Correlación entre el volumen tidal y la tasa de aclaramiento de pCO2 en los pacientes sometidos a ventilación mecánica no invasiva

Resumen

OBJECTIVE. To analyze the relation between tidal volume (Vt) and alveolar ventilation measured by changes in Pco2 in patients on noninvasive mechanical ventilation (NIV). METHODS. Prospective observational study of patients treated in the emergency department of Hospital General Universitario Reina Sofia. We recruited patients with hypercapnic respiratory insufficiency (indicated by a ratio of Pco2 to fraction of inspired oxygen [Fio2] < 300, pH < 7.35, and Pco2 > 45 mmHg) for whom NIV was indicated. Variables were recorded at the start of NIV and after 1 and 3 hours. RESULTS. Ninety-two patients with a mean (SD) age of 77.67 (10.86) years were included. We observed significant decreases in Pco2 levels over time, from 72.8 (15.06) mmHg at baseline to 68.1 (18.9) mmHg at 1 hour and to 66.4 (17.45) mmHg at 3 hours (P = .001). Mean Pco2 clearance went from 4.73 (12.4) mmHg/h at 1 hour to 1.68 (8.4) mmHg/h at 3 hours. Vt increased from 400.64 (143.22) mL at 1 hour to 430.81 (156.27) mL at 3 hours. The relation between the Vt calculated per ideal body weight (IBW) and Pco2 at 1 hour was significant at 0.309 (P = .003). Initial Fio2, initial expiratory positive airway pressure, and Vt per IBW at 1 hour were significant predictors according to logistic log regression (R2, 0.458; P < .001). CONCLUSIONS. The increase in Vt per IBW in patients with acute hypercapnic respiratory failure under NIV shows a weak to moderate positive correlation with alveolar ventilation measured by means of Pco2 clearance.