Thorax drainage apparatus with variable vacuum control
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to medical equipment used in thoracic medicine and more specifically to thorax drainage apparatuses. 
     2. Description of the Prior Art 
     It is necessary to drain air and fluid from the pleural space following operation or injury to organs within the thorax. If drainage of air and fluid from the pleural space is not sufficient, the lung will not be able to expand to fill the pleural space which may result in respiratory insufficiency or the development of infection. Many different types of drainage devices have been provided for draining the pleural space. One method of draining the pleural space is to insert a catheter into the chest with the distal end thereof sealed by a condom having the end removed, to a complicated system of up to five serially connected chambers having constricted connections. In the later systems, now the state of the art, a problem arises when there is a high volume air leak from the lung which is common in older patients with inherent lung disease. In such systems, high vacuum levels are required to remove such volumes of air. During normal respiration, a negative pressure is developed, with respect to atmospheric pressure, in the pleural space. This is the result of the lowering of the diaphragm and the increased volume of the chest with the rise of the rib cage during inspiration. The normal value of the negative pressure is 3.5-8.0 centimeters of water. The volume flow of air is governed by the Hagen-Poiseuille Law which states that for a given pressure gradient and tube length, the determinant of flow rate is the radius of the tube. Anesthesiologists are acutely aware of this and breathing circuits in anesthesia are maintained as large and short as possible. When a tube ends in an abrupt manner in a chamber, the flow is no longer laminar but becomes turbulent which introduces added resistance to flow. The length of the tube (or pathway) is also important when vacuum is applied. 
     According to the formula: ##EQU1## Where D is tube diameter 
     L is length of tubing pathway 
     C is air flow in Liters/Minute 
     For example: 
     L=2.5 ft. flow=28.9 L/min 
     L=4.5 ft. flow=14.5 L/min 
     L=10.0 ft. flow=7.2 L/min 
     Therefore, the optimum removal of air through a chest drainage device will occur when the largest tubing diameter is combined with the shortest pathway from the pleural space to the vacuum outlet. In addition, a minimum of abrupt changes from laminar flow to turbulent flow should interrupt the pathway. 
     The prior art devices do not meet these criteria. The pathway is by a series of connected chambers each of which contributes turbulence. Tubing pathways are unnecessarily long and in some cases, constructions are utilized to control flow or pressure all of which makes high vacuum a necessity to remove a given volume of air. Since the normal negative pressure required to keep the lung inflated and allow normal respiration is low, high vacuum negates the normal respiratory efforts. High vacuum can trap the lung against the intra pleural catheter thus occluding the catheter making the catheter ineffective and resulting in collapse of the lung. In addition, high vacuum overcomes the attempt of the lung tissue to seal itself thus causing the air leaks to continue or to increase. In applicant&#39;s earlier U.S. Pat. No. 4,738,672, a thorax drainage apparatus is disclosed which represented a significant advance in the art. However, it is believed that the instant invention represents a significant improvement over applicant&#39;s earlier patent. The standard method of vacuum control for chest drainage devices is by means of a column of water which is open to the atmosphere by means of a tube immersed to a depth equal to the amount of vacuum desired such as disclosed in the &#39;672 patent. When that amount of vacuum is exceeded, atmospheric air enters the chamber and bubbles to relieve the excess vacuum. While this simple and effective method has been used successfully in the relatively stable environment of the hospital, it does have a disadvantage in a mobile environment especially when rapid transport is necessary. In the &#39;672 patent, a simple chest drainage device was described which was admirably suited for such use. The device of the instant invention completes the requirements of stability without the hazards of a water column. 
     SUMMARY OF THE INVENTION 
     A thorax drainage apparatus is described which comprises a collection chamber having a first port formed in the upper end thereof which is in communication with a vacuum pump so that a negative pressure is created within the collection chamber. The collection chamber also has a second port formed therein which is adapted to be connected to a catheter tube extending to the patient&#39;s chest. A first valve is operatively mounted on the second port which is open during the respiratory exhalation mode and which is closed during the respiratory inhalation mode. A vacuum control mechanism is located on the upper surface of the chamber. The vacuum control mechanism consists of a plurality of openings fixed within the upper surface of the chamber and a cover which fits over the openings. The cover has a hole formed through its surface and the cover is designed to move so an individual opening may be lined up under the hole of the cover. Lining up the hole of the cover over an opening in the chamber releases pressure within the chamber and controls the force of the vacuum. The openings are of varying diameters which enables the operator of the device to vary the force of the vacuum. The cover may either be a round cover which rotates the hole over the opening in the chamber, or a rectangular cover which slides back and forth to align the hole over the opening in the chamber. A third alternative design is discussed below. 
     The upper end of the vent tube is in communication with the atmosphere. An exhaust port is also formed in the upper end of the collection chamber and is normally closed by a flap valve. The flap valve permits communication between the upper interior of the collection chamber and the atmosphere when a predetermined positive pressure is reached within the collection chamber. A needle port or valve is mounted in the second port so that excess negative pressure in the catheter tubing may be relieved at times. 
     As stated previously, the level of vacuum or negative pressure within the collection chamber is regulated by the vacuum control mechanism. The vacuum control mechanism does not have to be attached to the upper surface of the chamber. A third alternative design is to create a plurality of openings in the chest catheter tube in the same manner as on the surface of the chamber. A hollow, cylindrical covering is placed over the openings in the catheter tube. The hollow, cylindrical covering has a hole formed through the surface. By rotating the hollow, cylindrical covering, an individual hole is aligned over an opening in the catheter tube. 
     In the event that the vacuum pump fails in the closed position, air from the lung could build up pressure in the chamber to such a level which could collapse the lung. To prevent such lung collapse, the second valve or exhaust valve opens when the pressure within the collection chamber is greater than atmospheric pressure. 
     It is therefore a principal object of the invention to provide a new and improved thoracic drainage system. 
     More specifically, it is an object of the invention to provide a simplified system which provides the widest and shortest pathway for the removal of air and fluid from the pleural space. 
     It is a further object of the invention to provide an apparatus of the type described which permits the removal of excess negative pressure in the drainage tubing. 
     It is yet a further object of the invention to provide an apparatus of the type described including means for relieving excess pressure in the collection chamber. 
     Still another object of the invention is to provide a thoracic drainage apparatus including a vacuum control mechanism in parallel with the main collection chamber. 
     These and other objects will be apparent to those skilled in the art. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of the apparatus of this invention; 
     FIG. 2 is a top view of the apparatus of this invention; 
     FIG. 3 is a longitudinal sectional view of the apparatus of FIGS. 1 and 2; 
     FIG. 4 is a perspective view of the apparatus showing two alternative embodiments of the vacuum control device; 
     FIG. 5 shows the alternative vacuum control design of using openings formed in a catheter tube with a rotational cylindrical covering; and 
     FIG. 6 is a chart illustrating the relationship of the strength of the vacuum in comparison to the diameter of the opening used. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The thoracic drainage apparatus of this invention is referred to generally by the reference numeral 10 and includes a collection chamber or vessel 12 having an upper end 14 and lower end 16. Chamber 12 is provided with a port 18 provided at the upper end thereof which is adapted to be connected to a vacuum pump for creating a negative pressure within the collection chamber. 
     Collection chamber 12 is provided with an upper end portion 20 positioned at one end thereof. Mounted within upper end portion 20 is a port 22. The upper end of port 22 is connected to a drainage catheter tube extending from the pleural space within the chest. Port 22 has a valve means 24 mounted on the lower end thereof within upper end portion 20. Valve means 24 is of the &#34;condom&#34; type which is open during the respiratory exhalation mode but which is closed during the respiratory inhalation mode. 
     The thorax drainage apparatus 10 operates on the principle of creating a vacuum within the chamber 12 from an external source. The vacuum source draws air out of the chamber 12 through port 18 which has a catheter tube 42 connecting port 18 to the vacuum source. Pressure builds up within the chamber and draws in air through port 22. Port 22 also has a catheter tube attached to it which runs from port 22 to the pleural space within the chest. The vacuum draws fluids out of the pleural space within the chest and into collection chamber 12. As stated previously, valve means 24, mounted on the lower end of port 22, opens during respiratory exhalation but is closed during respiratory inhalation. 
     It is very important to have the ability to vary the force of the vacuum when desired. This is accomplished by the vacuum control means. FIG. 1 illustrates one type of vacuum control means which is rotational vacuum control means 30. Rotational vacuum control means 30 is comprised of a flat, round disc with a circular hole 32 formed through the disc. The disc is affixed above a series of six openings 34 in the upper end 14 of the collection chamber aligned in a circle directly below the disc. Each opening 34 has a different diameter. The diameter of the six openings are 0.052, 0.070, 0.082, 0.098, 0.110 and 0.128 inches, respectively. Rotational vacuum control means 30 operates by rotating in place. This allows hole 32 to be lined up directly over any of the six openings 34. The operator of the draining apparatus controls the force of the vacuum inside the collection chamber 12 by rotating the rotational vacuum control means hole 32 over an opening 34 which gives the desired vacuum force. Aligning the vacuum control means hole 32 over an opening 34 with a large diameter would have the effect of lessening the vacuum force inside the collection chamber 12 to a greater extent than aligning hole 32 over an opening 34 with a small diameter opening. This is clearly illustrated in FIG. 6. An operator can manipulate the vacuum force by choosing the appropriate sized opening. 
     Alternate embodiments are available with the vacuum control means. Rather than using a rotating vacuum control means, a sliding vacuum control means 36 is also available. Sliding vacuum control means 36 is rectangular in shape and is illustrated in FIG. 4. Instead of the openings formed in a circular fashion, the openings are formed in a straight line as shown by numeral 40 in FIG. 4. The principle operates in the same manner as in the rotational vacuum control means, but instead of rotating the opening, hole 38 slides over the various openings 40. By choosing the appropriately sized diameter opening to slide hole 38 over, the vacuum inside chamber 12 is controlled. 
     Another alternative embodiment for a vacuum control means is shown in FIG. 5. Instead of forming any openings in the collection chamber 12, the vacuum control means is formed within the catheter tube 42 which leads from port 22. This is illustrated in FIG. 5. The openings 44 are formed through the catheter tube 42 at a location above the port means 22. A rotational cylindrical covering 26 surrounds the catheter tube over the openings 44. A hole 28 is formed inside the rotational cylindrical covering and may be rotated over the openings 44 as desired. Again, the principle of controlling the vacuum force is the same as in the other embodiments. 
     In the event of vacuum pump failure in the closed position, air from the lung could build up pressure in the collection chamber to a level which could possibly collapse the lung. To prevent lung collapse, the relief or exhaust valve 50 is provided. When the positive pressure within the chamber reaches a predetermined level, exhaust valve 50 moves to the open position thereby preventing a pressure buildup within the storage chamber. 
     It can therefore be seen that the invention accomplishes at least all of its stated objectives.