fig1 illustrates schematically the principle of thoracic drainage . a patient has an air fistula 14 between a pulmonary lobe 13 and the pleural space 15 , which air fistula 14 may have occurred spontaneously or through injury or may be iatrogenic . air passes through the air fistula from the lung into the pleural space 15 . in order to aspirate the air , a catheter 4 extends into the pleural space . this catheter 4 is connected via a tube system , with suction tube 3 and auxiliary tube 5 , to a suction appliance 20 with an exchangeable collecting container 2 . the collecting container serves to separate bodily secretions that reach the suction appliance 20 along with the aspirated air . an example of a suitable suction appliance known per se is illustrated in fig2 . the suction appliance 20 has a suction pump 1 , which is driven by an electric motor 23 . the electric motor 23 is controlled by a control device 9 . the control device 9 has operating and display elements in the form of a main switch 24 and of a touchscreen display 25 . the control device and the electric motor are supplied with power from an energy store in the form of rechargeable batteries 22 , such that the suction appliance is self - contained and portable . the suction appliance in fig2 is described in detail in wo 2007 / 128156 , of which the entire content is incorporated by reference into the present description . a suction appliance of generally similar design is commercially available under the name medela thopaz ™. the mode of operation of such a suction appliance is illustrated schematically in fig3 . the catheter 4 is located with its proximal end in the pleural space t . the catheter is connected to the proximal end of the suction tube 3 and of the auxiliary tube 5 . at its distal end , the suction tube 3 opens into the collecting container 2 . the latter is connected to the suction pump 1 in order to generate a vacuum in the collecting container 2 . a first pressure gauge 8 and a flow meter 10 are connected between the collecting container 2 and the suction pump 1 and measure the pressure in the collecting container 2 and the volumetric gas flow through the collecting container 2 . the distal end of the auxiliary tube is connected to a controllable valve 7 and to a second pressure gauge 6 . when the valve 7 is closed , no gas flows through the auxiliary tube 5 , and the pressure gauge 6 therefore substantially measures the pressure at the proximal end of the auxiliary tube 5 . this pressure corresponds substantially to the pressure in the pleural space t . the control device 9 receives signals from the pressure gauges 6 , 8 and from the flow meter 10 and controls the suction pump 1 and the valve 7 . for further features of the suction appliance in fig3 , reference is made to wo 2005 / 061025 , of which the entire content is herewith incorporated by reference into the present description . in a preferred embodiment , the control device 9 is a digital control device , i . e . this device comprises a digital processor and , interacting with the latter , a memory 90 in which a computer program is loaded for execution by the processor . when the program is executed , the control device 9 carries out the adaptive algorithm illustrated in fig4 and explained step by step below . step 31 : start . in this step , the suction appliance 20 is started up and an initial vacuum is set . step 32 : documentation of initial vacuum . the initial vacuum is provided with a time stamp and stored in the memory 90 of the control device 9 for documentation purposes . step 33 : determination of a first value of the fistula size . the control device 9 determines a first value of a parameter indicating the size of the air fistula . for this purpose , the control device , using the second pressure gauge 6 , measures the value of the vacuum present in the pleural space and , using the flow meter 10 , measures the volumetric flow passing through the suction tube 3 from the pleural space . from this , the control device determines a size parameter for the fistula according to the following equation : q is the measured value for the volumetric flow ( expressed in milliliters per minute ), the result is generally a number between 0 and 5 . this number is provided with a time stamp and stored in the memory 90 of the control device , likewise the values q and p . step 34 : test of the fistula size . the size parameter is compared with a predetermined reference value ( which can in particular be equal to 1 ). step 35 : end . if the size parameter is smaller than or equal to the reference value , a corresponding end signal is output that tells the patient or the medical personnel that the air fistula is practically closed and the thoracic drainage can be expected to be completed . step 36 : vacuum increased by a first differential value . if the size parameter exceeds the reference value , the control device 9 increases the pump output such that the vacuum increases by 5 mbar . the new vacuum value is stored with time stamp in the memory 90 . step 37 : first waiting period . in this period ( e . g . one hour ), the new vacuum value is maintained . the air fistula has the chance to react to the new vacuum value . step 38 : determination of the second value of the fistula size . this step proceeds exactly like step 33 . step 39 : comparison of fistula sizes before and after : the first and second values of the size parameter are read out from the memory 90 and compared with each other . if the second value is greater than the first value , a branch is made after step 40 , otherwise after step 41 . step 40 : vacuum lowered by a second differential value . if the second value is greater than the first value of the fistula parameter , the control device reduces the output of the suction pump until the vacuum has dropped by 10 mbar . otherwise , the previous vacuum is maintained . the new vacuum value is stored with time stamp in the memory 90 . step 41 : second waiting period . in this period ( 3 hours ), the vacuum is once again maintained . steps 33 , 34 , 36 - 39 and 41 and , if appropriate , step 40 are now repeated in the same way until the method ends at step 35 . the stored values for the vacuum , the volumetric flow and the size parameter can be read out at any time via an interface or shown on the display . compared to the customary clinical practice to date , the frequent adjustments of the vacuum mean that the healing process can be better monitored and ideally sped up . in a patient 1 with an air fistula , the thoracic drainage system thopaz ™ was used . a vacuum of 10 mbar was initially set . this resulted in a volumetric flow of 100 ml / min . from this , a fistula size f = 2 . 15 was calculated using the above equation ( see step 33 ). the vacuum was then increased by 5 mbar to 15 mbar . after one hour , the volumetric flow was measured again . this was now 120 ml / min . from this , a fistula size f = 2 . 13 was calculated . the fistula had therefore functionally decreased in size . the vacuum of 15 mbar was therefore maintained for a further 3 hours . in a patient 2 , an initial vacuum of 10 mbar was likewise set . in this patient also , this resulted in a volumetric flow of 100 ml / min , from which a fistula size f = 2 . 15 was calculated . the vacuum was again increased by 5 mbar to 15 mbar , and the volumetric flow was measured after one hour . this was now 240 ml / min , corresponding to a fistula size f = 2 . 56 . the vacuum was therefore lowered by 10 mbar to just 5 mbar , and this value was maintained for a further 3 hours . it is clear that many modifications can be made to the appliances and methods that have been described above by way of example . thus , the suction device can be any other kind of suction device than the electrical suction pump in fig2 , e . g . an attachment for a central hospital vacuum system , as long as the vacuum level can be adjusted by a suitable pressure control . accordingly , the thoracic drainage system can also be of a completely different construction than that shown in fig2 and 3 . a great many such systems are known from the prior art . the adaptive algorithm can also be modified or supplemented in many different ways . in particular , the differential values of the vacuum and the waiting periods chosen can also be different , e . g . dynamically adapted to measured values . moreover , in addition to the fistula size , other parameters , e . g . the amount of liquid secretion , can also be measured automatically and used to automatically regulate the vacuum . it is possible in principle for steps 31 - 41 to be carried out completely manually , although an automated procedure is preferred .
devices and to methods for thoracic drainage for a patient having an air fistula . a vacuum is produced in the pleural cavity of the patient by means of a suction device . in order to adjust the vacuum on the basis of objective criteria , a suitable size measure for the air fistula is determined and the vacuum produced by the suction device is controlled according to said size measure . an adaptive algorithm includes : determining a first value of a size measure for the air fistula ; changing the vacuum by a first difference value ; determining a second value of the size measure after a first waiting period ; changing the vacuum by a second difference value having the opposite sign if the second measure is greater than the first measure ; repeating steps to after a second waiting period .