Drewry 1994.

Methods	Randomized controlled trial with blinding of investigators and participants. Sealed envelope method with stratification for presentation within 48 hours or more than 48 hours.
Participants	88 patients presenting with DCI (clinical diagnosis) and requiring recompression therapy.
Interventions	Control: intravenous hydration and recompression breathing 100% oxygen at 18 msw. If 80% or more improvement after 45 minutes, then USN TT6 recompression table is completed. If less than 80% improvement, then proceeded to 30 msw breathing 50% oxygen with 50% nitrogen. Complex algorithm if there is still poor response, with maximum compression to 50 msw. Active: intravenous hydration and recompression breathing 50% oxygen and 50% helium at 18 msw. If 80% or more improvement after 45 minutes, then completed an 18 msw maximum depth table breathing heliox with no air breaks. If less than 80% improvement, then proceeded to 30 msw breathing 50% oxygen with 50% helium. Complex algorithm if there is still poor response, with maximum compression to 50msw breathing 20% oxygen and 80% helium.
Outcomes	Proportion of participants requiring second recompression due to incomplete resolution of clinical symptoms or signs.
Notes	Full trial only reported in abstract form. Not analysed by intention to treat (18 withdrawals due to protocol violations and 14 others with results not reported). The first report did not give any results.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	No details given "Patients are randomly allocated to receive either 50/50 oxygen‐helium or 100% oxygen".
Allocation concealment (selection bias)	High risk	Methods not described in detail, but delivered treatment is unbalanced between arms (31 versus 25).
Blinding (performance bias and detection bias) All outcomes	Unclear risk	Patients are randomly allocated to receive either 50/50 oxygen‐helium or 100% oxygen and compressed to 2.8 Bars abs. Treatment depth, duration and frequency is determined by symptom response. Patients are evaluated by medical examination and psychometric testing after the first treatment, before discharge, after one month and at one year.
Blinding of participants and personnel (performance bias) All outcomes	Unclear risk	Poor description of how the patient and staff were blinded to allocation.
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	No indication that outcome assessors were unaware of allocation. "Patients are evaluated by medical examination and psychometric testing after the first treatment, before discharge, after one month and at one year."
Incomplete outcome data (attrition bias) All outcomes	High risk	High loss to follow up and unexplained different accrual rate in the two arms of the trial. "88 subjects have been entered, of whom 18 failed to meet the trial criteria (due to pregnancy, wrong diagnosis or failure to follow the study protocol). The one‐year follow‐up results for 56 subjects are available."
Selective reporting (reporting bias)	Unclear risk	Insufficent information available
Other bias	Unclear risk	It is possible that patients were selectively allocated to one arm of the trial in preference (31 and 25 in the two groups).

DCI = Decompression illness
 CAGE = Cerebral arterial gas embolus
 HBOT = Hyperbaric oxygen therapy
 USN TT6 = United States Navy treatment table six = an 18 m maximum pressure table breathing 100% oxygen
 MSW = Metres of seawater = (a measure of treatment pressure, 10 msw = 1 atmosphere)