The study has been in the works for more than a year but was delayed after the state Attorney General's Office halted the plan because of a conflict between state and federal research rules.

Several universities and hospitals then banded together to push for a change in the state rule that requires hospitals to gain consent from patients enrolled in clinical trials. In March, a state medical board approved a change that allows consent waivers under a narrow set of circumstances.

That cleared the way for Duke's study.

Patients who are bleeding heavily could, at random, receive the blood substitute, called PolyHeme, in the study. The substance will be potentially used on trauma victims being transported to Duke by ambulance, and then in the first 12 hours of hospitalization.

Critically injured patients typically receive a standard saline and electrolyte solution during transit. Researchers will compare the survival rates of people who receive the synthetic blood with those of patients who get standard treatment.

Because of the seriousness of their injuries, most people who are eligible for the study won't be able to give their consent.

People who wish to avoid participating in the study may do so by obtaining an "opt out" bracelet from Duke. To opt out, they should send a letter to Dr. Steven Vaslef, DUMC Box 2601, Duke University Medical Center, Durham, NC 27710, or contact Angela King at 668-8686 or king0037@@mc.duke.edu. "PolyHeme" or "Opt Out" should be written in the subject line.

To be eligible for the study, a trauma victim must be at least 18 years old, critically injured, losing a large amount of blood and in shock. Only patients who are to be transported to Duke by Durham County EMS ground ambulances will be considered for the trial.

Emergency workers completed training on how to administer PolyHeme this month.

Most ambulances do not carry blood on board because of storage, temperature and compatibility concerns, according to a Duke news release. Researchers say the blood substitute does not need to be matched by type and can deliver oxygen, unlike saline solution. It also has a longer shelf life than human blood.

Northfield Laboratories Inc. of Evanston, Ill., manufacturer of PolyHeme, is paying for the study.