Jansen
Successful blinding of a sham compression at 2MSW versus a compression to 15MSW
| 1. Blinding was successful in these volunteers. Their opinion of which treatment they received was not valid. 2. Blinding to treatment pressure is feasible in volunteers |
Citation/s: 1.Jansen T, Mortensen CR, TvedeMF. It is possible to perform a double-blind hyperbaric session: A double-blinded randomized trial performed on healthy volunteers. Undersea and Hyperbaric Medicine 2009;36(5):347-351
Lead author's name and fax: Jansen T. No electronic contact given (Hyperbaric Oxygen Treatment Unit, Copenhagen University Hospital, Rigshopitalet, DK-2100) Three-part Clinical Question: For volunteers with no history of compression exposure, can compression to a trivial pressure be distinguished from compression equal to a real hyperbaric treatment?
Search Terms: Placebo, compression, blinding
The Study: Double-blinded concealed randomised controlled trial with intention-to-treat. The Study Patients: Healthy adult volunteers Control group (N = 10; 9 analysed): Compression to 2 metres of sea water (MSW). Six minutes compression time, 30 minutes at pressure and then slow decompression. Noise, temperature and ventilation mimiced the true exposure. Experimental group (N = 12; 12 analysed): Compression to 15MSW (2.5 ATA) on exactly the same schedule as control.
- The Evidence:
| Outcome | Time to Outcome | Sham Group | 15MSW Group | Relative risk reduction | Absolute risk reduction | NNT |
| Correct answer when asked which exposure they received | Immediately after exposure | 0.20 | 0.67 | 234% | 0.47 | 2 |
| ^ | 95% CI: | 51% to 416% | 0.10 to 0.83 | 1 to 10 |
| Non-Event Outcomes | Time to outcome | Sham group | 15MSW group | P-value |
| Certainty of the answer '15 m' to: "Which exposure did you receive - 2MSW or 15MSW)?” VAS 0 (max uncertainty) to 10 (complete certainty) | Immediately after exposure | Median 9 (Range 5-10) | Median 10 (Range 7-10) | 0.33 |
| Certainty of the answer '2 m' to: "Which exposure did you receive, 2MSW or 15MSW)?” (VAS 0 to 10 as above) | Immediately after exposure | Not given | Median 6.4 (Range 3 to 8) |
- Comments:
1. Statistical approach was not fully explained in the paper. The authors have given us the proportion in each group that chose correctly and the confidence with which they chose. The latter does not appear to have been subject to analysis.
2. Although double-blinding success was claimed, the authors have tested blinding only in volunteers.
3. The differences in the proportion who chose correctly is statistically significant and interpreted as 'the volunteers have no valid opinion' as to their actual exposure.
4. Results may not automatically extend to patients or to monoplace chamber.
5. It is not clear from where the volunteers were drawn.
- Appraised by: Mike Bennett m.bennett@unsw.edu.au; Monday, 11 September 2017
Kill or Update By: January 2022
