Percutaneous dilatational tracheostomy (PDT) is becoming an accepted cost-effective alternative to surgical tracheostomy. PDT is performed by progressive dilatation of a tracheal opening placed under bronchoscopic guidance. Case reports of hypoventilation with associated hypercarbia during the performance of PDT have raised concerns about the utility of this procedure in patients in whom hypercarbia is problematic (e.g., patients with closed head injury). In a prospective cohort analysis of 11 critically ill patients, we evaluated the effect of PDT on ventilation during and after the procedure using end tidal capnography. We found that hypercarbia does not occur during or after the performance of PDT as compared to baseline levels.