Stress test and gastric-arterial Pco(2) measurement improve prediction of successful extubation

Objective: Correct early prediction of successful extubation decreases morb idity and mortality. The use of single time point measurements and surrogat e markers of true extubation success limits weaning studies. Our aim was to determine whether a "stress test" improves prediction of extubation outcom e 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 extuba tion, Interventions: We decreased pressure support from 5 to 0 cm H2O for 1 hr be fore extubation (stress test) while patients were on 5 cm H2O continuous po sitive airway pressure. Measurements and Main Results: We measured respiratory frequency, tidal vol ume, ratio of respiratory frequency to tidal volume (f/VT), airway occlusio n 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 al l patients were extubated, Failure of extubation was defined as reintubatio n within 24 hrs, Seventeen patients (25%) failed extubation, With pressure support of 5 cm H2O and continuous positive airway pressure of 5 cm H2O, xm ost predictors were not different between patients who failed and patients who were successfully extubated, After the stress test, Delta P(g-a)co(2) w as 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 D elta 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., extu bation) instead of the use of surrogate markers (e.g., tachypnea) distingui shes these results from previous studies.