Variable ventilation has been shown to improve lung function and reduce lung damage as well as inflammation in different models of the acute respiratory distress syndrome. Also, variable ventilation is able to recruit lungs. The present study will investigate whether variable as compared to non-variable ventilation improves post-operative lung function and reduces systemic inflammation in patients submitted to open abdominal surgery.

Inclusion Criteria:

• elective open abdominal surgery
• ASA classification 2-3
• age between 18 und 85 yrs
• expected duration of surgery > 3 h
• expected extubation in the operation room
• written informed consent

Exclusion Criteria:

• chronic lung disease (except to COPD stadium I and II, and asthma)

• Body Mass Index (BMI) > 40

• allergy to one of the drugs to be used for general anesthesia

• participation in another interventional trial within 4 weeks before enrollment

• addiction or any other disease that may interfere with the capacity of giving informed consent

• pregnant or breastfeeding women

• women in reproductive age, except to those who fulfill one of the following:

  • post-menopause (12 months natural amenorrhoea, or 6 months amenorrhoea and serum FSH > 40 mlU/ml
  • post-operative (6 weeks after two-sided ovariectomy)
  • routine and correct use of anticonceptional methods with failure rate < 1 % per year
  • sexually not active
  • vasectomy of the partner

• indication of low compliance with the protocol

• contraindication for MRI examination