Decompression Illness (DCI) Explained
Decompression illness occurs due to the accumulation of inert nitrogen gas accumulated during scuba diving or escaped gas due to a rapid ascent. When these bubbles affect the inner ear then it is termed an audio-vestibular or inner ear decompression illness (IEDCS).
The exact mechanism of this injury is poorly understood but the majority of divers experience vestibular symptoms with a few experiencing cochlear symptoms as well. Time of onset is usually 45-60 minutes after the dive, but decompression illness can present up to 72 hours after surfacing from a dive. Severity of symptoms can vary from a feeling of imbalance to severe vertigo.
In the acute setting it is important that the diver is seen by a dive doctor for recompression therapy as quickly as possible to minimise any damage caused by the nitrogen bubbles. IEDCS can be particularly resistant to recompression therapy so several repeat treatments may be required. The diver may have not had any vestibular rehabilitation during this time or guidance on how to cope with their symptoms.
IEDCS symptoms do overlap with inner ear barotrauma (perilymphatic fistula) caused by forcefully clearing the ears during diving. The HOOYAH criteria can be used to distinguish between the two with onset during the dive, evidence of barotrauma on otoscopic examination, and cochlear involvement pointing towards an inner ear barotrauma rather than IEDCS:
| HOOYAH criteria | Typical in IEBt | Typical in inner ear DCS | |
|---|---|---|---|
| H | Hard to clear | Present on descent or ascent; forceful Valsalva | Difficulty clearing not associated with inner ear DCS |
| O | Onset of symptoms | May occur on decent, ascent or on surface after diving | May occur on ascent (technical diving) or on surface after diving |
| O | Otoscopic examination | Association with MEBt | Normal otoscopic exam |
| Y | Your dive profile | profile with no/low risk of DCS; fast ascent or descent | Decompression diving; missed decompression stops; repetitive dives; any dive profile with risks for DCS |
| A | Additional symptoms | Isolated inner ear | Association with other DCS symptoms |
| H | Hearing | Very common; high frequency loss; fluctuating hearing loss | Vestibular symptoms more common; often right-sided symptoms |
Divers need to be seen by a dive doctor before they can return to diving after IEDCS, please seen the ‘Fitness to Dive Advice’ below.