the dripless cannula system 30 of the present invention is typically used with a blood pressure monitoring system 18 schematically shown in fig1 . a catheter 19 inserted into a patient , is connected to a fluid input line 21 . disposed in line 21 is a sampling site 20 having a housing 22 and input and output lines 27a , 27b and a stopcock 21a . the dripless cannula system 30 is provided on a syringe 52 for engagement with sampling site 20 to perform a blood draw . the preferred embodiment of the present invention is shown in fig2 - 7 , in which the sampling site or sampling port 20 comprises a body 22 having a septum or bung 24 of relatively soft or flexible material such as silicon disposed at one side to provide access to a fluid flow through path 26 in the site which is connected to input and output lines 27a , 27b . referring to fig2 the dripless cannula system 30 of the present invention comprises a cylindrical outer shield 32 in which a cylinder 36 extends downwardly from a base 34 . in this cylinder 36 is about 1 . 3 cm in diameter and 1 . 6 cm long , although size is not a critical factor and other lengths and diameters are possible . slots 33 are provided on opposite sides of shield 32 , at a lower end thereof . detents 33a project into slots 33 at the lower end thereof . also extending downwardly from the base 34 is a centrally mounted blunt outer cannula 37 . extending upwardly from the base 34 is a cylindrical vacuum chamber 38 , which is about half the diameter of the cylindrical outer shield 32 , or about 0 . 60 cm in the embodiment shown . the chamber 38 also can vary in length but is about 1 . 30 cm long in the preferred embodiment of fig2 - 7 . an end stop 38a is provided at the upper end of vacuum chamber 38 . a fitment 40 , disposed in the vacuum chamber 38 connects an inner cannula 42 to a syringe 52 . the fitment 40 is about 2 . 0 cm long in the embodiment of fig2 - 7 and at a lower end carries an annular shoulder 44 , which carries thereon an o - ring 44a which provides a seal for vacuum chamber 38 , the o - ring seal 44a shown near the bottom of vacuum chamber 38 in fig2 . the metallic inner cannula 42 is fixedly mounted at a proximal end thereof to the modified fitment 40 which fixedly engages inner cannula 42 at a lower end to connect the inner cannula to a flowthrough bore 40a of the fitment thereof slightly above the annular shoulder 44 . the upper end of fitment 40 includes luer lock section 46 connectable to the syringe 52 . disposed within the cannula luer lock section 46 is a duckbill one - way valve 50 which allows fluid flow in one direction only , through the inner cannula 42 , the channel 40a of fitment 40 and into the syringe 52 . although it may not be necessary to include a one - way valve to provide an operative dripless cannula system , the valve is shown in the preferred embodiment . the metallic inner cannula 42 is reciprocably moveable within the vacuum chamber 38 . in operation , the luer lock section 46 of fitment 40 is connected at a locking upper end 48 to the syringe 52 . the fitment 40 is lowered to the bottom of the vacuum chamber 38 to slide inner cannula 42 through outer cannula 37 to extend a distal end or tip 42a of the inner cannula about 0 . 60 centimeters below the inner end or tip 37a of the outer cannula 37 and dispose the sealing ring 44a at a lower end of the vacuum chamber 38 . then , as shown in fig3 the dripless cannula system 30 of the present invention is inserted into the slit reseal sampling site 20 , with the inner cannula 42 first entering the resealable slit 25 in the septum 24 and followed therein by the outer cannula 37 to place the inner cannula in the fluid path 26 of the sampling site 20 to enable a blood draw from the sampling site 20 . in the installed position of fig3 outer shield 32 overlies the site 20 to place input , output lines 27a , 27b in slots 33 , with detents 33a underlying lines 27a , 27b to hold cannula system 30 in place on the sampling site 20 . the outer cannula 37 is disposed within the septum 25 and displaced from the fluid path 26 , with the distal end of the inner cannula 42 in the fluid path 26 . at the sampling site 20 , arterial or venous blood is under pressure , typically 120 to 300 ml of mercury above atmospheric pressure . with the inner cannula 42 in fluid flow path 26 , a flood draw is commenced , such blood draw shown in progress in fig4 . once the blood draw is completed , the inner cannula 42 is withdrawn from the fluid path 26 , the septum slit 25 closes the inner cannula from the fluid path and seals over the tip end 42a of the inner cannula as shown in fig5 . once the inner cannula 42 has been withdrawn to a point where the inner cannula tip 42a is about even with the outer cannula tip 37a , the septum slit 25 will no longer seal off over the tip of the inner cannula and the small amount of fluid trailing the tip of the inner cannula is now exposed to the vacuum source . it is at this point that the vacuum chamber 38 will begin to draw up the excess fluid that is in the septum slit 25 between an inner closed end thereof and the cannula tip 42a . there is an interstitial space between the inner cannula 42 and the outer cannula 37 leading into the vacuum chamber 38 . as the inner cannula 42 is drawn up into the outer cannula 37 , the sealing ring 44a draws away from the bottom of the vacuum chamber 38 to create a vacuum therein which draws residual fluid along said interstitial space and into the vacuum chamber 38 . the one way valve 50 , located between the vacuum chamber 38 and the syringe 52 prevents blood from being drawn out of the syringe and back into the vacuum chamber . as the syringe 52 continues to draw the inner cannula 42 out of the slit 25 in the septum 24 , excess fluid in the slit 25 of the septum 24 continues to flow into the vacuum chamber 38 which now functions as a reservoir for excess blood . the inner cannula 42 reaches the end of its travel ( fig6 ). then the entire assembly pulls free of the sampling site 20 ( fig7 ). the system or assembly 30 is then removed from the syringe or blood collection tube 52 and discarded . an alternative embodiment of the dripless cannula system is shown in fig8 - 12 . the alternative system 101 has similar dimensions , is somewhat simpler than the preferred embodiment and includes a vacuum chamber 102 comprising a cylinder 104 having a distal end wall 106 and a proximal end 108 including a luer lock 109 connectable to the syringe 52 . cylindrical shield 110 extends downwardly from end wall 106 . disposed within the vacuum chamber 102 is a blunt cannula 112 carrying an annular retaining ring 114 at a distal end and an annular sealing member 116 carrying a sealing o - ring 116a fixedly mounted on a proximal end and disposed in the vacuum chamber 102 . the alternative embodiment is operated as follows . installation of the assembly on the syringe luer pushes the annular sealing member 116 to the upper end of the vacuum chamber 102 ( fig8 ). the inner cannula 112 is then fully inserted in the flow path 26 of sampling site 20 ( fig9 ). while the sampling process is in progress , blunt cannula 112 is disposed in fluid path 26 and sealing ring 116 remains at the upper end of vacuum chamber 102 ( fig1 ). once the sampling process is complete and a full blood draw has been taken from the sampling site 20 , cannula system 101 is pulled away from the sampling site 20 by the syringe 52 . in fig1 the annular retaining ring 114 disposed at the distal end of the cannula 112 engages septum 24 to draw the elastomeric seal 116 to the lower end of the vacuum chamber 102 and provides a vacuum in the vacuum chamber which draws residual fluid residing in the slit 25 in the septum up the cannula 112 and into the vacuum chamber ( fig1 and 12 ). however , because of the frictional engagement of the cannula 112 with the bung , the alternative system 101 may not require a retaining ring 114 to draw the seal 116a to the bottom of vacuum chamber 102 . one disadvantage of the embodiment of fig8 - 12 is that the stopcock 21a ( fig1 ) provided in the blood line 21 between the sampling site 20 and the catheter reposing in the patient must be closed . if stopcock 21a is not closed , the blood at the sampling site 20 is under arterial pressure and can be drawn into dripless cannula system 101 . a second alternative embodiment of the present invention shown in fig1 - 16 , in which a dripless cannula system 201 comprises a blunt cannula 202 having an annular retaining ring 204 at a distal end thereof and a luer lock fitting 206 connectable to a syringe 52 at an upper end thereof . a shield 208 comprises a cylindrical body having a base 210 , the base including a receptacle 211 and an open cylinder 212 extending down from the base . the shield 208 fits over the blunt cannula 202 through a central opening 214 in the base 210 . receptacle 211 receives a resistance plug 213 , which includes a central bore which is then trapped within the receptacle 211 by a two - sided adhesive patch 218 at one side thereof . the resistance plug 213 is formed of a material which resists movement of the cannula therethrough such as silicone rubber . one side of the two - sided adhesive patch 218 is secured to the inner end of base 210 of the shield 208 and an opposite side of patch 218 receives a compressible plug 220 having a layer of absorbent material 221 thereon , and a central bore 222 receiving the cannula 202a . fig1 shows modified cannula system 201 above a sampling site 20 . in fig1 , the tip of cannula 202 has been inserted through the bung 24 of the sampling site 20 and into fluid flow path 26 . in fig1 , plug 220 is compressed . as the cannula 202 is withdrawn from the bung 24 , resistance plug 213 slows withdrawal of the cannula 202 ( fig1 ) to enable the absorbent plug 220 to dwell at the sampling site 20 a longer time , thus to increase and enhance absorbency . as shown in fig1 , when cannula system 201 is fully withdrawn from sampling site 20 , compressible plug 220 is returned to its original size and shape . alternatively the embodiment of fig1 - 16 can be modified to remove receptacle 212 and resistance plug 213 . the present invention comprises a simple , effective , and efficient means of solving a serious problem in the hospital , that is the prevention of blood borne pathogens from reaching the care giver treating a critically ill patient . the invention is simple , comprising a minimum of parts , is effective because all of the parts are combined in an integrated and integral system and relatively inexpensive to provide . moreover the present system solves a problem that has not been adequately addressed in the prior art known today . while the description set forth describes a preferred embodiment of the present invention and two alternative embodiments thereof , it should be understood that within the parameters described other embodiments are possible . accordingly , the present invention should not be limited to the embodiments set forth in the description above but rather should be considered with respect to the claims recited hereafter .