Deadspace to tidal volume ratio predicts successful extubation in infants and children

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Abstract
Using a modification of the Bohr equation, single-breath carbon dioxide capnography is a noninvasive technology for calculating physiologic dead space (Vd/Vt). The objective of this study was to identify a minimal Vd/Vt value for predicting successful extubation from mechanical ventilation in pediatric patients. Prospective, blinded, clinical study. Medical and surgical pediatric intensive care unit of a university hospital. Intubated children ranging in age from 1 wk to 18 yrs. None. Forty-five patients were identified by the pediatric intensive care unit clinical team as meeting criteria for extubation. Thirty minutes before the planned extubation, each patient was begun on pressure support ventilation set to deliver an exhaled tidal volume of 6 mL/kg. After 20 mins on pressure support ventilation, an arterial blood gas was obtained, Vd/Vt was calculated, and the patient was extubated. Over the next 48 hrs, the clinical team managed the patient without knowledge of the preextubation Vd/Vt value. Of the 45 patients studied, 25 had Vd/Vt ≤0.50. Of these patients, 24 of 25 (96%) were successfully extubated without needing additional ventilatory support. In an intermediate group of patients with Vd/Vt between 0.50 and 0.65, six of ten patients (60%) successfully extubated from mechanical ventilation. However, only two of ten patients (20%) with a Vd/Vt ≥0.65 were successfully extubated. Logistic regression analysis revealed a significant association between lower Vd/Vt and successful extubation. A Vd/Vt ≤0.50 reliably predicts successful extubation, whereas a Vd/Vt >0.65 identifies patients at risk for respiratory failure following extubation. There appears to be an intermediate Vd/Vt range (0.51–0.65) that is less predictive of successful extubation. Routine Vd/Vt monitoring of pediatric patients may permit earlier extubation and reduce unexpected extubation failures.