Patent Publication Number: US-8535270-B2

Title: Trocar entry incorporating an airbag

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. patent application Ser. No. 13/224,361, filed on Sep. 2, 2011 now U.S. Pat. No. 8,235,940, which is a continuation of U.S. patent application Ser. No. 12/620,829, filed on Nov. 18, 2009, now U.S. Pat. No. 8,048,027, which claims priority to, and the benefit of, U.S. Provisional Patent Application Ser. No. 61/121,653, filed on Dec. 11, 2008. The disclosures of these prior applications are hereby incorporated herein by reference in their entirety. 
    
    
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates to a safety trocar assembly incorporating a structure to prevent overpenetration of the safety trocar assembly into an abdominal cavity. More particularly, the present disclosure relates to a safety trocar assembly incorporating an airbag and sensors associated with a distal end of the safety trocar assembly for detecting changes in conditions at the distal end of the safety trocar assembly. 
     2. Background of Related Art 
     During minimally invasive surgical procedures access ports or trocar assemblies are provided to penetrate an abdominal wall and provide a sealed pathway for insertion of surgical instruments into an abdominal cavity. These trocar assemblies typically include an access port or cannula having a housing and an elongate tubular member extending distally from the housing. A channel or lumen extends through the housing and elongate tubular member for receipt of surgical instruments. One or more valves or seals may be provided within the housing to seal against the surgical instruments. The trocar assemblies additionally include a tissue penetrating or incising device or obturator which is positioned through the cannula. The obturator typically includes a tissue penetrating tip at a distal end which, when assembled with the cannula, extends beyond the distal end of the cannula. Advancement of a trocar assembly against an abdominal wall causes the tissue penetrating tip of the obturator to penetrate the abdominal wall and allow passage of the distal end of the cannula into the abdominal cavity. 
     During insertion of the trocar assembly through the abdominal wall, care must be taken not to damage underlying organs by engagement with the tissue penetrating tip of the obturator or the distal end of the cannula. Various types of safety devices have been developed to shield underlying organs from the tissue penetrating tip of the obturator. In one type of safety trocar assembly, the obturator is maintained in a distal position relative to the cannula during insertion and is spring biased proximally such that upon penetration into the abdominal cavity the tissue penetrating tip of the obturator retracts within the distal end of the cannula. This shields underlying organs from the tissue penetrating tip of the obturator. In another type of safety trocar assembly, a spring biased outer sheath or shield is associated with the cannula such that, upon penetration of the abdominal wall by the tissue penetrating tip of the obturator, the outer sheath or shield advances distally to cover the tissue penetrating tip of the obturator again preventing damage to underlying organs. 
     While the known type of safety trocar assemblies incorporate methods of shielding underlying organs from the tissue penetrating tip of the obturator, these safety devices do not prevent continued advancement of the trocar assembly through the abdominal wall towards the underlying organs. 
     Therefore, a need exists for a safety trocar assembly which incorporates an expandable member located proximally of the distal end of the safety trocar assembly to prevent overpenetration of the safety trocar assembly through the abdominal wall. Further, a need exists for a safety trocar assembly having a sensor adjacent the distal end of the safety trocar assembly to detect changes in conditions at the distal end of the safety trocar assembly as it passes through the abdominal wall and into the body cavity. 
     SUMMARY 
     There is disclosed a safety trocar assembly including an airbag cannula and an obturator. The airbag cannula generally includes a housing and an elongate tubular member extending distally from the housing. An expandable member is positioned on the elongate tubular member proximal of a distal end of the elongate tubular member and is movable from a collapsed position to an expanded position. A sensor is provided including a sensor lumen formed through the elongate tubular member and having a sensor opening adjacent to the distal end of the elongate tubular member. A trigger mechanism is operatively associated with the sensor and the expandable member such that a change of condition sensed at the sensor opening operates to move the expandable member from the collapsed to the expanded position. 
     In one embodiment, the expandable member is an airbag positioned on the elongate tubular member. The elongate tubular member includes an inflation lumen in fluid communication with the airbag. The trigger mechanism includes a valve to inflate the airbag in response to a change in conditions detected by the sensor. A source of fluid pressure is operatively associated with the valve. 
     In one embodiment, the sensor is an air pressure sensor capable of detecting changes in air pressure at the sensor opening. 
     In an alternative embodiment, the sensor is an optical sensor including an optical fiber extending through the sensor lumen and terminating adjacent the sensor opening. 
     In a further alternative embodiment, the sensor is an ultrasound sensor. 
     In another embodiment, the sensor is a sonar sensor. 
     In a particular embodiment, a distal end of the airbag is longitudinally movable along and outer surface of the elongate tubular member. 
     In a further particular embodiment, the airbag includes a plurality of circumferentially spaced airbags. 
     In a specific embodiment, the airbag cannula includes an outer sheath overlying the airbag to restrain the airbag in the collapsed position. The outer sheath includes a perforation line which is separable upon inflation of the airbag from the collapsed to the expanded position. 
     There is also disclosed an airbag cannula having a housing and an elongate tubular member extending distally from the housing. An expandable member is positioned on the elongate tubular member proximal of a distal end of the elongate tubular member. The expandable member is movable from a collapsed position to an expanded position. A sensor is provided including a pair of sensor wires extending through the elongate tubular member and terminating in a pair of spaced apart sensor tips adjacent to the distal end of the elongate tubular member. A trigger mechanism is operatively associated with the sensor and the expandable member such that a change of condition sensed between the sensor tips operates to move the expandable member from the collapsed to the expanded position. 
     The sensor is an electrical sensor and the change in condition sensed between the sensor tips is a change in electrical resistance existing between the sensor tips. 
     The expandable member is an airbag positioned on the elongate tubular member. The elongate tubular member includes an inflation lumen in fluid communication with the airbag and the trigger mechanism includes a valve to inflate the airbag in response to a change in conditions detected by the sensor. 
     In one embodiment, a distal end of the airbag is longitudinally movable along and outer surface of the elongate tubular member. 
     In a further embodiment, the airbag includes a plurality of circumferentially spaced airbags. 
     The airbag cannula further includes an outer sheath overlying the airbag to restrain the airbag in the collapsed position. The outer sheath includes a perforation line which is separable upon inflation of the airbag from the collapsed to the expanded position. 
     There is also disclosed a method of preventing overpenetration of the distal end of a cannula into an abdominal cavity. The method includes providing a cannula having a housing and an elongate tubular member extending distally from the housing. An airbag is positioned on the elongate tubular member and the elongate tubular member includes an inflation lumen in fluid communication with the airbag. The airbag is positioned on the elongate tubular member proximal of a distal end of the elongate tubular member and is movable from a collapsed position to an expanded position. A sensor is provided including a sensor lumen formed through the elongate tubular member and having a sensor opening adjacent to the distal end of the elongate tubular member. A trigger mechanism is operatively associated with the sensor and the airbag, the trigger mechanism including a valve to inflate the airbag in response to a change in conditions detected by the sensor such that a change of condition sensed at the sensor opening operates to move the airbag from the collapsed to the expanded position. 
     The method includes the steps of positioning the distal end of the elongate tubular member adjacent an abdominal wall, such that the sensor opening is sealed against the abdominal wall, and sensing a first condition at the sensor opening. 
     The distal end of the elongate tubular member is advanced through the abdominal wall and into an abdominal cavity. A second condition is sensed at the sensor opening and the airbag is inflated from the collapsed position to the expanded position in response to a change in condition between the first condition and the second condition sensed at the sensor opening. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       Various embodiments of the presently disclosed safety trocar assembly are disclosed herein with reference to the drawings, wherein: 
         FIG. 1  is a perspective view of one embodiment of a safety trocar assembly including an obturator and an airbag cannula incorporating one embodiment of an airbag; 
         FIG. 2  is a perspective view of the safety trocar assembly of  FIG. 1  with a triggering mechanism removed: 
         FIG. 3  is a perspective view of the safety trocar assembly of  FIG. 1  with the obturator of the safety trocar separated from the airbag cannula of the airbag trocar; 
         FIG. 4  is a side view, shown in section, taken along line  4 - 4  of  FIG. 1 ; 
         FIG. 5  is a cross-sectional view of the airbag cannula of  FIG. 3  illustrating one embodiment of a sensor mechanism; 
         FIG. 5   a  is an enlarged area of detail view of  FIG. 5 ; 
         FIG. 6  is a cross-sectional view of the airbag cannula of  FIG. 3  illustrating another embodiment of a sensor mechanism; 
         FIG. 6   a  is an enlarged area of detail view of  FIG. 6 ; 
         FIG. 7  is a cross-sectional view of the airbag cannula of  FIG. 3  illustrating a further embodiment of a sensor mechanism; 
         FIG. 7   a  is an enlarged area of detail view of  FIG. 7 ; 
         FIG. 8  is perspective view of an alternative embodiment of a safety trocar assembly incorporating an alternative embodiment of an airbag cannula; 
         FIG. 9  is a cross-sectional view taken along line  9 - 9  of  FIG. 8 ; 
         FIG. 10  is a perspective view of a further alternative embodiment of a safety trocar assembly incorporating a further alternative embodiment of an airbag cannula; 
         FIG. 11  is an enlarged cross-sectional view of the airbag of  FIG. 10  in a first position; 
         FIG. 12  is an enlarged cross-sectional view, taken along line  12 - 12  of  FIG. 10 , illustrating the airbag in a second position; 
         FIG. 13  is a perspective view of another alternative embodiment of a safety trocar assembly incorporating multiple airbags; 
         FIG. 14  is an enlarged cross-sectional view taken along line  14 - 14  of  FIG. 13 ; 
         FIG. 15  is a perspective view of a further alternative embodiment of a safety trocar assembly incorporating a multiple airbag cannula; 
         FIG. 16  is an enlarged cross-sectional view taken along line  16 - 16  of  FIG. 15 ; 
         FIG. 17  is a side view, shown in section, of the safety trocar of  FIG. 1  during initial penetration of an abdominal wall; 
         FIG. 18  is a side view, similar to  FIG. 17 , of the safety trocar assembly during penetration of the abdominal wall; and 
         FIG. 19  is a side view, shown in section, of the safety trocar assembly after penetration of the abdominal wall. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Embodiments of the presently disclosed safety trocar assembly with airbag cannula will now be described in detail with reference to the drawings wherein like numerals designate identical or corresponding elements in each of the several views. As is common in the art, the term ‘proximal” refers to that part or component closer to the user or operator, i.e. surgeon or physician, while the term “distal” refers to that part or component further away from the user. 
     Referring initially to  FIGS. 1-3 , there is disclosed a safety trocar assembly  10  for use in surgical procedures. Safety trocar assembly  10  is designed to prevent overpenetration through the abdominal wall and thus prevent damage to underlying organs. Safety trocar assembly  10  includes an obturator  12  having a handle  14  and an elongate shaft  16  extending distally from handle  14 . Elongate shaft  16  terminates in a tissue penetrating tip  18  which is provided to puncture through an abdominal wall. Safety trocar assembly  10  further includes an airbag cannula  20  configured to receive obturator  12  therethrough. Airbag cannula  20  generally includes a housing  22  having a hollow, elongate tubular member  24  extending distally from housing  22 . A throughbore  26  extends through housing  22  and is in communication with a lumen  28  extending through elongate tubular member  24 . In the assembled condition, obturator  12  extends through throughbore  26  and lumen  28  of airbag cannula  20 . 
     Referring for the moment to  FIG. 1 , airbag cannula  20  includes an expandable member in the form of a balloon or airbag  30  positioned on an outer surface  32  of elongate tubular member  24 . Airbag  30  is formed of a flexible, non-expansible material. An inflation lumen  34  extends through elongate tubular member  24  and is in fluid communication with airbag  30 . Upon penetration of an abdominal wall, an inflation fluid is forced through inflation lumen  34  and into airbag  30  to move airbag  30  from a deflated to an inflated condition as described in more detail hereinbelow. 
     Referring back to  FIGS. 1-3 , an outer sheath  36  is provided to restrain airbag  30  in the deflated condition. Outer sheath  36  is affixed to outer surface  32  of elongate tubular member  24 . A separable perforation line  38  extends around outer sheath  36 . Upon inflation of airbag  30 , the pressure of airbag  30  forces perforation line  38  to separate thereby releasing airbag  30  to expand to the inflated condition. 
     As noted hereinabove, safety trocar assembly  10  is configured to avoid overpenetration of the abdominal wall. A sensor opening  40  is provided in a distal face  42  of elongate tubular member  24 . A sensor lumen  44  extends proximally from sensor opening  40 , through elongate tubular member  24 , and terminates within housing  22 . In order to manipulate housing  22  relative to an abdominal wall, housing  22  is provided with a pair of housing wings  46 . Additionally, a source of inflation fluid  48  is provided on housing  22  to transmit insufflation fluid through lumen  28  in elongate tubular member  24  in order to insufflate a body cavity to provide a working space for a surgical procedure. 
     In order to expand airbag  30  from the deflated to the inflated condition upon penetration of safety trocar assembly  10  through the abdominal wall, a trigger mechanism  50  is located on housing  22  and is provided to synchronize a change in condition sensed by a sensor associated with sensor opening  40  and sensor lumen  44 , as described in more detail hereinbelow, with the inflation of airbag  30 . Trigger mechanism  50  includes a trigger  52  which is provided to receive a signal from the sensor and operates to send inflation fluid through inflation lumen  34  and into airbag  30 . A control knob  54  is provided to adjust the sensitivity of trigger  52 . 
     With specific reference to  FIGS. 2 and 5 , trigger mechanism  50  includes a valve  56  which controls the flow of fluid into airbag  30 . Valve  56  is connected to inflation lumen  34  by an inflation hose  58 . In this embodiment, the particular sensor is an air pressure sensor  60  positioned within housing  22  and in fluid communication with a proximal end  62  of sensor lumen  44 . Air pressure sensor  60  is provided to detect changes in air pressure within sensor lumen  44 . Specifically, when distal face  42  of elongate tubular member  24  is positioned against tissue, air pressure sensor  60  pressurizes sensor lumen  44  with a predetermined amount of air pressure. Sensor opening  40 , being positioned on distal face  42  of elongate tubular member  24 , seals the distal end of sensor lumen  44  against the tissue in the manner described in more detail hereinbelow. 
     Trigger mechanism  50  may be formed as an integral part of housing  22  of cannula  20  or, as shown, may be formed as a detachable component. Air pressure sensor  60  includes a port  64  which is engageable with a connector  66  on trigger mechanism  50 . Trigger  52  is connected to, and operates, valve  56  by a control hose  68 . Thus, changes in air pressure detected by air pressure sensor  60  are communicated to trigger  52  which in turn operates to actuate valve  56 . 
     Referring now to  FIGS. 4 and 5 , inflation hose  58  is connected to a proximal port  70  of inflation lumen  34  ( FIG. 5 ) and a distal port  72  of inflation lumen  34  is in fluid communication with an interior  74  of airbag  30  ( FIG. 4 ). As shown, passage of a fluid such as, for example, a gas, through inflation lumen  34  and out of distal port  72  moves airbag  30  from the deflated condition ( FIG. 3 ) to the inflated condition as shown in  FIG. 4 . 
     With continued reference to  FIG. 4 , proximal and distal ends  76  and  78 , respectively, of airbag  30  are secured to outer surface  32  of elongate tubular member  24  by gluing, welding, heat sealing or shrinking, etc. or other known methods of securing a flexible material to a substrate. Similarly, proximal and distal ends  80  and  82 , respectively, of outer sheath  36  are secured to outer surface  32  of elongate tubular member  24 . 
     Referring to  FIG. 5 , it should be noted that inflation lumen  34  is formed within the wall  84  of elongate tubular member  24 . Similarly, with reference to  FIG. 5   a , sensor lumen  44  is also formed within wall  84  of elongate tubular member  24 . Airbag  30  along with outer sheath  36  are located at a position proximal of distal end  86  of elongate tubular member  24 . It should be further noted that, while sensor opening  40  is located at distal face  42  of elongate tubular member  24 , sensor opening  40  may be provided at other locations on distal end  86  of elongate tubular member  24  such as, for example, a side of distal end  86  of elongate tubular member  24 , etc. so long as sensor opening  40  is distal of airbag  30  and outer sheath  36 . 
     Referring now to  FIG. 6 , there is disclosed an alternative embodiment of a safety trocar assembly  90 . Safety trocar assembly  90  is similar to safety trocar assembly  10  described hereinabove and while not specifically shown here includes obturator  12 . Safety trocar assembly  90  additionally includes an airbag cannula  100  having a housing  102  and an elongate tubular member  104  extending distally from housing  102 . A throughbore  106  extends through housing  102  and a lumen  108  extends through elongate tubular member  104 . An airbag  110  is provided on an outer surface  112  of elongate tubular member  104 . Airbag  110  is substantially similar to airbag  30  described hereinabove. An inflation lumen  114  is formed within elongate tubular member  104  and includes a proximal port  116  and a distal end port  118  which is in fluid communication with airbag  110 . 
     Similar to safety trocar assembly  10  described hereinabove, safety trocar assembly  90  includes a trigger mechanism  120  including a trigger  122  having an adjustable control knob  124 . A valve  126  is included in trigger mechanism  120  and is connected to trigger  122  by a control hose  128 . An inflation hose  130  extends between valve  126  and proximal port  116  to provide a source of inflation fluid to airbag  110 . 
     Airbag cannula  110  includes an alternative sensing mechanism for detecting penetration of an abdominal wall. Specifically, an electrical sensor  132  is provided and includes a port  134  for engagement with a connector  136  of trigger mechanism  120 . Electrical sensor  132  detects the change in resistance between that provided by the abdominal wall and the interior of the body cavity after safety trocar assembly  90  has penetrated the abdominal wall. First and second sensor wires  138  and  140 , respectively, are provided in elongate tubular member  104 . First and second sensor wires  138  and  140  may extend through a sensor lumen similar to sensor lumen  44  described hereinabove with respect to safety trocar assembly  10 . In the presently disclosed embodiment, first and second sensor wires  138  and  140  are embedded within elongate tubular member  104 . First and second sensor wires  138  and  140  terminate in first and second wire distal ends  142  and  144  which are spaced apart from one another. First and second sensor wires  138  and  140  extend through a distal end  146  of elongate tubular member  104  and are exposed through a distal face  148  of elongate tubular member  104 . 
     Referring now to  FIG. 6   a , first and second sensor wires  138  and  140  are embedded in a side wall  150  of elongate tubular member  104 . As distal ends  142  and  144  of first and second sensor wires  138  and  140  are placed in contact with the abdominal wall, sensor  132 , and thus first and second sensor wires  138  and  140 , is energized and detects a specific amount of resistance between distal ends  144  and  142 . As distal end  146  of elongate tubular member  104  penetrates the abdominal wall and enters the body cavity, the resistance between distal ends  144  and  142  changes. This change in resistance is detected by sensor  132  which then signals trigger  124  to actuate valve  126  thereby inflating air bag  110 . Similar to airbag cannula  20  described hereinabove, airbag cannula  100  includes an outer sheath  152  which surrounds airbag  110 . Outer sheath  152  includes a separable perforation line (not shown) similar to perforation line  38  in outer sheath  36  described hereinabove. 
     Referring now to  FIGS. 7 and 7   a , it will be appreciated that airbag cannula  20 , described hereinabove, may be provided with a variety of other types of sensors in housing  22  and which extended through sensor lumen  44  to sensor opening  40 . Examples of such sensors include ultrasound sensors, sonar sensors, etc. As shown in  FIGS. 7 , airbag cannula  20  may be provided with an optical sensor  160  having a sensor fiber  162  extending distally from optical sensor  160  through sensor lumen  144 . Sensor fiber  162  has a proximal end  164  connected to optical sensor  160  and a distal end  166  which is positioned within sensor opening  40  at distal end  86  of elongate tubular member  24 . Sensor  160  includes a port  168  for receipt of connector  66  of trigger mechanism  50 . 
     In use, when distal end  86  of elongate tubular member  24  is in engagement with an abdominal wall, distal end  166  of optical fiber  162  receives a first amount of light or a first image. After distal end  86  passes through the abdominal wall into the abdominal cavity, distal end  166  of optical fiber  162  detects a second amount of light or second image different from the first amount of light or first image. This difference is communicated through optical fiber  162  to optical sensor  160  which then signals trigger  52  to actuate valve  56  thereby inflating airbag  30 . Thus, as distal end  86  of elongate tubular member  24  penetrates the abdominal wall, optical sensor  160  in combination with trigger mechanism  50  operate to instantaneously inflate airbag  30  thereby preventing any further advancement of elongate tubular member  24  through the abdominal wall. In this manner, underlying organs are protected from engagement with tissue penetrating tip  18  of obturator  12  and distal end  86  of airbag cannula  20 . 
     Referring now to  FIG. 8 , safety trocar assembly  10  is disclosed with an alternative airbag  170 . Safety trocar assembly  10  includes obturator  12  and airbag cannula  20  substantially as described hereinabove. As shown, airbag  170  forms a generally elongate doughnut shape around elongate tubular member  24 . Similar to those embodiments described hereinabove an outer sheath  172  having a perforation line  174  surrounds airbag  170 . In contrast to airbag  30  described hereinabove, distal and proximal ends  176  and  178  of airbag  170  are recurved inwardly and affixed to outer surface  32  of elongate tubular member  24  by welding, gluing, heat shrinking, etc. Likewise, distal and proximal ends  180  and  182  of outer sheath  172  are also recurved inwardly and secured against outer surface  32  of elongate tubular member  24 . 
     With specific reference to  FIG. 9 , upon inflation of airbag  170 , a distal end surface  184  of airbag  170  projects distally beyond distal end  176  of airbag  170  to provided a “bumper” for engagement with the abdominal wall to thereby limit any further advancement of elongate tubular member  24  through the abdominal wall. 
     Referring now to  FIGS. 10-12 , and initially with regard to  FIGS. 10 and 11 , safety trocar assembly  10  is illustrated with a further alternative embodiment of an airbag  190 . Safety trocar assembly  10  is substantially identical to that described hereinabove including obturator  12  and airbag cannula  20 . Airbag cannula  20  includes housing  22  having elongate tubular member  24  extending distally therefrom. Trigger mechanism  50  along with sensor  60  are provided to inflate airbag  190  after elongate tubular member  24  penetrates abdominal wall. 
     Airbag  190  includes a proximal end  192  which is secured to outer surface  32  of elongate tubular member  24  in a manner described hereinabove. An outer sheath  194  surrounds airbag  190  in the undeployed position and includes a proximal end  196  which may be secured to outer surface  32  of elongate tubular member  24  or, alternatively, may be secured to proximal end  192  of airbag  190 . In this embodiment, airbag  190  is configured to move distally along elongate tubular member  24  upon inflation to engage an abdominal wall. Specifically, a slide ring  198  is provided around elongate tubular member  24  and is longitudinally movable along elongate tubular member  24  from a proximal position wherein airbag  190  is in the deflated or undeployed condition to a distal position wherein airbag  190  is in the inflated condition. An O-ring  200  is provided between slide ring  198  and outer surface  32  of elongate tubular member  24  to seal airbag  190  against elongate tubular member  24 . A distal end  202  of airbag  190  is secured to slide ring  198 . A distal end  204  of outer sheath  194  may be temporarily secured to slide ring  198  and separates from slide ring  198  upon inflation of airbag  190 . 
     Referring out of  FIG. 12 , upon forcing inflation fluid through inflation lumen  34  and out port  70  into an interior  206  of airbag  190 , distal and  204  of outer sheath  194  separates from slide ring  198  and slide ring  198  moves distally along outer surface  32  of elongate tubular member  24  in response to the inflation of airbag  190 . In this manner, advancement of elongate tubular member  204  through an abdominal wall proceeds until distal end  202  of airbag  190  engages the abdominal wall. 
     Referring now to  FIGS. 13 and 14 , and initially with regard to  FIG. 13 , safety trocar assembly  10  including obturator  12  and airbag cannula  20  is illustrated with multiple airbags  210 ,  212  and  214  located on outer surface  32  of elongate tubular member  24 . An outer sheath  216  is provided to secure airbags  210 ,  212  and  214  against elongate tubular member  24  prior to inflation. As best shown in  FIG. 14 , recurved side edges  218  and  220  of airbag  210  are secured to outer surface  32  of elongate tubular member  24 . Likewise, recurved side edges  222  and  224  and  226  and  228  of airbags  212  and  214  are similarly secured to outer surface  32  of elongate tubular member  24 . Elongate tubular member  24  is formed with multiple inflation lumens terminating in inflation ports  230 ,  232  and  234  which are in fluid communication with airbags  210 ,  212  and  214  respectively. The provision of multiple airbags on safety trocar assembly  10  allows a surgeon to better view the incision in the abdominal wall as elongate tubular member  24  advances therethrough. 
     Referring now to  FIGS. 15 and 16 , and initially with regard to  FIG. 15 , safety trocar assembly  10  is substantially as described hereinabove including obturator  12  and airbag cannula  20 . Like those embodiments described hereinabove, airbag cannula  20  includes air pressure sensor  60  and trigger mechanism  50  to cause inflation of the disclosed airbags upon penetration of an abdominal wall by distal end  86  of elongate tubular member  24 . While the discussions here in are given in terms of distal end  86  of elongate tubular member  24  penetrating the abdominal wall, it will be appreciated that trocar assembly  10  as a whole is advanced against the abdominal wall such that tissue penetrating tip  18  of obturator  12  causes the penetration and informs the incision through the abdominal wall. Distal end  86  of airbag cannula  20  follows tissue penetrating tip  18  through the incision. 
     In this embodiment, as best shown in  FIG. 16 , a plurality of relatively small airbags such as, for example, airbag  240 , airbag  242  and airbag  244  are formed about the circumference of elongate tubular member  24 . Specifically, circumferential edges  248 ,  250  and  252  of airbags  240 ,  242  and  244 , respectively, are fixed to outer surface  32  of elongate tubular member  24 . Elongate tubular member  24  is provided with a plurality of longitudinally extending inflation lumens which terminate in inflation ports  254 ,  256  and  258  which are in fluid communication with airbags  240 ,  242  and  244  respectively. Similar to those embodiments described hereinabove, upon inflation of airbags  240 ,  242  and  244 , outer sheath  246  separates to expose the airbags. Similar to the embodiments disclosed hereinabove, airbags  240 ,  242  and  244  are located proximal of distal end  86  of elongate tubular member  24 . 
     Referring now to  FIGS. 17-19 , and initially with regard to  FIG. 17 , the use of safety trocar assembly  10 , including airbag cannula  20 , air pressure sensor  60  and airbag  30 , to penetrate abdominal wall will now be described. Initially, obturator  12  is inserted through airbag cannula  20  is such that tissue penetrating tip  18  extends beyond distal end  86  of elongate tubular member  24 . Airbag  30  is in a deflated condition and is restrained against elongate tubular member  24  by outer sheath  36 . Safety trocar assembly  10  is advanced against an abdominal wall AW such that tissue penetrating tip  18  begins to penetrate or incise abdominal wall AW. As discussed hereinabove, safety trocar assembly  10  is provided to penetrate abdominal wall AW so as to position distal end  86  of airbag cannula  20  within a body cavity BC underlying abdominal wall AW without danger of damaging an underlying organ UO by tissue penetrating tip  18  of obturator  12  or distal end  86  of airbag cannula  20 . 
     Referring now to  FIG. 18 , as tissue penetrating tip  18  of obturator  12  and distal end  86  of airbag cannula  20  are advanced into engagement with abdominal wall AW, sensor opening  40  is sealed against abdominal wall AW. Air pressure sensor  60  is activated to pressurize sensor lumen  44 . Air pressure sensor  60  detects and maintains a predetermined amount of air pressure within sensor lumen  44 . As shown, underlying organ UO is spaced a distance D 1  from abdominal wall AW. Thus, it is necessary to insert tissue penetrating tip  18  a distance less than distance D 1  into body cavity BC. This is accomplished by inflating airbag  30  upon penetration of abdominal wall AW by tissue penetrating tip  18  of obturator  12 . 
     Referring to  FIG. 19 , as tissue penetrating tip  18  of obturator  12  and distal end  86  of airbag cannula  20  penetrate through abdominal wall AW and into body cavity BC, sensor opening  40  in distal face  42  of airbag cannula  20  is exposed or open to body cavity BC. Because body cavity BC has a pressure less than the pressure maintained in sensor lumen  44 , the pressure in sensor lumen  44  drops. Sensor  60  detects the immediate change in pressure within sensor lumen  44  and signals trigger  52  of trigger mechanism  50 . In response thereto, trigger  52  actuates valve  56  to cause inflation fluid to flow through inflation hose  58  and into inflation lumen  34 . The inflation fluid passes through inflation port  72  into interior  74  of airbag  30  causing airbag  30  to rapidly expand. As airbag  30  expands, perforation line  38  of outer sheath  32  separates to release airbag  30  from the restrained condition. The rapid expansion of airbag  30  which, as noted hereinabove, is positioned adjacent to distal end  86  of elongate tubular member  24  acts as a stop or bumper to prevent further advancement of elongate tubular member  24  and tissue penetrating tip  18  of obturator  12  into body cavity BC. Thus, tissue penetrating tip  18  of obturator  12  is restrained a distance D 2  from underlying organ UO to prevent any damage to underlying organ UO. 
     It will be understood that various modifications may be made to the embodiments disclosed herein. For example, the disclosed airbags may be inflated manually by manually operating the valve of the trigger mechanism. Additionally, other forms of expandable members such as, for example, movable rigid stops, flexible wings, etc. may be provided and actuated by sensors to prevent overpenetration of an abdominal wall by tissue penetrating tip of an obturator. Further, other types of sensors may be provided to detect changes in conditions at the distal end of the cannula such as, for example, fluid pressure sensors, heat sensors, physical pressure sensors, mechanical devices such as movable rods within the sensor lumen etc. Additionally, the disclosed sensor detection mechanisms may be incorporated in other surgical instruments wherein proper positioning of distal ends of the surgical instruments may be detected by changes in conditions encountered by the distal ends of the surgical instruments. Still further, the disclosed airbag cannulas and sensors may be used in conjunction with known safety shields or penetrating tip retraction devices. Therefore, the above description should not be construed as limiting, but merely as exemplifications of particular embodiments. Those skilled in the art will envision other modifications within the scope and spirit of the claims appended hereto. 
     For example, while the various embodiments described and illustrated herein have the airbag  30  attached to an outer circumferential surface located near to the distal end of the cannula, it is also contemplated that the airbag may be located at any longitudinal position along the outer circumferential surface of the cannula. This position may reflect any one or more of various factors, such as the thickness of tissue to be penetrated, different internal distances D 1 , different types of tissue, and/or different thrust forces applied by the user. Still further, the length of the cannula may play a role in the appropriate position of the airbag  30  thereon. 
     Furthermore, while the various embodiments described and illustrated herein have the airbag  30  permanently attached to an outer circumferential surface of the cannula, it is also contemplated that the airbag may be selectively and/or adjustably attached to the outer circumferential surface of the cannula. In this manner, a user may adjust the position of the airbag  30  so as to accommodate different thickness of tissue (e.g., an obese patient may have a thicker tissue wall as compared to a thin patient), different internal distances D 1  (e.g., a surgical procedure that involves insufflating an abdominal cavity may have an internal distance that is greater than a surgical procedure that does not involve insufflating the cavity), different types of tissue (e.g., a patient that has substantial scar tissue might require different penetrative forces as compared to a patient that has no such scarring) and/or different thrust forces applied by the user (e.g., a male surgeon may employ greater thrust forces as compared to a female surgeon). 
     The user of such a selectively and/or adjustably attachable airbag  30  might determine a position of the airbag prior to using the trocar and then leave the airbag  30  in that position for the duration of the surgical procedure. Alternatively a user might selectively adjust the position of the airbag  30  one or more times while actually using the trocar. For example, if a user selects a first position of the airbag  30  prior to a surgical procedure and then determines, after attempting to penetrate the abdominal wall AW, that the selected first position was too close to the distal end of the cannula (e.g., such that the airbag  30  prevents the tissue penetrating tip  18  from fully penetrating the tissue of the abdominal wall AW), the user may then select to adjust the position of the airbag  30  to a slightly more proximal position prior to continuing with the penetration of the abdominal wall AW. Still further, the user might elect to remove the airbag  30  entirely, at any point of the surgical procedure, if desired. 
     Still further, while the various embodiments described and illustrated herein have the airbag  30  attached to an outer circumferential surface of the cannula, it is also contemplated that the airbag may be attached to any component of the trocar. For example, the airbag  30  may be attached to the distal face of the housing  22 . Of course, whatever component the airbag  30  is attached to, it is desirable that, when deployed, the airbag  30  is positioned so as to prevent over-penetration of the trocar through the abdominal wall AW and to avoid contact by the tissue penetrating tip  18  with the underlying tissues, e.g., internal organs.