Generalised Seizure in the Inside Attendant at 2.4 ATA

Inside the chamber (attendant or a trained patient, guided by the tender)

1. Remove the oxygen hood and place the attendant on air - either chamber air or a built-in breathing system (BIBS) supplied with air. This stops the oxygen exposure immediately and allows carbon dioxide to be exhaled.
2. Protect the head, loosen anything around the neck, position him to drain the mouth and prevent aspiration, and suction if available. Do not forcibly restrain the limbs.
3. Watch the airway and breathing continuously. If breathing stops, ventilate with air via the BIBS mask and bag, not with oxygen - the oxygen dose is the suspected cause.
4. Do not start decompression while the airway is unprotected or the convulsion is ongoing.

Outside the chamber

• Call the physician and tell him depth, time, gas, the nature and duration of the seizure, and current status.
• Call the stand-by diver and brief him for a possible assistance lock-in.
• Prepare to abort the treatment and have the ambulance on standby; check the oxygen analyser, the CO2 absorbent and the BIBS supply.

Reasoning for the first three

• Removing the oxygen removes the provoking agent and is the only intervention that changes the dose.
• At 2.4 ATA a DMT breathing 100% oxygen has a pulmonary oxygen partial pressure near 2.4 ATA, well into the range where central nervous system toxicity occurs; a convulsion at 32 minutes is the expected presentation.
• Decompressing a convulsing or recently convulsed patient risks pulmonary barotrauma and arterial gas embolism from a closed glottis, and risks aspirating blood and vomit during expansion - so the airway comes before the ascent.

Response: CNS oxygen toxicity is the leading diagnosis but it is not yet a diagnosis of exclusion. Before accepting it, consider hypoglycaemia, hypercapnia from a faulty hood, exhausted CO2 absorbent or poor fresh-gas flow, and a first epileptic seizure. These change management.

Immediate plan

• Check a capillary glucose as soon as the chamber can be opened or a sample passed; check the CO2 absorbent and hood function.
• The attendant does not breathe oxygen again today, whatever the cause.
• If he recovers fully within a few minutes with a normal neurological examination, the treatment may be completed with him on air throughout, provided the physician accepts responsibility and the tender can manage both him and the patients. Shorten the patients' oxygen periods and lengthen the air breaks for the remainder.
• If there is any persisting confusion, focal deficit, or a second seizure, abort the treatment: ascend at the normal controlled rate to the first stop and complete the required decompression, with the attendant on air, and arrange transfer for medical assessment.
• The stand-by diver should be called in if the tender needs help managing the chamber.

Decompression: he must still complete his decompression obligation for 2.4 ATA. Do not surface him rapidly in an attempt to get him to hospital - the risk of arterial gas embolism outweighs the speed advantage. Plan the ascent, complete the stops, then evacuate.

Reporting and investigation

• Complete an incident report and notify the medical director, the facility safety officer and the chamber's appointed doctor the same day. Record depth, times, gases, PO2, air-break schedule, analyser readings, absorbent status and the seizure timeline.
• Arrange medical review of the attendant: glucose, electrolytes, ECG, neurological examination, and a decision on whether an epilepsy work-up is needed. He should not return to chamber duty until reviewed.
• Investigate the root cause. An inside attendant breathing 100% oxygen for 32 minutes at 2.4 ATA is an avoidable high-dose exposure in most protocols; attendants normally breathe air (or chamber atmosphere) and receive oxygen only if there is a specific reason, with air breaks. This is a supervision and protocol failure, not just a patient event.
• Check the competence and supervision of a tender who qualified six weeks ago; this event required rapid decisions that a new tender may not be prepared for.
• Review the treatment table, the air-break policy, the O2 analyser calibration records, and the emergency drill for an in-chamber casualty.

If a patient had seized

• Same immediate actions: remove the oxygen source, protect the airway, do not decompress during the seizure.
• A single brief generalised seizure with full recovery does not automatically end the treatment: many services complete it with the patient on air or with shortened oxygen periods and full air breaks, because aborting exposes the patient to a second ascent and loses the treatment.
• Abort if the seizure is prolonged, recurs, or leaves any residual deficit.
• Document and report identically, and review whether the patient's PO2 exposure or the treatment table contributed.