A decrease in blood glucose levels (BGL) during hyperbaric oxygen treatment (HBOT) is a well-recognised phenomenon, but studies of this are limited and inconclusive. This study evaluated the effect of HBOT on BGL in patients with diabetes mellitus (DM), traumatic brain injury (TBI) or stroke and healthy volunteers in a prospective, open, controlled trial. Thirty-nine participants were enrolled and evaluated twice: once during HBOT (90 minutes at 203 kPa), and once during a control session on normobaric air. Sessions were held up to two weeks apart and participants were instructed to eat the same diet. BGL was measured before, during and at the completion of each session. For the whole study group, there was a small but statistically significant decrease in BGL in both the HBOT (7.27 ± 3.66 mmol⁻¹ before to 6.71 ± 3.88 mmol ⁻¹ after, P = 0.037) and control (air) sessions (7.43 ± 3.49 mmol L⁻¹ before to 6.71 ± 3.77 mmol L⁻¹ after, P = 0.004). This fall did not differ between the two conditions (P = 0.59). Examining the three groups separately, BGL fell in all three subgroups, but this fall was only statistically significant for the air session in the diabetic group. There were no statistically significant differences in the BGL reduction when HBOT was compared to normobaric air in any of the three subgroups. BGL may decrease during HBOT and accordingly it should be monitored before entering the chamber. However, this decrease in BGL should probably not be attributed to the hyperbaric environment per se.

Peleg, Fishlev, Bechor, Bergan, Friedman, Koren, Tirosh, Efrati, (2013). Effects of hyperbaric oxygen on blood glucose levels in patients with diabetes mellitus, stroke or traumatic brain injury and healthy volunteers: a prospective, crossover, controlled trial. Diving and hyperbaric medicine, 2013 Dec;43(4):218-21. https://www.ncbi.nlm.nih.gov/pubmed/24510327