Note: Descriptions are shown in the official language in which they were submitted.
Back round of the Invention ll~3~ 4~
g
Management of respiratory insufficiency requires knowledge and
control of the inspired oxygen concentration (FiO2) delivered to the
patient. In addition, control oE the oxygen concentration administered to
the patient is required if one is to avoid unnecessarily high inspired oxygen
concentrations, with the attendant risk of pulmonary oxygen toxicity.
When the patient is breathing through a closed system, such as
through an intratracheal tube, the inspired oxygen concentration can be
easily measured and controlled. When oxygen is delivered via an open
face mask, for instance, a mask having large holes in the cheek portion,
the true inspired oxygen concentration cannot readily be measured and may
be influenced by factors other than the oxygen concentration delivered to
the mask. These variables include the patient's respiratory rate and
pattern of breathing, the design and fit of the mask used, the flow rate
of the oxygen delivered to the mask, and air turbulence in the area surround-
lS ing the patient.
U. S. Patent 3, 850, 171 to G. J. Ball et al shows a medical face mask
having several apertures in the mask body. U. S. Patent 2, 843,121 to
C. H. Hudson also shows a mask having a large plurality of small open-
ings in the cheek portion rather than a single large opening. In fact,
U. ~;. Patent 2, 843, 121 specifically states that a series of small openings
instead of one large opening in each cheek portion is desirable to prevent
too free a passage of the gases in or out of the mask. U. S. Patents
1, 491, 674 to Coletti and 3, 288, 1~3 to Sachs, both show face masks having
cheek holes covered by extensions or enclosures. However, the masks
shown therein do not ha~e means for supplying oxygen to the mask and
both inhalation and exhalation is effected through these openings. ~he
main purpose of the extensions or enclosure is to direct exhaled air away
from the wearers face or to act to filter inspired air.
U. S. 3, 315, 672 to Cunningham et al also shows a mask with "air
- 1 - r-~
1(~35~
reflux fairings" over cheek holes. However, these enclosures also
perform a much different function than the shields of the present
invention. ~his mask is designed for use by a surgeon and cannot be
used for supplying oxygen to a patient. In the Cunningham et al mask,
inhalation is through the intake valves in the cheek portion of the mask
and exhalation is through an exhaust conduit positioned in front of the
users mouth. The purpose of the air reflux fairings is to prevent any
expired air from being directed onto a patient during any transitional
period between inspiration and exhalation when the intake valves may
not be completely closed against exhalation.
U. S. Patent 2, 416, 411 to Sharbaugh et al shows a face mask for
delivery of breathable oxygen to a pilot operating at high elevations. The
demand type mask includes a valve in the inlet duct, which opens only
on inhalation, and valves located in the cheek portion of the mask which
open on exhalation. These exhalation valves are completely enclosed by
a louver which is designed to protect the valve and to retain warm ex-
haled air in the vicinity of the valve to prevent the valve from freezing.
None of the masks described in these patents show or suggest the
mask described and claimed herein as none have, in combination,a means
for administering oxygen or an oxygen containing gas stream to the mask,
cheek holes which allow dilution of the oxygen in the mask and dispersion
of exhaled breath from the mask with a minimum of restric tion, and
open ended shields over the cheek holes to limit and/or prevent external
conditions from causing the oxygen concentration which reaches the
patient to be greatly different from that predicted to be delivered to the
patient.
1~?35~ 4
Summary of the Invention
The standard masks available for administration of oxygen or gas
mixtures containing oxygen to patients have unrestricted holes in the
cheeks of the mask which act 1) to dilute the oxygen fed to the patient and
2) allow exhaled breath from the patient to be dissipated. It has been found
that using such masks, the percent of oxygen fed to the patient cannot be
accurately controlled, high oxygen percentages cannot be administered,
and there are differences between the predicted inspired oxygen concen-
trations (Fi 2~ clinically measured with those predicted sources. Using
a completely enclosed mask, such as an anesthesia mask, or a mask with
one way vents or multiple small cheek holes is not desirable because these
structures cause undesirable restri ction of the patients breathing pattern
and the flow of gas in and out of the mask.
Clinical results obtained with the standard mask show a variation in
the relationship between the clinically measured and predicted inspired
oxygen concentrations (FiO2). Several possibilities were considered to
explain these results. For instance, the respiratory pattern in the patient
might change during the experiment and tidal volume during the experiment
might not be the same as the tidal volume measured with the anaesthesia
face mask before and after the experiment,or the mathematical model used
to predict Fi O2 might not have taken into consideration factors or variables
of importance.
Accordingly, a mechanical model was constructed in order to control
these variables as much as possible. However, even with the mechanical
model unexpected variations in the "tracheal'' oxygen concentration occurred.
It became apparent that there was a significant, though unpredictable, mixing
of incoming oxygen in the mask with ambient room air. This mixing, over
and above that attributable to the difference between the inspiratory flav
rate and the flow rate of oxygen delivered to the mask, is apparently caused
_ 3 _
1~3~4~L
by turbulence resulting ~rom conditions surrounding the patient such as air
flow from ventilation ducts, fans or air cond~itioners, disturbances caused
by persons passing by or administering to the patient, the patient's own
movement, as well as other extraneous sources, or turbulence generated
within the oxygen mask itself caused by the incoming stream of oxygen.
The shielded mask of the present invention eliminated all the adverse
effects caused by turbulence, either interior or exterior of the mask.
An object of the invention is to provide a vented face mask which will
deliver predictable oxygen concentrations.
Another object of the invention is t o provide a vented face mask for
delivery of oxygen to patient where the inspired oxygen concentration is not
subject to variation caused by external sources.
An additional object of the invention is to provide a vented face mask
which will allow the delivery of high oxygen concentrations to a patient.
Other objects and advantages of the invention will appear from the
following description of the preferred embodiment of the invention.
14~
BrieE Description of the Drawing
Figure 1 i9 a side perspective view of the invention.
Figure 2 is a front perspective view of the invention
Figure 3 is a second side perspective view of the invention.
Figure 4 is a graph showing clinical re~ults of mean inspired
oxygen concentrations measured on patients using a standard mask.
Figure 5 is a schematic drawing of a mechanical model used
to simulate respiration for comparison of the standard mask to the
mask of the invention.
Figure 6 is a graph showing a standard mask as tested under clinical
conditions compared with the same mask evaluated using the mechanical
model under both turbulent and turbulence free conditions.
Figure 7 is a graph showing the results of evaluation of the mask
of the invention (shielded mask) under the turbulent and turbulence free
conditions, using the mechanical model.
Figure 8 is a graph comparing the standard mask and the mask of
the invention (shielded mask) under non-turbulent conditions using the
mechanical model.
Figure 9 is a graph showing the standard mask and the shielded masks
compared under similar conditions in a controlled clinical experiment under
normal hospital conditions.
1~3~ lL4~
Description of the Preferred I3mbodiment
Referring now to the drawings, the shielded mask of the present
invention is shown in Figures 1 through 3. The mask 10 consists of a
flexible shell shaped to fit about the nose and mouth of a patient and to
be in contact with the face so as to prevent gas administered to the patient
from leaking around the edges of the mask. To aid in sealing the mask to
the face,a flange is provided at the outer edge of the mask. The top of the
mask 14 is shaped to fit on and approximate the bridge of the nose while the
lower end 16 is rounded to fit just under the patient's chin. Al~ong the side
of the mask and approximately half way between the top and bottom of the
mask are a pair of tabs 18. Attached to tabs 18 is an adjustable or elastic
retaining strap 20. In use, the strap 20 is placed behind the patient's head
thus retaining the mask on the patient and causing the flange 12 to make
intimate contact with the patient's face so that the administered oxygen
doe~ not leak around the edges of the mask.
Located in the upper part and in the center of the nose portion 21 of
the mask is a pin 22,Mounted on this pin is a nose clip 24. The nose clip
is a flexible material, preferably a thin metal which can be easily bent,
and when bent readily retains its new shape. After the mask is placed on a
patient, finger pressure placed on the nose clip 24 will bend it so that
the clip and the portion of the mask underlying the clip is shaped to conform
to the nose of the patient, thus effecting a good seal between the mask and
the patient's face surrounding the nose.
Attached to the lower end of the no~e portion 21 is an inlet part 26 sized
for the attachment of an aerosol connector 28, an oxygen dilution valve
(not shown) or tubing connected to a regulated source of oxygen ~not shown).
Located on both sides of the nose portion 21 are a pair of cheek holes 28
which allow expired air to leave the mask and which allow diffusion of am-
bient air to dilute a concentrated oxygen stream administered through the
inlet port 26. The cheek holes are preferably about 1/2 inch to 1 inch in
diametér but the size of the holes are not believed to be critical. In addition,
rather than a single large ~o~e on e~her side of the nose portion several
holes or a series of holes having a cross-sectional area approximately
the ~ame as the single cheek hole 28 would serve the same purpose as each
of the single cheek holes 28. Positioned over the cheek holes 28 are shields
3~ As ~hown in Figure 3 shields 30 are cup shaped flexible enclosures
which cover but do not obstruct the cheek holes 28. The lower portion of
the shields 32 are open to allow easy diffusion or flow of gases in and out of
the mask while the upper portion of the 6hields prevent flow of air outside
or past the mask from disturbing the oxygen concentration within the mask.
Using the shielded mask on patients it wa6 pos6ible to obtain a higher
inspired oxygen concentration than was possible with the standard ma~k and,
with the shielded ma~k, the tracheal oxygen concentration could be raised to
100% with a ~ufficiently high flow rate of oxygen delivery, also not pos~ible
with the unshielded mask. In addition, the concentration of the in6pired
oxygen could be more readily and accurately regulated. Greater standard
deviations at delivered flow rate~ of less than 15 litres per minute were
obtained u6ing the 6hielded mask but thi6 probably represent6 true breath-
to-breath variahons in a situation where the delivered oxygen flow doe6 not
approximate inspiratory flow requirements.
EXAMPLE 1
Intratracheal oxygen concentration was directly measured in patients
receiving oxygen by the use of a face mask having holes in the cheek portion
thereof. Each patient had had a tracheo~tomy tube removed several days
earlier but was breathing 6pontaneously through the upper airway with the
residual ~toma covered by an occlu6ive dressing. A catheter was passed
through this 6toma into the di6tal trachea through a small plastic plug which
completely occluded the rest of the stoma. The intratracheal catheter was
connected to a 6mall Y connector. One limb of the Y connector was used for
withdrawing sample~ of tracheal ga~ for oxygen analysis. The other limb
wa~ connected to a CO2 analyzer 6et to sample at 500 c. c. per minute. The
output of the CO2 analy~er wa6 continuously recorded on a strip chart recorder.
1~35~44
The total volume of the catheter Y piece and connecting tubing was 3. S c. c.
100% oxygen wa6 delivered to the patient through a nebulizer u6ing
calibrated flow meter~. Wide bore tubing (3/4") connected the nebulizer
to a standard aerosal oxygen mask, which wa~ substantially as shown in
Figure 1 except that the cheek shields were not present. An example of
`6uch a mask is 601d as Cat. No. 002610 by Inspiron Division of C. 1~. Bard,
Inc.
The continuous recording of the CO2 concentration in the trachea
served as a tracing of the respiratory cycie and permitted measurement of
the respiratory rate and the duration of the inspiratory phase of each respira-
tory cycle (the inspiratory fraction).
Samples of tracheal gas for oxygen analysis were a~pirated through the
limb of the Y connector used to withdraw samples into 50 c. c. plastic syringes
during several consecutive inspiratory cycle6 at a time when respiration was
-15 stable and the sampled gas was immediately analyzed u6ing a paramagnetic
oxygen analyzer.
In each patient the flow rate of 100% oxygen delivered to the ma6k was
succes6ively raised from 5 litres per minute to 30 litres per minute in 5
litre increment~. At each of these 6iX nOw rates, tracheal oxygen concen-
tration was measured during the inspiratory phase.
The patient's minute ventilation was measured with a respirometer
attached to an occlusive anaesthetic face mask, both immediately before
and immediately after the measurements of the tracheal oxygen concentra-
tion6 delivered by the pla6tic face mask. The duplicate values of minute
ventilation proved to be quite ~imilar, with the difference between the two
being less than 600 c. c. in each patiént. The average of the two minute
ventilation determinations wa~ uE;ed for sub6equent calculations. Tidal
volume was calculated by dividing the minute ventilation by the respiratory
frequency.
Figure 4 6hows results obtained in clinical studie6 using the standard
face mask. The tracheal oxygen concentration increase~ with increasing
flow rates o~ delivered oxygen as would be expected. However, even at
high flow rates, there is marked variation in FiO2 from patient to patient
(as reflected by the standard deviation). In addition. tracheal oxygen
concentration never reaches lOO"~o but rather appears to plateau as the flow
rate of oxygen to the mask is increasèd. In addition, it wa~ believed that
the environment surrounding the patient was affecting the amount o~ oxygen
actually delivered to the patient.
To evaluate the effect of the variables which might affect the inspired
oxygen concentration in patients, a mechanlcal model of the ventilatorv
system was con~tructed as shown in Figure 5. A sine-wave pump 34 was used
to simulate respiration. A 6tandard plastic aerosal mask 36 as described above
was mounted on a firm backing 38 and attached to the pump 40 with a tube the size
of a normal human trachea. A catheter ~2 was used to sample the F~O2 in the
mechanical "trachea". 100% o~ygen 41 was delivered ~wgh the same system
of flow meters 43 and nebulizer 44 used Eor the clinical studies. The pump was
set to daliver a tidal volume of 600 c. c. at a respirats>ry frequency of 15 cycles
per second and an inspiratory fraction of 0. 5 of the respiratory cycle.
Oxygen flow rates to the mask were varied from 5 litres to 30 litres per
minute as in the clinical studies. In addition the studies using the mechanical
model were carried out in botil a very still environment and in one containing
air currents generated by a small fan placed 6 feet from the face mask and
the effect of turbulence caused by the fan was determined. The test was then
repeated using the modified oxygen mask having shields over the side-holes
as illustrated in Figure 1.
Figure 6 shows the result obtained with the mechanical model using the
standard face mask in both a still and a turbulent environment. In the tur-
bulent en~,ironment, (with the fan on), the Fi 2 varies considerably and
unpredictably. In the still environment (fan off~, the FiO2 is higher and more
stable. However, in neither case did the oxygen concentration in the mechani-
cal trachea reach 100% even with oxygen delivered to the face mask at a rate
_q,
1~?3'~L4~ `
o~ 30 litre~ per minute. For comparison purposes the result of the clinical
trial shown in Figure 5 i3 also incorporated in Figure 6. As can be 6een, the
clinical situation i~ neither a still or turbulent condition but is instead an
intermediate condition.
Result~ obtained under similar circumstance~ with the shielded mask
of the invention, are shown in Figure 7. These figures illustrate two important
features of the modified mask. The fir~t is that room air turbulence has no
significant effect on the Fl 0 2 delivered with this mask. The second iæ that
the ~12 delivered with this mask i6 higher at any given flow rate of oxygen
delivery than the Fi02 measured under similar circumstances with the
unæhielded mask. With the shielded mask, inspired oxygen concentration in
the mechanical trachea reaches 100% at an oxygen flow rate of 30 litres per
minute. Even in the still environment, the FiO2 delivered with the shielded
mask is higher than with the un~hielded mask under similar circumstances.
The results for the mask with shields and the standard mask evaluated under
still conditions are shown in Figure 8.
Using both the ~hielded and standard maæk on each patient clinical
measurements of tracheal oxygen concentration were obtained. Tke results
of this study, shown in Figure 9, demonstrate that the Fi02 obtained with
the æhielded mask is consiætently higher than that obtained with the standard
mask under similar circumstances and values approaching 100% FiC2 could
oT~ly be attained using the shielded mask. In addition, when oxygen flow
to the mask is 15 litres per minute or greater, the standard deviation from
patient to patient using the shielded mask, is significantly less than the
standard deviation from patient to patient with the standard mask (P~. 005),
indicating that the shields reduced disturbances of the oxygen feed caused
by outside sources.
~ /6'--
