Room temperature heat exchanger for a ventilation circuit

Abstract

Ventilation circuit (14) for a patient, the ventilation circuit (14) comprising: an inspiratory branch (22) which supplies respiratory gases to the patient; an exhalation branch (32) which receives the patient's respiratory gases; Means for circulating respiratory gases (56) in the ventilation circuit (14) for delivering respiratory gases to the patient and for receiving respiratory gases delivered by the patient; a CO2 absorber (42) arranged in the ventilation circuit (14) between the expiratory branch (32) and the inspiratory branch (22) for removing CO2 from the respiratory gases exhaled by the patient; a heat exchanger (48) arranged downstream of the CO2 absorber (42) for reducing the temperature of the respiratory gases and removing moisture from the respiratory gases after the respiratory gases have passed through the CO2 absorber (42) and before the respiratory gases are delivered to the inspiratory branch (22); wherein the heat exchanger (48) comprises a plurality of tubes (88, 102) which receive the respiratory gases from the CO2 absorber (42) and conduct the respiratory gases to the inspiratory branch (22), wherein the water carried by the respiratory gases condenses within the plurality of tubes (88, 102) within the heat exchanger (48); and a sump (112) formed integrally with the heat exchanger (48), the sump (112) being arranged to collect moisture condensed from the respiratory gases as the respiratory gases flow through the heat exchanger (48), wherein the sump (112) is removably attached to the heat exchanger (48) and has a drain valve (120).

Description

BACKGROUND OF THE INVENTION

[0001] The invention generally relates to a ventilation circuit with a device for removing entrained water from the ventilation gas within the ventilation circuit. More specifically, the present invention relates to a heat exchanger arranged in a ventilation circuit for reducing condensation in other areas within the ventilation circuit.

[0002] A mechanical ventilator is often used to deliver and remove respiratory gases from a patient. The operation of the ventilator can assist and / or replace the patient's natural breathing alone or in conjunction with a patient anesthetic. A typical mechanical ventilator has an inspiratory section that delivers respiratory gases to the patient and an expiratory section that receives respiratory gases from the patient. The inspiratory and expiratory sections are each connected by branches of a Y-connector. A patient piece extends from a third arm of the Y-connector to an incubation tube or a patient face mask.

[0003] A typical mechanical ventilator design recirculates the patient's exhaled gases through a CO2 absorber back to the inspiratory branch for recirculation to the patient. A closed circuit prevents the loss of anesthetic agents to the ambient air. However, the CO2 absorber in such a circuit develops an exothermic reaction that heats the breathing gas and introduces additional water vapor into the breathing gas. For example, an additional amount of 15 mg of water can be added per breath to the breathing gas circulating through the CO2 absorber in the closed circuit.

[0004] Although it is desirable for the patient to receive moist, warm ventilation gases, the presence of vapor in the ventilation circuit causes several disadvantages. In particular, when the warm, moist ventilation gas delivered by the patient, which is at body temperature, is passed through the ventilation circuit, which is at room temperature, the water vapor in the ventilation gases can condense on components of the ventilation circuit. As ventilation of the patient continues, the condensed water accumulates and can interfere with the operation of valves, sensors, or other components of the ventilation circuit. In addition, the gases leaving the CO2 absorber are at an elevated temperature relative to room temperature. As the ventilation gases move further through the ventilation circuit, they cool, and the water vapor entrained with the ventilation gases can condense and accumulate within the ventilation circuit.

[0005] Various solutions have been proposed to address this. Water traps can be placed in the ventilation circuit near problem areas to collect water and prevent it from reaching critical components. These water traps simply respond to the problem and must be continuously monitored and emptied as the water traps fill.

[0006] Another solution is to heat the ventilation circuit to prevent water vapor condensation. Heating the ventilation circuit can be achieved using resistance heaters, such as wires wrapped around the branch tubes and around the sensors and valves. Heating devices add to the complexity of the ventilation circuit and are often undesirable.

[0007] A specific example of a system configured to remove water vapor from the respiratory gases in a breathing circuit is illustrated and described in U.S. Patent No. 6,619,289 B1, the disclosure of which is incorporated herein by reference. In U.S. Patent No. 6,619,289 B1, a carbon dioxide absorber vessel includes an integral moisture sump that collects condensate from difficult-to-drain areas of the breathing circuit, such as the carbon dioxide absorber canister itself.

[0008] While the integral moisture sump in the carbon dioxide absorber canister is an effective way to remove some of the water vapor, an approach that removes additional amounts of water from the breathing gas is desirable. In particular, an approach is being sought that lowers the temperature of the breathing gas downstream of the CO2 absorber without the use of any additional operating components.

[0009] Patent application GB 2 118 047 A discloses a portable ventilation device with a filter for chemically removing carbon dioxide from the breathing air. In contrast, WO 01 / 49 251 A1 discloses a ventilation circuit with a drying device, wherein the drying device comprises a thermoelectric cooling element or a water vapor-permeable membrane. SUMMARY OF THE INVENTION

[0010] The present invention relates to a patient ventilation circuit according to claim 1.

[0011] The ventilation circuit contains an inspiratory branch that delivers ventilation gases to a patient. The ventilation gases from the patient are received by an expiratory branch, which delivers the patient's ventilation gases to a CO2 absorber. The CO2 absorber is located within the ventilation circuit and receives the ventilation gases from the expiratory branch and removes the CO2 from the ventilation gases before rebreathing by the patient. The CO2 absorber removes the CO2 through an exothermic reaction that releases both heat and water to the ventilation gases within the ventilation circuit.

[0012] The ventilation circuit includes a heat exchanger located downstream of the CO2 absorber to receive the ventilation gases from the CO2 absorber. The heat exchanger serves to lower the temperature of the ventilation gases and remove moisture from the ventilation gases before the ventilation gases are delivered to the inspiratory branch. The heat exchanger includes a number of inflow tubes, each receiving the ventilation gases from the CO2 absorber. The inflow tubes direct the ventilation gases to a set of outlet tubes, which deliver the ventilation gases to the inspiratory branch. As the ventilation gases flow through the inflow and outlet tubes, the tubes communicate with the ambient room temperature air, which has a lower temperature than the ventilation gases.The heat exchanger tubes allow heat to be transferred from the respiratory gases to the ambient air, which lowers the temperature of the respiratory gases and causes water vapor to condense along the inner surfaces of the inlet and outlet tubes.

[0013] Each of the inlet and outlet tubes communicates with a sump located at a bottom end of the heat exchanger. The sump is positioned to collect water condensed from the breathing gases as the breathing gases flow through the heat exchanger. The sump is removably attached to the heat exchanger and includes a drain that allows the collected water to be removed from the sump.

[0014] The heat exchanger positioned within the ventilation circuit removes water vapor and reduces the temperature of the ventilation gases before they contact various sensors and components within the ventilation circuit downstream of the heat exchanger. The heat exchanger thus prevents unwanted condensation within various areas of the ventilation circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The drawings illustrate the best mode presently contemplated for carrying out the invention. In the drawings: Fig. Figure 1 is an overview of a ventilation circuit illustrating the preferred placement of the heat exchanger; Fig. Figure 2 is a partial side view of a ventilator with a heat exchanger; Fig. 3 is an exploded, partially sectional view of the heat exchanger as shown in Fig. 2 illustrates and Fig. 4 is a sectional view taken along line 4-4 of Fig. 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0016] Fig. 1 illustrates a ventilation system 10 for mechanically ventilating a patient 12. The ventilation system 10 includes a closed ventilation circuit 14. The closed ventilation circuit 14 includes a patient branch 16 that delivers ventilation gases to the patient 12 from a first leg 18 of a Y-connector 20.

[0017] The ventilation circuit 14 includes an inspiratory branch 22 connected to the inlet leg 24 of the Y-connector 20. The inspiratory branch 22 receives the flow of ventilation gases to be delivered to the patient 12 through a check valve 26. In the illustrated embodiment, an oxygen sensor 28 and a flow sensor 30 are disposed between the check valve 26 and the inspiratory branch 22.

[0018] The closed breathing circuit 14 includes an expiratory branch 32 connected to the outlet leg 34 of the Y-connector 20 to receive gases exhaled by the patient. The exhaled breathing gases flow through a flow sensor 36 and a check valve 38. The expiratory branch 32 is connected to the inlet 40 of a carbon dioxide absorber 42 (CO2 absorber). In a conventional closed breathing circuit, the outlet 44 of the CO2 absorber 42 is connected to the inhalation branch 22 to complete the closed breathing circuit. In the Fig. 1, the outlet 44 of the CO2 absorber 42 is connected to the inlet 46 of a heat exchanger 48, the details of which are described in more detail below.

[0019] The CO2 Absorber 42 is a conventional component containing soda lime (soda lime, sofno lime, sodium citrate) or another suitable CO2 absorbent. When the patient's respiratory gases pass through the CO2 Absorber 42, an exothermic reaction occurs, which both warms and humidifies the respiratory gases.

[0020] As in Fig. 1, the ventilation gases flow from the outlet 50 of the heat exchanger 48 through the check valve 26 and finally into the inspiratory branch 22. An anesthetic device 52 may be connected to the inspiratory branch 22 via a line 54 to introduce and retain an anesthetic agent in the ventilation gases within the circuit 14.

[0021] The Fig. The ventilation circuit 14 illustrated in Figure 1 includes means 56 for conveying the ventilation gases through the system. In the illustrated embodiment of the invention, the means 56 is a ventilator having a bellows assembly 58. The bellows assembly 58 includes an expandable bellows 60 connected to the exhalation branch 32 via a line 62. The line 62 includes a switching valve 64 that allows selection between the bellows 60 and a hand-operated bellows 66 as the driving force for the ventilation gases.

[0022] Upon patient exhalation, the drive gas within the housing 68 of the bellows assembly 58 is allowed to exit, allowing the bellows 60 to expand upward and receive the exhaled gases as the patient 12 exhales. The exhaled gases are delivered to the bellows 60 via the exhalation branch 32 and the switching valve 64.

[0023] Upon the next breath of patient 12, the bellows 60 is compressed by the driving gases within the housing 68 to deliver ventilation gases to the patient via the CO2 absorber 42, the heat exchanger 48, and the inspiratory branch 22. The CO2 from the ventilation gases previously exhaled by the patient is removed by the CO2 absorber 42.

[0024] The breathing circuit may include various sensors, such as flow sensors 30, 36, gas quality sensors, such as oxygen sensor 28, and various pressure sensors that monitor the operation of the breathing circuit 14. The patient leg 16 typically includes gas sampling tubes for the sensors, a bacterial filter, and other elements, collectively designated by reference numeral 70.

[0025] As in Fig. 1, the breathing circuit 14 includes the heat exchanger 48, which is disposed within the ventilation circuit 14 downstream of the CO2 absorber 42 and upstream of the inspiratory branch 22. As described above, the heat exchanger 48 includes an inlet 46 that receives the warm, moist exhaled respiratory gases that have been purified of CO2 by the CO2 absorber 42. In a typical embodiment, the respiratory gases exit the outlet 44 of the CO2 absorber at a temperature in the range of 37°C. Because typical room temperature is approximately 21°C, the temperature difference between the respiratory gases within the ventilation circuit 14 and room temperature is approximately 16°C when measured at the outlet 44 of the CO2 absorber 42.

[0026] In a closed breathing circuit that does not include a heat exchanger 48, the warm, humid breathing gases from the CO2 absorber 42 flow over the relatively cool, room-temperature surfaces of the various sensors and tubes present in both the inspiratory branch 22 and the patient branch 16, cooling the breathing gases and causing moisture to condense from the breathing gases and collect on the sensor device. The heat exchanger 48 is located between the CO2 absorber 42 and the inspiratory branch 22 and reduces the temperature of the breathing gases and removes moisture resulting from the water vapor.

[0027] Fig. Figure 2 illustrates a conventional ventilation and anesthesia machine 72. The anesthesia machine 72 includes a chassis 74 with a number of wheels 76 that allow easy transport of the machine 72. The anesthesia machine 72 includes a CO2 canister 78 that removes CO2 from the ventilation gases as described above. As illustrated, the anesthesia machine includes the heat exchanger 48, located downstream of the CO2 absorber 42, to remove moisture from the ventilation gases and lower the temperature of the ventilation gases before they are delivered to the inspiratory branch.

[0028] It will now Fig. 3, which illustrates the details of the heat exchanger 48. The heat exchanger 48 includes a connecting flange 80 with a flexible gasket for forming an airtight seal at both the outlet of the CO2 absorber and the inspiratory branch of the breathing circuit. The connecting flange 80 is formed as part of a top cap 84 having an internal channel in fluid communication with the inlet 46 of the heat exchanger. The top cap 84 receives the upper first end 86 of a number of inflow tubes 88. Each of the inflow tubes 88 extends from a first end 86 to a second end 90. In the illustrated embodiment of the invention, the heat exchanger 48 includes six inflow tubes, although different numbers of inflow tubes 88 are contemplated as being within the scope of the illustrated invention.

[0029] The second end 90 of each inlet tube 88 is received by the lower base 92 of the heat exchanger. The lower base 92 includes a flexible sealing ring 94 surrounding a bottom wall 96 with openings 98 sized to correspond to the row of inlet tubes 88.

[0030] The upper cap 84 of the heat exchanger 48 also includes a heat exchanger outlet 50 that is in fluid communication with a second end 100 of each of the plurality of outlet tubes 102. In the Fig. In the embodiment illustrated in Figure 3, the heat exchanger 48 includes six outlet tubes 102 arranged immediately adjacent to the six inlet tubes 88. The orientation and number of the inlet tubes and outlet tubes 88, 102 can be changed depending on specific requirements for the heat exchanger 48.

[0031] The first end 104 of the discharge tube 102 is received by the lower base 42 and aligned with one of the openings 98 formed in the lower wall 96. As shown in Fig. 3, the sealing ring 94 completely surrounds each of the openings 98 formed in the lower wall 96.

[0032] In the Fig. 3 and Fig. In the embodiment of the invention illustrated in Figure 4, each of the inflow tubes 88 and outflow tubes 102 is formed by an outer wall 106 defining an open interior space 108. In the illustrated embodiment of the invention, the free flow cross-section of the six tubes 88, 102 totals 471 mm2. The cross-sectional area maximizes the surface area and minimizes the flow resistance of the ventilation gas flowing through each of the tubes 88, 102.

[0033] The heat flow in the stationary state is given by the Fourier equation: Q=kAΔTd where Q = heat flow k = thermal conductivity A = transition area ΔT = temperature difference and d = distance for heat transfer.

[0034] As can be seen from the above equation, the heat flow depends on the heat flow of the transfer or contact area A and the distance d over which the heat flow extends. Thus, the length affects the number of tubes, and the size of each tube affects the heat flow in the heat exchanger 48. In the illustrated embodiment of the invention, each of the tubes 88, 102 has a length of approximately 270 mm and a cross-sectional area of 78.5 mm.

[0035] In the Fig. 3 and Fig. 4, each of the tubes 88, 102 is made of a polyester material, such as Hytrel®, available from Smooth-Bor. The polyester material used to form the heat exchanger tubes 88, 102 provides effective heat transfer between the respiratory gases carried by the tubes and the ambient air. Although polyester is described as a preferred embodiment of the invention, other materials may be used in accordance with the present invention. Additionally, although each of the inlet tubes 88 and outlet tubes 102 is illustrated as an externally smooth tube, it is contemplated that each of the tubes could include pleats to increase the surface area of the tube, and thus the heat flux from the respiratory gas to the atmosphere.

[0036] It will be Fig. 3, wherein the heat exchanger 48 includes an outer cover 110 extending between the upper cap 84 and the lower base 92 to provide a visually appealing appearance to the heat exchanger 48.

[0037] As in Fig. 3, the heat exchanger 48 includes a sump 112 arranged to collect condensed moisture from the respiratory gases as the respiratory gases flow through the inlet tubes 88 and the outlet tubes 102. The sump 112 includes a lower collection vessel 114 extending below an upper flange 116. The upper flange 116 is received within an outer rim 118 formed on the lower base 92. A gasket, which may be formed as part of the sealing ring 94, communicates with the opening to the lower collection vessel 114 to provide a fluid- and gas-tight seal between the sump 112 and the heat exchanger 48. The sump 112 includes a drain 120 that may be connected to a hose or pan to drain the collection vessel 114.Formed as part of the collection vessel 114 is a drain button 122 that can be depressed to allow water to flow through the drain 120. Preferably, the outer wall forming the collection vessel 14 is formed of a transparent plastic material so that an operator can see when the collection vessel 114 has filled with water.

[0038] During operation of the heat exchanger 48, the respiratory gases flow from the CO2 absorber 42 through the inlet 46 into the heat exchanger. The respiratory gases flow through the top cap 84 into the first end 86 of the plurality of inflow tubes 88. As the respiratory gases flow downward through the inflow tubes 88, the outer surface of the inflow tubes 88 is in contact with the surrounding room temperature air. Because the temperature of the respiratory gases from the CO2 absorber is in the range of 36°C to 38°C and room temperature is typically 21°C, heat is removed from the respiratory gases flowing through the inflow tubes 88. As the temperature of the respiratory gases decreases, water vapor condenses from the respiratory gases and collects along the inner surface 124 of the inflow tubes 88, as shown in Fig. 4 is illustrated.

[0039] Because each of the inlet pipes 88 extends vertically downwards, as shown in Fig. 3, the condensed water deposited on the inner surface of each inlet tube 88 flows downward toward the second end 90 and is finally collected in the collection vessel 114 of the sump 112.

[0040] After the ventilation gases leave the inlet tubes 188, they enter the sump 112 and flow into the first end 104 of each outlet tube 102. The ventilation gases then flow upward to the second end 100 of each outlet tube 102. As the ventilation gases flow in this upward direction, heat is again removed from the ventilation gases and additional vapor condenses along the inner surface 124 of each outlet tube 102. Again, the vertical orientation of the outlet tubes 102 causes the condensed water to flow downward and be collected in the sump 112.

[0041] It will now Fig. 4, the outer cover 110 defines an open interior space 126 surrounding all of the inlet tubes 88 and outlet tubes 102. In the illustrated embodiment, the open interior space 126 receives a flow of ambient air at room temperature, which helps remove heat from the respiratory gases. Alternatively, the open interior space 126 may receive a flow of air at a temperature lower than room temperature to assist in the removal of additional heat and thus moisture from the respiratory gases.

[0042] In addition to reducing the temperature of the ventilation gases and removing moisture from the ventilation gases, the heat exchanger 48 also acts as a holding area for the fresh gas from the anesthesia machine 52 during the exhalation phases of the ventilation cycle. Specifically, during the exhalation phase, the fresh gas coming from the anesthesia machine 52 is drawn along the path of least resistance and flows into the bellows assembly 58. In a closed ventilation circuit that does not include a heat exchanger 48, the fresh gases from the anesthesia machine can flow back into the CO2 absorber. Because the output gases from the anesthesia machine 52 are typically very dry and may contain an anesthetic agent, the backflow of these gases into the CO2 absorber 42 can cause undesirable problems.

[0043] When the heat exchanger 42 is arranged in the closed ventilation circuit 14, the output gases from the anesthesia machine 52 are initially drawn into the outflow tubes and the inflow tubes 88 of the heat exchanger 48 during the patient's exhalation. The combined volume of the inflow and outflow tubes within the heat exchanger 48 is sufficient to absorb and retain the volume of gas coming from the anesthesia machine 52 during the exhalation phase of the respiratory cycle. The heat exchanger blocks the gases coming from the anesthesia machine 52 as they enter the CO2 absorber 42. Thus, the heat exchanger 48 serves as a buffer between the anesthesia machine 52 and the CO2 absorber 42 during the exhalation phase of the respiratory cycle.

[0044] As from Fig.2, the sump 112 may be selectively removed from the remaining portions of the heat exchanger 48 for cleaning or other purposes. Additionally, a sump 112 with a larger collection vessel 114 may be used to collect larger volumes of water from the heat exchanger 48, which would require less frequent draining of the sump 112.

[0045] Various alternatives and embodiments are considered to be within the scope of the following claims, which particularly point out and claim the subject matter of the invention. PARTS LIST: 10 Ventilation system 12 patients 14 closed ventilation circuit 16 patient branch 18 first leg 20 Y-connectors 22 Inspiratory branch 24 inlet legs 26 Check valve 28 Oxygen sensor 30 flow sensor 32 Exhalation branch 34 outlet legs 36 Flow sensor 38 Check valve 40 entrance 42 CO2 absorbers 44 Outlet 46 Entrance 48 heat exchangers 50 outlet 52 anesthesia machine 54 channel 56 Means of Circulation 58 Bellows arrangement 60 bellows 62 channels 64 switching valve 66 hand bellows 68 housings 70 sample tubes 72 anesthesia machine 74 Base 76 wheels 78 CO2 containers 80 connecting flange

Claims

[1] Ventilation circuit (14) for a patient, the ventilation circuit (14) comprising: an inspiratory branch (22) which supplies respiratory gases to the patient; an exhalation branch (32) which receives the patient's respiratory gases; Means for circulating respiratory gases (56) in the ventilation circuit (14) for delivering respiratory gases to the patient and for receiving respiratory gases delivered by the patient; a CO2 absorber (42) arranged in the ventilation circuit (14) between the expiratory branch (32) and the inspiratory branch (22) for removing CO2 from the respiratory gases exhaled by the patient; a heat exchanger (48) arranged downstream of the CO2 absorber (42) for reducing the temperature of the respiratory gases and removing moisture from the respiratory gases after the respiratory gases have passed through the CO2 absorber (42) and before the respiratory gases are delivered to the inspiratory branch (22); wherein the heat exchanger (48) comprises a plurality of tubes (88, 102) which receive the respiratory gases from the CO2 absorber (42) and conduct the respiratory gases to the inspiratory branch (22), wherein the water carried by the respiratory gases condenses within the plurality of tubes (88, 102) within the heat exchanger (48); and a sump (112) formed integrally with the heat exchanger (48), the sump (112) being arranged to collect moisture condensed from the respiratory gases as the respiratory gases flow through the heat exchanger (48), wherein the sump (112) is removably attached to the heat exchanger (48) and has a drain valve (120). [2] The breathing circuit (14) of claim 1, wherein a plurality of tubes (88, 102) are each formed of polyester. [3] The ventilation circuit (14) of claim 1, wherein the number of tubes (88, 102) in the heat exchanger (48) comprises: a plurality of inlet tubes (88), each having a first end (86) communicating with the CO2 absorber (42) and a second end (90) in fluid communication with the sump (112), and a plurality of exhaust tubes (102), each having a first end (104) in fluid communication with the sump (112) and a second end (100) in fluid communication with the inspiratory branch (22). [4] The breathing circuit (14) of claim 3, wherein the respiratory gases flow from the second end (90) of the inflow tubes (88) into the sump (112) and from the sump (112) into the first end (104) of the outflow tubes (102). [5] The ventilation circuit (14) of claim 3, wherein the inflow tubes (88) and the outflow tubes (102) extend in opposite directions. [6] The ventilation circuit (14) of claim 3, further comprising: an anesthesia machine (72) arranged in communication with the inspiratory branch (22) of the ventilation circuit (14), the second end (100) of each outflow tube (102) being in fluid communication with the anesthesia machine (72). [7] Ventilation circuit (14) according to claim 6, wherein the gases from the anesthesia machine (72) are taken up by the outflow tubes (102) and the inflow tubes (88) of the heat exchanger (48) during an exhalation phase of the patient.

Images