WO2008044792A1

WO2008044792A1 - Heat and moisture exchanger for patient breathing

Info

Publication number: WO2008044792A1
Application number: PCT/JP2007/070208
Authority: WO
Inventors: Akito Ohmura; Kunihisa Eguchi; Tetsuya Miyaji; Katsuyoshi Goto
Original assignee: Furrex Co., Ltd.
Priority date: 2006-10-10
Filing date: 2007-10-10
Publication date: 2008-04-17
Also published as: JP2010505455A; JP5124570B2

Abstract

A heat and moisture exchanger, configured to be located between a respiratory system of a patient and an anesthesia circuit connected to an anesthesia apparatus, or a respiratory circuit connected to a respirator for maintaining a temperature and humidity of an aspired gas required to a patient under anesthesia or artificial respiration, comprises a thermal storage unit, and a heat and humidity regenerating material added to the thermal storage unit. At least one of density, number of cells of the thermal storage unit, and an added amount of the heat and humidity regenerating material in the thermal storage unit is set to decrease from the patient side to the side of the anesthesia apparatus or the respirator along a flow direction of a respiratory gas in the thermal storage unit.

Description

DESCRIPTION

HEAT AND MOISTURE EXCHANGER FOR PATIENT BREATHING

Technical Field

The present invention relates to a heat and moisture exchanger (HME) to humidify and warm a dry gas aspired by a patient for medical applications to an anesthesia device, a respirator, or other device.

Background Art

Two kinds of devices have been usually employed to humidify and warm an aspired dry gas when using an anesthesia device, a respirator, or other devices. One is a heat and moisture exchanger (HME, called an

"artificial nose") of a passive type, and the other is a warmer/humidifier of an active type operated with a heat source .

The passive HMEs are further categorized into three types : - a type having hydrophilic material charged with hydroscopic substance;

- a type having hydrophobic material charged with hygroscopic substance; and a type having a combination of hydrophobic and hydrophilic layers.

For example, Japanese Patent Application Laid-open

Publication No. H06-63141 discloses the third type HME . In the reference, entitled "Heat and Moisture Exchanger (Filter)

-Element Device and Humidification-", Japanese Journal of Respiratory Care Medicine 21-1, P.1-7, edited by K. Ishii, described in detail are the HMEs .

For all types, it is understood that some amount of water vapor in the expiratory gas is condensed at a dew point in spaces minutely formed in an element of the HMEs, and meanwhile, the aspiratory gas serves to evaporate the condensed water for humidification. In case of warming of aspiratory gas, it is predicted that there will occur cyclic and local phenomena of thermal storage.

At present, the passive types are prevailing because of the advantages of being compact, lightweight, and low-cost while minimizing the risk of medical accidents, mainly arising from usage of a heat source and lack of humidifying due to failure in supplying additional water in the active type. However, it is a fact that as far as performance in warming and humidifying is concerned, the passive types are generally inferior when compared to the active ones.

The above conventional HMEs, however, have the following problems. One problem is that an airway of a patient tends to dry because of poor warming and humidifying capability and a fatal complication may be resulted by suffocation of the airway due to hardening of secretions. Another problem is clogging caused by condensed water accumulated in the HME.

In order to solve the above problems, it is required to store larger amount of water in an expiratory gas and release the stored water into an aspiratory gas. The amount of water to be stored in the HME is preferably 44mg/l, a saturated vapor amount in the air of 37⁰C of a normal body temperature. It is very important that in aspiration, the aspired gas is required to be near at the patient body temperature, as well as to keep high recovery of the absolute humidity. In storing and releasing of the above-mentioned water amount, the thermal storage capability of the HMEs has to be improved for maintaining the required temperature.

In order to achieve the same purpose, HMEs with a thermal storage unit made of metal or the like, have been proposed. However, those metal type HMEs have several problems such as its bulkiness and heavy weight, and necessity of cleaning every time secretions stick thereto. Thus, the disposable HMEs, being small, light-weight, and inexpensive, have become in use . On the other hand, it is not always preferable that the higher thermal storing effect is equipped with HMEs. For example, in the case that a humid expiratory gas of 37⁰C enters into an anesthesia circuit via an HME from a patient in an operating room, condensation in the circuit is likely to occur because of large difference in temperature between the expiratory gas and typical room environment (23°C).

Furthermore, if a dead cavity and/or a flow resistance are increased, there may occur a risk of increased burden on the patient required for breathing. When anesthesia or artificial respiration is applied, the patient requires the aspiratory gas of 44 mg/1 in absolute humidity, corresponding to relative humidity of 100% at a body temperature of 37⁰C. It is desired that the temperature of the aspiratory gas is adjusted closer to a body temperature for the required absolute humidity. If the temperature of the aspiratory gas is lower than the body temperature, the absolute humidity of 44mg/l may not be achieved even if the humidity is increased.

In the meantime, in the preferable HMEs: an employed material and a manufacturing cost must be feasible in single-use; a thermal resistance must be provided such that the temperature of an expiratory gas becomes approximately 23⁰C at the side of anesthesia circuit or the respiratory circuit; a thermal storage effect is required to regulate the temperature of the expiratory gas closer to the above temperature, 23⁰C, while avoiding increase in size, weight, dead cavity, flow resistance, and the like.

Summary of the Invention

To solve the above and other problems, one aspect of the present invention is a heat and moisture exchanger configured to be located between a respiratory system of a patient and an anesthesia circuit connected to an anesthesia apparatus, or a respiratory circuit connected to a respirator for maintaining a temperature and humidity of an aspired gas required to a patient under anesthesia or artificial respiration, comprising a thermal storage unit, and a heat and humidity regenerating material added to the thermal storage unit. At least one of a density of the thermal storage unit, a number of cells of the thermal storage unit, and an added amount of the heat and humidity regenerating material in the thermal storage unit is set to decrease from the patient side to the side of the anesthesia apparatus or the respirator along a flow direction of a respiratory gas in the thermal storage unit.

The thermal storage unit may include polyurethane and/or cellulose.

A density of the thermal storage unit may be in the range of 20-80 kg/m³. The density of the thermal storage unit at the patient side may be adjusted 1/2-2/3 of that at the side of the anesthesia apparatus or the respirator. The number of cells of the thermal storage unit may be in the range of 5-80 cells per inch.

The thermal storage unit may include at least one of calcium chloride, calcium carbonate, and calcium sulfate.

In the above heat and moisture exchanger, a heat storing capacity can be larger at the parts where at least one of density of the thermal storage unit, number of cells of the thermal storage unit, and an added amount of the heat and humidity regenerating material in the thermal storage unit is set larger, i.e., at the side closer to the patient. In the _meantime, condensation in the anesthesia circuit or the respiratory circuit can be prevented by decreasing the flow resistance and gradual lowering of the gas temperature at the parts where at least one of density of the thermal storage unit, number of cells of the thermal storage unit, and an added amount of the heat and humidity regenerating material in the thermal storage unit is set smaller, i.e., at the side closer to the anesthesia/respiratory circuit.

Brief Description of the Drawings

Fig. 1 shows a cross-sectional view of the three-staged HME according to one embodiment of the present invention;

Fig. 2 shows a schematic cross-section of a conventional single-staged HME;

Fig. 3 is a schematic diagram of the experimental setup for evaluation of the HMEs;

Fig. 4 compares variations in aspiratory temperature of the HMEs tested; Fig. 5 is a graph showing variation of absolute humidity of aspiratory gas of tested HMEs;

Fig. 6 shows a schematic view of a three-staged thermal storage element of the one embodiment of the present invention;

Fig. 7 shows a schematic view of a single-staged thermal storage element with a gradient structure for another embodiment of the present invention;

Fig. 8 shows a schematic view of a two-staged thermal storage element for further embodiment of the present invention; and Fig. 9 shows a schematic view of a thermal storage element with a density gradient for further embodiment of the present invention.

Detailed Description of the Invention The present invention will be described in detail below in accordance with the embodiments of the present invention.

As shown in Figs.l and 6, a three-staged HME 10 comprises a thermal storage unit 14 and a housing 12 containing the same.

The thermal storage unit 14 further includes three thermal storage elements 14a-14c, each being made of polyurethane with a different density. Each element 14a-14c may include/consist of cellulose . The elements 14a-14c are arranged in series along a gas flow direction, as the density decreases from the patient side, so as to obtain a three-staged HME 10 according to one embodiment of the present invention. A density of each element 14a-14c is arranged 80, 57, and 30 kg/m³ in descending order. To demonstrate its effectiveness, a test sample, a conventional single-staged HME 10 with a thermal storage unit 14 of no density difference in Fig .2 is evaluated for comparison of performance . The density of the thermal storage unit 14 of the test sample amounts to 57 kg/in³, an averaged density of the above three elements 14a-14c for the present embodiment. In addition, an artificial nose of commercial type, though not shown here, is also tested for comparison. The same housing of the same size is employed for both the present embodiment and test sample for containing the thermal storage element (s). The thermal storage unit 14 may be configured with combining four or more thermal storage elements so that the elements each having a different density are laid on each other along the direction of a gas flow.

Fig. 3 is a schematic diagram of the present experimental circuit 30. The measurements are made in a room-temperature range of 20 to 30⁰C, and 40 to 60% relative humidity. In the experimental circuit 30, the HME 10 of the present embodiment and the test sample are positioned between a mouth of a patient

(actually a participant of the test) 32 and a ventilator 38 via a breathing-flow separator 34. In the experiments, a ventilator 38 (Type e500, Newport Medical Instruments, Inc.) is employed to provide an air-breathing volume of 600 ml with a respiration rate of 15 cycles/min for the participant, where a time ratio of expiration and aspiration is two. A sensor system 36 for recording temperature and relative humidity

("MOISCOPE™" manufactured by S. K. I.Net, Inc.), is used to measure temperature and moisture of the aspiratory gas in a breathing-flow separator 34. The measured results are shown in Figs.4 and 5.

Referring to Fig. 4, 10 minutes after start of the measurement, the HME of the present embodiment indicates a temperature increase (ΔT) , as labeled "C", of approximately 4.0K whereas the single-staged test sample without density difference, as labeled "B" shows approximately 1.9K. At the same time, it is also demonstrated the temperature increase effect is improved as compared to the conventional commercial product, as labeled "A". As shown in Fig. 5, it is appreciated the absolute humidity as labeled "C" is more increased than the conventional product.

In addition to the density of the thermal storage unit, difference in a number of cells of the thermal storage unit and/or an added amount of the heat and humidity regenerating material in the thermal storage unit contribute to improvement in performance of warming and humidifying. The "number of cells" is defined herein as a number of cells observed along a length of one inch on a cross-sectional surface of a material such as polyurethane . Furthermore, as shown in Fig. 7, providing a gradient in at least one physical property among density of the thermal storage unit 14, number of cells of the thermal storage unit 14, and an added amount of the heat and humidity regenerating material in the thermal storage unit in a single thermal storage unit 14, i.e., a gradient structure in the single thermal storage unit 14, results in improvement of warming and humidifying characteristics. In this configuration, the physical property is set larger at the side closer to a patient.

As shown in Figs. 8 and 9, providing two thermal storage elements 14a, 14c each having difference in at least one physical property among density of the thermal storage unit 14, number of cells of the thermal storage unit 14, and an added amount of the heat and humidity regenerating material in the thermal storage unit 14 in an HME also results in improvement in warming/humidifying characteristics. In this configuration, the physical property is set larger at the side closer to a patient.

Hereinafter, a preferable numerical range of the physical properties are discussed. Regarding the density, if the largest value exceeds 80 kg/m³, a patient will experience difficulty in respiration due to an increased flow resistance of the HME. If the smallest value is below 20 kg/m³, shortage of thermal capacity will decrease a thermal storage effect, thus unpreferable increase in size is required. Consequently, the density is preferably in the range of 20-80 kg/m³. For the same reasoning, the number of cells is preferably in the range of

5-80 cells per inch.

Moreover, in the difference in the density of the thermal storage unit from the patients side to the anesthesia/respiratory circuit, in order to achieve optimal balance between the thermal storage effect and the flow resistance, the ratio of the density at the patient side and that of the anesthesia/respiratory circuit side is preferably set half to two-thirds.

Industrial Applicability

The present invention is applied successfully to a respiratory circuit, attached to an anesthesia device, a respirator, and so on.

Claims

1. A heat and moisture exchanger configured to be located between a respiratory system of a patient and an anesthesia circuit connected to an anesthesia apparatus, or a respiratory circuit connected to a respirator for maintaining a temperature and humidity of an aspired gas required to a patient under anesthesia or artificial respiration, comprising: a thermal storage unit/ and a heat and humidity regenerating material added to the thermal storage unit, at least one of density of the thermal storage unit, number of cells of the thermal storage unit, and an added amount of the heat and humidity regenerating material in the thermal storage unit being set to decrease from the patient side to the side of the anesthesia apparatus or the respirator, along a flow direction of a respiratory gas in the thermal storage unit.

2. A heat and moisture exchanger claimed in Claim 1, wherein the thermal storage unit includes polyurethane and/or cellulose.

3. A heat and moisture exchanger claimed in Claim 2, wherein a density of the thermal storage unit is in a range of 20 to 80 kg/m³.

4. A heat and moisture exchanger claimed in Claim 3, wherein the density of the thermal storage unit at the side of the anesthesia apparatus or the respirator is adjusted half to two-thirds of that at the patient side.

5. A heat and moisture exchanger claimed in Claim 2, wherein the number of cells of the thermal storage unit is in the range of 5 to 80 cells per inch.

6. A heat and moisture exchanger claimed in Claim 2, wherein the thermal storage unit includes at least one of calcium chloride, calcium carbonate, and calcium sulfate.