Title: System and elements for managing therapeutic gas administration to a spontaneously breathing non-ventilated patient
Abstract: A system controls and manages administration of a therapeutic gas, such as NO, O2, or the like, to a spontaneously breathing, non-ventilated patient such that concentrated NO is as low as reasonably possible while delivering the desired amount of NO to the distal portions of the lungs. The system includes an entrainment cell that provides remote, turbulent mixing with low temporal latency and can be used with a nasal cannula or a mask. The entrainment cell uses room air to dilute the therapeutic gas; however, supplementary gases can also be used. A baffle can be included to promote mixing and a flow sensor can also be used if desired. Multiple ports can be included in the entrainment cell. An equalizing valve is also disclosed.
Patent Number: 6,986,351 Issued on 01/17/2006 to Figley, et al.
| Inventors:
|
Figley; Curtis B. (Edmonton, CA);
Hunt; Darin W. (Edmonton, CA);
Miller; Christopher C. (North Vancouver, CA)
|
| Assignee:
|
Pulmonox Technologies Corporations (Edmonton, CA)
|
| Appl. No.:
|
691649 |
| Filed:
|
October 24, 2003 |
| Current U.S. Class: |
128/205.24; 128/205.18; 128/205.22; 137/505.25; 251/368 |
| Current Intern'l Class: |
A62B 7/00 (20060101); A62B 7/10 (20060101); A62B 9/02 (20060101); F16K 31/00 (20060101); F16K 31/12 (20060101) |
| Field of Search: |
128/20022,201.28,200.24,204.18,204.22,204.23,204.24,204.25,205.14,205.16,205.18,205.21,205.22,205.24,204.29
137/505.11,505.12,505.25,505.28,505.42,907,908,535-538,540-543
251/300.5,368
|
References Cited [Referenced By]
U.S. Patent Documents
| 4173986 | Nov., 1979 | Martin.
| |
| 4699173 | Oct., 1987 | Rohling.
| |
| 5662100 | Sep., 1997 | Fox et al.
| |
| 5722455 | Mar., 1998 | Caminada.
| |
| 5950677 | Sep., 1999 | Bhide.
| |
| 6155258 | Dec., 2000 | Voege.
| |
| 6167882 | Jan., 2001 | Almqvist et al.
| |
| 6202645 | Mar., 2001 | Brown.
| |
| 6240943 | Jun., 2001 | Smith.
| |
| 6286543 | Sep., 2001 | Davidson.
| |
| 2003/0131849 | Jul., 2003 | Figley et al.
| |
| 2005/0004511 | Jan., 2005 | Figley et al.
| |
Primary Examiner: Mitchell; Teena
Attorney, Agent or Firm: Gernstein; Terry M.
Parent Case Text
The present application is a divisional application of application Ser. No. 09/688,229
filed on Oct. 16, 2000 now U.S. Pat. No. 6,668,828.
Claims
What is claimed is:
1. A low dead volume pressure equalizing device for high purity gas circuits
comprising: means for providing a flow versus pressure dead band, and means for
providing zero flow in either direction at non-zero differential pressures.
2. The device defined in claim 1 further including an inlet fitting to a gas
circuit and means for connecting the device to said inlet fitting and further including
a pin for minimizing dead space.
3. The device defined in claim 2 further including a plunger, first and second
sealing surfaces, opposed springs acting on said plunger, and an intermediate region
of plunger travel during which flow will be prohibited.
4. The device defined in claim 3 wherein said dead band is symmetric in differential
pressure about zero with respect to non-zero flow in either direction.
5. The device defined in claim 3 wherein characteristics of said springs determine
whether said dead band is symmetric or asymmetric in differential pressure about
zero with respect to non-zero flow in each direction.
6. The device defined in claim 5 further including safety means for preventing
flow rates beyond a preset value in an event of otherwise unconstrained flow.
7. The device defined in claim 6 wherein said safety means includes means for
changing flow restriction based on flow rates.
8. The device defined in claim 1 wherein the pressure equalizing device is located
inside an inlet fitting to a gas circuit.
Description
TECHNICAL FIELD OF THE INVENTION
The present invention relates to the general art of surgery, and to the particular
field of introducing material to a patient for therapeutic or diagnostic purposes,
most specifically, the invention relates to NO therapy.
BACKGROUND OF THE INVENTION
The use of therapeutic gases to treat a human or animal patient has been known
in the art for many years. A number of different gases may be added to a respiratory
gas that is inhaled by a spontaneously breathing, non-ventilated patient. These
gases may be used to achieve some therapeutic effect, service a diagnostic function
or have some other desirable purpose. Such gases will be referred to herein as
"therapeutic gases." One skilled in the delivery of therapeutic gas will understand
that the disclosure can be used to teach either human or animal patients. Accordingly,
no limitation to human is intended by references to patient in this disclosure.
One therapeutic gas is nitric oxide (NO), which is administered by inhalation
in low concentrations to treat primary or secondary pulmonary hypertension or other
diseases. In many cases, nitric oxide or other therapeutic gases come from a high
concentration source such as a high concentration compressed gas cylinder. The
gas source may be pure or may contain some concentration of therapeutic gas in
a carrier gas. There may also be cases where more than one therapeutic gas is used,
with or without a carrier gas or gases. It is often necessary to dilute therapeutic
gas to a lower concentration and mix it with air and/or oxygen prior to delivery
to the patient. This dilution may be necessary to achieve a desired dosage concentration
and/or to avoid or reduce adverse bioeffects that may occur if high concentration
gas is delivered to the patient. If the therapeutic/carrier gas is not sufficiently
oxygenated, it is necessary to mix it with air prior to delivery to the patient.
In some cases, it is necessary to add supplemental oxygen to the mixture to avoid
a hypoxic respiratory mixture or to enrich the oxygen content of the respiratory
gas above twenty-one percent. In the latter case, the oxygen will also be considered
as a therapeutic gas.
NO is one of a number of therapeutic gases that are administered to a patient
and require dilution from a high concentration form to a lower, safer concentration
before administration to a patient. NO will be the primary focus of this disclosure;
however, one skilled in the surgical arts will understand that the disclosure can
be used to teach other gases as well. Accordingly, no limitation to NO is intended
by the references to NO in this description.
The art contains several devices and systems to deliver therapeutic gas to a
spontaneously breathing, non-ventilated patient. However, as will be discussed,
each of the known systems and devices has drawbacks.
A system that has continuous flow to a mask is one such known system. A therapeutic
gas, oxygen and air are supplied from sources such as compressed gas cylinders
or a hospital wall. A continuous flow of these gases is titrated together before
delivery to a patient. The flow rate of each gas is set to achieve the desired
concentration of the therapeutic gas and oxygen in the respiratory gas. The total
flow rate is set greater than the peak inspiratory flow rate. If a reservoir bag
is added to the inspiratory portion of the overall circuit, then the total flow
can be reduced, but must still be greater than the minute volume of the patient.
The mixed gas is connected into the mask, from which the patient inhales. Exhaled
gas and excess inhalation gas flow from an outlet side of the mask and may be scavenged.
This system has the disadvantage of wasting gas since not all therapeutic gas is
inhaled by the patient. Scavenging is required to prevent the therapeutic gas from
entering the environment. In addition, large volumes of air and/or oxygen must
be supplied to dilute/mix the therapeutic gas. Also, therapeutic gas is delivered
to the entire respiratory tract, not just the areas where it is needed. This may
increase adverse bioeffects and the possibility of undesirable reaction products
from the therapeutic gas. The mask also makes eating and talking difficult and
is also aesthetically unappealing. Still further, a mask may make some patients
nervous and cause anxiety by making them feel confined.
Yet another system uses a bolus pulse of therapeutic gas to, a mask. In this
system, therapeutic gas is delivered to the patient as a bolus of gas that is delivered
via the mask. The bolus of therapeutic gas is delivered over a short period of
time and is not significantly diluted by inhaled air or supplemental oxygen. Supplemental
oxygen may also be delivered via the mask. The patient's breathing waveform is
monitored and the bolus of therapeutic gas is delivered to the mask intermittently,
in synchronization with the respiratory waveform so,that the therapeutic gas is
inhaled at a set phase of the respiratory waveform. The bolus is preceded and/or
followed into the respiratory tract by air/oxygen. This system and method has the
disadvantage that it does not dilute the therapeutic gas, so a high concentration
source cannot be used. In addition, the short duration of the bolus means that
a higher concentration of therapeutic gas is required to deliver the same number
of molecules of the gas to the patient. This could have adverse bioeffects. This
method does not have the flexibility of varying *the concentration of the therapeutic
gas at various times during inspiration. The mask has the same drawbacks as heretofore discussed.
Yet another system and method uses an undiluted pulse via a nasal cannula. A
nasal cannula is a device that can be used to transmit therapeutic gas from one
or more therapeutic gas sources to the nose of a patient for inhalation. It includes
one or more connectors at one end of the device to connect to one or more therapeutic
gas sources, one or more long lumens to transmit the gas, and nasal prongs at the
other end to inject one or more therapeutic gases into the patient's nose. The
word "lumen" will be used in this disclosure to represent a long, narrow, flexible
fluid conduit that is less than 0.8 cm in internal diameter. A nasal cannula is
typically much less obtrusive than a mask and allows the patient to talk and eat
while receiving gas therapy. In the method of undiluted pulse delivery via a nasal
cannula, therapeutic gas is delivered via a nasal cannula as an intermittent flow
pulse during inspiration. Air pressure in the nares drops at the start of inspiration.
This pressure drop is transmitted through the cannula and is detected in the pulse
delivery device. Therapeutic gas flow is turned on for a period of time during
inspiration. The therapeutic gas flows directly into the nares from the cannula.
While overcoming many disadvantages associated with a mask, this method also has
disadvantages as practiced in the known art. For example, the therapeutic gas is
not diluted prior to entering the nares in many known systems. If a high concentration
source is used, high concentration gas may contact the tissues before it is diluted
in the respiratory tract. This may have adverse bioeffects. If lower concentration
gas is used, the source lifetime/size advantages of a high concentration source
are lost. Also, the final dilution concentration in the respiratory tract is limited.
It is lower for any given volume of therapeutic/carrier gas, and this volume must
be limited to avoid a hypoxic respiratory gas mixture. Still further disadvantages
will be discussed below in reference to the use of known cannulas.
Still another known method and system for administering therapeutic gas to
a patient includes an undiluted pulse via a nasal cannula and oxygen via another
lumen. In this method, gas may be delivered as discussed above, with the addition
of supplemental oxygen delivered via a second lumen in a dual lumen cannula. This
method has all the disadvantages discussed above, except that it allows a higher
diluted concentration to be delivered to the respiratory tract without having a
hypoxic mixture. This has the accompanying disadvantage of requiring a supplemental
oxygen source.
A diluted pulse to a cannula can also be used. In this method, the therapeutic
gas may be delivered by a nasal cannula and diluted prior to entering the nares.
This can be done by mixing it with a diluent gas from a diluent gas source before
it leaves the cannula. The therapeutic gas concentration can be reduced to a safe
level prior to entering the nares. It is further diluted in the respiratory tract
by entrained air from the room. This method has the disadvantage of requiring a
diluent gas source. If supplemental oxygen therapy is desired, oxygen or enriched
air may be used as the diluent gas, but it is more difficult to control the oxygen
concentration reaching the respiratory tract because a minimum diluent gas flow
is required to dilute the therapeutic gas to a safe concentration in the cannula.
Still another known method includes a continuous flow of therapeutic gas and
supplemental oxygen delivered to the patient via a nasal cannula. This method has
therapeutic gas delivered continuously via a nasal cannula by titrating the therapeutic
gas with air and/or oxygen before the cannula or in the cannula before it reaches
the flares. The therapeutic gas concentration can be reduced to a safe level prior
to entering the nares. It is further diluted in the respiratory tract by entrained
air from the room, This method has the disadvantage of requiring a diluent gas
source. If supplemental oxygen is required, a source of air and a source of oxygen
will be required or it will be difficult to control the oxygen concentration reaching
the respiratory tract.
Yet another known method of administering therapeutic gas to a patient includes
use of a transtracheal catheter. In this method, therapeutic gas can be delivered
directly to the trachea of the patient via a transtracheal catheter. Therapeutic
gas, flow might be continuous or pulsed. This method has the disadvantage that
the therapeutic gas is not diluted prior to entering the respiratory tract. If
a high concentration source is used, high concentration gas may contact the tissues
before it is diluted in the respiratory tract. This may have adverse bioeffects.
If lower concentration gas is used, the source lifetime/size advantages of a high
concentration source are lost. Also, the final diluted concentration in the respiratory
tract is limited. It is lower for any given volume of therapeutic/carrier gas and
this volume must be limited to avoid a hypoxic respiratory gas mixture. The transtracheal
catheter is invasive, which is often undesirable.
The art has also developed methods which deliver therapeutic gas to a patient
during certain times. In such systems, gas delivery is pulsed on during inspiration.
Other systems also include means for adjusting dosages, durations, flow rates and
the like.
It is noted that not every patient has the same breathing pattern as other patients
so a pulse configuration and time that is suitable for one patient may not be completely
efficient for another patient. The shape of the gas pulse (flow rate versus time
profile) of a first gas may be an approximately arbitrary shape. Some devices for
pulsed gas delivery to spontaneously breathing patients use a pulse of a set flow
rate and vary the duration of the pulse to change the dosage of gas to a patient.
This results in an approximately rectangular flow versus time shape of the pulse.
Other devices use a constant pulse duration but flow rate is altered to change
dosage. Flow rate is constant during any single pulse and the pulse shape is approximately rectangular.
There is a need for a system that is adaptable to customizing the pulse shape,
can easily adjust the dose, is adaptable to various conditions and modes of operation
for various patients having individual requirements and is easily maintained by
various caregivers.
Still further, some patients require delivery of more than one therapeutic
gas. Therefore, there is a need for a system that is amenable to delivering more
than one therapeutic gas to a patient if necessary.
Since many patients have individual requirements, it is necessary that a therapeutic
gas delivery system be amenable to use by a variety of caregivers ranging in expertise
from professional nurses and doctors to laymen in a home environment. In order
to be most efficient and effective, the system should efficiently deliver therapeutic
gas to the patient at all desired times, even if a primary source of gas is being
changed. This may be particularly important in some applications such as nitric
oxide therapy where interruption of the therapy can result in a "rebound" effect
where patient symptoms become as bad as or worse than they were before the therapy
began. To be most versatile, the system should be amenable to use with either a
nasal cannula (nasal prongs) or a mask and be easily used, monitored and maintained
by a variety of caregivers.
There is thus a need for a system which is amenable to use by a variety of
caregivers and which has means for delivering, therapeutic gas in an uninterrupted
manner when desired.
More specifically, even though there are several cannulas known in the art,
these known cannulas have various drawbacks that may vitiate advantages obtained
from customizing a therapeutic gas delivery system in order to overcome the drawbacks
associated with known systems.
For example, known cannulas do not have means for efficiently controlling mixing
of gases and do not have a gas mixing area that is most efficient or most efficiently located.
Therefore, there is need to improve the cannulas now used in connection
with therapeutic gas administering systems.
More specifically, many known cannulas do not provide a location for mixing
gases that is remote from a patient's nares. Such a remote mixing location can
be advantageous for better control of the final mixture administered to the patient.
Such a remote location can also be controlled without inhibiting a patient in any
way. However, since known cannulas do not have such an element, they have disadvantages.
Still further, many known cannulas have designs that waste therapeutic gas.
Further, many known cannulas cannot be used in a system that can precisely detect
breathing patterns of a patient and cannot be used to precisely and accurately
control dosage, concentration and flow rates of the gases.
Therefore, there is a need for a cannula that efficiently administers
therapeutic gas to a patient in a manner that overcomes the drawbacks of known cannulas.
Still further, many systems that are used to administer therapeutic gas to
a patient include primary gas sources in the form of pressurized cylinders. Some
of these systems include a "flow direction" check valve downstream of the inlet
to seal the system when the supply pressure is removed. However, a check valve
system may have drawbacks if used in certain circumstances.
For example, when a pressurized source is exchanged, there exists the possibility
that air will be trapped within the volume Of the system plumbing that is exposed
to air during the exchange. It is desirable to keep that volume of air as small
as possible so the resulting trapped air volume is reduced. Any trapped air will
degrade the quality of the high purity gases contained within the remainder of
the system when intervening valves are opened. This degradation is proportional
to the volume of trapped air. Therefore, it is desirable to maintain this dead
volume to a minimum.
Furthermore, it is advantageous to provide a system sealing action as
close to the supply inlet as possible to further minimize the dead space volume
upstream of the sealing surfaces. A flow direction check valve is not able to achieve
all of these goals. Therefore, there is a need for an equalizing valve that can
minimize dead space volume.
It is noted that it is possible to flush or purge the system to remove contaminated
gas from some dead space regions. However, for purging to be effective, the dead
space must be substantially swept out during periods of gas flow. If there are
poorly swept regions within the dead space, purging will have to be extended to
allow for diffusion and other mechanisms to dilute the contaminated regions. Therefore,
there is a need for a means for ensuring proper purging of a system used to administer
therapeutic gas to a patient.
Furthermore, purging requirements are strongly dependent on the relative
size of the contaminated volumes. Purging is often complicated in many situations
due to possible toxic effects of the therapeutic gases; and the high cost of medical
grade gases.
Therefore there is a further need for a valve that will make purging most
efficient and effective while overcoming the just-mentioned problems.
It is also noted that an autonomous gas delivery system should be able to detect
the supply pressure so when a pressurized cylinder has been attached and the supply
valve opened, a control system is signaled. This requires suitable positioning
of a pressure sensing element.
However, in order to maintain low dead space, a pressure sensor must be
located on the downstream side of an inlet sealing mechanism. In the prior art,
a simple back flow prevention check valve has provided this function. A check valve
will seal when there is a lower supply pressure on the downstream side of the check
valve. If the check valve seals, the pressure sensor, which is located further
downstream of the check valve, will continue to show the pressure when the check
valve is closed and will not indicate the actual supply pressure. If, subsequent
to this, a supply is attached that is at a lower pressure than the "checked" pressure,
the system will not be able to detect the connection.
Therefore, there is a need for a means for sealing a system such as disclosed
herein which will be able to fully detect and control the flow of the system during
changing of gas sources.
In general, it is desirable to close off the inlet of a system such as disclosed
herein when a supply is detached and to maintain the inside of the high purity
system at a positive pressure with respect to atmospheric pressure. By closing
off the inlet, the chance of contamination is reduced. By maintaining a positive
internal pressure, any small leaks that may be present will tend to leak in an
outward fashion helping to prevent atomospheric gas from entering the system.
Therefore, there is a need for a means for connecting the system of the
present invention to a source of gas that will reduce the possibility of contamination
of the system.
OBJECTS OF THE INVENTION
It is a main object of the present invention to provide a system and elements
for delivering NO to a spontaneously breathing, non-ventilated patient.
It is another object of the present invention to manage NO delivery to a spontaneously
breathing, non-ventilated patient such that concentrated NO is as low as reasonably
possible while delivering the desired amount of NO to the distal portions of the
patient's lungs.
It is another object of the present invention to provide a system and elements
for delivering NO to a spontaneously breathing, non-ventilated patient that is
compatible with periodic, routine or continuous modes of operation.
It is another object of the present invention to provide a system and elements
for delivering NO to a spontaneously breathing, non-ventilated patient that is
easily used by patients, clinical staff and other caregivers with a wide and varying
range of skills.
It is another object of the present invention to provide a system and elements
for delivering NO to a spontaneously breathing, non-ventilated patient that is
easily cleaned, purged and maintained.
It is another object of the present invention to provide a system and elements-for
delivering NO to a spontaneously breathing, non-ventilated patient that is easily monitored.
It is another object of the present invention to provide a system and elements
for delivering NO to a spontaneously breathing, non-ventilated patient that has
any limited lifetime elements thereof easily replaced.
It is another object of the present invention to provide a system and elements
for delivering NO to a spontaneously breathing, non-ventilated patient which will
minimize concentration of therapeutic gases delivered to any tissue that requires treatment.
It is another object of the present invention to provide a system and elements
for delivering NO to a spontaneously breathing, non-ventilated patient which will
accurately and efficiently deliver a desired concentration and dose to the patient.
It is another object of the present invention to provide a system and elements
for delivering NO to a spontaneously breathing, non-ventilated patient which can
be adapted for use with a cannula or a mask while still accurately and efficiently
delivering desired doses and concentrations of therapeutic gases to the patient.
It is another object of the present invention to provide a system and elements
for delivering NO to a spontaneously breathing, non-ventilated patient which can
deliver any desired therapeutic gas or combination of gases to the patient in an
efficient and effective manner.
It is another object of the present invention to provide a system and elements
for delivering NO to a spontaneously breathing, non-ventilated patient which has
alarms and alarm systems.
It is another object of the present invention to provide a system and elements
for delivering NO to a spontaneously breathing, non-ventilated patient which includes
locks to prevent undesired operation of the system or its elements.
It is another object of the present invention to provide a system and elements
for delivering NO to a spontaneously breathing, non-ventilated patient which has
means for providing system operational history.
It is another object of the present invention to provide a system and elements
for delivering NO to a spontaneously breathing, non-ventilated patient which is
adaptable to a wide variety of conditions and system requirements.
It is another object of the present invention to provide a system and elements
for delivering NO to a spontaneously breathing, non-ventilated patient which has
means for delivering desired therapeutic gases even while a main source of gas
is being replaced.
It is another object of the present invention to provide a system and elements
for delivering NO to a spontaneously breathing, non-ventilated patient which is portable.
It is another object of the present invention to provide a system and elements
for delivering NO to a spontaneously breathing, non-ventilated patient which is autonomous.
It is another object of the present invention to provide a system and elements
for delivering NO to a spontaneously breathing, non-ventilated patient which can
respond to changes in patient parameters such as breath rate and tidal volume.
It is another object of the present invention to provide a system and elements
for delivering NO to a spontaneously breathing, non-ventilated patient which can
respond to changes in environmental parameters.
It is another object of the present invention to provide a system and elements
for delivering NO to a spontaneously breathing, non-ventilated patient which has
a low transit time of gases through an entrainment cell.
It is another object of the present invention to provide a system and elements
for delivering NO to a spontaneously breathing, non-ventilated patient which has
an entrainment cell that is easily cleaned and maintained.
It is another object of the present invention to provide a system and elements
for delivering NO to a spontaneously breathing, non-ventilated patient which has
an entrainment cell that is not prone to clogging.
It is another object of the present invention to provide a system and elements
for delivering NO to a spontaneously breathing, non-ventilated patient which has
an entrainment cell that efficiently mixes gases.
It is another object of the present invention to provide a system and elements
for delivering NO to a spontaneously breathing, non-ventilated patient which has
an entrainment cell that can monitor flow rates.
It is another object of the present invention to provide a system and elements
for delivering NO to a spontaneously breathing, non-ventilated patient which has
an entrainment cell that is spaced from a patient's face.
It is another object of the present invention to provide a system and elements
for delivering NO to a spontaneously breathing, non-ventilated patient which has
an entrainment cell with an efficient and effective geometry.
It is another object of the present invention to provide a system and elements
for delivering NO to a spontaneously breathing, non-ventilated patient which has
an entrainment cell with an entrainment cell that can be efficiently flushed during operation.
It is another object of the present invention to provide a system and elements
for delivering NO to a spontaneously breathing, non-ventilated patient which has
an entrainment cell that is easily inspected.
It is another object of the present invention to provide a system and elements
for delivering NO to a spontaneously breathing, non-ventilated patient which has
an entrainment cell that has a total flow rate of gases during inspiration which
is a large fraction of a patient's inspiratory flow rate.
It is another object of the present invention to provide a system and elements
for delivering NO to a spontaneously breathing, non-ventilated patient which has
an entrainment cell with a low dwell time of therapeutic gases as compared to the
desired delivery flow rate.
It is another object of the present invention to provide a system and elements
for delivering NO to a spontaneously breathing, non-ventilated patient which has
a means for effectively and efficiently equalizing pressure between a source of
pressurized gas and the system, but keeping the system pressurized slightly above
atmospheric pressure if the gas source is removed.
It is another object of the present invention to provide a system and elements
for delivering NO to a spontaneously breathing, non-ventilated patient that maintains
dead volume to a minimum
It is another object of the present invention to provide a system and elements
for delivering NO to a spontaneously, breathing, non-ventilated patient that includes
an equalizing valve that can minimize dead space volume
It is another object of the present invention to provide a system and elements
for delivering NO to a spontaneously breathing, non-ventilated patient that includes
a means for ensuring proper purging of a system used to administer therapeutic
gas to the patient.
It is another object of the present invention to provide a system and elements
for delivering NO to a spontaneously breathing, non-ventilated patient that includes
a valve that will make purging most efficient and effective while overcoming the
problems associated with the prior art.
It is another object of the present invention to provide a system and elements
for delivering NO to a spontaneously breathing, non-ventilated patient that includes
a means for sealing a system such as disclosed herein which will be able to fully
detect and control the flow of the system during changing of gas sources.
It is another object of the present invention to provide a system and elements
for delivering NO to a spontaneously breathing, non-ventilated patient that includes
a means for connecting the system to a source of gas that will reduce the possibility
of contamination of the system.
SUMMARY OF THE INVENTION
These, and other, objects are achieved by a system that administers therapeutic
gas to a spontaneously breathing, non-ventilated patient which accurately manages
and supervises the delivery of gas. The system dilutes a high concentration therapeutic
gas to a lower concentration prior to delivering it to a patient for inhalation.
The system delivers the gas via nasal prongs or via a mask. It effects this delivery
without requiring a source of pressurized diluting gas such as from a pump or compressed
gas cylinder. Dilution can be accomplished with room air of close to local atmospheric
pressure. The system also allows supplemental oxygen to be added to the respiratory
gases if desired and works with a pulsed delivery device.
The system also includes a special cannula that further improves the overall
effectiveness of the system. The cannula has an entrainment cell that is sized
and shaped to produce a gas transit time therethrough that is most effective to
properly mix, dilute and deliver the therapeutic gas to the patient. The entrainment
cell is also sized and shaped to inhibit clogging and can be transparent if desired
to provide a visual indication of the inside of the cell. The entrainment cell
has ports and other elements that are located and positioned to thoroughly mix
the gas with room air in a manner that is most effective and efficient. Furthermore,
one form of the entrainment cell includes flow sensors that can be used so gas
administration is accurate and precise. The flow sensor can act as an interlock
to help ensure that sufficient room air is entrained for adequate dilution. Other
forms of the cell include check valves, baffles and other ports. The entrainment
cell provides desired mixing control that is suitable for the accurate system and
is located remote from the patient's nares whereby patient safety and comfort are
enhanced. The cell also is closed except for the ports and thus gas is not wasted
due to leakage. Flow sensors can also be used to transmit pressure signals from
the patient's nose through the therapeutic gas lumen so the beginning of inspiration
may be detected.
The entrainment cell can be used with a cannula or with a mask as desired.
The system of the present invention can deliver one or more therapeutic gases
to a patient for inhalation and can dilute the therapeutic gas with room air prior
to delivering the gas to the patient. The room air for dilution is entrained by
the respiratory effort of the patient so no supplementary air source such as compressed
air or an air pump is required. The total flow rate of gases in the device during
inspiration, including entrained air, is a large fraction of the patient's inspiratory
flow rat and the total flow rate of the,gases in the device is equal to the sum
of the flow rate of each therapeutic gas plus the flow rate of entrained air. One
form of the invention delivers a low flow rate of nitric oxide during inspiration
where the nitric oxide flow rate is very small compared to the inspiratory flow
rate. In such a case, the flow rate of entrained air is a large fraction of the
patient's inspiratory flow rate. The high fraction of inspired air flowing through
the device is achieved in part by the geometry and size of an entrainment cell
and associated elements. The geometry gives a low flow resistance in the air entrainment
port, entrainment cell, outlet lumen and nasal prongs used in conjunction with
the entrainment cell. The size of the nasal prongs is a factor in the resistance
to flow around the prongs and into the patient's nose. A form of the invention
that includes a mask allows an even greater fraction of the inspired gas to travel
through the device.
The entrainment cell is small, lightweight and relatively unobtrusive and the
dwell time of therapeutic gas in the cell is low compared to the desired delivery
flow rate because of the size of the entrainment cell. One form of the device includes
a check valve at the outlet of the therapeutic gas lumens and these lumens are
usually small to limit the gas conductivity thereat. The entrainment cell also
ensures proper turbulent mixing of the gases prior to delivery to the patient.
The cell can also include a narrowing of flow paths near the outlet of the entrainment
cell to increase the turbulence for improving mixing as gas leaves the cell.
One important performance characteristic of the therapeutic gas delivery system
is its temporal response. The temporal response of the system depends partially
on its geometry, one aspect of which is the mixing location for the therapeutic
gas. In one embodiment, the therapeutic gas is mixed near the inlet end of the
entrainment cell. In another embodiment, the therapeutic gas is mixed between a
baffle in the entrainment cell and the outlet end of the cell. In yet another embodiment,
the therapeutic gas is mixed near the patient. In connection with this, we define
several temporal characteristics.
- Cannula latency TC is the delay from therapeutic gas metering
from the gas controller until the therapeutic gas reaches the patient.
- Therapeutic lumen propagation latency Tp is the delay for
a flow rate to propagate from the metering valve in the gas controller to the outlet
of the therapeutic gas lumen. This delay is very small in all cases relevant to
the disclosed system and will be neglected.
- Cell inlet latency Tci is the delay for a therapeutic gas
to travel from a mixing region near the inlet end of the entrainment cell to the
outlet lumen.
- Cell baffle latency Tcb is the delay for a therapeutic gas
to travel from a mixing region between the baffle and the outlet end of the entrainment
cell to the outlet lumen.
- Near patient mixing latency Tnp is the delay for a therapeutic-gas
to travel from a mixing region-near the patient to the patient.
- Outlet lumen latency TO is the delay for gas to travel from
the beginning of the outlet lumen at the entrainment cell to the patient.
The Cannula latency will depend on where the therapeutic gas is injected from
the therapeutic gas lumen. If therapeutic gas is injected at the inlet end of the
entrainment cell, then
TC=Tci+TO
If therapeutic gas is injected between the baffle and the outlet end of the entrainment
cell, then
TC=Tcb+TO
If therapeutic gas is injected near the patient, then
T
C=T
np
Where approximations have been made because the therapeutic lumen propagation
latency has been neglected.
A small cannula latency is established using the present invention. The cell
inlet
latency and cell baffle latency are made small by having a small entrainment cell
internal volume compared to the volume of gas flowing through the cannula during
inspiration. The outlet lumen latency is made small by keeping the outlet lumen
internal volume small compared to the volume of gas flowing through the cannula
during inspiration. The near patient mixing latency may be made arbitrarily small
by making the mixing location as close to the patient as desired.
One form of the entrainment cell has an air inlet port located in an end wall
thereof. This location of the air inlet port helps prevent blockage of the port.
The location of a therapeutic gas lumen next to the air inlet port and parallel
to the cell axis also helps prevent blockage.
One form of the entrainment cell is also designed to be flushed out with each
patient breath. A combination of a small internal volume and flow design achieves this.
The entrainment cell is easy to clean as it has a fairly simple internal structure.
The cell in one embodiment is transparent for easy inspection. One form of the
entrainment cell includes a flow sensor that can be used to accurately ensure that
sufficient air is entrained to properly dilute the therapeutic gas as well as to
measure the inspiratory flow of the patient and to detect the beginning of inspiration.
The flow sensor can also be used to control the pulse rate and size of the gas
delivery system.
The small size of the entrainment cell reduces the low pass filtering effect
(provides a better transient response). The entrainment cell transmits the waveform
of the therapeutic gas to the patient with minimal distortion other than dilution.
The flow rate of therapeutic gas injected from the therapeutic gas lumen may vary
with time. The same waveform of therapeutic gas is delivered to the patient along
with the room air and any other therapeutic gas with the system of the present
invention. A low pass filtering effect exists due to the particular geometrical
characteristics of the device such as the small diameter and the length of the
gas lumens and the volume of the entrainment cell. A small entrainment cell volume
and narrow lumens reduce the filtering effect.
Some forms of the entrainment cell include check valves on the air entrainment
port or ports to prevent therapeutic gas from escaping from the cell even if the
therapeutic gas flow rate is large. Thus, the desired amount of therapeutic gas
reaches the patient.
Some forms of the entrainment cell have interlocks for connecting the cell to
the remainder of the flow circuit.
The present invention also includes an equalizing valve that equalizes pressure
in low dead volume conditions. The equalizing valve simultaneously satisfies a
number of objectives and overcomes the problems associated with the prior art as
discussed above.
The equalizing valve of the present invention satisfies the above-stated objects.
The valve has inlet sealing surfaces withing the valve fitting that engages a supply
fitting of a source of pressurized gas at the closest possible location to the
supply inlet. The remaining volume of the inlet is reduced by substantially filling
that volume with a pin, leaving a thin annulus for gas to pass into the system.
This geometry helps preserve the downstream gas purity and will significantly reduce
the required amount of purge gas.
The valve of the present invention maintains a sufficient positive internal pressure
to ensure that air does not migrate into the high purity gas regions. Furthermore,
gas is not allowed to enter the high purity regions until a sufficiently high supply
pressure is attached to the system. As an added safety feature, the valve of the
present invention permits flow to automatically throttle itself at very high rates
in the event of a massive leak.
BRIEF DESCRIPTION OF THE DRAWING FIGURES
FIG. 1 is a schematic showing the overall system embodying the present invention.
FIG. 2 is a flow versus time curve showing a rectangular pulse delivery.
FIG. 3 is a flow versus time curve showing a pulse delivery with delivered gas
flow rate proportional to inspiratory flow rate.
FIGS. 4A-4C show a connector for connecting an electrical circuit and therapeutic
gas to an entrainment cell embodying the present invention.
FIG. 5 shows a nasal cannula used to administer NO to a patient in accordance
with the teaching of the present invention.
FIG. 5A is a diluting cannula with two nasal prongs and adapted to administer
two therapeutic gases to a patient.
FIG. 5B is a short entrainment cell used in conjunction with the system embodying
the present invention.
FIG. 5C is a diluting cannula with two nasal prongs and adapted to administer
two therapeutic gases with mixing near an upstream end of an entrainment cell.
FIG. 5D is a diluting cannula with two nasal prongs and adapted to administer
two therapeutic gases with mixing of one therapeutic gas near a patient's nose.
FIG. 6 is a flow versus time curve of various flows in the cannula and nose
when the second therapeutic gas flow Q
2≠0.
FIG. 7 is a flow vs time curve of various flows in the cannula and nose and
a curve of the concentration of gas wxiting the cannula when the second therapeutic
gas flow Q
2=0.
FIG. 8 is a nasal cannula with mixing near the nose.
FIG. 9 is an entrainment cell used in the system embodying the present invention.
FIG. 10 is an alternative form of an entrainment cell having a baffle.
FIG. 11 is an alternative form of an entrainment cell having a plurality of
air inlet ports.
FIG. 12 is an alternative form of an entrainment cell having a check valve mounted
to control air flow through an air inlet port.
FIGS. 13A and 13B are alternative forms of an entrainment cell having a flow sensor.
FIG. 13C is an alternative form of an entrainment cell having a lumen for directing
gas to a mixing region near the patient.
FIGS. 14A-14D show an alternative form of the invention in which an entrainment
cell is used in conjunction with a mask.
FIG. 15 is a pressure equalization valve in conjunction with a source of gas
as used in conjunction with a system embodying the present invention.
FIG. 16 shows the pressure equalization valve of FIG. 15 in a first condition.
FIG. 17 shows the pressure equalization valve of FIG. 15 in another condition.
FIGS. 18A-18F show block diagrams of supervisory and control elements used
in the system embodying the present invention.
FIG. 19 shows an alternative form of the system of the present invention in
which the entrainment cell is located in a convenient location, behind a patient's ear.
FIG. 20 shows an alternative form of the present invention in which a shaped
orifice is located inside the entrainment cell.
FIG. 21 shows flow rate versus AP for the equalizing valve of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION
Other objects, features and advantages of the invention will become apparent
from a consideration of the following detailed description and the accompanying drawings.
Overall System
Referring first to FIG. 1, a description of the overall system for administering
therapeutic gas to a spontaneously breathing, non-ventilated patient will be described.
It is noted that for reference, unless otherwise stated, the terms "upstream" and
"downstream" will refer to a flow direction of gas from a source toward a patient.
Other terms such as "inlet" and "outlet" will refer to the same flow direction.
The overall system
10 is shown schematically and includes a source of first
compressed gas
14 which is fluidically connected via a valve
15 and
a pressure equalization valve
16 to a flow restrictor
17. Alternatively,
a large source of gas
14′ can be connected via a pressure regulator
R which reduces the pressure and a flow conduit C to the inlet of the system. During
normal operation of system
10, when a cylinder is connected., the pressure
on the system side (i.e., downstream of valve
16) of valve
16 is
equal to the cylinder pressure minus the equalization pressure (for example, 50
psi). When the cylinder is disconnected, a small amount of gas flows out of the
cylinder side of the valve until the pressure on the system side of the valve reaches
equalization pressure. This pressure is measured by a pressure sensor
18,
with flow restrictor
17 being part of the equalization valve assembly. The
pressure equalization valve/flow restrictor limits the maximum flow of the first
gas in the case of a device failure. A pressure gauge
19 indicates cylinder
pressure +/- the equalization pressure when a cylinder is connected. A burst diaphragm
20 is included for safety to vent if a cylinder is connected that is pressurized
to greater than the rated inlet pressure of the system. A pressure regulator
21
reduces the pressure of the first gas from the cylinder pressure (+/- equalization
pressure) to a desired level (for example, 100 psi). A solenoid valve
24
closes when system
10 is turned off or if a cylinder is disconnnected or
is empty. Valve
24 seals the inlet side of the system to keep contaminants
out when system
10 is off and to keep a reservoir from discharging through
the inlet of the system when the cylinder is not connected. A purging solenoid
valve
26 is fluidically connected to the system. When an adequately pressurized
cylinder is connected and valve
15 is opened, a small amount of gas flows
through pressure equalization valve
16 and the system side of valve
16
rises to the cylinder pressure minus the equalization pressure. This gas will contain
some air that was trapped between cylinder valve
15 and equalization valve
16. Pressure sensor
18 detects the pressure rise and the system will
know that a new cylinder has been connected. Solenoid valve
26 will be opened
so gas from the cylinder flows through the inlet and the circuit upstream of valve
24. This gas flows out through muffler
27. If a large cylinder is
connected, the medium pressure hose C and regulator R must also be purged so the
purge duration will be longer. The user enters the cylinder size to indicate whether
an extended purge is required.
At the end of the purge cycle, valve
26 is closed. The pressure at sensor
18 drops when valve
26 is opened and will rise when valve
26
is closed. If this does not occur, a proper purge was not carried out and the system
is designed to include control elements to respond accordingly. If pressure at
sensor
18 rises to a high enough pressure, valve
24 will open. A
pressure relief valve
28 is present for safety purposes and a reservoir
29 is located downstream of valve
24. Reservoir
29 is pressurized
to the outlet pressure of regulator
21 (for example, 100 psi) during normal
operation when a pressurized cylinder is connected. A pressure sensor
30
senses reservoir pressure and a pressure switch
31 switches at some pressure
slightly above atmospheric pressure (for example, 5 psi). If switch
31 switches,
it indicates that pressurization was lost in the reservoir and the system may have
been contaminated. The system includes means for monitoring this switch at all
times, even when the system is off. A pressure regulator
32 regulates to
some pressure lower than regulator
21 (for example, 10 psi). It drops the
pressure to an appropriate value for inlet of valve
33. When a source cylinder
is disconnected or drops below an adequate pressure, this is sensed by sensor
18
and valve
24 is closed. The system will continue to deliver gas from the
supply in reservoir
29. The reservoir pressure will begin to drop, but delivery
will be unaffected as long as the presure remains high enough that regulator
32
can properly regulate. The system further includes means to monitor the reservoir
pressure and calculate and indicate the remaining lifetime of reservoir
29.
A pressure relief valve
34 is for safety purposes. A small space
35
(e.g., 50 ml) is located downstream of regulator
32. This acts as a gas
capacitor so that the pressure upstream of valve
33 does not fluctuate too
much when valve
33 is operated. Valve
33 is a proportional control
valve that meters the first gas flow to a patient. A differential pressure sensor
37 measures the pressure drop across an orifice
36 to determine the
flow through valve
33. An ambient temperature sensor
39 and an ambient
pressure sensor
40 generate signals connected to monitoring elements of
the system by leads
39L and
40L. The signals are monitored by the
system and used in calculations made by other elements of the system, such as computers
or the like. The computing elements of the system are not shown but it is understood
that such elements are included when and where necessary. The ambient temperature
should be approximately equal to the temperature of the gas downstream of valve
33 under most conditions. Using ambient temperature, the pressures at pressure
sensor
37 and sensor
40 and knowing the characteristics of orifice
36, the mass flow through valve
33 can be calculated. This flow may
be used as a feedback to control valve
33. A solenoid valve
41 is
closed when system
10 is off to keep the gas channel pressurized. A pressure
sensor
42 is located to detect the patient's breath. When the patient inhales
through their nose, the pressure in the nares drops. This pressure drop is transmitted
through a nasal cannula NC to pressure sensor
42. When this pressure drops
below a threshold value, the start of inspiration is indicated and delivery starts.
Sensor
42 may also detect the pressure during expiration and this data may
be used in delivery algorithms. It may also be possible to detect the start of
inspiration using the flow sensor
251 to detect the flow of air in the entrainment
cell which will occur with inspiration.
It is understood that the feedback loops and circuits as well as the signal generators,
signal receivers and signal processors for pressure, temperature and flow measurements
as well as valve actuators and various detectors used in the system use electrical
circuits that are not shown, but are included as required. By way of example, block
diagrams of such circuitry and control elements are shown in FIGS. 18A-18F. These
circuits and elements are used when functions are mentioned herein with reference
to operation of system
10.
A pressure relief valve
44 protects the patient. If the pressure at valve
44 is too high, valve
44 will vent. Cannula NC is connected downstream
of valve
44. When a breath is detected, valve
33 opens to deliver
the desired gas pulse. The gas flows into a first gas lumen of cannula NC. Mixing
and dilution proceed as described below.
The second gas source is a medium pressure source (for example 20 to 50 psi)
such as a pressure regulated cylinder or gas from a hospital wall source. The second
gas channel is much simpler than the first and includes a filter
50 and
a pressure regulator
250 that regulates pressure of a second gas to some
low pressure (e.g., 2 psi), solenoid valve
51, a flow restrictor
52
and a flow sensor
53. When a pulse of the second gas is to be delivered,
valve
51 is opened and gas flows. The flow rate is set by flow restrictor
52 and dosage is adjusted by adjusting the duration of the pulse. Flow sensor
53 senses flow to verify that flow is present and approximately of the correct
magnitude. A pressure relief valve
54 protects the patient by venting if
the pressure is too high. The second gas channel is fluidically connected to cannula
NC downstream of pressure relief valve
54.
As discussed above, the system embodying the present invention can deliver customized
pulses of a first and/or a second gas to the patient during inspiration. The shape
of the gas pulse (flow rate versus time) of the first gas may be approximately
arbitrary and with system
10, many pulse shapes are possible. This opens
up many possibilities for gas delivery to a patient. FIG. 2 shows a typical respiratory
waveform along with a rectangular delivery pulse. The resultant concentration of
the delivered gas when it is mixed with the respiratory gas is also shown. FIG.
3 shows the respiratory waveform along with a customized gas delivery pulse. The
pulse has been tailored to have a flow rate that is proportional to the respiratory
flow rate during the pulse. This results in a constant delivered gas concentration
after mixing. Many pulse shapes are possible and the shape and size may be determined
by different methods as will occur to those skilled in the art based on the teaching
of this disclosure. The pulse shapes may be predetermined and programmed into the
system
10. For example, pulse flow rate can be proportional to the respiratory
flow rate in a typical breath to give a constant concentration over the duration
of the pulse. This concentration is the concentration after the delivered gas is
diluted by the other inhaled gases.
Another example includes setting pulse timing so gas is delivered during
a desired part of the breath. This results in gas delivery to a desired part of
the respiratory tract.
Yet another example includes varying pulse amplitude during different parts of
the breath so different amounts of gas are delivered to different parts of the
respiratory tract.
Using system
10, the breath waveform (inspiratory flow rate versus time)
may be monitored and an algorithm may be used that is based on inspiratory flow
rate to determine the delivered flow rate.
Also using system
10, the frequency of breathing may be monitored and
the delivered flow rate may be determined from an algorithm that is based on the
breath frequency.
As discussed above, delivery algorithms are possible that adjust gas delivery.
The delivery may be adjusted based on measured patient parameters or environmental parameters.
For example, a constant concentration delivery on a large time scale is possible
using system
10. The concentration of the delivered gas during a pulse,
after dilution by the other inhaled gases, is kept constant on a time scale of
several breaths. The delivered flow rate
