Arrangement for the determination of the effective pulmonary blood flow

Abstract

The invention relates to a device to determine effective pulmonary blood flow (PBF) by means of partial CO 2 rebreathing. The device is characterized in that it comprises an endotracheal tube whose conduit leading from the patient to the respirator is divided up into two lanes between a controllable three-way valve ( 4 ) and a Y-piece; one lane builds a larger dead area ( 6 ) for CO 2 rebreathing whereby, in order to measure CO 2 elimination and end expiratory partial CO 2 pressure a CO 2 sensor ( 3 ) and a respiration flow sensor ( 1 ) are provided on the endotracheal tube of the patient. The calculation of effective pulmonary blood flow is provided by a microprocessor/controller ( 7 ) which also controls the three-way valve ( 4 ) which provides the switching between both lanes.

1 . Arrangement for the determination of the effective pulmonary blood flow by means of partial CO 2  rebreathing characterized in that 
 the line from the endotracheal tube of the patient (tube) to the respirator between a controllable 3-way valve ( 4 ) and a Y-fitting ( 5 ) is split into two branches,    one branch forms a bigger dead space ( 6 ) for the CO 2  rebreathing whereby for measurement of the CO 2  elimination and expiration termination CO 2  partial pressure a CO 2  sensor ( 3 ) and a respiratory flow sensor ( 1 ) at the endotracheal tube of the patient and for calculation of the effective pulmonary blood flow a microprocessor/controller ( 7 ) is provided,    the switching between the two branches is carried out by the 3-way valve ( 4 ) that can be controlled through the microprocessor/controller ( 7 ),    the calculation of the effective pulmonary blood flow is performed using the equation                P                 B                 F     =       (       V                 C                     O   2          (     N                 R     )         -     V                 C                     O   2          (   R   )           )         f        (       P                 e                 t                 C                     O   2          (   R   )         ,     P                 e                 t                 C                     O   2          (     N                 R     )         ,     H                 b       )       ×   F                 s         ,                     whereby    VCO 2 (NR) is the CO 2  elimination (ml/min) during the nonrtbreathing period measured as the mean value of the CO 2  elimination of complete respirations within 60 s until immediately before the beginning of the rebreathing period,    PetCO 2 (NR) is the expiration termination CO 2  partial pressure (mmHg) in the respiratory air during the rebreathing period measured as the mean value of the expiration termination CO 2  partial pressures of complete respirations within 60 s until immediately before the beginning of the rebreathing period,    VCO 2 (R) is the CO 2  elimination (ml/min) during the rebreathing period measured as the mean value of the CO 2  elimination of complete respirations within 15 to 30 s after the patient has begun to be respired through the big dead space ( 6 ) (after switching the 3-way valve ( 4 ) into the rebreathing position),    PetCO 2 (R.) is the expiration termination CO 2  partial pressure (mmHg) in the respiratory air during the rebreathing period measured as the mean value of the expiration termination CO 2  partial pressures of complete respirations within 15 to 30 s after the patient has begun to be respired through the big dead space ( 6 ) (after switching the 3-way valve ( 4 ) into the rebreathing position),    Fs is a scale factor for the representation of the effective pulmonary blood flow in 1/min with Fs=10,    PBF is the effective pulmonary blood flow (1/min) whereby    f(PetCO 2 (R), PetCO 2 (NR), Hb) is the standardised CO 2  dissociation curve in blood and is calculated by inserting the measured values into the equation              f        (       P                 e                 t                 C                     O   2          (   R   )         ,     P                 e                 t                 C                     O   2          (     N                 R     )         ,     H                 b       )       =       ΔCCO   2     =                  11   ,   02   ×     (       P                 e                 t                 C                       O   2          (   R   )         0   ,   396         -     P                 e                 t                 C                       O   2          (     N                 R     )         0   ,   396           )       -     0   ,   015   ×     (     15   -     H                 b       )     ×       (       P                 e                 t                 C                     O   2          (   R   )         -     P                 e                 t                 C                     O   2          (     N                 R     )           )     .                             
     
     
         2 . Arrangement to  claim 1  characterized in that the volume of the dead space ( 6 ) is 100, 200, 300, 400 or 500 ml.  
     
     
         3 . Arrangement to  claim 1  or  2  characterized in that the respiratory flow sensor ( 1 ) is inserted into the line at the endotracheal tube of the patient (tube).  
     
     
         4 . Arrangement to  claim 1 ,  2  or  3  characterized in that the CO 2  sensor ( 3 ) is an infrared sensor.  
     
     
         5 . Arrangement to  claim 4  characterized in that the infrared sensor is positioned in a CO 2  ( 2 ) cuvet.  
     
     
         6 . Arrangement to any of  claims 1  to  5  characterized in that the dead space ( 6 ) is an exchangeable tube or cylinder.