Chest
Volume 91, Issue 4, April 1987, Pages 496-499
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Clinical Investigations
Prediction of Successful Ventilator Weaning Using Airway Occlusion Pressure and Hypercapnic Challenge

https://doi.org/10.1378/chest.91.4.496Get rights and content

We studied eleven patients during 14 attempts at weaning from mechanical ventilation to determine whether central ventilatory drive, measured as airway occlusion pressure 0.1 s after onset of inspiration (P0.1), during spontaneous breathing before and during a brief hypercapnic challenge, could accurately predict the success or failure of the attempt. All patients were recovering from acute respiratory failure and could breathe spontaneously for 20 minutes on a T-piece but were judged clinically to be marginal weaning candidates. Minute ventilation ( V˙I) and P0.1 were measured while breathing spontaneously and were repeated during a hypercapnic challenge that raised end-tidal Pco2 approximately 10 mm Hg. Seven of the 14 weaning attempts were unsuccessful, requiring reinstitution of mechanical ventilation. Although the failure group had lower mean maximum inspiratory force and higher spontaneous respiratory rate, no threshold value separated the failure from the success group. Ventilation increased more during hypercapnic challenge in those patients whose weaning attempt was successful, but overlap of results between the two groups rendered this test inaccurate for predicting weaning success. In contrast, successfully weaned patients had greater augmentation of P0.1, during hypercapnia, expressed as the ratio of P0.1 during CO2-stimulated to P0.1 during baseline values, than did those who failed weaning (p<0.005). This ratio succeeded, and was thus both specific and sensitive as a predictor of successful weaning from mechanical ventilation in these patients.

Section snippets

MATERIALS AND METHODS

We selected patients recovering from acute respiratory failure of a variety of medical and surgical etiologies, who were considered on clinical grounds to be ready for a weaning trial. All were clinically stable and afebrile for at least 24 hours before the study. During a brief trial of spontaneous ventilation, each could match the minute volume that was being delivered by the mechanical ventilator. The PaO2 was at least 75 mm Hg on Flo, of 0.50 or less, and arterial pH was less than 7.55 and

RESULTS

The 11 patients studied (eight men, three women) ranged in age from 32 to 73, mean 54 years. Etiologies of acute respiratory failure were chronic obstructive pulmonary disease (three patients), adult respiratory distress syndrome (two patients), drug overdose (three patients), flail chest (two patients), and sepsis (one patient). The duration of mechanical ventilation prior to study ranged from 1 to 193 days, with a mean of 58 days. Patients 1, 2, and 3 were restudied after 17, 24, and 14

DISCUSSION

This study demonstrates that in patients with a multitude of causes of respiratory failure, central respiratory drive, as measured by P0.1, was not significantly different between those patients who succeeded and those who failed to wean from mechanical ventilation. An examination of common predictors of successful weaning failed to find a predictor that was 100 percent sensitive and specific in this heterogeneous group. Surprisingly, though, bedside measurement of P0.1 during spontaneous

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Manuscript received June 5; revision accepted September 29.

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