Apparatus and Method for Identifying FRC and PEEP Characteristics

A method for determining the extent to which a change in the functional residual capacity of a patient, occurring responsive to an alteration in a PEEP applied to the patient, results from recruitment/de-recruitment of lung volume, said method comprising the steps of

• (a) providing breathing gases to the patient from a source of breathing gases during inspiration and allowing the removal of breathing gases from the patient during expiration;
• (b) applying a PEEP to the lungs of the patient at the end of expiration;
• (c) establishing an initial level of PEEP for the patient;
• (d) determining the functional residual capacity of the patient at the initial PEEP level;
• (e) altering the PEEP from the initial level to a higher or lower level;
• (f) determining the functional residual capacity of the patient at the altered PEEP level;
• (g) obtaining the relationship between lung gas pressures and breathing gas volumes during inspiration and expiration by the patient with the lower of the initial or altered PEEP levels applied to the patient;
• and
• (h) determining the difference in lung volume between the functional residual capacity for the higher of the initial or altered PEEP levels and the lung volume indicated by the lower PEEP level, pressure-volume relationship at a pressure corresponding to the higher PEEP level, the difference in lung volume comprising the lung volume recruited/de-recruited as a result of the alteration of the PEEP.

A ventilator for ventilating a patient and for determining the extent to which a change in the functional residual capacity of the lungs of a patient, occurring responsive to an alteration in a PEEP applied to the patient by the ventilator, results from recruitment/de-recruitment of lung volume, said ventilator comprising:

• at least one gas flow control valve in a flow path for breathing gases of the patient for establishing and altering the PEEP applied to the patient at a plurality of different levels:
• a gas analyzer measuring a compositional characteristic of the breathing gases for the patient;
• a sensor measuring a quantitative characteristic of the breathing gases of the patient;
• central processing unit means coupled to said at least one gas flow control valve for operating same to establish a first level of PEEP applied to the patient and to alter the PEEP to a second level higher or lower than said first level, said central processing unit means being coupled to said gas analyzer and said sensor for determining the functional residual capacities of the patient at the differing levels of PEEP, for obtaining the relationship between lung gas pressures and breathing gas volumes during inspiration and expiration by the patient with the lower PEEP level applied to the patient, and for determining the difference in lung volume between the functional residual capacity for the higher PEEP level and the lung volume indicated by the lower PEEP level, pressure-volume relationship at a pressure corresponding to the higher PEEP level, the difference in lung volume comprising the lung volume recruited/de-recruited as a result of the alteration of the PEEP;
• and
• a display coupled to said central processing unit means and presenting the levels of PEEP applied to the patient and related recruited/de-recruited lung volumes.