The purpose of this study is to determine whether breathing in helium reduces indications of injury to the skeletal muscle seen in blood tests after knee replacement surgery.

The ability to reduce the risk of skeletal muscle injury may help improve patient safety by providing protection to the area of the body having its blood supply interrupted during a particular surgery.

During hospitalization, beginning the day after surgery, additional tests will be added to the daily standard of care blood samples. When daily blood samples are not ordered as part of a study participants care after surgery, blood samples only for the study tests, may be done.

Up to 60 study participants will be selected to be in one of two possible groups.

After hospital discharge the study participants physical therapist will be contacted for copies of the notes and reports about the participants progress in physical therapy. This information will be used to evaluate if the different breathing gases have any impact on how quickly people recover after surgery.

Inclusion Criteria:

• Scheduled for an elective total knee arthroplasty
• > 18 years of age
• Expected to require inhaled oxygen concentrations < 25%
• Able to provide informed consent

Exclusion Criteria:

• Expected to require inhaled oxygen concentrations > 25%
• < 18 years of age
• Member of a defined vulnerable population (e.g. pregnant, mentally handicapped, prisoners, etc.).