Impairment from gas narcosis when breathing air and enriched air nitrox underwater.

Background: Nitrogen (N2) in air causes cognitive impairment from gas narcosis when breathed at increased ambient pressures. This impairment might be reduced by using enriched air nitrox (EANx) mixtures, which have a higher oxygen and lower N2 content compared to air. This study aimed to investigate if divers differed in memory ability and self-assessment when breathing air and EANx30.

Methods: The effect of depth (shallow vs. deep) and breathing gas (air vs. EANx30) on memory ability and subjective ratings of impairment was compared in 20 divers.

Results: Memory performance was significantly worse in deep water (Air: M = 22.1%, SD = 21.7%; EANx30: M = 22.1%, SD = 17.2%) compared to shallow water (Air: M = 29.2%, SD = 18.3%; EANx30: M = 33.3%, SD = 18.2%), but this impairment did not differ significantly between air and EANx30. Subjective ratings of impairment increased significantly from shallow water (Air: M = 5.2, SD = 5.9; EANx30: M = 3.0, SD = 4.4) to deep water (Air: M = 36.8, SD = 25.3; EANx30: M = 24.8, SD = 16.1) when breathing both air and EANx30. However, ratings were significantly lower when breathing EANx30 compared to air when in the deep water.

Discussion: It was concluded EANx30 does not reduce narcotic impairment over air. Additionally, divers were able to make a correct global self-assessment they were impaired by narcosis, but were unable to make a finer assessment, leading them to erroneously believe that EANx30 was less narcotic than air.