Ventilator apparatus

VENTILATOR APPARATUS

This invention relates to ventilator apparatus of the kind including a source of breathing gas having an outlet connected with a breathing device, such as a mask, via a CPAP device.

Various different ventilation methods and therapies are used on patients who have respiratory difficulties. For patients who are not breathing spontaneously, PEEP (positive end expiratory pressure) may be employed in which the pressure in the lungs during expiration is maintained above atmospheric pressure, typically at 5mmHg to lOmmHg above atmosphere. This pressure maintains alveolar inflation sufficiently to prevent the lungs collapsing during expiration. Various devices can be used to achieve PEEP. These usually involve a pneumatic or mechanical resistance to flow in the expiratory path. PEEP valves are available from various sources including Ambu and Drager. For patients who are spontaneously breathing, a CPAP (continuous positive airway pressure) therapy may be used that provides a continuous inspiratory gas flow. This also maintains alveolar inflation as the patient exhales against the pressure of this inspiratory gas flow. CPAP devices are available, for example, from Smiths Medical under the EzPAP name. However, for some patients the work required to breathe out with a CPAP may be arduous. In these cases a bi-level positive airway pressure ventilator may be used. Such ventilators can be described as pressure controlled ventilation in both the inspiratory and expiratory phases during spontaneous breathing providing two distinct pressure levels. These systems use variable levels of air pressure instead of continuous steady pressure. The pressure rises when inhaling and drops when exhaling, making breathing easier. It can also be described as a continuous positive airway pressure (CPAP) system with a time-cycled change of the applied CPAP level. As with a pressure-controlled, time-cycled mode, the duration of each phase as well as the corresponding high and low pressure levels can be adjusted independently.

Bi-level positive pressure therapy may be prescribed for patients with sleep apnoea (a sleep disorder characterized by failure of the brain to signal the chest muscles to breathe) if CPAP therapy is too uncomfortable. It is also helpful in cases of ventilatory muscle fatigue, congestive heart failure and different types of lung disorders, particularly patients who have above-normal carbon dioxide levels. It has also been applied in situations where the more invasive procedures of intubation or tracheostomy are considered too detrimental or inappropriate. A bi-level positive pressure ventilator can be spontaneously timed. Such a ventilator is arranged to initiate a breath for the patient automatically if the patient does not take a breath spontaneously. Depending on the spontaneous breathing activity, bi-level positive pressure systems can be subdivided into: no spontaneous breathing; spontaneous breathing at the lower pressure level; spontaneous breathing at the upper pressure level; and spontaneous breathing at both CPAP levels, that is, genuine bi-level PAP.

Bi-level PAP ventilation enables a progressive, controlled transition from all levels of augmented mechanical ventilation, so may be a suitable mode for the entire period of mechanical ventilation of the patient. There are no difficulties choosing the correct moment for switching or the further respiratory management of the ventilated patient under bi-level PAP. The necessary adaptation (ventilation, oxygenation) can be tailored to the individual on the basis of blood gas analyses which may be accomplished by the inclusion of pulse oximetry within the setup as-described. With bi-level PAP an increase or reduction of the invasive extent of ventilation can be attained without any problems. Furthermore, spontaneous breathing of the patient does not necessitate any switching of the mode of ventilation. The transition from controlled to augmented ventilation is smooth. Bi-level PAP enables the therapist to let the patient breathe freely even under the most invasive of ventilation conditions.

Conventional bi-level PAP ventilators tend to be expensive, complex and bulky so do not lend themselves to home use or to portable use so that the patient is confined to the region of the ventilator system during therapy and is unable to move normally. It is, however, a well-established modern medical principle for patients to become mobile and to walk around as soon as possible after treatment.

It is an object of the present invention to provide an alternative ventilator apparatus.

According to the present invention there is provided ventilator apparatus according to the above-specified kind, characterised in that the apparatus includes a PEEP device connected with the breathing device, and that the apparatus is arranged such that the expiratory path from the breathing device is preferentially via the PEEP device and bypasses the CPAP device on exhalation. The apparatus preferably includes a non-return valve connected between the CPAP device and the breathing device. The source of breathing gas may include a cylinder of oxygen. The PEEP device is preferably arranged to provide an impedance to gas flow to maintain a pressure at an outlet of the breathing device during expiration in the range 5 mmHg to 10 mmHg. The apparatus may further include a blood gas sensor arranged to provide an output to the gas supply to control flow of gas from the supply in accordance with the patient's sensed blood gas levels. The apparatus may include a support by which the gas source is mounted on the patient's body. The support may be in the form of a vest with a front panel supported by two shoulder straps, the gas source being mounted on the front panel.

Ventilator apparatus according to the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 shows the ventilator apparatus schematically; and

Figures 2A and 2B show the front and rear respectively of ventilator apparatus

incorporated in an ambulatory support.

With reference first to Figure 1 there is shown ventilator apparatus capable of delivering bi-level PAP ventilation. The apparatus includes a gas source 1 the outlet 10 of which is connected to the inlet of a CPAP device 2. The outlet 20 of the CPAP device 2 is connected to the inlet 30 of a patient's breathing device 3. The outlet 31 of the breathing device 3 is connected with the inlet 40 a PEEP device 4, the outlet 41 of which opens to atmosphere. The gas source 1 may be provided by various different arrangements such as by a cylinder 11 of compressed oxygen connected to the outlet 10 via a regulator 12. Alternatively, the gas source could be provided by other means, such as, for example, an air pump or compressor or by a hospital oxygen wall supply. The CPAP device 2 may be of any conventional kind that provides a continuous flow of breathing gas at a pressure sufficient to keep the airways open. The CPAP device 2 incorporates a demand valve that allows the patient to breath spontaneously. One example of a CPAP arrangement is described in WO2014/162107. The outlet 20 of the CPAP device 2 may be connected to the inlet 30 of the breathing device 3 via a one- way or non-return valve 5. The purpose of the non-return valve 5 is to ensure that all, or most, of the exhaled gas from the patient is prevented from flowing back through the CPAP device 2 and instead bypasses the CPAP device and flows to the PEEP device 4. The non-return valve 5 may not be necessary if the CPAP device 2 itself provides a greater impedance to flow than the PEEP device 4 so that most of the exhaled gas flows out via the PEEP device. The non-return valve 5 could be incorporated into the breathing device 3 so that gas flows into the breathing device via the inlet 30 and flows out via the outlet 31.

The breathing device 3 is typically a breathing mask but could alternatively be an airway or breathing tube, such as an endotracheal or tracheostomy tube, or a laryngeal mask.

The PEEP device 4 is arranged to provide an impedance to gas flow so as to maintain a pressure of about 5 mmHg to 10 mmHg at the outlet 31 of the breathing device 3, to maintain alveolar inflation sufficient to prevent the lungs from collapse during expiration. The PEEP device 4 may be of conventional construction.

The apparatus could also include a blood gas sensor such as in the form of a pulse oximeter 6 externally connected to the patient such as on his finger, earlobe or any other suitable part of the anatomy. The gas sensor 6 would provide an output to the gas supply 1 to control the flow of gas at its outlet. For example, if the sensor 6 were to detect a fall in Sp0₂ this could be arranged to cause the gas supply to increase flow to the outlet 10, and hence to the patient.

The ventilation apparatus described may be contained in a single desk-top unit or it may be incorporated into an ambulatory support of the kind shown in Figures 2 A and 2B. The support takes the form of a vest 60 having a front panel 61 with two side straps 62 and 63 extending laterally from the lower end of the panel. The side straps 62 and 63 are terminated by a buckle 64 or other fastener and are long enough to extend around the waist of the user and to fasten at his back. The vest 60 also has two wide shoulder straps 65 and 66 that extend upwardly from the upper end of the front panel 61 and over the shoulders of the user. The ends of the wide shoulder straps 65 and 66 continue as narrow fastening straps 67 and 68 that are fastened to respective lower straps 69 and 70 extending upwardly from the rear of the side straps 62 and 63 by means of buckles 71 and 72 or other fasteners on the lower straps. The gas source, in the form of a small oxygen cylinder 1 is supported on the front panel 61 by retaining straps 80 or by other means, such as a small pocket. Gas tubing 81 extends from the cylinder W along a part of one of the shoulder straps 66. Figure 2A shows the tubing 81 supporting a CPAP device 2' in line with a face mask 3'. Alternatively, however, the CPAP device could be supported on the front panel 61 of the vest 60 such as in a pocket. The mask 3' has a separate inlet 30' and outlet 3 , the tubing 81 being connected to the inlet. The outlet 3 is connected to a PEEP device 4' supported by tubing 82, although this could also be supported on the front panel 61 of the vest 60. The outlet 41 ' of the PEEP device 4' opens to air. It will be appreciated that the face mask could have a single opening that functions as both an inlet and outlet. In such an arrangement a single length of tubing would extend from the mask and would divide at some point along its length into two parallel channels for the inlet supply from the CPAP and the outlet path via the PEEP device.

Typically, a non-return valve would be connected at the outlet of the CPAP device so that exhaled gas flows only to the PEEP device. This ambulatory apparatus could also include a pulse oximeter.

Other arrangements for supporting the ventilator apparatus on the patient's body could be used, such as about the waist or on the back of the patient.

This arrangement of the ventilator apparatus makes it much easier for the patient to walk around while continuing to be ventilated. Modern medical practice encourages the patient to walk as soon as possible because of evidence that this helps speed recovery.