Compliance of the respiratory system as a predictor for successful extubation in very-low-birth-weight infants recovering from respiratory distress syndrome

J Smith, C H Pieper, D Maree, R P Gie
South African Medical Journal 1999, 89 (10): 1097-102

OBJECTIVE: To develop additional criteria to predict for successful extubation of very-low-birth-weight infants recovering from respiratory distress syndrome.

DESIGN: Prospective study.

SETTING: Neonatal intensive care unit at a university teaching hospital.

INTERVENTIONS: Infants ready for extubation according to clinical, ventilatory and blood gas criteria were studied. Before extubation, tidal volume (Vt), minute ventilation, respiratory rate/Vt and mean inspiratory flow were measured during two different ventilatory settings: (i) during intermittent mandatory ventilation (IMV); and (ii) while breathing spontaneously with endotracheal continuous positive airway pressure (CPAP). Tidal volume was obtained through electronically integrated flow measured by a hot-wire anemometer. Total respiratory compliance (Crs) was determined during IMV and was derived from the formula Vt/PIP-PEEP, where the difference between peak inspiratory pressure (PIP) and positive end-expiratory pressure (PEEP) represented the ventilator inflation pressure.

MEASUREMENTS AND MAIN RESULTS: Each of 49 infants was studied once before extubation. 33 infants (67%) were successfully extubated and 16 (32.6%) required reintubation. Infants in the success and failure groups were matched for gestation, post-conceptional age, study weight and methylxanthine therapy at the time of study. Successful extubation was associated with a higher mean absolute Crs value (ml/cm H2O) specific Crs value (standardised for body length; ml/cm H2O/cm) compared with infants in whom extubation failed (0.67 v. 0.46; P = 0.01 and 0.018 v. 0.014; P = 0.03, respectively). Analysis of ROC curves detected thresholds for Crs (0.5 ml/cm H2O) and Vt (7 ml) for predicting successful extubation. An absolute Crs value 0.5 ml/cm H2O or more improved the likelihood of successful extubation when compared with clinical/ventilator and blood gas criteria. The likelihood of successful extubation was 81% if the Crs value was > or = 0.5 ml/cm H2O. A tidal volume of 7 ml or more was less sensitive in contributing to successful extubation (sensitivity 69%). The major causes for extubation failure included atelectasis (diffuse and/or localised) and the presence of a patent ductus arteriosus.

CONCLUSIONS: In addition to following very precise ventilatory criteria for extubation, we found that bedside measurement of total respiratory system compliance added to the likelihood of extubation success in infants recovering from respiratory distress syndrome. Prospective studies are needed to validate the findings of this study.

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