Patients were ventilated with a Monsoon I or Monsoon III jet ventilator (Acutronic Medical Systems, Hirzel, Switzerland, distributed by IfM GmbH, Wettenberg, Germany) combined with a standard respirator, Evita XL (Draeger, Lübeck, Germany) or Hamilton G5 (Hamilton Medical, Bonaduz/Switzerland, distributed by Heinen & Löwenstein GmbH, Bad Ems, Germany).