Device for flushing a deadspace in mechanical ventilation

Details Device for flushing a deadspace in mechanical ventilation Device for flushing a deadspace in mechanical ventilation

1999-10-07

2001-10-09

Weiss, John G. (Department: 3761)

Surgery

Respiratory method or device

Means for supplying respiratory gas under positive pressure

C128S205120

Reexamination Certificate

active

06298848

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a device for flushing a deadspace of a mechanically ventilated patient during an expiration phase of artificial ventilation in order to reduce the rebreathing of expired gas.
2. Description of the Prior Art
In the mechanical ventilation of a patient carbon dioxide (CO
2
) may collect in the patient's airways during an expiration phase of a breathing cycle. The collected CO
2
then will be re-breathed during the next inspiration phase of the breathing cycle. It is known that CO
2
can be at least partly eliminated from the upper airways by flushing the airways with a flushing gas, preferably a CO
2
-free flushing gas, during at least a final part of the expiration phase. One known device used to flush the airways in this manner is described in a technical note entitled “Expiratory Flushing of Airways: a Method to Reduce Deadspace Ventilation” by B. Jonson et al (Eur. Respir. J 1990, 3, 1202-1205). This device has a source of pressurized gas, being either a standard gas bottle or a mechanical ventilator (for example of the type ServoVentilator 900C from Siemens-Elema AB, Solna, Sweden). The pressurized gas source supplies breathing gas as the flushing gas after the inspiration phase, and is coupled via a controllable valve system to one end of a conduit. The opposite end of the conduit is insertable into the trachea of the patient so that flushing gas may be supplied into the patient's airway. An electronic control unit' is also provided in operable connection between the mechanical ventilator and the valve system and controls the valve system so that flushing gas, either in pulses or as a continuous stream, is supplied into the conduit during the final part of the expiration phase. Acting on timing information provided to it from the control system of the ventilator, the electronic control unit operates the valve system to supply the flushing gas during a final part of the expiration phase, in this case after 50% of the expiration phase has elapsed and until 10% remains.
This known device has the disadvantages that a specialized flushing source is required, either in the form of a source separate from the mechanical ventilator or in the form of a ventilator that can supply breathing gas even during an expiration phase, and that a relatively complex electronic control system is required to regulate the supply of flushing gas to the patient.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a flushing device in which the aforementioned disadvantages associated with known device are at least alleviated.
The above object is achieved in accordance with the principles of the present invention in a device for flushing a deadspace during mechanical ventilation of a subject with a ventilator which provides pressurized breathing gas to the patient during an inspiration phase of a breathing cycle of the patient, the device having a source of pressurized flushing gas and a conduit with a first end, which is insertable into the patient's airways, and a second end connectable to the source of pressurized flushing gas, and wherein the source of pressurized flushing gas includes a variable-volume reservoir which receives and holds pressurized breathing gas from the ventilator during the inspiration phase and which supplies, at least during a final portion of an expiration phase, the received breathing gas as pressurized flushing gas to the first end of the conduit, dependent on a pressure at the first end of the conduit.
By providing a source of flushing gas in the form of a reservoir which is stocked with pressurized breathing gas supplied by a mechanical ventilator during an inspiration phase, the need is removed for a separate source or for a ventilator adapted as described above in relation to the known flushing device.
Moreover, a relatively simple regulation of flushing gas is achieved by providing an outlet in pressure communication with pressure at the first end of the conduit and operable to supply the flushing gas when a pressure difference across the outlet, due to a reduced pressure at the first end of the outlet as compared to the pressure within the reservoir, reaches or exceeds a predetermined value.
In use, breathing gas supplied through the inlet
25
, during an inspiration phase, forces the piston head
23
to move toward the rigid wall
20
and consequently the bias spring
24
is compressed, thereby “storing” pressure from the breathing gas. During the expiration phase the pressure communicated from the patient's airways
4
, via the lumen
8
and the line
11
, to the outlet
26
reduces compared to that existing during the inspiration phase. When this communicated pressure falls below that pressure “stored” by the spring
24
, the piston head
23
moves under the pressure exerted by the compressed spring
24
to force stored breathing gas through the outlet
26
for supply as a pressurized flushing gas.


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