Abstract:
A portable oxygen delivery system supplies oxygen during prolonged transport via ambulance or helicopter to patients who are critically ill and in need of ventilatory support. The system includes two sets of oxygen tanks delivering oxygen to a manifold having two valve regulators. Oxygen flows from the first set of oxygen tanks through the first valve regulator, which remains open while the second valve regulator is closed, to the patient&#39;s portable ventilator. When the pressure from the first set of tanks drops below a given threshold, the first valve regulator closes and the second valve regulator opens, allowing oxygen to flow from the second set of oxygen tanks through the second valve regulator to the patient&#39;s ventilator. This system thereby maintains a continuous flow of oxygen to the patient&#39;s ventilator.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to portable ventilator systems used in transporting critically ill patients, and more particularly, to a system of dual sets of oxygen tanks delivering oxygen to a high-flow switchover manifold apparatus. 
     2. Description of the Related Art 
     Critically ill patients with respiratory failure require mechanical, assisted ventilation. When they are being transported to and from the hospital, for example in an ambulance or helicopter, such patients are typically given ventilatory assistance manually by means of a bag mask (e.g., Ambu™ bag) and 100% oxygen delivered from an oxygen tank. Such a bag mask consists of a face mask that fits over the patient&#39;s nose and mouth, and an attached hand-held bag for manually inflating and deflating the patient&#39;s lungs. Such bag-mask ventilation is inherently unreliable because it depends on the skill and judgment of the operator of the bag mask to inflate and deflate the patient&#39;s lungs at the proper frequency and tidal volume. As a result, wide interoperator variation is observed in a given patient&#39;s delivered tidal volume and respiratory rate. In addition, wide intraoperator variation is also observed from patient to patient by the same operator because of differences in patient size, lung compliance, and other factors. 
     This means that the patient may be over- or underventilated, depending on the minute ventilation, which is the product of respiratory rate and tidal lung volume, being delivered by the operator. As a result, significant hypercapnia from CO 2  retention by the patient, with concomitant respiratory acidosis; or hypocapnia, with concomitant respiratory alkalosis, may occur. When respiratory acidosis occurs as the result of underventilation, it compounds any underlying metabolic acidosis, such as lactic acidosis caused by poor tissue oxygenation (which is nearly always present in patients with respiratory failure), or diabetic ketoacidosis caused by inadequate insulin availability. In transport situations, this problem is worsened, as the acid-base balance and oxygenation status of the patient are unknown because one cannot readily perform an arterial blood gas analysis in the field. 
     In addition to the inherent unreliability of operating a bag mask, there is a significant risk to the patient of barotrauma, including pneumothorax, pneumomediastinum, and subcutaneous emphysema. These complications occur primarily when relatively noncompliant lungs are overinflated, with resulting small perforations in the pleura, alveoli, or other pulmonary structures. 
     One problem with using mechanical ventilators in transport settings, for example in an ambulance, is that such ventilators typically require oxygen flow pressures around 40 lbs. per square inch (“psi”), which is the typical oxygen pressure in oxygen delivery systems within the walls of hospitals. Normally, ventilators are in fact connected to wall-oxygen systems in hospitals and nursing homes. Even portable ventilators, such as the VDR-3C Universal Logistical Precussionator Ventilator, available from Percussionaire Corporation, is designed for use with low-pressure (e.g., 40 psi) oxygen delivery systems. Oxygen tanks, on the other hand, although portable, deliver oxygen at pressures typically from 100 to 2,200 psi, which is too high for delivery to mechanical ventilators. 
     In addition, there is a problem in delivering adequate quantities of oxygen for prolonged transport using a mechanical ventilator. Typically, one or two oxygen tanks will not last a sufficiently long period to allow patients to be mechanically ventilated with a moderate to high fraction of inspired oxygen (“FI 0   2 ”) (e.g., 100% FI 0   2 ) over the course of a trip of, for example, 20 -40 minutes duration. 
     SUMMARY OF THE INVENTION 
     The present invention addresses the need for an oxygen delivery system that can enable high-flow, high-pressure oxygen tanks to be adapted to portable mechanical ventilators, and that will allow sufficient oxygen to be administered throughout the course of prolonged transport of a patient while retaining portability. 
     There is provided in accordance with one aspect of the present invention an oxygen delivery system for portable mechanical ventilation. The oxygen delivery system includes at least a first set and a second set of individual oxygen tanks. A first intake tube is interposed between the first set of oxygen tanks and a first regulator, and the first regulator contains a valve which remains open until the pressure of oxygen flowing through the first regulator drops below a predetermined threshold pressure level. A second intake tube is interposed between the second set of oxygen tanks and a second regulator, and the second regulator contains a valve which remains closed until the pressure in the second regulator drops to approximately the predetermined threshold pressure level. One or more outtake tubes connect the first and second regulators, and a central tube is interposed between these outtake tubes and a mechanical ventilator. 
     In accordance with one aspect of the present invention, the threshold pressure level is within the range of 90 to 100 pounds per square inch. In a firther aspect of the present invention, there are only two sets of oxygen tanks. 
     In a further aspect of the present invention, one or more pressure gauges are attached to the regulators. In other aspects of the present invention, one or more pressure gauges are attached to the central tube and measure the pressure of oxygen flowing to the mechanical ventilator. 
     In accordance with another aspect of the present invention, there is provided a method of delivering oxygen to a portable ventilator during transport of a patient. The method includes providing a first set of oxygen tanks connected by tubing to a first regulator, and providing a second set of oxygen tanks connected by tubing to a second regulator. The method further includes causing a valve within the first regulator to close when the oxygen pressure within the first regulator drops below a particular pressure threshold, thereby causing the flow of oxygen through the first regulator to cease; and causing a valve within the second regulator to open at approximately the same threshold pressure, thereby causing oxygen to flow from the second set of oxygen tanks through the second regulator to the patient&#39;s ventilator. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic front view of the high-flow switchover manifold apparatus used in conjunction with two sets of oxygen tanks. 
     FIG. 2 is a detailed cross-sectional view of the high-flow switchover manifold apparatus taken along line  2 — 2  of FIG.  1 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 illustrates an oxygen delivery system and high-flow switchover manifold apparatus for use in mechanical ventilation during transport. Although the description below is primarily directed to transporting pediatric and neonatal patients, the system and apparatus described may be used eoually well in transporting adults. 
     In the illustrated embodiment, the oxygen delivery system includes two sets of oxygen tanks  1   a  and  1   b . Both the first set of oxygen tanks  1   a  and the second set of oxygen tanks  1   b  has three individual oxygen tanks  2 . In other embodiments, fewer or more than three oxygen tanks can be utilized. Each oxygen tank is connected by a hose  4  to a yoke device  6   a ,  6   b  which entrains oxygen from all three tanks  2  by one or more one-way valves  7 . In other embodiments, there may be no one-way valves  7  present, and the system can be operative without these one-way valves. 
     The oxygen delivery system includes a high-flow switchover manifold apparatus  8 . The high-flow switchover manifold apparatus includes, among other parts, a first intake tube  9 , and a first regulator  10 , a second intake tube  17 , a second regulator  14 , one or more one-way valves  12 , central tubing  11 , a pressure gauge  20 , and an export tube  24 . The first regulator  10  contains a one-way valve (shown as  32  in FIG.  2 ). Similar to the first regulator  10 , the second regulator  14  has a valve within it (shown as  32  in FIG.  2 ). In one embodiment, the oxygen flow pressure through each regulator  10 ,  32  can be read on one or more external gauges  16 . Alternatively, no external gauges need be present. A first outtake tube  13  and a second outtake tube  19  are connected to the first regulator  10  and the second regulator  14 , respectively. The outtake tubes  13 ,  19  can each may have one or more one-way valves  12 , and a central tube  11  within the manifold apparatus  8 . An export tube  24  attached to the central tube  11  leads to the patient&#39;s ventilator (not pictured). One or more additional pressure gauges  20  connected to the manifold allow measurement of the pressure of or flow rate of oxygen flowing through the export tube  24  to the patient&#39;s ventilator. 
     In some embodiments, there are one or more one-way valves  12  positioned within the tubing. In other embodiments, no one-way valves  12  are present. A flow indicator knob  42  can also be present in certain embodiments to indicate to the operator which sets of oxygen tanks is being utilized. 
     Entrained oxygen flows into the high-flow switchover manifold apparatus  8 . The oxygen flowing through the yoke device  6   a ,  6   b  attached to the first set of oxygen tanks  1   a  flows into the first intake tube  9  of the manifold apparatus  8 . Oxygen then flows into the first regulator  10 . The one-way valve (shown as  32  in FIG. 2) of the first regulator  10  is opened while oxygen flows at high pressure or flow rates from the first set of oxygen tanks  1 . As used herein, the term “regulator” is any device with an input port and an output port for flowing fluid (in either the gas or liquid state) into and out of the device, respectively, and that serves to control the output pressure of fluid. In one embodiment, the oxygen flow pressure in the first regulator  10  or the second regulator  14  may be read on one or more external gauges  16 . In other embodiments, however, it is not necessary to include any external gauges. From the regulator  10 , oxygen flows through a first outtake tube  13 . The outtake tube  13  can have one or more one-way valves  12  within it to maintain the flow of oxygen in one direction. In other embodiments, no one-way valves  12  are present in the outtake tube  13 . Oxygen next flows from the outtake tube  13  and the central tube  11  to the export tube  24 . From the export tube  24 , oxygen flows into the patient&#39;s ventilator (not pictured). One or more additional pressure gauges  20  can be attached to the export tube  24 , to measure the pressure or flow rate of oxygen flowing through the export tube  24  to the patient&#39;s ventilator. 
     As oxygen flows from the first set of oxygen tanks  1   a  through the first regulator  10 , the second regulator  14  is closed to oxygen flow. More specifically, the second regulator  14  has a valve within it (shown in FIG. 2) which remains closed approximately as long as oxygen is flowing through the valve within the first regulator  10 . 
     Oxygen flowing through the first regulator is generally at a pressure of 70 to 2,200 psi. When the oxygen pressure drops below a particular threshold, typically between 90 and 100 psi, the valve  32  within the first regulator  10  closes and, at approximately the same time or at approximately the same threshold pressure, the valve  32  within the second regulator  14  opens, thereby allowing oxygen to flow from the second set of oxygen tanks  1   b  through a set of tubes  4  and through a second yoke device  6   b . This phenomenon is referred to herein as a “switchover” of oxygen flow. The predetermined pressure level, which triggers valve closing or valve opening, can be a discrete pressure level, or it can be within a range of pressures. As used herein, “approximately” the same threshold pressure means within about 50 psi of the same threshold pressure, and preferably within about 10 psi. 
     After the switchover, oxygen flows into a second intake tube  17 , through the second regulator  14  into the second output tube  19 . In some embodiments, there are one or more one-way valves  12  positioned within the tubing. In other embodiments, no one-way valves  12  are present. Oxygen thence flows from a second output tube  19  into the central tube  11  and through the export tube  24  into the patient&#39;s ventilator. The switchover occurs as the first regulator  10  closes while the second regulator  14  opens. In a preferred embodiment, the switchover of oxygen flow from the first set of oxygen tanks  1 a to the second set of oxygen tanks  1   b  occurs approximately at the same time, typically between 70 and 120 psi and preferably around 90 to 100 psi. In other embodiments, the second valve  14  opens prior to the closing of the first valve such that oxygen is flowing from both sets of oxygen tanks  1   a  and  1   b  simultaneously. A flow indicator knob  42  can also be present in certain embodiments. This allows the operator to turn the flow indicator knob  42  to indicate which set of oxygen tanks is currently flowing oxygen to the patient&#39;s ventilator. 
     One type of the first regulator  10  and second regulator  14  is herein described. There are many types of regulators which will allow valves to open and/or close at predetermined pressure thresholds. These particular regulators will be apparent to those of ordinary skill in the art. One such regulator is manufactured by AirGas Corporation (Los Angeles, Calif.) and includes a central control unit high-flow switchover assembly (Part No. NEOCCU98081126), a left pigtail assembly for three cylinders (Part No. NEOLPT36061138), and a right pigtail assembly for three cylinders (Part No. NEORTP98081138). 
     One type of the first regulator  10  is schematically demonstrated in FIG.  2 . In one embodiment of the present invention, the first regulator  10  includes a housing  30 , which contains a valve  32  and a spring mechanism  34 . This is shown as a simple mechanism in FIG. 2, although there is a wide variety of valve mechanisms which may accomplish the same goal, namely to have the valve  32  close when the pressure flowing from the first set of oxygen tanks  1  through the intake valve  9  drops below a certain threshold. 
     One type of the second regulator  14  is also illustrated in FIG.  2 . The second regulator  14  includes a housing  33 , which contains a valve  32 , coupled to a spring mechanism  38 . There is a wide variety of valve mechanisms which may accomplish the desired goal in the second regulator  14 , namely to open the valve  32  when the pressure in the central tubing  11  and/or in the second outflow tube  19  drops below a predetermined threshold pressure or pressure range. These mechanisms will be readily apparent to those of skill in the art. For example, the valve mechanisms within the regulators ( 10  and  14 ) can be controlled electronically. Alternatively, the regulators can be mechanically controlled by simple hydraulics, pneumatics, or fluid mechanics, relying on, for example, absolute pressure or flow through the regulators or the intake tubes ( 9  and  17 ), outtake tubes ( 13  and  19 ), central tube  11 , or comparative pressures or flows between the two regulators ( 10  and  14 ) and/or tubes. For example, an electronic or mechanical sensor can sense the time, or approximate time, when oxygen flow through the first regulator has ceased, and an electronic or mechanical signal can be sent to trigger the opening of the valve in the second regulator. 
     The embodiment illustrated in FIG. 2 shows a spring mechanism  38  which is designed to keep the valve  32  closed until the pressure in the central tubing  11  as well as the second outflow tube  19  drops below a certain threshold, for example 90 to 100 psi. Once this pressure drops below the preset threshold, the valve  32  within the second regulator  14  opens, allowing oxygen to flow through the second intake tube  17  into the regulator  14  and thence into the second outflow tube  19  the central tube  11 , and onto the patient&#39;s ventilator through the export tube  24 . Also illustrated is the flow indicator knob  42 , which can be present in certain embodiments. The operator can turn the flow indicator knob  42  to indicate which set of oxygen tanks is currently flowing oxygen to the patient&#39;s ventilator. 
     In a further embodiment of the present invention, the second regulator  14  may have a valve which remains closed until oxygen flow through the first regulator  10  ceases. The information concerning the oxygen flow through the first regulator  10  may be sensed electronically or mechanically, in ways that are well known to those of skill in the art, and that information may be transmitted to the second regulator  14  in order to trigger the valve opening in the second regulator  14 . 
     As used herein and as pertaining to valves, “open” means substantially open, permitting oxygen to flow through a valve. Furthermore, as used herein and as pertaining to valves, “closed” means substantially closed, limiting the flow of oxygen through a valve relative to the “open” position of the valve. Also, when it is stated that one causes the flow of oxygen through the first regulator to “cease,” it is meant that the flow of oxygen through the first regulator diminishes greatly, if not totally ceases. 
     Other embodiments in the invention will become apparent to those of skill in the art in view of the disclosure herein. Accordingly the scope of the present invention is not intended to be limited by the foregoing, but rather by reference to the attached claims.