A true blind for subjects who receive spinal manipulation therapy

To determine if short-duration anesthesia (propofol and remifentanil) can blind subjects to the provision or withholding of spinal manipulative therapy (SMT).

Placebo control.

Day-procedure ward, University of Alberta Hospital.

Human subjects with uncomplicated low back pain (LBP) (n=6).

In each subject, propofol and remifentanil were administered intravenously. Once unconsciousness was achieved (3-5min), subjects were placed in a lateral recumbent position and then randomized to either a control group (n=3) or an experimental group (with SMT, n=3); subjects received a single SMT to the lumbar spine. Subjects were given a standardized auditory and visual cue and then allowed to recover from anesthesia in a supine position (3-5min).

Before anesthesia and 30 minutes after recovery, a blinded evaluator asked each subject to quantify their LBP by using an 11-point scale. This same evaluator then assessed the ability of each subject to recall specific memories while under presumed anesthesia including events related to treatment and specific auditory and visual cues.

In either the experimental or control group, subjects could not recall any event while under anesthesia. Some SMT subjects reported pain reduction greater than the minimally important clinical difference and greater than control subjects. No adverse events were reported.

Short-duration, low-risk general anesthesia can create effective blinding of subjects to the provision or withholding of SMT. An anesthetic blind for SMT subjects solves many, if not all, problems associated with prior SMT blinding strategies. Although further studies are needed to refine this technique, the potential now exists to conduct the first placebo-controlled randomized controlled trial to assess SMT efficacy.