This study is an ancillary (add-on) study to the clinical trial entitled Red Cell Storage Duration Study (RECESS), which has clinicaltrials.gov identifier NCT00991341. The RECESS study randomizes cardiac surgery patients to receive either red blood cell units stored for no more than 10 days, or red blood cell units stored for at least 21 days, if they need any red blood cell transfusions during their hospital stay for the surgery.

This ancillary study is entitled Impact of Blood Storage Duration on Physiologic Measures: RECESS Ancillary Physiologic Study (RECAP). The hypothesis of the RECAP study is that there will be differences between the two randomized treatment groups in how much the following measurements change, from shortly before a red blood cell transfusion to shortly after a red blood cell transfusion, and from before surgery to 24 hours after surgery:

• Oxygen saturation in the hand
• Oxygen saturation in the brain
• Blood flow in the small blood vessels under the tongue.

The RECAP study will also investigate whether changes in the measurements listed above are associated with clinical outcomes, including

• The Multi-Organ Dysfunction Score
• Death from any cause
• Major cardiac events
• Major pulmonary events

Inclusion Criteria:

• Eligible and randomized in the RECESS study (NCT00991341)
• At least 18 years old
• Willing to comply with protocol and provide written informed consent for both RECESS and RECAP
• Scheduled to undergo coronary artery bypass (CABG), valve, or combined CABG plus valve surgery

Exclusion Criteria:

• Prior randomization into the RECESS or RECAP studies
• Undergoing off-pump cardiac surgery
• Undergoing a significant concomitant surgical procedure
• Known sickle cell disease
• Participation in a clinical trial (except observational studies or RECESS) within the previous 30 days
• Received any investigational product within prior 30 days
• Not able to be randomized in RECESS

Cardiac surgery patients enrolled in the RECESS study (NCT00991341) at selected hospitals