What Is Sudden Sensorineural Hearing Loss?
Sudden sensorineural hearing loss is defined as a loss of at least 30 dB across three or more consecutive frequencies, occurring within a period of 72 hours without an identifiable cause.
It is an otological emergency. Every delay in starting treatment reduces the likelihood of complete recovery, as the cochlear hair cells responsible for transmitting auditory information are extremely sensitive to ischaemia and metabolic stress.
The condition usually affects only one ear and is often first noticed upon waking in the morning. Patients suddenly realise that their hearing is reduced or completely absent on one side, sometimes accompanied by tinnitus, a sensation of fullness in the ear or vertigo.
The cause remains unknown in 85% to 90% of cases, which are therefore classified as idiopathic. However, possible underlying mechanisms include viral infection, vascular dysfunction and autoimmune activity.
Characteristics of Sudden Sensorineural Hearing Loss
Cochlear hair cells have exceptionally high energy requirements. They function continuously and depend on a stable supply of oxygen. Their blood supply relies entirely on the labyrinthine artery, with no collateral circulation capable of compensating for sudden ischaemia.
This anatomical characteristic explains why even a temporary disruption in blood flow may result in permanent hearing impairment.
A defining feature of sudden sensorineural hearing loss is the uncertainty surrounding spontaneous recovery. Approximately one-third of patients recover spontaneously, another third responds to treatment and the remaining third experience permanent hearing loss.
Therapeutic intervention may significantly influence the patient’s outcome, with early initiation of treatment representing the most critical determining factor.
Clinical Trials and Studies
Sudden sensorineural hearing loss is the most extensively documented otological indication for hyperbaric oxygen therapy internationally.
Randomised clinical trials, systematic reviews and meta-analyses have demonstrated significantly higher rates of hearing recovery in patients who received hyperbaric oxygen therapy as an adjunct to conventional corticosteroid treatment, compared with those who received pharmacological treatment alone.
The Undersea and Hyperbaric Medical Society (UHMS) and the European Committee for Hyperbaric Medicine (ECHM) recognize sudden sensorineural hearing loss as an approved indication, with particular emphasis on the importance of timing. Treatment initiated within the first two weeks after symptom onset is associated with significantly better outcomes, while initiation after the fourth week is considered to reduce the likelihood of a favorable response substantially.
The Role of Hyperbaric Oxygen Therapy in Sudden Sensorineural Hearing Loss
In sudden sensorineural hearing loss, hyperbaric oxygen therapy is used as an adjunct to primary treatment with systemic or intratympanic corticosteroids, never as an alternative. This combination takes advantage of their complementary mechanisms of action: corticosteroids reduce inflammation and swelling, while hyperbaric oxygen therapy directly restores oxygenation to cochlear tissue through the increased dissolution of oxygen in the fluids of the inner ear.
The increased oxygen tension within the endolymph and perilymph—the fluids surrounding the cochlear hair cells—creates more favorable conditions for the survival and reactivation of cells that are under metabolic stress but have not yet undergone irreversible injury. Each day that passes without treatment increases the risk of permanent hearing impairment.
A typical treatment course consists of 10 to 20 daily sessions during the intensive phase, always under specialist otological supervision with regular audiometric assessment.