Arrangement for the determination of the effective pulmonary blood flow

• US 20040087867A1
• Filed: 03/27/2003
• Published: 05/06/2004
• Est. Priority Date: 09/28/1996
• Status: Active Grant

• Current Assignee: Technische Universitat Munchen
• Original Assignee: Technische Universitat Munchen
• Inventors: Albrecht, Detlev Michael, Gama De Abreu, Marcelo
• Granted Patent: US 6,840,906 B2
• Time in Patent Office: Days
• US Class Current: 600/529
• CPC Class Codes: A61B 5/029 Measuring or recording blood output from the heart, e.g. minute volume A61B8/065 takes precedence

Abstract

The invention relates to a device to determine effective pulmonary blood flow (PBF) by means of partial CO₂ 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 lines between a controllabe three-way valve (4) and a Y-piece; one line forms a larger dead area (6) for CO₂ rebreathing whereby, in order to measure CO₂ elimination and end expiratory partial CO₂ pressure, a CO₂ 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 lines.

Claims

1. Apparatus for the determination of the effective pulmonary blood flow by means of partial CO₂ rebreathing characterized in that

the tube from the endotracheal tube of the patient 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 CO₂ rebreathing whereby for measurement of the CO₂ elimination and expiration termination CO₂ partial pressure a CO₂ 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:

$\mathrm{PBF}=\frac{\left({\mathrm{VCO}}_2<br><br>\left(\mathrm{NR}\right)-{\mathrm{VCO}}_2<br><br>\left(R\right)\right)}{f<br><br>\left(f_1<br><br>\left({\mathrm{PetCO}}_2<br><br>\left(R\right)\right),f_2<br><br>\left({\mathrm{PetCO}}_2<br><br>\left(\mathrm{NR}\right)\right),\mathrm{Hb}\right)\times <br><br>F_s}$

wherein VCO₂(NR) is the CO₂ elimination (ml/min) during the nonrebreathing period measured as the mean value of the CO₂ elimination of complete respirations within 60 s until immediately before the beginning of the rebreathing period, the nonrebreathing period being about 60 s or longer or shorter or being the period immediately after the rebreathing period, the CO₂ elimination being measured taking variations of CO₂ stored in the lungs into account and compensating for the variations when the respiratory pattern is not regular,

PetCO₂(NR) is the expiration termination CO₂ partial pressure in mmHg in the respiratory air during the rebreathing period measured as the mean value of the expiration termination CO₂ partial pressures of complete respirations within 60 s until immediately before the beginning of the rebreathing period,

f₁ is a function to better approximate the PetCO₂ to the end-capillary CO₂ partial pressure PcCO₂ during the nonrebreathing period, the function f₁ representing the simple sum of the difference between the CO₂ partial pressure in arterial blood PaCO₂ as determined invasively, the estimation of the difference between PcCO₂ and PetCO₂ according to gas exchange models that use alveolar deadspace and/or functional residual capacity values that have been measured or estimated by normograms or a combination of invasively determined PaCO₂ and gas exchange models,

VCO₂(R) is the CO₂ elimination in ml/min during the rebreathing period measured as the mean value of the CO₂ 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, the rebreathing period being as long as 60 s or more and as short as 25 s or less, CO₂ elimination being alternatively measurable taking variations of CO₂ stored in the lungs into account and compensating for that variation when the respiratory pattern is not regular, VCO₂(R) being measurable alternatively from the first breath in the rebreathing period talking the FRC and the variation of breath-to-breath PetCO₂ or PcCO₂ differences into account in a gas exchange model, and curve fitting procedures being applicable to the breath-by-breath VCO₂ values measured or estimated in the rebreathing period in order to improve the estimation of VCO₂(R),

PetCO₂(R) is the expiration termination CO₂ partial pressure in mmHg in the respiratory air during the rebreathing period measured as the mean value of the expiration termination CO₂ 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, a time window of 15 to 30 s for taking the mean value being subject to being shortened or extended, alternatively, PetCO₂ values being subject to a curve fitting procedure to estimate PetCO₂ at equilibrium,

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(PetCO₂(R), PetCO₂(NR), Hb) is the standardised CO₂ dissociation curve in blood and is calculated by inserting the measured values into the equation

f(PetCO₂(R), PetCO₂(NR), Hb)=Δ

CCO₂=11.02×

(PetCO₂(R)^0.396−

PetCO₂(NR)^0.396)−

0.015×

(15−

Hb)×

(PetCO₂(R)−

PetCO₂(NR))

2. Apparatus of claim 1 characterized in that the volume of the dead space (6) is adjustable.

3. Apparatus of claim 1 characterized in that the respiratory flow sensor (1) is inserted into the line at the endotracheal tube of the patient.

4. Apparatus of claim 1 characterized in that the CO₂ sensor (3) is an infrared sensor.

5. Apparatus of claim 4 characterized in that the infrared sensor is positioned in a CO₂ cuvet.

6. Apparatus of claim 4 characterized in that the infrared sensor is a mainstream or a sidestream sensor.