Portable breathing system

Abstract

A portable breathing system for delivering a high reaction of inspired oxygen (FiO2) to a patient. The system comprises an oxygen concentrator 1 arranged to provide oxygen into a rebreather system 11,

Description

The present invention relates to a portable breathing system designed to deliver a high fraction of inspired oxygen (FiO2) to individuals requiring respiratory support. The system is suitable for use with both spontaneously breathing and mechanically ventilated patients, and is particularly advantageous in remote or resource-limited environments where conventional oxygen deliver infrastructure may be unavailable. Administering early supplemental oxygen is a standard of care for trauma casualties to minimise the deleterious effects of hypoxaemia and improve their potential outcome. Forward deployment of oxygen using pressurised cylinders is challenging, e.g. logistics (weight and finite resource) and environmental risk (fire and explosion), particularly for unsupported military medical and surgical teams. Ventilation systems currently available do not fulfil the size, weight and power requirements of portable medical units, in particular they are not lightweight. Efforts are made to avoid hypoxaemia in trauma patients because hypoxaemia increases mortality and morbidity, particularly when combined with severe traumatic brain injury. It is known in the art that early administration of oxygen reduces mortality in trauma patients and significantly improves survival time in an experimental studies of blast lung injury and prolonged hypotensive resuscitation. Forward deployment and administration of oxygen in a military setting is challenging. Oxygen cylinders can be problematic: they are heavy, pressurised, and pose both a logistical burden and inherent risk in a ballistic or constrained environment. Oxygen concentrators may provide an alternative source of medical grade oxygen as “oxygen enriched air” containing approximately 90% oxygen. Oxygen concentrators are known in the art and have shown it is possible to deliver a FiO2 in excess of 0.8 at a clinically-relevant ventilator minute volume of 6 L min'1. The required oxygen flow output, however, typically needs a concentrator weighing approximately 25 Kg and is also reliant on an external power supply, adding to the weight burden for forward deployment for administration of oxygen, and therefore is not a realistic option for administering oxygen to patients in remote or resource-limited environments. It also known in the art that smaller, battery powered, oxygen concentrators having a weight of 5.5 Kg are also available but these smaller concentrators only provide an FiO2 of 0.5-0.6 when used in conjunction with a ventilator and therefore is not adequate for providing higher FiO2 levels when required. There is therefore a need for a lightweight, portable breathing system for early and efficient delivery of oxygen to trauma patients in remote or resource-limited environments. In a first aspect of the invention, there is provided a portable breathing system for patients, comprising: an oxygen concentrator, a ventilator, a rebreather system and a reservoir, wherein the oxygen concentrator is arranged to provide oxygen into the rebreather system and the ventilator is arranged to support ventilation of an individual via the rebreather system and wherein the reservoir is arranged to retain exhaled breath in order for the exhaled breath to be recirculated through the rebreather system. This portable breathing system provides the advantage of enabling early and effective administration of oxygen to patients who are located far from substantial medical facilities, and continues to provide the effective administration of oxygen to the patient until they are transported to a substantial medical facility. The portable breathing system is preferably lightweight, and therefore easily portable and can be transported on an emergency responder’s person, as the system is not overly burdensome or cumbersome by size or weight, which is a disadvantage with portable breathing systems that are currently available. By oxygen concentrator it is meant a portable oxygen concentrator providing an alternative source of medical grade oxygen as oxygen enriched air, and contains approximately 90% oxygen. Preferably the oxygen concentrator weighs 5.5 Kg or less and can be used in conjunction a lightweight turbine ventilator in a remote setting, such as a military setting. Preferably the oxygen concentrator is designed to be used in either an open or semi-closed circuit configuration. The oxygen concentrator reliably synchronises pulses of oxygen at the respiratory rate set on the ventilator. A low pressure oxygen enrichment adapter may optionally be used in conjunction with an oxygen concentrator. The ventilator used in conjunction with the oxygen concentrator may be a small, lightweight clinical ventilator. Alternatively, ventilation may also be provided manually by squeezing an air bag, or bellows, by hand, but a lightweight clinical ventilator is preferable as this provides the advantage of a known volume of air being consistently provided into the portable breathing system and consequently to the patient. Preferably the ventilator is connected to the rebreather circuit in a lateral position via a port on the CO2 absorber section of the rebreather circuit. Preferably a rebreather circuit is used in the portable breathing system, having at least one one-way valve, wherein the valve is used to relieve the breathing system of becoming over pressured. The rebreather circuit further comprises and inhalation hose, an exhalation hose and a CO2 absorber, also known as a CO2 scrubber. The rebreather circuit recirculates the patient’s exhaled breath for subsequent inhalation, thereby minimising loss of oxygen. Expired CO2 is chemically removed during passage through a CO2 absorber (‘scrubber’) that is part of the circuit, and oxygen to replace that consumed by the patient is added from an external source, such as inhalation of atmospheric air, enriched by an oxygen concentrator, or by a pressurised cylinder. The CO2 absorber may be interchangeable, so that once one CO2 absorber has been used up, it can be readily replaced with a fresh absorber. Preferably, there is a reservoir for collecting overflow exhaled air so that the exhaled air can be recirculated back into the rebreather circuit. The reservoir may be in the form of a bag, pouch or additional length of tubing. More preferably, the volume of the reservoir is greater than the tidal volume of the ventilator. The reservoir is preferably a length of tubing, situated between the ventilator connector tubing and the rebreather circuit. Each exhalation of oxygen-rich gas from the rebreather circuit will be held in the reservoir tube, and pushed back into the rebreather circuit by air from the ventilator during the inspiratory cycle, thereby preserving the benefit of the rebreather circuit. The reservoir being in the form of an additional length of tube has a surprising effect in that the reservoir tubing led to an elevation of FiO2 to 0.78 in comparison to 0.36 observed where the portable breathing system has the same configuration without the reservoir tubing. Preferably the system is modular, wherein each feature of the system is interchangeable and can be assembled or replaced independently for a new component when a component is broken or expired. Having a modular system provides the advantage of being rapidly reconfigured to support either a spontaneously breathing casualty, or an individual requiring ventilation. Preferably the system has an overflow valve, situated between the reservoir tubing and the ventilator so that the breathing system does not become over pressured. The valve is situated in this location so that maximum retention of the exhaled breath can be contained in the reservoir tubing, rather than being lost through the valve before reaching the tubing, but the overflow valve still prevents the breathing system from exceeding its full capacity. Specific embodiment of the invention The invention will now be described, by way of example, with reference to the accompanying figures, in which; Figure 1 depicts a schematic diagram of the portable breathing system, indicating the rebreather circuit (11), oxygen concentrator (1), ventilator (7) and reservoir tubing (6). Figure 1 further depicts the rebreather circuit (11) consisting of an inhalation hose (3), an exhalation hose (4) and a CO2 absorber (5), wherein the CO2 absorber (5) is replaceable once the absorber (5) has been fully consumed. There is also a valve (8) present, which in this specific embodiment is situated along the length of the reservoir tubing (6). This specific embodiment has been tested using a simulated lung to represent the lungs of a trauma patient (10). Figure 2 shows FiO2 and FiCO2 measured in the circuit over time. FiO2 delivered by the ventilator in the lateral position, wherein the portable breathing circuit includes a reservoir tube, to a simulated lung at the highest concentrator output setting on the specific concentrator used (Inogen S6). Ventilator tidal volume 500 ml and respiratory rate 12 breaths / min. Supplementary oxygen was delivered directly into the rebreather circuit. Data shown in Fig.2 as mean values (95% reference range) Figure 3 shows FiO2 delivered to a simulated lung at three concentrator output settings (Inogen S2, S4 and S6). Ventilator tidal volume 500 ml, and respiratory rates 12, 16 and 20 breaths / min in panels a-c respectively. Open circuit (no rebreather circuit), ventilator connected laterally to the rebreather circuit without a reservoir tube. The supplementary oxygen was delivered either into the low pressure oxygen adapter of the ventilator (O2 S) or directly into the rebreather circuit (O2 W). Data shown as mean values (95% reference range). Where there are no bars indicating the 95% reference range are visible, they are smaller than the symbol denoting mean values. Using a portable commercial oxygen concentrator (1) (such as Inogen One G5, Inogen Inc.), small lightweight clinical ventilator (7) (such as Ventway Sparrow VWSP-900, Inovytec Medical Solutions Ltd.) combined with a medical semi-closed re-breather circuit (such as Wenoll-System, Emergency Oxygen system, EMS GmbH). A portable breathing system (Figure 1), using at least one one-way valve (8), recirculates the patient’s exhaled breath (9b) for subsequent inhalation (9a), minimising the loss of oxygen. The expiration breath is collected in the reservoir (6). The reservoir (6) in this particular embodiment has a deadspace of 626 ml, which is intentionally greater than the tidal volume (500 ml) of the ventilator. When the ventilator (7) delivers each cycle of air into the breathing system, the expired air that has been collected in the reservoir (6) is then recirculated back into the rebreather circuit (11) by the force of the air delivered into the system by the ventilator (7). The CO2 from the retained exhaled air in the reservoir (6) is then chemically removed during passage through the CO2 absorber (‘scrubber’) (5) that is part of the circuit. Oxygen is added from an external source, such as an oxygen concentrator (1), connected to the inhalation tube (3) of the portable breathing system via a length of tubing (2). As can be seen when comparing the graphs of Figures 2 and 3, the inclusion of a reservoir tube (Fig. 2) in the portable breathing circuit increases the FiO2 provided to the simulated lung used in this study from 0.5 FiO2 to 0.8 FiO2, when comparing the ventilator tidal volume 500 ml and respiratory rate 12 breaths / min.

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