[The role of physiologic dead space measurement in predicting extubation success]

Dead space ventilation (Vd/Vt) is a valuable parameter which indicates the ventilated but not perfused lung areas. The normal range is between 30-50% in mechanically ventilated patients. Increased levels could be observed in many pulmonary diseases such as pulmonary embolism, acute respiratory distress syndrome and chronic obstructive pulmonary disease. Vd/Vt is also used for the prediction of extubation success and a value of < 55-60% indicates successful extubation according to several studies. The aim of this study is to evaluate the value of baseline capnographic measurements on extubation success. A total of 35 patients were included in this prospective study; and 25 (71%) of them who were extubated successfully were named as group 1 and the remaining 10 (29%) patients with extubation failure were named as group 2. When the two groups were compared, Vd/Vt value, measured at the first 24 hours of hospitalization, was found to be higher in group 2 (0.66 vs. 0.54, p< 0.05). The sensitivity, specificity, positive predictive value, negative predictive value and accuracy of baseline Vd/Vt ≥ 0.60 for predicting extubation failure according to ROC curve were 70%, 72%, 58%, 81% and 71%, respectively. In conclusion, results of this study suggest that, higher Vd/Vt values measured on the first day of hospitalization may be an early predictor of extubation failure.