Passive Spirometry Used to Evaluate Pulmonary Function in Patients Receiving Mechanical Assistance to Ventilation

A method for obtaining passive expiratory volume in one second (PEV1) and passive vital capacity (PVC) is described. These measurements require no patient cooperation and can be made on patients who are receiving mechanical assistance to ventilation (MAV). The PEV1 and PEV1/PVC% correlated with FEV1 and FEV1/FVC% obtained at the same time, and also where FEV1 and FEV1 / FVC% were determined when the patients were not acutely ill. These measurements can be used to assess pulmonary function in patients who are too ill to perform active vital capacity maneuvers and are on respirators. The PEV1 and PEV1/PVC% can also be used to assess a patient's ability to stay off assisted ventilation for at least 24 hours. All seven patients in whom PEV1 was greater than 600 ml were successfully tried off MAV. Of 11 patients with a PEV1 of less than 500 ml, all except one continued to require MAV. Also, a trial of unassisted breathing was successful in 13 of the 19 patients with a PEV1/ PVC% greater than 60 percent, while it failed in all the eight patients with a PEV1/PVC% of less than 60 percent.