Classifications

• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61M—DEVICES FOR INTRODUCING MEDIA INTO, OR ONTO, THE BODY; DEVICES FOR TRANSDUCING BODY MEDIA OR FOR TAKING MEDIA FROM THE BODY; DEVICES FOR PRODUCING OR ENDING SLEEP OR STUPOR
  • A61M16/00—Devices for influencing the respiratory system of patients by gas treatment, e.g. mouth-to-mouth respiration; Tracheal tubes
  • A61M16/08—Bellows; Connecting tubes ; Water traps; Patient circuits

Definitions

• a portable partial rebreathing circuit to set and stabilize end tidal and arterial PCO2 despite varying levels of minute ventilation
• the purpose of this invention is to provide a portable breathing circuit that provides ambient air to breathe unless the minute ventilation exceeds the rate of ambient air entry into the circuit and further if minute ventilation does exceed the rate of ambient air entry into the circuit then the difference between minute ventilation and the rate of ambient air entry into the circuit is composed of rebreathed alveolar gas in preference to dead space gas. All gas entering the circuit is breathed before exiting the circuit.
• Blood from various parts of the body is mixed in the right side of the heart (resulting in the formation of mixed venous blood) and pumped to the lungs.
• the blood vessels break up into a net of small vessels surrounding tiny lung sacs (alveoli).
• the vessels surrounding the alveoli provide a large surface area for the exchange of gases by diffusion along their concentration gradients.
• a concentration gradient exists between the partial pressure of C0 2 (PC0 2 ) in the mixed venous blood (PvC0 2 ) and that in the alveolar PC0 2 .
• the C0 2 diffuses into the alveoli from the mixed venous blood from the beginning of inspiration until an equilibrium is reached between the PvC0 and the alveolar PC0 2 at some time during the breath.
• the first gas that is exhaled comes from the trachea and major bronchi which do not allow gas exchange and therefore will have a gas composition similar to that of inhaled gas.
• the gas at the end of exhalation is considered to have come from the alveoli and reflects the equilibrium CO2 concentration between the capillaries and the alveoli; the PC0 2 in this gas is the end-tidal PC0 2 (PETC0 2 ).
• the arterial PC0 2 When the blood passes the alveoli and is pumped by the left side of the heart to the arteries in the rest of the body it is known as the arterial PC0 2 (PaC0 2 ).
• the arterial blood has a PC0 2 equal to the PC0 2 at equilibrium between the capillaries and alveoli. With each breath some C0 2 is eliminated from the lung and fresh air containing little or no C0 2 (CO2 concentration is assumed, to be 0% is inhaled and dilutes the residual alveolar PC0 2/ establishing a new gradient for C0 2 to diffuse out of the mixed venous blood into the alveoli.
• N minute ventilation
• C0 2 e.g., as a result of fever or exercise
• more C0 is produced and carried to the lungs.
• C02 production is normal, the PaC02 falls, if one increases one's ventilation (hyperventilation); conversely, if C02 production remains normal, the PaC02 rises if the ventilation falls (hypoventilation).
• N contributes to elimination of C0 2 .
• Some N goes to the air passages (trachea and major bronchi) and alveoli with little blood perfusing them, and thus contributes minimally to eliminating C0 2 .
• This N is termed “dead space” ventilation and gas in the lung that has not participated in gas exchange with the blood is called “dead space” gas.
• That portion of N that goes to well-perfused alveoli and participates in gas exchange is called the alveolar ventilation (NA) and exhaled gas that has participated in gas exchange in the alveoli is termed "alveolar gas".
• W098/41266 filed by Joe Fisher there is taught a method of accelerating the resuscitation of a patient having been anaesthetized by providing the patient with a source of fresh gas and a source of reserve gas (see below).
• a source of fresh gas and a source of reserve gas (see below).
• all of the inhaled gas is made up of fresh gas.
• the patient's minute ventilation exceeds the fresh gas flow, the inhaled gas is made up of all of the fresh gas and the additional gas is provided by "reserve gas” consisting of fresh gas plus CO2 such that the concentration of C0 2 in the reserve gas of about 6% has a partial pressure equal to the partial pressure of CO2 in the mixed venous blood.
• a source of fresh gas is provided for normal levels of minute ventilation, typically 5 L per minute and a supply of reserve gas is provided for levels of ventilation above 5 L per minute wherein the source of reserve gas includes approximately 6% carbon dioxide having a PCO2 level substantially equal to that of mixed venous blood.
• the source of fresh gas usually consisting of pressurized gas or mechanical gas pump
• a passive system wherein the act of inhaling by the subject results in a constant sub- atmospheric pressure inside the circuit, independent of the extent of breathing or the size of the breaths, providing the pressure gradient driving atmospheric air into the circuit.
• the opening into the circuit from the atmosphere consists of tubing whose length and diameter provides for a particular flow of ambient air into the circuit for a given pressure gradient.
• the pressure gradient, and hence the flow of ambient air into the circuit will remain constant.
• the expired gas reservoir consists of a flexible bag, preferably of approximately 3 L capacity, containing a tubular structure at the point of gas entry and a tubular structure at the point of gas exit.
• the reserve gas can be replaced by previously exhaled gas.
• the gas at the end of exhalation has substantially equilibrated with mixed venous gas and thus has a PCO2 substantially equal to it.
• rebreathed gas contains anesthetics in anesthetized patients
• the use of rebreathed gas to prevent the decrease in PCO2 with increased ventilation instead of separately constituted reserve gas to prevent the decrease in PCO2 with increased ventilation will not promote the enhancement of elimination of anesthetics.
• the present inventive circuit would share some of the advantages set out in the prior application of such as, but not limited to: a) raising PCO2 i) during pregnancy to improve placental and fetal brain blood flow, ii) to prevent shivering, iii) to increase tissue perfusion, and iv) protect tissue from oxidative damage after a period of severe hypoxia or ischemia by permitting resuscitation with normal atmospheric oxygen concentrations and meeting tissue oxygen demand through C0 2 -mediated increased tissue blood flow.
• Canadian Patent Application No. 2,304,292 from which priority is claimed has previously described a circuit which when fresh gas flow is provided, maintains PCO2 independent of minute ventilation by supplying the difference between fresh gas flow and minute ventilation from gas expired from a previous breath.
• the circuit contains a fresh gas reservoir bag whose relaxed position is collapsed then fills passively with fresh gas when and only when fresh gas is forced into the circuit under pressure. Fresh gas is forced into the circuit at a constant rate independent of the phase of breathing.
• the expired gas reservoir consists of a long tube open to atmosphere. When a volume of expired gas is rebreathed, an equal volume of outside air enters the tube and mixes with expired gas. As this will dilute the expired gas and decrease the effectiveness of the circuit in maintaining a constant PC0 2 with increased minute ventilation, the tubular expired gas reservoir must be as long as possible to separate the expired alveolar gas from expired gas diluted by atmospheric air.
• the present circuit exploits the same principle in maintaining PCO2 constant; however it replaces the fresh gas reservoir bag with a substantially flexible container which is actively collapsed by the inspiratory effort of the patient during inspiration and passively expands during expiration drawing into itself and the circuit atmospheric air through a port provided for that purpose.
• the expiratory reservoir is provided with a flexible bag so that the volume of expired gas rebreathed is displaced by collapse of the bag rather than entrainment of atmospheric air, thus preventing the dilution of CO2 in the expired gas reservoir.
• a method of establishing a constant flow of fresh gas in the form of atmospheric air the flow of which is forced as a result of breathing efforts by the patient but independent of the extent of ventilation.
• This flow is delivered into a breathing circuit such as that taught in the priority application designed to keep the PCO2 constant by providing expired gas to be inhaled when the minute ventilation exceeds the flow of fresh gas.
• a compact expired gas reservoir capable of organizing exhaled gas so as to be preferentially inhaled during re-breathing when necessary by providing alveolar gas for re-breathing in preference to dead space gas.
• the preferred circuit in effecting the above-mentioned method includes a breathing port for inhaling and exhaling gas, a bifurcated conduit adjacent said port, preferably being substantially Y-shaped, and including a first and second conduit branch, said first conduit branch including an atmospheric air inlet the flow through which is controlled by a resistance for example that being provided by a length of tubing, and a check valve disposed proximate the port, said check valve allowing the passage of inhaled atmospheric air to the port but closing during exhalation, said second conduit including a check valve which allows passage of exhaled gas through said check valve but prevents flow back to the breathing port once the gas passes through the check valve, said first conduit branch having located proximate the terminus thereof, an atmospheric air aspirator (AAA) consisting of a collapsible container tending to recoil to an open position, said second conduit branch having located proximate the terminus thereof, an exhaled gas reservoir, preferably being a thin walled flexible bag approximately 3 L in capacity containing
• this particular circuit uses for this particular circuit are those described in the priority application and in addition this circuit is particularly useful for maintaining isocapnia when atmospheric air is a suitable form of fresh gas and it is inconvenient or impossible to access a source of compressed gas or air pump to provide the fresh gas flow.
• this circuit is particularly useful for maintaining isocapnia when atmospheric air is a suitable form of fresh gas and it is inconvenient or impossible to access a source of compressed gas or air pump to provide the fresh gas flow.
• PCO2 During mountain climbing or working at high altitude some people tend to increase their minute ventilation to an extent greater than that required to optimize the alveolar oxygen concentration. This will result in an excessive decrease in PCO2 which will in turn result in an excessive decrease in blood flow and hence oxygen delivery to the brain.
• a limit can be put on the extent of decrease in PCO2 and thus maintain the oxygen delivery to the brain in the optimal range.
• a method of enhancing the results of a diagnostic procedure or medical treatment comprising the steps of: providing a circuit that does not require a source of forced gas flow which is capable of organizing exhaled gas so as to provide to the patient preferential rebreathing of alveolar gas in preference to dead space gas, (for example the circuit described above) when the patient is ventilating at a rate greater than the rate of atmospheric air aspirated, and when inducing hypercapnia is desired, by decreasing the rate of aspirated atmospheric air and passively provide a corresponding increase in rebreathed gas so as to prevent the PCO2 level of arterial blood from dropping despite increases in minute ventilation, continuing inducing hypercapnia until such time as the diagnostic or medical therapeutic procedure is completed, wherein the results of said diagnostic or medical procedure are enhanced by carrying out the method in relation to the results of the procedure had the method not been carried out. Examples of such procedures would be MRI or preventing spasm of brain vessels after brain hemorrhage, radiation
• a method of treating or assisting a patient, preferably human, during a traumatic event characterized by hyperventilation comprising the steps of: providing a circuit that does not require a source of forced gas flow which alveolar ventilation is equal to the rate of atmospheric air aspirated and increases in alveolar ventilation with increases in minute ventilation is prevented by a circuit (for example the preferred circuit described above) which is capable of organizing exhaled gas so as to provide to the patient preferential rebreathing alveolar gas in preference to dead space gas following ventilating the patient at a rate of normal minute ventilation, preferably approximately 5L per minute, and when desired inducing hypercapnea so as to increase arterial PC0 2 and prevent the PCO2 level of arterial blood from subsequently dropping below that achieved as r a result of decreasing the fresh gas flow, continuing maintaining normocapnia despite the ventilation at an increased rate until such time as the traumatic event and concomitant hyperventilation is completed, wherein the effects of hyperventilation experienced during
• the preferred circuit prevents rebreathing at a minute ventilation equal to the rate of air being aspirated into the atmospheric air aspirator because the check valve in the interconnecting conduit does not open to allow rebreathing of previously exhaled gas unless a sub-atmospheric pressure less than that generated by the recoil of the aspirator exists on the inspiratory side of the conduit of the circuit.
• the circuit provides that after the check valve opens, alveolar gas is rebreathed in preference to dead space gas because the interconnecting conduit is located such that exhaled alveolar gas contained in the tube conducting the expired gas into the expiratory reservoir bag will be closest to it and dead space gas will be mixed with other exhaled gases in the reservoir bag.
• the exhaled gas reservoir is preferably sized at about 3 L which is well in excess of the volume of an individual's breath.
• the reservoir bag collapses to displace the volume of gas extracted from the bag, minimizing the volume of atmospheric air entering the bag.
• a breathing port through which a subject inhales and exhales
• an inspiratory port communicating to the breathing port with an inspiratory
• the breathing port to the inspiratory port, the inspiratory port having an atmospheric air
• an expiratory port communicating to the breathing port with an expiratory
• the expiratory port having an expiratory
• gas reservoir to store gas exhaled by the subject flowing across the expiratory valve
• a bypass conduit communicating the inspiratory and expiratory ports with a
• bypass valve allows a one-way flow of air from the expiratory port
• the atmospheric air aspirator further comprises:
• an inspiratory port nozzle located between the inspiratory valve and the first
• a first tube attached to the inspiratory port nozzle
• the atmospheric air aspirator furthermore, preferably
• the expiratory gas reservoir further comprises:
• alveolar gas reservoir has the other end extending into the expiratory the gas
• the alveolar gas reservoir has a
• the expiratory gas reservoir has a capacity in excess of a volume of a
• a breathing port through which a subject exhales and inhales
• a bifurcated conduit adjacent and connected to the breathing port including a
• first conduit branch and a second conduit branch, the first conduit branch further
• an inspiratory check valve located between the breathing port and the
• the second conduit branch further including an
• collapsible container formed to recoil to an open position; a flexible expiratory gas reservoir, having an entrance tubing through which
• the flexible expiratory gas reservoir is connected to the second conduit, and an exit
• breathing apparatus having a one way inspiratory port in communication with an
• a breathing port through which a subject inhales and exhales
• inspiratory limb also in communication with an atmospheric air aspirator to provide
• expiratory port also in communication with an expiratory gas reservoir to store gas
• bypass valve the bypass valve allowing a one-way flow of gas from the expiratory
• the atmospheric air aspirator further comprises: a first end plate, where the inspiratory port opens to;
• an inspiratory port nozzle located between the inspiratory valve and the first
• a first tube attached to the inspiratory port nozzle
• the atmospheric air aspirator further comprises a spring to recoil the atmospheric air aspirator
• the expiratory gas reservoir further comprises:
• the expiratory gas reservoir is sealed and extends into the expiratory the gas
• the alveolar gas reservoir has a
• the expiratory gas reservoir has a
• isocapnia circuit comprising:
• a breathing port through which a subject exhales and inhales
• a bifurcated conduit adjacent and connected to the breathing port including a
• first conduit branch and a second conduit branch, the first conduit branch further
• a one way inspiratory check valve located between the breathing port and
• the second conduit branch further including a one way expiratory check
• valve located between the breathing port and an exhaust outlet
• collapsible container formed to recoil to an open position
• a flexible expiratory gas reservoir having an entrance tubing through which
• the flexible expiratory gas reservoir is connected to the second conduit, and an exit
• branches having a one-way check valve therein, and responding to a predetermined
• said atmospheric air aspirator may further comprise a second port for
• Figure 1 illustrates schematically the nature of the breathing circuit not dependent on an external source of fresh gas flow and components enabling the PCO2 to remain constant despite increase in minute ventilation.
• Figures 2 and 3 are charts of our data resulting from utilizing the method and circuit of the present invention.
• the patient breathes through one port of a Y-piece (1).
• the other 2 arms of the Y-piece contain 1-way valves.
• the inspiratory limb of the Y-piece contains a one-way valve, the inspiratory valve (2) which directs gas to flow towards the patient when the patient makes an inspiratory effort but during exhalation acts as a check valve preventing flow in the opposite direction.
• the other limb of the Y- piece, the expiratory limb contains a one-way valve, the expiratory valve (3), positioned such that it allows gas to exit the Y-piece when the patient exhales but acts as a check valve preventing flow towards the patient when the patient inhales.
• the expiratory reservoir bag (5) contains a second length of tubing termed 'exhaust tubing' (6) with a smaller diameter than the alveolar gas reservoir preferably at its distal end where expired gas exits to atmosphere (7) and is situated such that most of the tubing is contained within said bag (5) and with said bag sealed to the circumference of the tube at its distal end.
• the alveolar reservoir tube (4) is preferably about 35 mm in diameter, and its length is such that the total volume of the tubing is about or greater than 0.3 L when it is being used for an average (70 Kg) adult.
• the expiratory gas reservoir bag (5) has preferably a capacity of about 3 L.
• the exhaust tubing (6) has a diameter of preferably less than 15 mm at its distal end.
• the inspiratory port opens into a cylindrical container composed of a rigid proximal end plate (8), a collapsible plicated tube (9) extending distally from the circumference of the proximal plate (8) and a rigid plate sealing the distal end of the collapsible plicated tube (10).
• the tube When not in use, the tube is kept open by the force of gravity on the distal plate (10) and/or by the force of a spring (11) and/or by intrinsic recoil of the plicated tubing.
• the inspiratory port is open to atmosphere by means of a nozzle (12) to which a length of tubing (13) is attached.
• the distal end plate is open to a nozzle (15) to which a length of tubing (16) is attached.
• the proximal end plate contains a protuberance (16) pointing into the tube that is aligned with the internal opening of the distal end plate nozzle (14).
• the combined proximal end plate (8), plicated tubing (9), distal end plate (10) spring (11), inspiratory port nozzle (12), tubing attached to inspiratory port nozzle (13), distal end plate nozzle (14), tubing attached to distal end plate nozzle (15), proximal end plate protuberance (16) are in aggregate referred to as the 'atmospheric air aspirator' (AAA).
• a bypass conduit (17) connects the expiratory limb and the inspiratory limb. The opening of the conduit to the expiratory limb is preferably as close as possible to the expiratory one-way valve.
• This conduit contains a one-way valve (18) allowing flow from the expiratory to the inspiratory limb.
• the conduit's one-way valve requires an opening pressure differential across the valve slightly greater than the pressure difference between the inspiratory limb pressure and atmospheric pressure that is sufficient to collapse the plicated tube. In this way, during inspiration, atmospheric air contained in the atmospheric air aspirator and the air being continuously aspirated into the inspiratory limb is preferentially drawn from the inspiratory manifold.
• each inspiration is drawn initially from the atmospheric air aspirator, collapsing the plicated tubing (9) and approximating the distal end plate (10) to the proximal end plate (8).
• the tubing is partially collapsed, there is a constant sub-atmospheric pressure in the inspiratory limb of the circuit. Said sub-atmospheric pressure creates a pressure gradient drawing atmospheric air into the inspiratory limb of the circuit through the nozzle (12) and tubing (13).
• the one-way valve opens and exhaled gas is drawn back from the expired gas reservoir into the inspiratory limb of the Y-piece and hence to the patient.
• the opening pressure of the bypass valve is close to the pressure generated by the recoil of the atmospheric air aspirator, there will be little change in the flow of atmospheric air into the circuit during inspiration after the atmospheric air aspirator has collapsed.
• the last gas to be exhaled during the previous breath termed 'alveolar gas' is retained in the alveolar gas reservoir (4) and is the first gas to be drawn back into the inspiratory limb of the circuit and inhaled (rebreathed) by the subject.
• the rest of the gas in the expiratory gas reservoir (5) contains mixed expired gas.
• the mixed expired gas from the expired gas reservoir replaces the gas drawn from the alveolar gas reservoir and provides the balance of the inspired volume required to meet the inspiratory effort of the patient.
• the greater restriction in the diameter of the second tube (6) than in the alveolar gas reservoir (4) results in the gas being drawn into the alveolar gas reservoir being displaced by the collapse of the expired gas reservoir bag in preference to drawing air from the ambient atmosphere.
• the second tube in the expiratory bag (6) provides a rout for exhaust of expired gas and acts as a reservoir for that volume of atmospheric air that diffuses into said expiratory gas reservoir bag through the distal opening, tending to keep such atmospheric air separate from the mixed expired gas contained in the expired gas reservoir.
• the atmospheric air aspirator can be modified adding a second port for air entry at, for example, the distal end plate (14) such that the total flow from the two ports provides the desired total flow of air into the circuit under the recoil pressure of the atmospheric air aspirator.
• the second port (14) is occluded by the protuberance (16), the remaining port (12) providing a greater resistance to air flow to offset the greater pressure gradient being that gradient required to open the bypass valve (18).
• the embodiment described above assumes that the force of gravity acting on the distal plate provides the recoil pressure to open the atmospheric air aspirator.
• the disadvantage to this configuration is that the distal end plate must be fairly heavy to generate the sub-atmospheric pressure. This may be too heavy to be supported by attachment to a face mask strapped to the face. Furthermore movement such as walking or running or spasmodic inhalation will cause variations in the pressure inside the atmospheric air aspirator and hence variation in flow of air into the atmospheric air aspirator. In such cases it is better to minimize the mass of the distal endplate and use a different type of motive force to provide recoil symbolized by the spring (11).
• NA FGF + (N - FGF) (PvC0 2 - PCO2 of exhaled gas)/PvC0 2
• the first gas to exit the mouth comes from the trachea where no gas exchange has occurred.
• the PCO2 of this gas is identical to that of the inhaled gas and is termed 'dead space gas'.
• the last gas to exit the mouth originates from the alveoli and has had the most time to equilibrate with mixed venous blood, has a PCO2 closest to that of mixed venous blood and is termed 'alveolar gas'. Gas exhaled between these 2 periods has a PCO2 intermediate between the two concentrations.
• the equation cited above explains why rebreathing alveolar gas would be the most effective in maintaining the PCO2 at a constant level when minute ventilation increases.
• All of the fresh gas, in the form or atmospheric air, is inhaled by the subject and contributes to alveolar ventilation when minute ventilation is equal to or exceeds the rate of atmospheric air aspirated into the AAA.
• the 'alveolar gas' is preferentially rebreathed when minute ventilation exceeds the fresh gas flow.
• the circuit as described above is installed in a case to render it fully portable.
• the case may include the appropriate number of capped ports to allow proper set up and use of the circuit.

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• 2002
  • 2002-03-12 WO PCT/CA2002/000338 patent/WO2002072185A1/en not_active Application Discontinuation
  • 2002-03-12 EP EP02706568A patent/EP1370319A1/de not_active Withdrawn

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