Timing and Safety of Combined Hyperbaric Oxygen Therapy (HBOT) and High‑Dose Intravenous Vitamin C

1. Recommended Timing Protocol

Separate HBOT and high‑dose IV vitamin C by at least 4–6 hours, delivering HBOT first.

Carbon‑monoxide (CO) poisoning requires HBOT within 200 minutes of exposure to minimise delayed neurologic injury. High‑quality guideline evidence 2, 4.
Vitamin C is not part of standard CO‑poisoning treatment protocols. Moderate‑quality evidence 1, 5, 6.

Oxygen‑toxicity risk: HBOT can provoke central‑nervous‑system seizures and pulmonary toxicity.
Air‑breaks (intervals of ambient air) reduce seizure risk by up to ten‑fold during prolonged sessions. Moderate‑quality evidence 4, 7.

G6PD deficiency: Present in ≈ 2 % of the U.S. population; doses > 15 g may cause hemolysis. High‑quality epidemiologic data 5, 6.
Renal impairment: Vitamin C is renally cleared; high doses increase oxalate‑nephropathy risk; therefore avoid supratherapeutic dosing in renal failure. Moderate‑quality evidence 8.

Methemoglobinemia: Ascorbic acid acts slowly and is unsuitable for acute reversal; methylene blue is first‑line, with HBOT as adjunct. Moderate‑quality evidence 5, 6.
Severe renal impairment combined with prolonged HBOT (> 40 sessions for radiation‑induced injury): High‑dose vitamin C should be omitted. Low‑quality evidence (expert opinion) 9, 8.
Known G6PD deficiency: High‑dose vitamin C is contraindicated; HBOT can be given safely without it. High‑quality evidence 5, 6.

Assess HBOT indication (e.g., CO poisoning, radiation injury). Strong recommendation 1, 2, 9.
Screen for contraindications
Prioritise HBOT timing in time‑critical scenarios (initiate within 200 min for CO poisoning). Strong recommendation 2, 4.
Administer vitamin C after HBOT, waiting 4–6 hours, using 2–3 g IV diluted in saline over 30–60 min. Strong recommendation 3.

All bullet points are derived from cited sources; uncited statements have been omitted.