining
ⱖ60 L/min. Moreover, 6 L/min oxygen was sufficient to
generate an air-flow output of 60 L/min without CPAP but
maintained a very low F
IO
2
. The Ventumask generated
good air-flow outputs at a CPAP of 5–15 cm H
2
O, but
total air-flow output decreased to 25 L/min at a CPAP of
20 cm H
2
O, with a consequent increase in F
IO
2
(50%).
Moreover, 10 L/min oxygen was needed to generate a total
Fig. 5. Ventumask (A), Ventukit (B), EasyVent (C), and EVE Coulisse (D) air-flow outputs at different CPAP levels (5, 10, 15, and 20 cm H2O)
and an input flow of 15 L/min are shown, as well as F
IO
2.
CPAP IN EMERGENCY SETTINGS
6RESPIRATORY CARE •●●VOL ●NO●
RESPIRATORY CARE Paper in Press. Published on September 29, 2015 as DOI: 10.4187/respcare.04134
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and proofread. However, this version may differ from the final published version in the online and print editions of RESPIRATORY CARE
air-flow output of 60 L/min at zero CPAP. The differences
between these 2 devices in air-flow output may be due to
the technical construction of the 2 jet entrainment systems.
In fact, with the EasyVent, oxygen flow enters the system
in parallel with air flow entrained from the external envi-
ronment, generating laminar air flow, whereas with the
Ventumask, oxygen flow enters at an acute angle to the
ambient air flow and entrains less air, possibly due to
the generation of turbulence.
Of the helmet devices, the EasyVent and EVE Coulisse
were similar in effectiveness, and this result was expected
because they both incorporate the same jet entrainment
systems applied to 2 different interfaces (mask vs helmet).
The Ventukit incorporates the same jet entrainment system
as the Ventumask, but the total air-flow output differed
between these 2 devices. Inside the helmet at the air-flow
output point, the Ventukit includes a plug to reduce the
noise generated by the jet entrainment system. This plug
certainly reduces the noise inside the helmet, but adds a
resistance, measured by the authors as 6 cm H
2
O per 50
L/min, significantly reducing the effectiveness of air en-
trainment. Unfortunately, this reduction in air entrainment
limits the use of the Ventukit because the air-flow output
was ⬎60 L/min only at a CPAP of 5 cm H
2
O, with an
oxygen consumption of 14 L/min. An air-flow output ⬎60
L/min is important in helmets not only to reduce the pa-
tient’s work of breathing, as with masks, but also to avoid
CO
2
rebreathing.
26,27
The EVE Coulisse maintained a total
air-flow output well over 60 L/min with CPAP set from 5
to 20 cm H
2
O and consumed from only 8 L/min oxygen at
a CPAP of 5 cm H
2
O to 13 L/min oxygen at a CPAP of 20
cm H
2
O.
Our data also support the clinical relevance of an air-
flow threshold of 60 L/min, which is recommended in
CPAP guidelines.
20,21
We found increased pressure excur-
sion and negative pressure spikes during the inspiratory
phase whenever 60 L/min was not reached (see Fig. 6).
Comparisons between devices systematically showed sig-
nificantly larger pressure excursion for those devices that
did not reach the 60 L/min threshold. In helmets, low total
air flow also resulted in lower pressures during the inspira-
Fig. 6. Relation between pressure excursion and gas output flow in
air-entrainment devices. A steep decrease in the first was ob-
served above a threshold of 60 L/min.
Fig. 7. Pressure excursion (maximum pressure-minimum
pressure⫽excursion pressure) of Ventumask and Easy Vent (panel
A) and Ventukit and Eve Coulisse (panel B) during the dynamic
bench test. Input flow, pressure, obtained output flow, and F
IO
2are
reported. * Significantly lower than the other device compared at
the same pressure and input flow (P⬍.001). The Boussignac
CPAP system was not included in this graph because its applied
CPAP cannot be adjusted, and it does entrain ambient air.
CPAP IN EMERGENCY SETTINGS
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tory phase, although pressure remained positive because of
the buffering effect of the high internal capacitance of the
helmet. Nevertheless, a minimum air-flow output of 60
L/min when applying CPAP through helmets is necessary
to avoid the risk of CO
2
rebreathing due to a low washout
flow, in addition to minimizing work of breathing.
The effectiveness of CPAP via mask or helmet at iden-
tical air flow and pressure is comparable.
28
The choice of
device depends on other factors, such as operator experi-
ence, device availability, expected time of support, and
patient’s tolerance. Normally, the mask is more readily
available and easier to apply, thus making it suitable for
ambulance transport. In the emergency department or the
wards, however, the helmet allows greater patient comfort
and avoids risk of skin lesions. Despite these general con-
siderations, the use of helmets in prehospital settings is
feasible, efficient, and safe.
5,7
The efficiency of CPAP devices is an important topic
especially during prehospital use. In fact, in some coun-
tries, oxygen availability on ambulances is limited, and
transportation times can vary greatly. Furthermore, oxy-
gen sources in ambulances in some countries can generally
deliver only up to a maximum of 15 L/min. Therefore,
when higher oxygen flows are needed, as with the Bous-
signac CPAP system, it is necessary to use 2 tanks simul-
taneously to achieve a gas delivery of 30 L/min.
The use of prehospital CPAP has increased consider-
ably in recent years due to the growing evidence regarding
the importance of early treatment of pathologies such as
acute cardiogenic pulmonary edema
5,6
and acute hyper-
capnic respiratory failure.
6,9,29
However, the most recent
studies offer little agreement about the utility of CPAP in
improving a patient’s outcome.
30-32
This is, in our opinion,
due to the heterogeneity of the approaches used to provide
CPAP: many did not specify which CPAP device was
used,
9,33
or they used the Boussignac CPAP system.
23,24,34,35
In contrast, the studies using air-entrainment CPAP sys-
tems concluded that CPAP in prehospital setting is highly
effective.
8,36,37
Due to the variable performance highlighted
by this bench study, it is clear that results of clinical trials
may be at least partially dependent on the effectiveness of
the device used.
Our study has some limitations that need to be addressed.
First, the devices were tested only in an in vitro circuit. As
a result, we were able to accurately describe and compare
the effectiveness and efficiency of each device, but we
were not able to reproduce different clinical conditions.
Thus, our results cannot be directly extrapolated to the
clinical scenario, and larger studies on healthy volunteers
and subjects with various respiratory conditions are needed.
Second, the devices tested were all CPAP devices for am-
bulance and emergency settings and are commercially avail-
able in Europe. Some new CPAP devices with similar
characteristics have recently been developed in the United
States. Owing to the heterogeneity of our results obtained
with the devices tested in this study, it would be advisable
to test with similar methodology the new CPAP devices in
the United States but not yet available in Europe.
Conclusions
In summary, we found considerable differences in per-
formance among the 5 CPAP devices tested. The EasyVent
and EVE Coulisse achieved the best overall performance
in terms of effectiveness and efficiency; the Ventumask
and Ventukit presented more limited air-flow outputs at
lower positive pressures; and the Boussignac CPAP sys-
tem delivered low total air-flow outputs, low positive pres-
sures, and high non-adjustable F
IO
2
. Clinicians and prehos-
pital caregivers should be aware of specific device
performance characteristics to optimize effective applica-
tion of CPAP in prehospital and emergency settings.
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8RESPIRATORY CARE •●●VOL ●NO●
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RESPIRATORY CARE Paper in Press. Published on September 29, 2015 as DOI: 10.4187/respcare.04134
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