GB2465358A - Tubing for assisted breathing apparatus with heat exchange arrangement - Google Patents

Abstract

A generator for use in nasal continuous positive airway pressure and nasal intermittent positive pressure ventilation therapies in which a first channel 4 for transporting fresh gas and a second channel 5 for communicating proximal pressure levels are ported for tube connections being made within the third channel 3 for carrying exhaled gas. The device extends over the portion of length that is within the patient's environment. The 3 channels may connect to a manifold with 3 separate external patient circuit connection ports 8, 9 and 10. The arrangement allows for heat exchange between the inhalation and exhalation gasses to reduce the temperature differential and help eliminate condensation and is further designed to improve the speed and ease of use.

Description

Nasal CPAP and IPPV pressure generator This invention relates to the mechanical design configuration of a universal patient interface for use in Nasal Continuous Positive Airway Pressure (NCPAP) and Nasal Intermittent Positive Pressure Ventilation (NIPPV) therapies where a fresh gas flow is delivered to the patient in a continuous or variable manner. NCPAP and NIPPV are well known modes of respiratory support in infant intensive care.

For present purpose "fresh gas" means air or an oxygen enriched air-oxygen mixture or a treatment gas containing other therapeutic gasses. The required proportions of the constituent gasses in the "fresh gas" are determined by the practitioner of a therapy, according to the procedure being performed and the condition of the patient. It is therapeutically desirable that the fresh gas enters the patient's airway at patient body temperature and at 100% relative humidity.

"Exhaled gas" means gas exiting the form patient's airway following the gas exchange between oxygen and carbon dioxide performed by the patient's lung. By nature of being somewhat depleted of oxygen and somewhat enriched with carbon dioxide, exhaled gas has low therapeutic value and its re-breathing, in significant proportion to fresh gas, should be avoided. Exhaled gas is close to body temperature and 100% relative humidity.

Publication W09006149 describes a nasal pressure generator with prongs inserted into the nasal cavity and that has a first channel for supplying fresh gas and a second channel for exhausting exhaled gas. The term "nasal generator" is well known and describes a device performing a flow to static pressure conversion with a fluidic mechanical entrainment boost feature that is relative to patient demand on inhalation. The gas entrained during the boost period is largely the fresh gas that has accumulated in the nearest portion of the exhalation channel, during the dwell time between the patient exhaling and inhaling. Derivative generator devices currently being marketed, and as described in US5975077 and in W02007064668, are configured with a third channel for communicating pressure levels proximally to the patients airway. Another derivative generator device described in W09924101 has a short exhalation channel with exhalation occurring inside the patient environment. The said exhalation within the patient environment has drawbacks of water condensation as described later in this document.

The wider system and tube for transporting fresh gas to the generator's fresh gas channel encompasses heating and humidification elements for achieving the desired said fresh gas temperature and humidity saturation. For purpose of reducing bulk and eliminating potential hazards from electric heating elements within the patient environment, the final portion of tubes connecting to a nasal generator head remains unheated. The said unheated portion of the fresh gas tube causes a loss of temperature, with resulting desaturation/condensation from humidity. The degree of heat loss depends on the ambient temperature within the patient environment. It is not uncommon for the said condensation to cause undesirable water droplets to enter the patient's lung. The said condensation can also enter and occlude the proximal pressure tube and thereby adversely affect the therapy monitoring system.

Generators of prior art as described in W09006149,

US5975077, W09924101, W02007064668, and their commercial variants produced over more that 15 years are configured with a stacked sequence of separate spaced apart ports for connecting tubes to their said channels.

The said stacking or otherwise sequencing of spaced apart ports has a number of drawbacks. Firstly, the said stacking or sequencing adds to the relative size and height of a generator. An increased height of a generator reduces its stability and makes it more prone to tilting in its interface with the patient's nose. The said tilting opens the cushioning seal between the generator and the patient's nose, with resulting leakage and loss of treatment gas pressure. Secondly, the said tilting can also causes mechanical pressure points on the patient's skin. Nasal trauma and injuries caused to infant patients by NCPAP devices has been reported to occur in 20% of treatment sessions (Robertson N.J. et al. "Nasal deformities resulting from flow driver continuous positive airway pressure". Arch Dis Child Ed 1996;75:F209-212). Thirdly, the said separation of the fresh gas tube exposes the wall of the said tube to the lower temperature ambient environment, with resulting cooling and formation of water droplet within the generator.

Fourthly, the said separation of channels results in two or, more commonly, three tubes being routed across the patient's face and head. The said multiplicity of tubes increases complexity in fitting of the generator to the patient and increases risk of inadvertent adverse pulling and/or entanglement when handling an infant patient, such as during feeding, cleaning and examination.

One variant generator device described in application WO2007040828 is constructed with a short, tube-less, exhalation channel and side ports for connecting interface tubes. This said configuration has benefits in being relatively lower in profile and smaller in size. However, the said device does not address or overcome the cause of water condensation in the generator. The said device exhausts exhaled gas immediately into the patient environment, where the mixing of humid warm exhalation gas with ambient air can cause added water condensation in the generator and patient environment. The entrainment effect in the said device draws air from the ambient environment, as opposed to from a fresh gas supply that has accumulated within a longer exhalation channel. The said entrainment of ambient air will have an effect of diluting the oxygen concentration in an oxygen-enriched fresh gas. Although such dilution can be compensated for by further enriching the relative oxygen concentration, such enrichment compensation would result in an increased consumption/waste of relatively costly medical oxygen during exhalation and during the breathing dwell time between exhalation and inhalation.

The present invention is a mechanical design configuration of a nasal generator where a first channel for transporting fresh gas and second channel for communicating proximal pressure levels are ported for tube connections being made within the third channel for carrying exhaled gas. The said configuration is such that it enables a smaller diameter fresh gas tube and a smaller diameter proximal pressure tube being installed inside a larger diameter exhalation tube over the portion of length that is within the patient environment.

The present invention overcomes important drawbacks in prior art. Firstly, the present invention affects a heat exchange between the fresh gas and warm exhalation gas, through the wall of the fresh gas tube located inside the exhalation tube. The said heat exchange helps equalize any undesirable temperature differential and eliminates the formation of condensation inside the generator. Secondly, the said configuration enables a relatively lower profile in the construction of the generator to help improve fitting stability and reduce adverse tilting, thereby improving patient comfort and the gas pressure seal. Thirdly, the said enablement of installing the fresh gas tube and proximal pressure tube inside the single exhalation tube reduces complexity from multiplicity when fitting to a patient and also reduces the risks of entanglement or inadvertent pulling on tubes. The present invention encompasses a mistake-proof manifold branching and connecting the said three generator tubes to a conventional flow driver circuit.

The present invention will now be described by way of example and with reference to the accompanying drawings in which: Figure 1 shows the present generator as part of one example conventional NCPAP treatment system.

Figure 2 is a representative illustration of a prior art type generator fitted to a patient.

Figure 3 shows the present generator fitted to a patient.

Figure 4 shows a cross-section of an assembled present generator.

Figure 5 shows an exploded parts view of the present generator and manifold connector.

In figure 1 a flow driver 16 is connected to a source of first gas 17 and a source of second gas 18. The flow driver 16 has a first control for setting the blend proportions of the two said input gasses 17 and 18 into a fresh treatment gas. The flow driver 16 has a second control for setting the rate of flow of fresh gas. Tubes for fresh gas transport and proximal pressure communication between a flow driver 16 and a generator 15 are commonly referred to as a "patient circuit". The fresh gas is transported via a first portion of a patient circuit fresh gas tube l9a to a humidifier chamber 20 containing water. The humidifier chamber 20 is in conductive contact with a heating element 21. Heating of the water causes it to evaporate into the fresh gas flow, raising the temperature and relative humidity of the said fresh gas. A second portion of the patient circuit fresh gas tube 19b contains an electric resistive heating wire 22 for maintaining the temperature and relative humidity of the fresh gas. The power in the heating wire 22 is typically feedback controlled with a temperature sensor placed near the end of the patient circuit fresh gas tube (not shown here) . The heating wire 22 terminates short of the patient environment and generator 15. The generator 15 performs a heat exchange between exhaled gas and fresh gas, as described later for figure 3. The patient circuit may or may not have an extension tube 23 for carrying the exhalation gas 24 further away from the patient, such as to the outside of an incubator. The patient circuit proximal pressure tube is in communication with the entrance to the patient's upper airway via the generator 15. The proximal pressure monitor 26 performs surveillance of the pressure at the entrance to the patient's upper airway via the patient circuit proximal pressure tube 25.

In figure 2 a prior art type generator head 2 is tied by lateral straps 12 to a bonnet 11 that is pulled onto the patient's head 1. The generator head 2 has separate and spaced apart ports for connecting a fresh gas tube 4 and a proximal pressure tube 5 and an exhalation tube 6. The three said separate tubes 4, 5 and 6 are individually tied to the bonnet 11 by bonnet tie straps 7. The generator head 2 has a relatively tall profile affecting stability. The fresh gas tube 4 is exposed to the patient's ambient environment. The three said generator tubes 4, 5 and 6 are typically terminated with three independent connectors for connection to a conventional patient circuit. A first connector 9 is a typically smallest in size for connecting to a conventional patient circuit pressure tube. A second connector 10 is typically medium in size for connecting to a conventional patient circuit fresh gas tube. A third connector 8 is typically largest in size for connecting to a conventional exhalation tube. An international standard exists for dimensioning conventional patient circuit type connectors.

In figure 3 the generator head 3 of the generator is tied by lateral straps 12 to a bonnet 11 that is pulled onto the patient's head 1. The generator head 3 converts the fresh gas flow into a static patient airway pressure by a fluid mechanical principle similar to prior art. The generator head 3 has a single external visible port to which the exhalation tube 6 is connected. The generator head 3 has a lower profile relative to the profile of the prior art type generator head 2 shown in figure 2. In figure 3, a section cut 13 into the exhalation tube 6 (made here for illustration purpose) shows how the fresh gas tube 4 and proximal pressure tube 5 is installed inside the exhalation tube 6. The installation of the generator fresh gas tube 4 inside the generator exhalation tube 6 functions as a heat exchanger between the exhalation gas from the patient and fresh gas to the patient. At the opposite end to the generator head 3, the three said tubes enter a manifold 14 in which the tubes-in-tube branch out into three independent connectors. A first connector 9 is a smallest in size for connecting to a conventional patient circuit pressure tube.

A second connector 10 is medium in size for connecting to a conventional patient circuit fresh gas tube. A third connector 8 is largest in size for connecting to a conventional exhalation tube. The size differences between the three said connectors safeguard against user mistakes in connecting the generator to a conventional patient circuit.

In figure 4 a generator head upper shell 27 and a generator head lower shell 28 comes together to form an exhalation channel and enclose an accelerator part 29. The two generator head shell parts 27 and 28 are held together by a snap-on prongs plate 32 and snap-on swivel connector 35. The swivel connector 35 inserts into an exhalation tube 6. A soft elastomeric prong 34 pushes on to prong plate 32 and provides an interface with the patient's nose and nostrils.

The accelerator 29 has three functions of, firstly, receiving and retaining the first end of the fresh gas tube 4 into an orifice port 30 and, secondly, dividing the fresh gas channel and the exhalation channel and, thirdly, funnelling the fresh gas flow into two smaller jet orifices 31 through which the fresh gas is accelerated to a higher velocity, lower pressure flow. The internal face of the prong plate 32 has a hollow spigot 33 for receiving and retaining the first end of the proximal pressure tube 5. A manifold first shell part 36 has a first orifice 38 for receiving the second end of the fresh gas tube 4 and a second orifice 39 for receiving the second end of the proximal pressure tube 5. A manifold second shell part 37 covers and clamps the fresh gas tube 4 and proximal pressure tube 5. The two manifold shell parts 36 and 37 when pushed together form a spigot for pushing the exhalation tube 6 on to and lock the manifold shell parts 36 and 37 together and form a continuation of the exhalation channel.

In figure 5 an accelerator 29 enclosed within a generator head 3 has an orifice port 30 situated within the exhalation channel for connecting a first end of a fresh gas tube 4 installed within the said exhalation channel. The said accelerator 29 funnels the fresh gas flow into two smaller orifices 31 to form two higher velocity jets passing through a 6mm deep portion of the exhalation channel and entering the patient's nostrils. A prong plate 32 has a hollow spigot 33 situated within the exhalation channel for push connecting a first end of a proximal pressure tube 5 installed within the said exhalation channel. The hollow spigot 33 forms an open communication between the proximal pressure tube 5 and a side port 40 opening into the portion of the elastomeric prong 34 inserted into the patient's nostril. A manifold 14 branches the second end of the proximal pressure tube 5 into a conical connector 9 for connecting to a conventional patient circuit proximal pressure tube (as label 25 in figure 1) . The said manifold 14 also branches the second end of the fresh gas tube 4 into a conical connector 10 for connecting to a conventional patient circuit fresh gas tube (as label 19b in figure 1) The said manifold 14 receives the generator exhalation tube 6 and provides a continuation of and terminates the exhalation channel in a conical connector 8 for connecting to a conventional patient circuit exhalation tube (as label 23 in figure 1)

Claims (3)

1. Claims 1. A nasal pressure generator design configuration where both a first channel for transporting fresh gas and second channel for communicating proximal pressure levels are ported for tube connections being made within a third channel for transporting exhaled gas such that it enables the first end of a smaller diameter fresh gas tube and the first end of a smaller diameter proximal pressure tube being connected to the said generator and the said tubes being installed inside a larger diameter exhalation tube with the said exhalation tube's first end being connected to the said generator and the collection of the said three tubes being extending over the portion of length that is within the patient environment.
2. 2. A generator design in accordance with claim 1 where the second end of the said fresh gas tube and second end of the said proximal pressure tube and second end of the said exhalation tube are connected to a manifold with extracting channels branching into three separate and external patient circuit connection ports.
3. 3. A set of 3 tube channels in accordance with claims 1 and 2 where the tubes are combined into a single co-extruded part and where the fresh gas channel and proximal pressure channel figure inside the wall enclosure of the exhalation channel.Amendments to the claims have been filed as follows: 1. A nasal pressure generator design configuration where both a first channel for transporting fresh gas and second channel for communicating proximal pressure levels are ported for tube connections being made within a third channel for transporting exhaled gas such that it enables the first end of a smaller diameter fresh gas tube and the first end of a smaller diameter proximal pressure tube being connected to the said generator and the said tubes being installed inside a larger diameter exhalation tube with the said exhalation tube's first end being connected to the said generator and the collection of the said three tubes extending over the portion of length that is within the patient environment, to affect a generator profile of less than 30mm in height and to transfer heat between inhaled and exhaled gasses through the generator internal channels partition walls.2. A generator design in accordance with claim 1 where the second end of the said fresh gas tube and second end of the said proximal pressure tube and second end of the said exhalation tube are connected to a manifold with extracting channels branching into three separate and external patient circuit connection ports.* 3. A set of 3 tube channels in accordance with claims 1 and 2 where the tubes are combined into a single co-extruded part and where the fresh gas channel and proximal pressure channel figure inside the wall enclosure of the exhalation channel. * * * * * S *-