Abstract
Introduction: It is well known that non invasive ventilation in chronic respiratory diseases improves arterial blood gases by enhancing alveolar ventilation without relevant changes in ventilation-perfusion (VA/Q) relationships. (O.Diaz et al., Am J Res Crit Care 1997;156:1-6). The adequate patient-ventilator synchronism throughout the breathing cycle should be a priority to ensure appropriate alveolar ventilation.
Hypothesis: We hypothesize that Pressure Support Ventilation (PSV) may be a useful modality of non invasive ventilation in hypercapnic patients with a restrictive ventilatory defect due to Obesity Hypoventilation Syndrome (OHS).
Aims: To this end, the effects of PSV versus VSV (volume support ventilation) on pulmonary gas exchange were analyzed in twenty hospitalized patients with hypercapnic respiratory failure due to OHS (BMI: 39±3 kg/m2). Blood Gases at the time of the study (FIO2 0.21): pH (7.34±0.05), PaO2 55±10 mmHg, PaCO2 62±5 mmHg, (A-a)O2 21±7mmHg.
Methods: Pulmonary gas exchange were measured at 30' in each of the conditions: a) baseline; b)PSV (BiPAP Vision System, Respironics) or VSV (BREAS, PV) in random order; keeping FIO2 and PEEP (4cm H2O) unchanged. The ventilatory settings were established according to patient's confortability.
Results: Compared with baseline, PSV increased PaO2 (64±10 mmHg, p<0.02) and decreased PaCO2 (50±8 mmHg, p<0.01) similar to VSV (PaO2 62±12 mmHg, ns, PaCO2 52±10 mmHg, p<0.01).
Conclusions:
PSV and VSV showed a similar improvement of respiratory arterial blood gases compared with baseline.
Changes in PaO2 during PSV and VSV were explained by enhanced alveolar ventilation.
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