Surgery – Respiratory method or device – Means for supplying respiratory gas under positive pressure
Reexamination Certificate
1998-12-04
2001-08-28
Lewis, Aaron J. (Department: 3761)
Surgery
Respiratory method or device
Means for supplying respiratory gas under positive pressure
C128S204170
Reexamination Certificate
active
06279574
ABSTRACT:
BACKGROUND
1. Field of the Invention
This invention relates to ventilation systems for use in supplying breathable gas to a patient and more particularly to a ventilation system that supplies treated gas under variable pressure and in accordance with selected modes.
2. State of the Art
The use of mechanical ventilators to deliver a mixture of oxygen and air to a patient's airway in medical treatment situations including, for example, intensive care facilities is known. Known ventilation devices are configured to deliver large volumes of therapeutic gases under positive pressure at frequencies that generally match the normal inhalation rate of the patient. For example, a volume ventilator may deliver a measured quantity of gas at a fixed rate or in response to patient respiratory effort. Use of large gas volume systems has typically been limited to pediatric and adult patients.
Another type of ventilator presently in use typically for neonatal and pediatric patients is the time cycled, pressure limited device schematically depicted in FIG.
1
. As shown, air and oxygen are blended to a desired ratio by a BLENDER. After passing through a regulator, the mixed gas is heated and humidified in a HUMIDIFIER. The mixed gas then flows from the HUMIDIFIER through the inhalation limb of a patient breathing circuit to a WYE connector. The WYE connector has one end connected to an endotracheal tube for positioning in the trachea of a patient. In turn, the mixed gas is presented to the patient for inhalation through the endotracheal tube. Upon exhalation and during periods where inhalation has been terminated, the mixed gas and exhaust gas then return through the exhalation limb of the breathing circuit to a variable orifice EXHALATION VALVE.
When the EXHALATION VALVE is closed, the flow of the mixed gas into the exhalation limb is blocked or diverted from the exhalation circuit into the endotracheal tube. When the EXHALATION VALVE is open, the gas in the exhalation limb escapes to atmosphere and the patient is free to exhale.
As depicted, the EXHALATION VALVE may be a pneumatically controlled diaphragm valve. Should the pressure in the airway exceed the closing gas pressure of the EXHALATION VALVE, the EXHALATION VALVE would automatically open to relieve the over pressure. Mechanical ventilation may be initiated by varying the control pressure to the EXHALATION VALVE so that the pressure in the airway to the patient varies between a low setting termed the positive end-expiratory pressure (PEEP) to a higher value termed the peak inspiratory pressure (PIP). For the time-cycled pressure-limited ventilator described, the EXHALATION VALVE control pressure is varied from high to low at some fixed rate and the airway pressure automatically limited as described. The bias gas flow to the EXHALE CONTROL VALVE may be adjusted to regulate the EXHALATION VALVE and in turn increase or decrease the PIP pressure, the volume delivered and the flow rate of gas delivered with each inspiratory cycle. Typically the bias gas flow pressure approximates the desired PIP. As a result, the large volume of relatively low pressure gas present in the breathing circuit dictates a relatively slow response time to changes in the control signals to the EXHALATION VALVE from the EXHALE VALVE CONTROL. As a result, systems such as the one illustrated in
FIG. 1
typically can not respond to very rapid changes in demand for flow or pressure as in the beginning of inhalation or exhalation. The rapid changes can arise so fast (e.g., a few milliseconds) that the changes are sometimes stated to be “instantaneous.” The time lag in supplying sufficient gas or pressure increases the work of spontaneous breathing for the patient when some respiratory therapies are provided which are intended to help limit the work required of the patient to breath but do not in fact assist in limiting the work to the degree desired.
In the treatment of certain respiratory illnesses, it is known to be advantageous to deliver pulses of air and oxygen at frequencies much greater than the normal respiratory rate of the patient. So called high frequency ventilators are designed to deliver small volumes of gas at relatively high rates which typically are greater than one hundred and fifty (150) breaths per minute. Examples of such systems are described in U.S. Pat. Nos. 4,481,944, 4,538,604, and 5,239,994. One known high frequency ventilator uses a jet nozzle to direct gas into the airway of the patient.
Known high frequency ventilator systems do not generally incorporate humidifiers or other components employed in mechanical ventilation. Further, present ventilation systems are bulky and difficult to transport other than on some sort of wheeled cart. Further, such systems do not offer rapid response times along with the ability to select various modes of operation at different pressures and rates.
SUMMARY OF THE INVENTION
It is the object of the present invention to provide a single device that will provide any number of ventilation modes over a range of patient sizes.
It is also an object of the present invention to provide a self contained ventilation system to be portable and in turn facilitate ventilation therapy during patient transport.
It is a further object of the invention to minimize the response time of the system to accommodate synchronous ventilation modes in neonatal and pediatric patients.
It is an additional object of the invention to eliminate positive-pressure bias flow and dead space in the breathing circuit and thereby reduce the work of breathing for the patient undergoing ventilation therapy.
It is yet another object of the invention to measure selected physiologic variables at selected times and to graphically display the physiologic variables including illustrations of the patient's pulmonary function as an aid to the clinician in determining appropriate therapy.
It is a further object of the current invention to provide a system wherein subsequent improvements or modifications to existing treatment protocols may be accomplished via software upgrades.
A ventilation system of the present invention uses a jet of gas directed towards the patient airway to develop a number of controlled gas pressure and flow profiles.
The ventilation system includes a source of both oxygen and air connected to a mixer configured to mix or blend the air and oxygen and to supply one of the air, oxygen or mixture as a breathable gas. The breathable gas is then heated and humidified and supplied to a proportional valve located as near the patient's endotracheal tube as is practical in an effort to minimize the response time of the system to essentially instantaneous changes in demand. The proportional valve is servo-regulated to optimize its performance for any particular demand. The breathable gas is supplied at a relatively high pressure to reduce the response time of the ventilation system. The response time is also regulated and reduced by use of a jet nozzle to deliver breaths to the patient. Further, use of a jet nozzle with a proportional valve positioned close to the patient eliminates the long lengths of large diameter tubing used in conventional breathing circuits and reduces the resistance to flow and delays inherent in these systems.
The electronic microprocessor-based controller includes an interactive display and touch-screen that is desireably configured to act as an input device for establishing operating modes and parameters as well as to graphically display patient status, changes in status over time, pulmonary function curves and protocol management strategies.
The ventilation system is desirably housed in two chassis that are interconnected together. One chassis contains the gas sources, the mixing means and the means to humidify and heat the gas supplied to the proportional valve as well as batteries intended to operate the device during transport or loss of mains power. The other chassis contains the proportional valve and is sized to be small and light weight so it may be placed in proximity to the patient's head.
Bunnell J. Bert
Orth Jeffrey L.
Richardson Peter
Bunnell Incorporated
Holme Roberts & Owen LLP
Lewis Aaron J.
Mitchell Teena
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