FACTORS AFFECTING LUNG VOLUME IN POST EXTUBATED NEONATES

Abstract

Extubated neonates previously treated with endotracheal continuous positive airway pressure (CPAP) maintain arterial oxygen tension (PaO₂) and functional residual capacity (FRC) equivalent to values at 2-3 cm CPAP without alteration in inspired oxygen concentration. To determine the factors that maintain PaO2 and FRC after extubation we studied arterial blood gases, lung mechanics, and FRC in 15 neonates weighing 1.4 to 4.4 kg. Intraesophageal pressure, air flow, and tidal volume provided for calculation of lung compliance (C_L), and lung inspiratory (RI) and expiratory (RE) resistance. Following extubation at zero CPAP, increases occurred in mean (± SEM) PaO2 from 59.3 (± 5.8) to 79.5 (± 4.0) mm Hg (P<0.05); FRC from 53.9 (± 6.0) to 67.3 (± 10.0) ml; RE from 148.0 (± 17.3) to 167.5 (± 25.7) cm H₂O/L/second, and CL from 1.70 (± 0.33) to 2.09 (± 0.4) ml/cm H2O. I:E ratio decreased from 0.95 (± 0.05) at zero CPAP to 0.83 (± 0.07) after extubation (P<0.05). A significant correlation existed between FRC and expiratory resistance for all patients (P<0.01). No significant alterations occurred in PaCO₂, base excess, minute ventilation, tidal volume, respiratory rate and heart rate. The changes in FRC with changes in expiratory resistance after extubation indicate that upper airway resistance, possibly at the laryngeal level may have a major role in maintenance of an adequate FRC after extubation.

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