Surgery – Respiratory method or device – Means for mixing treating agent with respiratory gas
Reexamination Certificate
2000-06-14
2002-11-05
Lewis, Aaron J. (Department: 3761)
Surgery
Respiratory method or device
Means for mixing treating agent with respiratory gas
C128S204180, C128S204230, C128S204260
Reexamination Certificate
active
06474333
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method for purging a medical fluid gas administration system of undesired fluids. The invention may find use in a variety of applications such as purging a therapeutic nitric oxide (NO) gas administration system of nitrogen dioxide (NO
2
) or purging a diagnostic sulfur hexafluoride (SF
6
) administration system to ensure proper administration of such a gas to a patient.
In connection with the former application, is it now widely recognized that the administration of NO gas to a patient increases pulmonary capillary vasodilatation. The NO gas is administered by placing it in the breathing gases inhaled by the patient, typically in very small concentrations of, for example, 0.5 nanomoles to 5.0 micromoles of NO per breath. The increase in vasodilatation improves blood-gas exchange between breathing gases and the blood providing efficacious treatment for respiratory and other diseases. The NO gas is usually supplied from a high pressure cylinder through a pressure regulator to a gas administration system. The gas administration system establishes the NO dosage and supplies same for mixing with the breathing gases prior to, or during, inhalation. The NO so supplied may be mixed with the breathing gases to provide a generally constant concentration of NO in the inhaled breathing gases. Or, the NO may be A provided to the inhaled breathing gases as short pulse doses of gas, one of which is delivered in each inhalation, usually at the beginning of inhalation.
In many cases the administration of NO is carried out when the patient is on a respirator that assists or supplants the patients own breathing action.. The respirator is connected to the patient by a breathing circuit comprised of a inspiratory limb, a Y-piece connector, an expiratory limb, and a patient limb. The inspiratory limb extends from an inspiration outlet of the respirator to the Y-piece connector. The expiratory limb connects the Y-piece connector with the respirator expiration inlet. The patient limb connects the Y-piece connector to an endotracheal tube or a breathing mask forming a conduit from the Y-piece connector to the patient's airways and lungs. When a respirator is in use, the NO gas is delivered to the patient limb or inspiratory limb of the breathing circuit to be provided to the patient during the inspiratory phase of the patient's respiratory cycle.
In other cases, the NO gas is provided to a spontaneously breathing patient through a face mask or nasal appliance.
A problem in the administration of NO is that NO reacts with oxygen to form nitrogen dioxide (NO
2
). Nitrogen dioxide is toxic even at very low concentrations and human exposure, for example in an occupational setting, is usually limited to 2-3 parts per million. For patients, who typically are already ill, there should be almost no exposure to NO
2
. The amount of NO
2
formed during the reaction depends on the concentrations of oxygen and NO that are present and the time during which the two gases are in contact with each other.
In an NO gas administration system, NO
2
can form when air and NO are both present in the gas delivery conduits of the system. The presence of air can arise during the connection of the apparatus to the high pressure NO source cylinder and pressure regulator, through leakage or migration of air into the system during and between uses, due to gas diffusion through the materials of the system when in long term storage, and for other reasons. For example, when the cylinder pressure regulator is connected to the NO supply cylinder, the internal volume of the pressure regulator contains air at ambient pressure. On connection to the cylinder, this. air can diffuse backward into the cylinder, form NO
2
, and contaminate the contents of the cylinder. Typical cylinder connection protocols thus call for purging of the pressure regulator and system immediately following connection of the system to the NO gas supply cylinder. While this may eliminate this source of NO
2
, the causes noted above, and others, remain resulting in NO
2
being formed in the gas administration system.
Several approaches have been developed for purging NO gas administration systems prior to use to ensure that NO
2
is removed before the administration of NO to the patient begins. For example, U.S. Pat. No. 5,558,083 and European Patent Publication No. 879,612 show the use of a purging valve for system purging purposes. To purge the system, the system is placed in operation to deliver NO gas from the supply source through the system. The purging valve is operated to connect the outlet of the administration system to a gas exhaust rather than to the breathing circuit or other means for delivering NO to the patient. The NO gas moving through the system flushes the NO
2
out of the system and into a gas scavenger or the ambient environment. After the purging has been completed, the purging valve is operated to reconnect the outlet of the system to the breathing circuit or other means to deliver NO gas to the patient. The European patent publication further shows the use of the NO delivery control valve in the system for purging purposes rather than a separate purging valve dedicated to purging purposes. The delivery control valve is operated either automatically or through a prompt device alerting the user to purge the delivery system when the administration of NO is commenced. Use of the NO delivery control valve for purging has the advantage of reducing the number of components needed in the NO gas administration system. A disadvantage in utilizing the same control valve and pathway for purging as for delivery is that the patient must be instructed not to use the device until after the purging is complete.
European Patent Publication No. 937479 shows purging of an NO gas administration system if the NO delivery is not triggered by the patient's breathing within a predetermined time. This prevents the formation of NO
2
in the delivery device from the migration of ambient air into the system.
Sulfur hexafluoride (SF
6
) is used to determine the functional residual capacity of a patient's lungs and for other pulmonary diagnostic purposes. Small, precisely determined amounts of such an indicator gas are entrained in the inhaled breathing gases to the patient. The amount of indicator gas exhaled by the patient is measured and the exhaled and inhaled gas measurements used in computational techniques that provide the desired diagnostic information. Purging of the delivery line for the indicator gas assists in accurately administering the indicator gas since with purging the gas content of the delivery line is known.
In other cases, it is desired to administer drugs by placing them in the inhaled breathing gases of a patient. Commonly such drugs are in liquid form and are atomized to a fine mist by a nebulizer as they are placed in the inhaled breathing gas. When the drug is to be changed, it is desirable to purge the supply line from the drug reservoir to the nebulizer to ensure the drugs are not mixed.
BRIEF SUMMARY OF THE INVENTION
The present invention provides a technique for purging a fluid administration system of undesired fluids, in a manner that both avoids the need for additional components, such as purging valves, and eliminates the possibility of the patient inhaling the purged fluids. The present invention lends itself to automatic purging of the system on startup and/or before administration of breathing gases to the patient without the need for patient intervention.
In the technique of the present invention, the expiration phase of the patient's respiratory cycle is sensed. A bidirectional sensor in the breathing gas flow path of the patient may be used to sense the direction of gas flow, and hence the expiration phase of the respiratory cycle. The fluid administration system is operated during the expiration phase to pass the administered fluid through the system for discharge at its outlet. The administered fluid moving through and out of the system carri
Andrus Sceales Starke & Sawall LLP
Erezo Darwin P.
Instrumentarium Corp.
Lewis Aaron J.
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