Dear Sir or Madam,

Thank you for showing interest in this study.

The PROBESE trial is directed to optimize mechanical ventilation in obese patients undergoing general anesthesia for surgery. We, the trial investigators, aim at minimizing pulmonary complications after a surgical intervention.

While under anesthesia, you will not be able to breathe on your own. Instead, a machine will take over the work of breathing for you. This is called 'mechanical ventilation'. Pressurized air flows into your lungs, resulting in a breath. Then the pressure is reduced, allowing the lungs to exhale. Due to completely relaxed abdominal muscles (an effect of the anesthesia), the lung actually exhales more air than it would in an awake, non-anesthetized state. This causes parts of the lung to collapse, which in turn impedes normal lung function and can lead to complications. Obese patients have a very high risk for impaired lung function, not only during surgery, but especially in the period after the operation. The anesthesiologist can improve airflow to all parts of the lung by administering a constant positive pressure in both in- and exhalation. This positive pressure may not only improve lung function during general anesthesia, but also in the period after surgery, during your recovery. Mechanical ventilation with higher positive pressure may reduce the possibility of pulmonary complications such as pneumonia or low blood oxygen (called 'hypoxia'). This could improve your well-being after surgery as well as even shorten your hospital stay.

As of yet, a higher continuous positive pressure is not in routine clinical use because it is not known how high it actually needs to be to provide healthy, safe anesthesia. Current practice is to use a relatively low pressure, deliberately allowing parts of the lung to collapse and maintaining only a minimum of lung function. On the other hand, a higher pressure will improve the distribution of air in the lung, but may also cause blood pressure to drop. In some cases this requires extra medication.

The main objective of this trial is to find out, whether a higher continuous positive pressure during mechanical ventilation can influence lung-associated complications. We have good reason to believe that a higher pressure will not only improve lung function during surgery but also prevent complications during recovery.

First, an anesthesiologist will use special criteria to determine if you are a suitable candidate for the trial. By giving your written consent, you can enroll. Before surgery, the trial doctor will take your history and vital signs, conduct a physical examination and draw blood. After all the standard preparations have been made, general anesthesia will begin and you will receive mechanical ventilation with either a higher or lower pressure for the entire duration of the operation. You are assigned either the high or low pressure strategy by a randomizing computer algorithm - patients and doctors cannot influence this decision. Moreover - as part of the study, you will not know about the modality of ventilatory management you personally received. Directly before the end of anesthesia, the trial doctor will draw blood one more time. While you are recovering, another trial doctor will visit you every day for the first five days and on the day before your hospital discharge. The physician will also call you by telephone after at least three month after surgery. The trial has no influence on the length of your hospital stay and does not include any additional tests after you go home. Your treatment will follow international standard patient guidelines.

If you decide to take part in the trial, you will be asked to:

• Read and sign an informed consent form
• Schedule and agree to follow-up telephone call
• Answer additional questions at follow-up
• Report any problems to your treating physician

We strongly believe that mechanical ventilation with a higher continuous pressure can reduce the risk of lung-associated complications. In this respect, you will probably benefit from participation in this trial. In the event that you are randomly assigned to receive mechanical ventilation with low pressure, you will still receive the state-of-the-art care that our anesthesia teams provide on a regular basis. Regardless of the type of mechanical ventilation you receive, an added benefit of participating is the extended care and closer observation the trial provides, especially during recovery (daily visits by the trial doctor, etc.).

Mechanical ventilation with high pressure can cause temporary drops in blood pressure. This situation is easily manageable with medication. In addition, the pressure will always be adjusted if lung function worsens or blood pressure falls significantly. The recovery visits by the trial doctor do not include any invasive or painful tests. Trial-related blood tests will be drawn with routine ones whenever possible, keeping additional venipunctures at a minimum. Blood sampling always carries a small risk of infection, bleeding or nerve injury.

You DO NOT have to consent. It is your free decision whether or not to participate. If you do decide to take part, you will be asked to sign a consent form. It is important for you to understand that you may withdraw your consent at any time during the trial without stating your reasons. If you decide to withdraw your consent, or decline your consent now, this will in no way affect the care you receive from our healthcare providers.

Participation in the trial is completely voluntary. Even after you have agreed to participate, you can withdraw your consent at any time. The information collected up until the time of your withdrawal may still be used. This is important for the integrity of the trial. You can withdraw your consent at any time without negative consequences for you or the care you receive from your physician. It is important that you carefully consider all of your treatment options before giving your consent.

All research protocols that are conducted in patients are reviewed carefully by an independent research ethics committee, which aims to protect your safety, rights, well-being and dignity. This trial has been approved by the ethics committee that is responsible for your hospital.

If you decide to participate in the PROBESE trial, your medical information will be forwarded to the Coordinating Centre for Clinical Trials (CCCT) at the Medical Faculty of the Dresden University of Technology, Germany, which is coordinating the trial. However, YOUR NAME WILL NOT be reported to the coordinating center. Occasionally, staff from local regulatory authorities in your country may visit your hospital to review your records and confirm that the information being provided is correct. Physicians involved in your care will be kept fully informed, but otherwise all information about you and your treatment will remain completely confidential. We need to keep your name and address on file for the follow-up, but this information will be stored separately from your medical data. Everyone involved in the trial has a duty of confidentiality to you as a research participant.