INTRODUCTION
The Oxylator EM-100™ (CPR Medical Devices) has recently
been cleared (FDA, HPB and TUV) as a ventilatory device for
use during resuscitation. This manually-triggered constant-flow
generator delivers pure oxygen when the operator depresses the
oxygen-release button. In the manual mode, the operator is instructed
to use a 2-second inspiratory time (TI) in order to produce
a tidal volume (VT) which follows the JAMA recommendations (1).
The pressure-relief safety valve must initially be set at 25
H2O if the operator believes that a higher peak inspiratory
pressure is necessary to deliver an appropriate VT (TI of 2
seconds for adults) to a specific patient.
At the Royal Victoria Hospital (Montreal, Canada) two anesthesiologists
have used the Oxylator™ EM-100 extensively for more than
two years. This study was designed to evaluate if other health
professionals with no previous experience with this device could
perform adequate mask ventillation when using it in the manual
mode. A secondary objective of this study was to assess the
effect of training in these health professionals.
METHODS
Following approval by the Hospital Ethics Comittee, an informed
consent was obtained from 40 healthy patients (ASA I or II).
These patients had normal upper airways and were at no increased
risk for regurgitation. A first group of twenty volunteers were
ventilated by two anesthesiologists (MD:10 patients each) having
more than two years of experience with the Oxylator™ EM-100.
A second group of twenty patients were ventilated by five respiratory
technicians (RRT:4 patients each), with no previous experience
with the Oxylator™ EM-100.
While pre-oxygenating the patient prior to scheduled surgery,
anesthesia was induced with vecuronium 0.5 mg, fentanyl 5 µ/kg,
thiopental 5-7 mg/kg and succinylcholine 2 mg/kg. After obtaining
complete muscle relaxation, mask ventilation with 100% oxygen
was provided with the Oxylator™ EM-100, following the
man-ufacturer's recommendations. The operator was instructed
to press the oxygen-release button for two seconds (counting
"a thousand and one, a thousand and two") and to release
it for three seconds, and to repeat this breathing cycle for
one minute. The pressure-relief setting was placed at 25 cmH2O
and this setting was not modified for any of these 40 patients.
After one minute of ventilation by mask, endotracheal intubation
was (ETT 7.5 mm or 8.5 mm I.D.) was performed and another one-minute
period of ventilation was provided by the same operator following
the same instructions.
Oxygen flow was measured with a heated Fleisch #1 pneumotachometer
positioned between the Oxylator™EM-100 and the mask (or
ETT). The pressure drop across the pneumotachograph was measured
by a differential piezoresistive pressure transducer (MicroSwitch
163PCO1D36, Honeywell). Airway pressure was measured with a
piezoresistive transducer (Fujikura, FPM-02PG) inserted in a
lateral tap of the connection between the pneumotachograph and
the mask (or ETT). The signals from the two piezoresistive pressure
transducers were amplified and then passed through 5-pole Bessel
low-pass filters (902L, Frequency Devices) with their corner
frequencies set at 30 Hz. Finally the signals were sampled |
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ABSTRACT
The Oxylator EM-100™ has recently been approved
as a ventilatory device for use during resuscitation.
This study compares the efficacy of mask ventilation provided
by anaesthetists (MD) or respiratory technicians (RRT)
using the EM-100. Twenty healthy volunteers were ventilated
by two MD's with more than two years of experience with
the EM-100™. A second group of twenty healthy volunteers
was ventilated by 5 RRT's (four patients each) who never
previously used the EM-100 . Immediately after induction
of anaesthesia and also following endotracheal intubation
(ETT), ventilation was accomplished by pressing the inspiratory
flow button of the EM-100 for 2 seconds, then releasing
it for the following three seconds, and repeating this
breathing for one minute. Oxygen flow was measured with
a heated Fleisch pneumotachometer and airway pressure
with a piezoresistive transducer. Usin a mask or an ETT,
MD's and RRT's provided ventilation which followed the
JAMA recommendations for manually triggered devices. During
mask ventilation, a peak airway pressure of 19.3±
3.5 cmH2O was required to achieve a 1-litre
tidal volume (VT) and 13 patients required more than 20
cmH2O. The expired VT represented 93.2±7.7% of
the VT obtained with a ETT for the MD's and 93.8±8.2%
for the RRT's. Compared to the two MD's, RRT's only had
a larger variability of TI and breathing frequency. During
mask ventilation, mre than 93% of the inspired oxygen
reached the lungs. Most of this difference is likely explained
by leaks around the mask which were sometimes felt. Gastric
inflation was not identified in any of these 40 patients.
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at 100 Hz and
then fed into a 12-bit analog-digital converter (DT2801A, Data
Translation) installed in a 386 personal computer. All data
were collected and analyzed using LABDAT and ANADAT software
(RHT-InfoDat inc.).
After initial testing with ANOVAs, differences between the means
were tested with appropriate (paired or unpaired) t-tests using
the Bonferroni correction. The level of statistical significance
was P<0.05.
RESULTS
Using a mask or an ETT, MD's and RRT's provided ventilation
which followed the JAMA recommendations for manually-triggered
devices (1). The average breathing frequency was 12.3 breaths/minute
and no difference was found between MD's and RRT's. or between
ventilation by mask or with an ETT. The expired VT (cf. Figure
1a) was not different between MD's and RRT's. However, significant
differences in the expired VT were found between ventilation
by mask or with an ETT for both MD's(P<0.01) and RRT's (P<0.001).
This could have been related to a difference in TI but no such
difference was found (cf. Figure 1b). As the Oxylator™
EM-100 generates a constant inspiratory flow, in order to assess
the efficiency of mask ventilation as compared to ventilation
with an ETT, we used the "effective" inspiratory flowrate
(VT/TI) which is estimated by dividing the expired VT by TI.
No difference in VT/TI was observed between MD's and RRT's (cf
Figure 1c). However significant differences in the VT/TI were
found between ventilation by mask or with an ETT for both MD's
(P<0.001) and RRT's (P<0.01). During mask ventilation,
the VT/TI represented 93.2±7.7% of the VT/TI obtained
with an ETT for the MD's and 93.8±8.2% for the RRT's.
Furthermore, no "training effect" was identified for
these 5 RRT's, as no difference was found between the ventilatory
parameters obtained with their four consecutive patients.
During mask ventilation, a peak inspiratory pressure of 19.3±
3.5 cmH2O was required to achieve a "1-litre" tidal
volume (cf. Figure 2) and 13 patients required more than 20
cmH2O. During ventilation with an ETT, the required peak inspiratory
pressure was 23.6± 3.7 cmH2O, and 32 patienst required
more than 20 cmH2O.
DISCUSSION
As compared to the two MD's, RRT's produced very similar ventilatory
patterns which only had a larger variability of TI and breathing
frequency. Furthermore, no training effect was demonstrated
in these 5 RRT's. Using the Oxylator™EM-100 in manual
mode, health care professionals provided adequate ventilation
in 40 consecutive patients. Previous experience wiht the Oxylator™EM-100
does not seem to be required for trained personnel.
During mask ventilation, more than 93% of the inspired oxygen
reached the lungs. Most of this difference is likely explained
by leaks around the mask which were sometimes felt. Gastric
inflation was not identified in any of these 40 patients. During
mask ventilation, 13 of these anesthetized and paralyzed patients
required more than 20 cmH2O of peak inspiratory pressure. During
CPR, it is quite possible that even a higher percentage of patients
will require a peak inspiratory pressure greaer than 20 cmH2O.
REFERENCE
1-JAMA 268(16): 2200, 1992. |
