Feasibility of blinding in a randomized controlled trial comparing preoperative autologous blood donation and acute normovolemic hemodilution in adult cardiac surgery

BACKGROUND: Acute normovolemic hemodilution and preoperative autologous don ation have been shown to be effective techniques for decreasing the exposur e of patients to allogeneic blood during cardiac surgery. They have not, ho wever, been compared to each other, because of perceived difficulties in bl inding in such a clinical study. The feasibility of blinding was tested in a pilot trial. STUDY DESIGN AND METHODS: Ten patients were randomly assigned to undergo pr eoperative autologous blood donation or acute normovolemic hemodilution dur ing cardiac surgery. Patients were blinded during this process by shielding of the arm and by insertion of an intravenous line in each patient. Every attempt was made to blind the clinical staff during and after surgery. The effectiveness of this blinding was determined by using a questionnaire. RESULTS: In the 10 cases, six patients, four surgeons, and one anesthetist answered, "I do not know," with respect to whether preoperative autologous blood donation had occurred. The remaining people interviewed believed the blinding was unsuccessful. However, correct answers were given by 75 percen t of the patients (95% Cl, 19-99%), 83 percent of the surgeons (95% Cl, 36- 99.6%), and 66 percent of the anesthetists (95% Cl, 29.9-92.5%). The freque ncy of correct answers did not differ significantly from the 50 percent exp ected by chance, but the Cls are wide. CONCLUSIONS: Blinding of patients and all members of the surgical team duri ng both the preoperative donation process and acute normovolemic hemodiluti on in the operating theater was successful most of the time, as the frequen cy of correct answers did not differ significantly from the 50 percent expe cted by chance. However, more accurate estimates of the success of blinding require a study with a larger sample. Ii: is possible that, with a larger series, the physician's ability to determine patient assignment would be si gnificantly better than that by chance alone.