Method of maintaining constant arterial PCO2 and measurement of anatomic and alveolar dead space

• US 20020185129A1
• Filed: 04/30/2002
• Published: 12/12/2002
• Est. Priority Date: 05/04/2001
• Status: Active Grant

• Current Assignee: Alex Vesely, Hiroshi Sasano, Joseph Fisher, Ronald Somogyi, Steve Iscoe
• Original Assignee: Alex Vesely, Hiroshi Sasano, Joseph Fisher, Ronald Somogyi, Steve Iscoe
• Inventors: Vesely, Alex, Fisher, Joseph, Somogyi, Ronald, Sasano, Hiroshi, Iscoe, Steve
• Granted Patent: US 6,799,570 B2
• Time in Patent Office: Days
• US Class Current: 128/203.25
• CPC Class Codes: A61B 5/0836 Measuring rate of CO2 production
• CPC Class Codes: A61B 5/087 Measuring breath flow
• CPC Class Codes: A61B 5/4821 Determining level or depth of anaesthesia A61B5/1106 takes precedence
• CPC Class Codes: A61M 16/12 by mixing different gases
• CPC Class Codes: A61M 16/208 Non-controlled one-way valves, e.g. exhalation, check, pop-off non-rebreathing valves
• CPC Class Codes: A61M 2202/0007 introduced into the body
• CPC Class Codes: A61M 2202/0225 Carbon oxides, e.g. Carbon dioxide
• CPC Class Codes: Y10S 128/914 Rebreathing apparatus for increasing carbon dioxide content in inhaled gas

Abstract

A method to maintain isocapnia for a subject. A fresh gas is provided to the subject when the subject breathes at a rate less than or equal to the fresh gas flowing to the subject. The fresh gas flow equal to a baseline minute ventilation minus a dead space gas ventilation of the subject contains a physiological insignificant amount of CO₂. An additional reserve gas is provided to the subject when the subject breathes at a rate more than the fresh gas flowing to the subject. The reserve gas has a partial pressure of carbon dioxide equal to an arterial partial pressure of carbon dioxide of the subject. A breathing circuit is applied to the method to maintain isocapnia for a subject. The breathing circuit has an exit port, a non-rebreathing valve, a source of fresh gas, a fresh gas reservoir and a reserve gas supply.

Claims

1. A method of maintain PCO₂ constant, comprising setting a fresh gas flow equal to baseline minute ventilation minus anatomical dead space ventilation.

2. A method of maintain PCO₂ constant, comprising providing a reserve gas with a PCO₂ substantially equal to arterial PCO₂.

3. A method of setting up a fresh gas flow equal to baseline minute ventilation minus anatomical dead space ventilation, comprising:

having a subject breathing on a breathing circuit;

providing a fresh gas flow equal to a baseline minute ventilation of the subject;

gradually decreasing the fresh gas flow provided to the breathing circuit with a decrement small enough to avoid affecting an arterial PCO₂ of the subject; and

obtaining an inflection point at which the arterial PCO₂ suddenly rises exponential, and the inflection point reflecting the fresh gas flow equal to baseline minute ventilation minus anatomical dead space.

4. The method of claim 3, further comprising a step of having the subject breathing on a rebreathing circuit.

5. The method of claim 3, further comprising a step of having the subject breathing on a non-rebreathing circuit.

6. The method of claim 3, further comprising a step of having the subject breathing on a portable breathing circuit.

7. The method of claim 3, further comprising a step of gradually increasing the fresh gas flow with a decrement of about 200 mL/minute.

8. The method of claim 3, further comprising a step of obtaining the anatomical dead space ventilation by subtracting the baseline minute ventilation with the fresh gas flow at the inflection point.

9. A method to maintain isocapnia for a subject, comprising:

providing the subject a fresh gas to the subject when the subject breathes at a rate less than or equal to the fresh gas flowing to the subject, wherein fresh gas flow is equal to a baseline minute ventilation minus a dead space gas ventilation of the subject and providing the subject the fresh gas and a reserve gas when the subject breathes at a rate more than the fresh gas flowing to the subject.

10. The method of claim 9, wherein the reserve gas has a partial pressure of carbon dioxide equal to an arterial partial pressure of carbon dioxide of the subject.

11. The method of claim 9, wherein the fresh gas provided to the subject contains a physiologically insignificant amount of CO₂.

13. The isocapnia circuit of claim 12, wherein the source of gas, the fresh gas reservoir and the reserve gas supply are disposed on a side of the non-rebreathing valve remote from the exit port.

14. The isocapnia circuit of claim 12, further comprises a pressure relief in communication with the source of fresh gas and the fresh gas reservoir.

15. The isocapnia circuit of claim 12, wherein the reserve gas supply comprises a demand valve regulator which opens when an additional gas is required by the patient, and closes when the additional gas is not required.

12. An isocapnia circuit, comprising:

an exit port, from which gases exit from the isocapnia circuit to a patient;

a non-rebreathing valve, permitting gases delivered to the exit port for the patient, but preventing gases from passing therethrough to the isocapnia circuit;

a source of fresh gas, containing a physiologically insignificant amount of CO₂ in communication with the non-breathing valve to be delivered to the patient;

a fresh gas reservoir, in communication with the source of fresh gas flow for receiving excess fresh gas not breathed by the patient; and

a reserve gas supply, containing CO₂ having a PCO₂ approximately equal to PCO₂ in the arterial blood of the patient provided to the patient to make up amount of gas required by the patient for breathing that is not fulfilled from the gases delivered from the source of fresh gas and the fresh gas reservoir.