NASAL VENTILATION IN ACUTE EXACERBATIONS OF CHRONIC OBSTRUCTIVE PULMONARY-DISEASE - EFFECT OF VENTILATOR MODE ON ARTERIAL BLOOD-GAS TENSIONS

Background - There are no controlled trials of the use of different mo des of nasal intermittent positive pressure ventilation (NIPPV) in pat ients with exacerbations of chronic obstructive pulmonary disease (COP D). This study describes the effect on blood gas tensions of four diff erent modes of nasal ventilation. Methods - Twelve patients with acute exacerbations of COPD were studied (mean (SD) FEV(1) 0.59 (0.13) 1, P aO2 (air) 5.10 (1.12) kPa, PaCO2 9.28 (1.97) kPa, pH 7.32 (0.03)). Eac h patient underwent four one-hour periods of nasal ventilation in rand omised order: (a) inspiratory pressure support 18 cm H2O; (b) pressure support 18 cm H2O + positive end expiratory pressure (PEEP) 6 cm H2O (IPAP + EPAP); (c) continuous positive airway pressure (CPAP) 8 cm H2O ; and (d) volume cycled NIPPV. Arterial blood samples were obtained be fore each period of ventilation and at one hour. Results - Pressure su pport, CPAP, and volume cycled NIPPV all produced significant improvem ents in PaO2; there was no difference between these three modes. The c hange in PaO2 with IPAP + EPAP did not reach statistical significance. None of the modes produced significant changes in mean PaCo2; patient s with higher baseline levels tended to show a rise in PaCO2 whereas t hose with lower baseline levels tended to show a fall. Conclusions - A lthough PaO2 improved in all patients there are differences in efficac y between the modes, while the changes in PaCO2 were variable. The add ition of EPAP conferred no advantage in terms of blood gas tensions.