Abstract:
A tourniquet cuff has minimal flow restrictions within its pneumatic passageway under normal operating conditions, has a substantially reduced likelihood of partial or complete obstructions or interruptions of the pneumatic passageway under foreseeable operating conditions, can indicate exposure of the cuff to external agents that are capable of affecting the integrity of the pneumatic passageway before use, and can be manufactured economically.

Description:
FIELD OF THE INVENTION 
     This invention pertains to pneumatic tourniquet cuffs commonly used for stopping arterial blood flow into a portion of a surgical patient&#39;s limb to facilitate the performance of a surgical procedure, and for facilitating intravenous regional anesthesia. 
     BACKGROUND OF THE INVENTION 
     A typical surgical tourniquet system of the prior art includes a tourniquet cuff for encircling a patient&#39;s limb at a desired location and a tourniquet instrument that includes flexible instrument tubing for connecting to the tourniquet cuff. The tourniquet cuff typically includes an inflatable portion, and the inflatable portion of the cuff is typically connected through a cuff port having a port connector to the flexible instrument tubing of the tourniquet instrument, thereby establishing a pneumatic passageway from the tourniquet instrument through the instrument tubing and the cuff port into the inflatable portion of the cuff. In some prior-art systems, the tourniquet instrument includes a pressure transducer to sense the pressure of gas at the instrument end of the pneumatic passageway and to enable the sensed pressure to be displayed for surgical staff. Some prior-art tourniquet instruments include a pressure regulator to increase and decrease the pressure of gas in the pneumatic passageway, and to maintain the pressure in the inflatable portion of the cuff at a pressure above a minimum pressure required to stop arterial blood flow past the cuff during a time period suitably long for the performance of a surgical procedure. Many types of pneumatic surgical tourniquet systems, including tourniquet cuffs and tourniquet instruments, have been described in the prior art, such as those described by McEwen in U.S. Pat. No. 4,469,099, U.S. Pat. No. 4,479,494, U.S. Pat. No. 5,439,477 and by McEwen and Jameson in U.S. Pat. No. 5,556,415 and U.S. Pat. No. 5,855,589. 
     Some tourniquet cuffs of the prior art have only a single port for connection to the tourniquet instrument and thus establish only a single pneumatic passageway between a tourniquet instrument and the inflatable portion of such cuffs. The pressure in the inflatable portion of such single-port tourniquet cuffs must be sensed indirectly from the tourniquet instrument, through the same pneumatic passageway that is used by the tourniquet instrument to increase, decrease and regulate cuff pressure during surgery. The flow resistance of the pneumatic passageway affects the accuracy and speed of regulation of pressure within the inflatable portion of such single-port tourniquet cuffs as well as the accuracy of the indirectly sensed tourniquet cuff pressure. 
     Other tourniquet cuffs of the prior art have dual ports to establish two separate pneumatic passageways between the tourniquet instrument and the inflatable portion of the cuff, to achieve increased safety and performance by enabling the tourniquet instrument to provide surgical staff with a more accurate indication of cuff pressure and by enabling the tourniquet instrument to increase the speed and accuracy of cuff pressure regulation. Representative dual-port tourniquet cuffs of the prior are described in U.S. Pat. No. 4,635,635, U.S. Pat. No. 5,454,831, U.S. Pat. No. 5,439,477, U.S. Pat. No. 5,741,295 and U.S. Pat. No. 5,649,954. In one dual-port tourniquet system of the prior art, described in U.S. Pat. No. 4,469,099, the pneumatic pressure regulation elements within the tourniquet instrument communicate with the inflatable portion of the tourniquet cuff through one pneumatic passageway of the tourniquet cuff, and a pressure sensor within the tourniquet instrument communicates pneumatically with the inflatable portion of the cuff through a separate pneumatic passageway of the cuff. 
     With both single and dual-port tourniquet systems, the speed and accuracy of pressure regulation and indication are improved if flow restrictions in the pneumatic passageway are minimized. Typical port connectors of the prior art have a male barbed connection portion which fits inside the pneumatic passageway of the port, creating a region of reduced pneumatic flow area and increasing flow resistance between the cuff and the tourniquet instrument. 
     One hazard associated with all pneumatic tourniquet cuffs of the prior art is the obstruction of the pneumatic passageway within the cuff. For example, in a single-port tourniquet cuff, a complete obstruction within the pneumatic passageway may allow the actual pressure in the inflatable portion of the cuff to decrease substantially below the desired tourniquet pressure to a level where the cuff may be completely depressurized, or to increase substantially above the desired tourniquet pressure, without any indication to the surgical staff. In effect, the monitoring and regulation of cuff pressure by a prior-art tourniquet instrument stops at the location of the obstruction. As another example, a complete obstruction within a region of the inflatable portion of the cuff may isolate all or part of the inflatable portion and thus may prevent the pressure throughout the entire inflatable portion of the cuff from being sensed and regulated near the desired pressure by the tourniquet instrument. Any isolated region may be hazardous, either by permitting arterial blood to flow into the limb past a region of lower cuff pressure or by requiring surgical staff to set the tourniquet instrument to an unnecessarily high pressure to stop blood flow past the cuff. Also, any complete obstruction of the pneumatic passageway within a tourniquet cuff of the prior art may render ineffective any audio-visual safety alarms of a connected prior-art tourniquet instrument intended to warn of hazardous over-pressurization or under-pressurization of the cuff, such as the safety alarms described by McEwen in U.S. Pat. No. 4,469,099. 
     Another hazard associated with tourniquet cuffs of the prior art is partial obstruction of the pneumatic passageway. A partial obstruction of the pneumatic passageway at the port connector, or elsewhere within the port or inflatable portion of a prior-art cuff may increase the pneumatic flow resistance at the partial obstruction, and thus may affect the ability of a connected tourniquet instrument to rapidly and accurately regulate pressure past the partial obstruction and throughout the inflatable portion of the tourniquet cuff. Increased flow resistance from a partial obstruction may also reduce the ability of a connected tourniquet instrument to accurately and rapidly indicate changes of the pressure in the tourniquet cuff to surgical staff. Further, a partial obstruction of the pneumatic passageway within a region of the inflatable portion of the cuff may affect the ability of the tourniquet instrument to uniformly regulate pressure throughout the entire inflatable portion of the cuff. 
     In addition to the hazards of complete and partial obstructions that may affect the integrity of the pneumatic passageway, another hazard associated with prior-art cuffs is the interruption of the passageway due to unanticipated detachment of the port connector from the tourniquet instrument, or detachment of the port connector from the port, thus separating the inflatable portion of the tourniquet cuff from the tourniquet instrument. A related hazard is a leak at the port connector that is sufficiently large to prevent a connected tourniquet instrument from maintaining cuff pressure near the desired pressure. Such a large leak may result, for example, from deterioration or deformation of the connector of a single-use disposable tourniquet cuff as a result of reprocessing and reuse of the disposable tourniquet cuff in multiple surgical procedures in a manner neither intended nor anticipated by the manufacturer. 
     Many disposable tourniquet cuffs of the prior art are designed to be used in only one single surgical procedure and then discarded. Many such disposable tourniquet cuffs are sterilized at time of manufacture and supplied to users as sterile products, because such cuffs are typically intended to be suitable for use within sterile surgical fields. As a result, the design characteristics of such prior-art cuffs are intended to allow them to be applied and used safely and reliably within a sterile surgical field during one surgical procedure, and to be discarded cost-effectively after that procedure. For example, some disposable tourniquet cuffs of the prior art have a port that includes a very flexible thermoplastic tubing portion having a length sufficient to allow a user to easily bend the port away from the surgical site and position the port connector beyond the sterile surgical field. Although such long and flexible port tubing facilitates connection of the port to non-sterile instrument tubing away from the sterile surgical field, it may also increase the possibility of partial or complete obstruction of the pneumatic passageway within the port, for example by accidental kinking, bending, or pinching of the tubing. The various materials and components from which such prior-art disposable tourniquet cuffs are assembled are chosen to be sufficiently inexpensive to allow the cuff to be economically discarded after a single use, and also to be capable of sterilization by exposure to a specific sterilizing agent within a specific sterilizing process determined by the manufacturer, with no significant deterioration or change of properties that would impair the safety or performance of the cuffs after such sterilization. 
     Efforts have been made to reprocess and reuse tourniquet cuffs of the prior art that were originally supplied by their manufacturers as sterile, single-use products. Reprocessing efforts typically involve saving rather than discarding a disposable tourniquet cuff after surgery, visually examining the cuff to identify any obvious deterioration that might suggest reprocessing is not appropriate, attempting to remove any blood and other surgical debris by washing the cuffs with water combined with any of a variety of detergents or other cleaning liquids, in some cases conducting some functional tests of the cuff, re-packaging the cuff and then sterilizing the re-packaged cuff by exposing it to a sterilization agent within a sterilization process that may be different from that determined by the original manufacturer to be safe and effective. Reprocessing of disposable tourniquet cuffs may be carried out within hospitals or surgery centers or by third-party reprocessors, and the quality and methods of reprocessing are highly variable. 
     Reprocessing, cleaning and re-sterilizing of disposable tourniquet cuffs may result in hazards for the surgical patients on whom such cuffs are subsequently used. The hazard arises from the use of any of a variety of chemical or physical agents that are attendant with the reprocessing, cleaning or re-sterilizing processes. For example, exposure of a cuff to liquids during cleaning may allow the liquids to enter the pneumatic passageway of the cuff, where they may remain to partially or complete obstruct the pneumatic passageway of the cuff within the port or inflatable portion. Water remaining within the pneumatic passageway after cleaning may subsequently react chemically with ethylene oxide, a sterilizing agent commonly used in reprocessing, to form ethylene glycol, a sticky substance that may completely or partially block the pneumatic passageway. Exposure of prior-art cuffs to sterilizing agents different than the sterilizing agent employed at the time of manufacture may produce a change and deterioration in the properties of some cuff materials and components, for example due to a chemical reaction or exposure to radiation. Exposure of a prior-art cuff containing flexible thermoplastic materials to an elevated temperature during cleaning or sterilization by known prior-art processes may soften thermoplastic materials and components, increasing the likelihood of hazardous deformation of some components. For example, an elevated temperature during reprocessing may result in substantial deformation of the thermoplastic stiffener included in some prior-art cuffs, thus impairing the application of pressure by such a cuff to an underlying limb upon subsequent use in surgery. Also, an elevated temperature during reprocessing may deform the thermoplastic connectors of some prior-art cuffs, or may weaken the retention force of typical thermoplastic barb-type port connectors, so that such connectors cannot establish or reliably maintain a gas-tight passageway between the tourniquet cuff and tourniquet instrument upon reuse. An elevated temperature associated with cleaning or re-sterilization increases the likelihood that the pneumatic passageway within the cuff may become partially or completely obstructed, as described above, as a result of such reprocessing. Repeated cleaning, re-sterilization and reuse of a disposable tourniquet cuff in multiple surgical procedures may progressively increase the hazard for the surgical patients on whom the cuff is used. 
     There is a need for a tourniquet cuff that has minimal flow restrictions within its pneumatic passageway under normal operating conditions, that has a substantially reduced likelihood of partial or complete obstructions or interruptions of the pneumatic passageway under foreseeable operating conditions, that can indicate exposure of the cuff to one or more external agents that are capable of affecting the integrity of the pneumatic passageway before use, and that can be manufactured economically. The present invention addresses this need. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a pictorial representation of the preferred embodiment in a surgical application. 
         FIG. 2  shows the cuff portion of the preferred embodiment. 
         FIG. 3   a  is a section taken from  FIG. 2 , with the uninflated cuff applied to the patient&#39;s limb as shown in  FIG. 1 . 
         FIG. 3   b  is a section taken from  FIG. 2 , with the cuff applied to the patient&#39;s limb and inflated. 
         FIG. 4  is a view looking on the bottom surface of the bladder sealing flange. 
         FIG. 5  is a section taken from  FIG. 4 . 
         FIG. 6   a  is a section taken from  FIG. 2 , showing the preferred embodiment. 
         FIG. 6   b  is a sectional view like  FIG. 6   a , but showing an alternative embodiment. 
         FIG. 7   a  is a detail view of the areas indicated in  FIG. 3   a  and  FIG. 3   b , showing the preferred embodiment. 
         FIG. 7   b  is a detail view of the areas indicated in  FIG. 3   a  and  FIG. 3   b , showing an alternate embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  is a pictorial representation of the preferred embodiment in a surgical application, showing the tourniquet cuff  10  applied to patient limb  12  and pneumatically connectable to tourniquet instrument  14 . Cuff  10  includes cuff port  16 , which comprises bladder sealing flange  18 , port tubing  20 , and port connector  22 . In the preferred embodiment shown, cuff  10  is a single port cuff, where cuff port  16  provides a single pneumatic passageway to the inflatable portion of cuff  10 . Those skilled in the art will appreciate that the features described in the preferred embodiment may also be applied to tourniquet cuffs having more than one port, such as those described by U.S. Pat. No. 4,469,099, U.S. Pat. No. 4,479,494, and U.S. Pat. No. 5,254,087. Cuff port  16  is pneumatically connected to tourniquet instrument  14  via instrument connector  24  and instrument tubing  26 . In the preferred embodiment cuff port  16  is of sufficient length to allow pneumatic connection between cuff  10  and instrument  14  to be made outside a sterile surgical field. Port connector  22  is a locking connector (based on the connector of the tourniquet cuff described by McEwen in U.S. Pat. No. 5,649,954 and similar in some design aspects to connector DSM2202, Colder Products Company, St. Paul, Minn.) which allows cuff port  16  to form a releasable pneumatic connection with instrument connector  24 . 
     As described below, cuff  10  is constructed of materials that are appropriate for a single-use sterile disposable tourniquet cuff. To permit cuff  10  to be used in a sterile surgical field, cuff  10  is sterilized at time of manufacture by exposure to a sterilizing agent within a sterilizing process determined to be safe and effective. To prevent deterioration of the cuff, and to maintain the integrity of the pneumatic passageways within cuff  10 , a sterilization agent and process that will not harm the materials or components of cuff  10  is selected by the manufacturer. In the preferred embodiment cuff  10  is sterilized by exposure to gamma radiation or electron beam radiation. 
     The cost of materials is an important consideration in the manufacture of tourniquet cuffs intended for a single use and then disposal. To minimize the cost of materials and assembly of cuff  10 , materials are selected which are not intended to withstand exposure to subsequent sterilization and cleaning processes. The subsequent sterilization or cleaning of cuff  10  by agents and processes commonly used in health care facilities, such as ethylene oxide gas sterilization, hydrogen peroxide gas sterilization, high temperature and pressure steam sterilization, sterilization by other chemical agents, and pasteurization, are all capable of adversely affecting the integrity of the pneumatic passageways of cuff  10 . As described further below, cuff  10  includes one or more components that act as visual indicators to warn a user that cuff  10  has been subjected to a subsequent sterilization or cleaning process capable of adversely affecting cuff  10  and that cuff  10  may no longer be safe to use. 
       FIG. 2  shows the cuff  10  of the preferred embodiment, which is similar in design and construction to the cuffs described by McEwen in U.S. Pat. No. 5,741,295, U.S. Pat. No. 5,649,954, U.S. Pat. No. 5,484,831 and by Robinette-Lehman in U.S. Pat. No. 4,635,635. In the preferred embodiment shown, cuff  10  is rectangular with a length sufficient to encircle an adult arm as shown in  FIG. 1 . Those skilled in the art will appreciate that the features described in the preferred embodiment may also be incorporated in cuffs of various sizes and shapes, such as those described by McEwen in U.S. Pat. No. 5,649,954. In addition to cuff port  16 , cuff  10  comprises tie ribbon  28 , loop material  30 , edge trim  32 , sewn joint  34 , and hook material  36 . In use, cuff  10  is wrapped snugly around the limb  12  (see  FIG. 1 ) and secured circumferentially around the limb when the user engages hook material  36  to loop material  30 . Tie ribbon  28  is a soft fabric ribbon material (Grosgrain ⅝″ wide, Dynatex Textiles Inc., Toronto, Ontario, Canada) and allows the user to pull cuff  10  snug around the limb. When cuff  10  is in position and secured circumferentially around the limb, the user ties tie ribbon  28  as shown in  FIG. 1  to help prevent the cuff from sliding proximally or distally on the limb when inflated. Edge trim  32  is made of similar material to tie ribbon  28  and helps prevent chafing of the patient&#39;s limb by the edges of cuff  10 . 
       FIG. 3   a  is a section taken from  FIG. 2 , however with cuff  10  applied to the limb  12  (as shown in  FIG. 1 ) and cuff  10  uninflated. Top layer  38  and bottom layer  40  are made of woven nylon cloth coated with thermoplastic material (for example, 200 Denier nylon cloth coated in thermoplastic polyurethane 0.006″ thick) on the surfaces that face middle layer  42 . Middle layer  42  is made of thermoplastic sheet material (for example, 0.020″ thick polyurethane). Stiffener  44  is made of plastic sheet cut to a rectangular shape fitting within the perimeter of cuff  10 . The stiffener  44  has greater stiffness than layers  38 ,  40 , and  42  but is flexible enough to be wrapped around the limb (for example 0.020″ thick polyethylene sheet). Top layer  38 , middle layer  42 , and bottom layer  40  are joined around a continuous perimeter within the perimeter of cuff  10  at bladder seal  46 , thereby forming inflatable bladder  48  between middle layer  42  and bottom layer  40  and enclosing thermoplastic stiffener  44  between top layer  38  and middle layer  42 . Bladder  48  therefore has a width at the port location as shown in  FIG. 3   a , a typical value being 3.5 inches, and a length extending along the length of the cuff (see  FIG. 2 ) and sufficient to encircle the limb. When secured circumferentially around the limb as shown in  FIG. 1 , stiffener  44  helps direct the expansion of inflatable bladder  48  radially inwards towards the limb upon inflation of the cuff. The stiffener thus provides uniformly distributed pressure onto limb  12 . 
     Bladder seal  46  is formed by a heat and pressure joining process, typically radio-frequency welding using a selected sealing die. The heat of the joining process is selected to temporarily melt a portion of the thermoplastic materials in layers  38 ,  40 , and  42 , causing them to fuse together in the area of bladder seal  46 . The pressure of the joining process in combination with the shape of the sealing die is selected to squeeze a predetermined portion of the melted thermoplastic materials in layers  38 ,  40 , and  42  out of the area of bladder seal  46 , forming a continuous bead  50  along the perimeter of inflatable bladder  48 . When the joining process is complete, bead  50  solidifies back to the original rigidity of the thermoplastic materials in layers  38 ,  40 , and  42  and has thickness  51  (shown in  FIG. 3   b  only for clarity). Thickness  51  is proportional to the selected amount of thermoplastic material squeezed out during the formation of bladder seal  46 , and is selected to be large enough to form and maintain bladder pneumatic passageway  52  when bottom layer  40  is compressed against middle layer  42  during certain conditions of use, which are described in more detail below. 
     Cuff port  16  of cuff  10  comprises port connector  22 , port tubing  20 , and bladder sealing flange  18 , which are permanently joined together with pneumatically sealed joints to form port tubing pneumatic passageway  54  and port connector pneumatic passageway  55  (see  FIG. 7   a ) which form a continuous pneumatic passageway extending from distal port end  53  to inflatable bladder  48 . Bladder sealing flange  18  has flange top surface  56  which is permanently joined to middle layer  42  by a heat sealing process similar to that used to form bladder seal  46  (as described above). Bladder sealing flange  18  also has bottom surface  58 . Port tubing  20  has a length between bladder end  59  and port connector  22 , which is at minimum greater than the bladder width at the port location, and preferably 30 inches, which is sufficient to extend outside the sterile surgical field. Bladder sealing flange  18  forms a portion of pneumatic passageway  54  extending from port tubing bladder end  59  and formed to enter inflatable bladder  48  in a direction normal to top surface  56  and bottom surface  58  of bladder sealing flange  18 , and thereby normal to the area of middle layer  42  around bladder sealing flange  18 . 
       FIG. 3   b  is a section taken from  FIG. 2 , however with cuff  10  applied to the limb  12  (as shown in  FIG. 1 ) and cuff  10  inflated. Inflatable bladder  48  is shown expanded radially inwards towards the limb. 
       FIG. 4  is a view looking on bottom surface  58  of bladder sealing flange  18 . Bladder sealing flange  18  is made of thermoplastic polyurethane by injection molding (in a similar manner to existing sealing flanges such as 167ACU-BK, Halkey Roberts Corp., St. Petersburg, Fla. which are currently used in tourniquet cuffs). A plurality of channels  60  are formed in surface  58  extending from the outer perimeter of flange  18  to port pneumatic passageway  54 . 
       FIG. 5  is a section taken from  FIG. 4 , showing a typical channel  60  formed in the area between flange bottom surface  58  and flange top surface  56 . Because bladder sealing flange  18  must be heat sealed to middle layer  42 , channels  60  may be formed in to surface  58  by correspondingly shaped ridges on the sealing die and therefore are formed during the heat sealing process of bladder sealing flange  18  to middle layer  42  with no additional per item cost compared to the typical prior-art tourniquet cuffs. 
     Referring to  FIGS. 1 ,  3   a ,  4 , and  5 , when port connector  22  is connected to instrument  14 , a pneumatic passageway is established from instrument  14  through port pneumatic passageway  54  (formed by the openings in port connector  22 , port tubing  20 , and bladder sealing flange  18 ), channels  60  in bladder sealing flange bottom surface  58  into inflatable bladder  48 . Bead  50  acts to hold open the bladder  48  near the bladder seal  46  thereby establishing a bladder pneumatic passageway  52  around the perimeter of inflatable bladder  48 , allowing pneumatic communication throughout the bladder. 
     If bladder sealing flange  18  is compressed against limb  12  (for example if the flange area of the cuff is lying between the limb and the operating room table or bolster on which the limb is resting, or cuff  10  is applied to limb  12  too tightly), bottom layer  40  may be pressed against flange bottom surface  58  as shown in  FIG. 3   a . On bladder sealing flanges typically used in tourniquet cuffs of the prior art (for example see 167ACU-BK, Halkey Roberts Corp., St. Petersburg, Fla.), surface  58  is flat and smooth. Using prior-art flanges in the condition shown in  FIG. 3   a , pneumatic communication between inflatable bladder  48  and port pneumatic passageway  54  is closed off or restricted. In the current invention, however, channels  60  form a plurality of pneumatic passageways between inflatable bladder  48  and port pneumatic passageway  54  in the area between flange bottom surface  58  and flange top surface  56 , which remain open when bottom layer  40  is compressed against flange bottom surface  58 . 
     Furthermore, if any area of the cuff containing inflatable bladder  48  is compressed against the limb, bottom layer  40  may be pressed against middle layer  42  in some areas (as shown in  FIG. 3   a ) which may restrict or close pneumatic communication between different regions of inflatable bladder  48 . Bead  50  separates middle layer  42  and bottom layer  40 , thereby establishing bladder pneumatic passageway  52  extending around the entire perimeter of inflatable bladder  48  as noted above. The size of bead  50  is selected such that bladder pneumatic passageway  52  is maintained under the compression forces between bottom layer  40  and middle layer  42  expected in surgical use, thereby maintaining pneumatic communication among all regions of bladder  48 . 
     In addition to the conditions described above which may occur during the normal use of cuff  10 , exposure of cuff  10  to an elevated temperature or pressure, or exposure of cuff  10  to certain chemicals, or a combination of these conditions may occur during storage, shipping, or subsequent cleaning and sterilization processes and may cause bottom layer  40  to adhere to flange bottom surface  58  or areas of middle layer  42  by softening the thermoplastic materials. If the materials adhere, pneumatic passageways will nonetheless be maintained by bead  50  and channels  60 . 
       FIG. 6   a  is a section taken from  FIG. 2 , showing the cross-sectional profile of port tubing  20  of cuff port  16 , extending from bladder end  59  (see  FIGS. 3   a  and  3   b ) to port tubing end  61  (see  FIG. 7   a ). Port tubing  20  is formed by an extrusion process and is made of a blend of thermoplastic polyurethane and sterilization indicator formulated to change color when exposed to certain agents that, as noted above, may have a deleterious effect on the integrity of the pneumatic passageway. In this embodiment, the sterilization indicator does not react to change color during the initial sterilization of cuff  10  by gamma or electron beam radiation at time of manufacture. In the preferred embodiment, the thermoplastic material is formulated to undergo a distinct and permanent color change upon exposure to predetermined minimum levels of one or more selected sterilizing agents different than the agent employed at time of manufacture and typical of those commonly used within health care facilities and by reprocessors. Ethylene oxide gas is one such secondary sterilizing agent that may be used in a reprocessing sterilization process. Other agents are hydrogen peroxide gas, high temperature steam, and other chemical sterilizing agents. This color change occurs over the length of port tubing  20  and is visually perceptible by the user to indicate that cuff  10  has undergone a subsequent sterilization capable of affecting the pneumatic communication described above and shown in  FIG. 3   a . To enhance the appearance of the color change that takes place within port tubing  20  upon exposure to a subsequent sterilizing process, a portion of port tubing  20  may be marked with a substance that does not change color upon exposure to the sterilization process. For example, port tubing  20  may be formed from a thermoplastic material that normally has a clear color and changes to a brown color upon exposure to the ethylene oxide sterilization process. Port tubing  20  may also be marked with a white stripe which runs the length of port tubing  20 . When port tubing  20  is exposed to the sterilization process the printed white stripe provides visual contrast to the underlying, brown colored tubing. 
     In the preferred embodiment the secondary sterilization indicator described above is formulated from a color-forming compound pre-selected to react with a predetermined minimum level of ethylene oxide in a secondary sterilization process. Color-forming compounds such as 4-(hydrazinocarbonyl) pyridine, 4-nitrobenzylpyridine, or other pyridines that react with ethylene oxide may be used alone or in combination to produce a non-reversible color change reaction upon exposure to ethylene oxide gas. The color-forming compound may also include catalysts that further promote the color change reaction. To increase utility, the secondary sterilization indicator of the preferred embodiment may be mixed with additional color-forming compounds known in the art that react to change color in the presence of hydrogen peroxide gas or high temperature steam. The sterilization indicator may also include other non-reactive pigments pre-selected to enhance the visibility of the color-forming compound in its reacted state, thereby making a color change more visually perceptible by a user. 
     To further indicate to a user that cuff  10  has been exposed to a second sterilization agent within a sterilization process different than that used at time of manufacture, the secondary sterilization indicator may be carried on another component of cuff  10 , such as a label attached to cuff  10 , or the surface of port tubing  20  or the surface of tie ribbon  28 . For example, tie ribbon  28  may be selected to be initially white in color and upon the subsequent sterilization of cuff  10  by ethylene oxide sterilization change color to brown. 
     To indicate exposure of cuff  10  to a physical agent such as heat at a temperature that is capable of deforming, obstructing or otherwise adversely affecting the integrity of pneumatic passageways  54  or  55  or portions of inflatable bladder  48 , an irreversible thermochromic indicator compound is carried on a selected surface of cuff  10 , for example a surface of port tubing  20 . Thermochromic indicators are known in the art and may be formulated to react by irreversibly changing color at a predetermined temperature to indicate that exposure to the predetermined temperature has taken place. The preferred thermochromic indicator is unaffected by the initial sterilization of cuff  10  at time of manufacture. By carrying the preferred thermochromic indicator on a selected surface of cuff  10 , an indication perceptible by a user of cuff  10  is produced when cuff  10  has been exposed to a potentially damaging and hazardous temperature. Alternately, exposure of cuff  10  to an elevated temperature that is potentially damaging and hazardous may be indicated by a temperature-indicating compound that liquefies at the predetermined temperature. For example, a temperature-indicating compound (Tempilaq G TL0175, Tempil Inc., South Plainfield, N.J., which is applied like paint, re-liquifies upon reaching the predetermined temperature, then re-solidifies upon cooling below the predetermined temperature) may be carried on port tubing  20 . Port tubing  20  of the preferred embodiment is made of a transparent thermoplastic polyurethane having a clear color and thus a distinct pattern of temperature-indicating compound having a different color may be applied or printed in a particular pattern along inner surface  64  so that, if inner surface  64  reaches or exceeds the predetermined temperature, the compound reacts by liquefying and, causing the pattern to spread out and change to a colored smear. This distinct change of the printed pattern carried on inner surface  64  provides a visual indication perceptible by a user cuff  10  has been exposed to an elevated temperature at least equal to the predetermined temperature and that cuff  10  thus may be unsafe to use. 
     A water-indicating compound (such as a water-soluble ink) may be formed into a printed pattern carried on a selected surface of cuff  10 , as described in the preceding paragraph for an elevated temperature-indicating compound. Introduction of water or other liquid agents into pneumatic passageway  54  during any reprocessing could partially or completely obstruct pneumatic passageway  54 . Moreover, the water could indirectly obstruct the passageway by reacting chemically with secondary sterilizing agents such as ethylene oxide. A water-soluble pattern of colored ink carried on inner surface  64  of port tubing  20  would react to and indicate the introduction of water into pneumatic passageway  54  by changing the pattern, and the change would be readily perceptible by a user. 
     It will be appreciated that the indicating compounds described above for water, temperature and secondary sterilizing agents may be used alone or in combination, and carried on selected surfaces of cuff  10  or combined when forming components of cuff  10 , to indicate to a user that cuff  10  has been subjected to a subsequent sterilization or cleaning process capable of adversely affecting cuff  10  and that cuff  10  may no longer be safe to use. 
     Referring again to the cross-sectional profile of port tubing  20  shown in  FIG. 6   a , port tubing  20  has outer surface  62  having a circular cross-sectional shape, inner surface  64 , and ridge  66 . Outer surface  62 , inner surface  64 , and ridge  66  together form wall  68  having a non-uniform thickness, and pneumatic passageway  54  which has a non-circular cross-sectional shape. Ridge  66  protrudes into pneumatic passageway  54  and thereby prevents complete occlusion of pneumatic passageway  54  if port tubing  20  is kinked or flattened. In contrast, existing flexible tubing typically used in tourniquet cuffs has inner and outer surfaces of a circular cross-sectional shape, and do not have ridge  66 . Due to the stiffening properties of the cross-sectional shape shown in  FIG. 6   a  the cross-sectional area of wall  68  is selected to be similar or less than that of existing flexible tubing currently used in disposable tourniquet cuffs, resulting in an equivalent volume of material per unit length, and the constant cross-sectional shape of port tubing  20  allows manufacture by well proven and cost-effective extrusion methods as used for prior-art tubing, resulting in a cost of manufacture of port tubing  20  that is similar to that of the prior-art tubing. 
       FIG. 6   b  is a section taken from  FIG. 2 , showing an alternate cross-sectional profile of port tubing  20  of cuff port  16 , having a plurality of ridges  66  providing increased resistance to occlusion compared to the cross section shown in  FIG. 6   a . Those skilled in the art will recognize that the size, shape, and number of ridges  66  may be selected to provide an anti-occlusive effect for a particular overall size and stiffness of port tubing  20 , and selected to minimize the required cross-sectional area of wall  68  and thereby minimize the cost of port tubing  20 . 
       FIG. 7   a  is a detail view taken from  FIGS. 3   a  and  3   b , showing the preferred embodiment. Port connector  22  is formed by an injection molding process, like the process used to form connectors of type DSM2202 (Colder Products Company, St. Paul, Minn.) that are used in commercial tourniquet cuffs derived from the cuff described by McEwen in U.S. Pat. No. 5,649,954. However, unlike these prior-art connectors, port connector  22  is made of a blend of thermoplastic polyethylene and sterilization indicator formulated to change color when exposed to the predetermined conditions described above for port tubing  20 . The polyethylene component of the material used to make port connector  22  is selected to have similar stiffness, strength, sliding, and sealing properties to the polyethylene material of the connectors in the McEwen &#39;954 cuff and of the DSM2202 connectors in related commercial cuffs of the prior art, thereby ensuring compatibility with female connectors intended for use with the DSM2202 connector. The secondary sterilization indicator of unauthorized reprocessing is as described above for port tubing  20 . Alternatively or in addition, port connector  22  may carry a temperature indicating compound on one or more selected surfaces as described above for port tubing  20 . Port connector  22  may also carry a water-indicating compound on one or more selected surfaces, as described above for port tubing  20 . 
     A change in the color of port connector  22  from a first predetermined color to a second predetermined color as described above provides an indication that is visually perceptible by a user of cuff  10 . Further, the above-described change of color of port connector  22  can be remotely and automatically detected by connected tourniquet instrument  14 , for example by incorporating the apparatus described by McEwen in U.S. Pat. No. 6,682,547 and U.S. Patent Application No. 20030167070, both of which documents are hereby incorporated by reference. In this regard, the instrument is provided with a light emitter and light detector (such as a photodiode) arranged so that changes in the color of the port connector (or the color change of other part of the cuff that is in the optic path between the emitter and detector) will corresponding alter the light intensity reaching the detector so that the output signal associated with the detector is indicative of the color change, hence automatically indicating the exposure to the agent that caused the color change. 
     Port connector  22  includes actuating flange  70 , annular groove  72 , and deformable ring  74  as described by McEwen in U.S. Pat. No. 5,649,954 and similar in design to the existing DSM2202 connector, thereby making port connector  22  compatible with female connectors intended for use with the DSM2202 connector. However while the prior-art connectors typically have a male barbed portion that fits inside flexible plastic tubing having a circular inner cross section, port connector  22  is adapted for easy assembly to port tubing  20  that has inner surface  64  of a non-circular cross section (see  FIGS. 6   a  and  6   b ). Port connector  22  is joined to port tubing  20  by sliding female cylindrical flange  76  over outer surface  62  and bonding at the mating surface. This arrangement forms port connector pneumatic passageway  55  extending from port tubing end  61  to distal port end  53  and provides greater pneumatic flow area compared to the existing DSM2202 connector by eliminating the male barbed portion of the connector inside pneumatic passageway  54  and allowing the cross-sectional area of the port connector pneumatic passageway  55  to be equal to or greater than that port tubing pneumatic passageway  54  of port tubing  20 . This greater flow area improves the speed of inflation and deflation of cuff  10  and makes pneumatic passageways  54  and  55  less likely to become occluded by kinking, compression, or debris. Furthermore bonding port connector  22  to port tubing  20  on outer surface  62  increases bond area compared to the typical arrangement seen in the prior art (inserting a male connection portion of the port connector into the inner surface of the flexible plastic tubing), which improves the strength and pneumatic sealing properties of the bond. The volume of material in female cylindrical flange  76  is similar to that of the male barbed portion of the existing DSM2202 connector, and the mold required to form female cylindrical flange  76  is simpler, so the cost of manufacture of port connector  22  is similar to or less than that of the prior-art connector. 
       FIG. 7   b  is a detail view taken from  FIGS. 3   a  and  3   b , showing an alternate embodiment in which port connector  22  (see  FIG. 7   a ) is integrated with port tubing  20  to reduce manufacturing cost. In this embodiment, the end of port tubing  20  is formed to create actuating flange  70 , annular groove  72 , and deformable ring  74 . The thermoplastic material is as described above for port connector  22  and undergoes a distinct color change upon exposure to predetermined conditions. This alternate embodiment eliminates the assembly and bonding of port connector  22  to port tubing  20  as described in the preferred embodiment.