Stress test and gastric-arterial Pco2 measurement improve prediction of successful extubation

Objective: Correct early prediction of successful extubation decreases morbidity and mortality. The use of single time point measurements and surrogate markers of true extubation success limits weaning studies. Our aim was to determine whether a "stress test" improves prediction of extubation outcome and to determine the most predictive variables. Design: Observational study. Setting: Intensive care unit of a teaching hospital. Patients: A convenience sample of 68 patients judged to be ready for extubation, Interventions: We decreased pressure support from 5 to 0 cm H2O for 1 hr before extubation (stress test) while patients were on 5 cm H2O continuous positive airway pressure. Measurements and Main Results: We measured respiratory frequency, tidal volume, ratio of respiratory frequency to tidal volume (f/VT), airway occlusion pressure after onset of inspiration (P-0.1), and gastric-arterial Pco(2) (Delta P(g-a)co(2)) both on 5 cm H2O and 0 cm H2O pressure support. Then all patients were extubated, Failure of extubation was defined as reintubation within 24 hrs, Seventeen patients (25%) failed extubation, With pressure support of 5 cm H2O and continuous positive airway pressure of 5 cm H2O, xmost predictors were not different between patients who failed and patients who were successfully extubated, After the stress test, Delta P(g-a)co(2) was 2 (-5; 15) mm Hg (median; quartiles) in successfully extubated patients vs. 28 (-9; 48) in failures (p = .0003), tidal volume was 473 (387; 558) vs, 400 (323; 435) mL (p = .02), and P-0.1 was 2.8 (2; 4.1) vs. 4.1 (2.7; 5.3) mm Hg (p = .03), respectively. The stress test increased specificity of Delta P(g-a)co(2) from 0.45 to 0.94 and positive predictive value from 0.85 to 0.97. The specificity and positive predictive values for f/VT after the stress test were 0.23 and 0.78. Conclusions: A simple stress test improves prediction of extubation outcome. Delta P(g-a)co(2) has superior specificity and positive predictive value compared with other variables. The use of true clinical outcome (i.e., extubation) instead of the use of surrogate markers (e.g., tachypnea) distinguishes these results from previous studies.