COMPARISON OF 2 DIFFERENT MODES FOR NONINVASIVE MECHANICAL VENTILATION IN CHRONIC RESPIRATORY-FAILURE - VOLUME VERSES PRESSURE CONTROLLED DEVICE

The most commonly used mode of noninvasive mechanical ventilation (NMV ) is volume-controlled intermittent positive pressure ventilation (IPP V). Pressure support ventilation has recently become increasingly popu lar, but its merits have not been clearly defined. In an open, nonrand omized follow-up study, we evaluated two modes of NMV, volume-controll ed IPPV) and pressure-controlled ventilation (PCV) over 6 months in 30 consecutive patients (24 males and 6 females, aged 49+/-19 yrs) with chronic respiratory failure (CRF). The baseline assessments comprised both physiological and subjective data. In all cases, nasal IPPV was i nitially administered for 1 month, followed by a second month of nasal PCV. Thereafter, responders or nonresponders to PCV were defined acco rding to the patients' subjective symptom score and/or the recurrence of hypercapnia. During the IPPV phase, in all but two patients the sub jective and objective parameters improved significantly. During the fo llowing 1 month PCV phase, stabilization was maintained in 18 patients (''responders''), while 10 patients were defined as ''nonresponders'' . In nonresponders, hypercapnia increased (arterial carbon dioxide ten sion (Pa,CO2): 5.7+/-0.4 to 6.6+/-0.5 kPa; p<0.05) and symptom scores decreased. Compared with responders, nonresponders had a fewer mean no cturnal arterial oxygen saturation (Sa,O-2) (p<0.05) and a higher dayt ime Pa,CO2 (p<0.05) at baseline. We conclude that the majority of pati ents suffering from chronic respiratory failure who are initially sati sfactorily ventilated with intermittent positive pressure ventilation may also be adequately maintained with pressure-controlled ventilation . However, there is a subgroup with more severe chronic respiratory fa ilure at baseline, in whom pressure-controlled ventilation is inadequa te. After 4 weeks of treatment with pressure-controlled ventilation, t he subjective scores and the arterial carbon dioxide tension values re liably distinguished between long-term responders and nonresponders to pressure-controlled ventilation.