Double-Blinded, Single-Blinded, or Just Blind?

To the Editor: I read with great interest the article by Liu et al. (1). They conducted a prospective randomized study to compare the analgesic effect of preoperative lumbar intrathecal opioids (sufentanil, morphine, or a combination of the two) combined with postoperative morphine IV patient-controlled analgesia (IVPCA) versus postoperative morphine IVPCA alone after thoracotomy. I strongly support their study and believe that if the full potential of the intrathecal modality is to be realized, evaluation of opioid combinations will be required. However, it is unclear to me how their study was double-blinded. The hallmark of a double-blinded, randomized clinical trial is that both the investigator and patient are blinded as to the treatment to which each patient is randomly assigned. The authors indicated that “all physicians and nursing staff in charge of the patients during and after surgery were blinded as to treatment,” yet 20 patients randomized to the control group received only “local anesthesia of the skin over the lumbar spine.” It appears that the treating physicians and nursing staff were blinded only to the specific intrathecal opioid administered and not to the assigned randomized treatment. This is not a trivial matter. Bias is a significant methodologic limitation in many studies comparing regional and IV techniques for postoperative pain control. Bias can impact a clinical study by influencing a measurement, observation, or process. I fully understand, although do not entirely agree with, their Ethical Committee’s decision not to allow a “sham” intrathecal injection. Unfortunately, a truly double-blinded protocol was given up with that decision. The conclusions of their study remain both important and valid but would have been significantly strengthened if both patient and treating clinician were blinded as to the assigned treatment. Edward J. Norris, MD, MBA