Souday
Enriched air nitrox reduced pulmonary artery bubble counts and the rate of clinical DCS in volunteer divers.
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Clinical bottom line 1. Breathing enriched air nitrox reduced bubble counts at all time points. |
Citation/s:1.Souday V, Koning NJ, Perez B, Grelon F, Mercat A, Boer C, et al. (2016) Enriched Air Nitrox Breathing Reduces Venous Gas Bubbles after Simulated SCUBA Diving: A Double-Blind Cross-Over Randomized Trial. PLoS ONE 11(5): e0154761. https://doi.org/10.1371/journal.pone.0154761
Lead author's name and fax: Pierre Asfar piasfar@chu-angers.fr
Three-part Clinical Question:For scuba divers, does breathing enriched air nitrox, compared to air, result in a reduction in decompression stress?
Search Terms: Nitrox; bubble disease; doppler
The Study:Double-blinded randomised controlled trial with intention-to-treat.
The Study Patients: Fit qualified divers with no h/o decompression sickness and who demonstrated bubble grades 2 or above on test compression.
Control group (N = 12; 12 analysed): Air breathing for a compression to 28 metres of seawater (3.8 ATA) for 55 minutes with decompression stops at 6m and 3m. 5 minute exercise period on a static bicycle at depth.
Experimental group (N = 12; 12 analysed): As above but breathing Nitrox 36 (36% oxygen and 64% nitrogen).
The Evidence:
Outcome |
Time to Outcome |
Control dive |
EAN dive |
Relative risk reduction |
Absolute risk reduction |
NNT |
|
Minor DCS (clinical diagnosis) |
1 hour |
0.25 |
0 |
100% |
0.25 |
4 |
95% CIs: |
0.005 to 0.5 |
2 to 200 | ||||
Non-Event Outcomes |
Time to outcome/s |
Control group |
Experimental group |
P-value |
|
Bubble score (median[IQR]) |
30 minutes |
2 [1–3] |
0 [0–1] |
0.008 |
Comments:
1. Study based on the assumption that bubble numbers detected correlate with decompression stress and the chance of clinical decompression sickness.
2. All exposures took place in a hyperbaric chamber rather than immersed.
3. 47 divers had a test compression in the chamber (profile unknown) and 12 of these were selected for the study because of high bubble grades (>or= to Grade 2 - bubbles in 25 to 50% of cardiac cycles).
4. Block randomisation in groups of four and a crossover design. Divers and assessors were blinded to exposure.
5. Planned to do 17 divers but stopped at 12 as they found a difference in the primary outcome.
6. Bubble numbers reduced at all time points after the dive (30, 60, 90 minutes) when breathing Nitrox.
7. 14 total DCS incidences including the initial selection dives. Mostly cutaneous itching. Appraised by:Mike Bennett m.bennett@unsw.edu.au; Saturday, 10 April 2021
Kill or Update By: April 2023
