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Revised guideline for central nervous system oxygen toxicity exposure limits when using an inspired PO2 of 1.3 atmospheres
Joseph Hoyt1, F Gregory Murphy2, Neal W Pollock3,4, Dawn Kernagis5, Nicholas Bird6, Michael Menduno7, John Bright8, Simon J Mitchell9,10,11
1 NOAA Diving Program, National Oceanographic and Atmospheric Administration, Seattle, WA, USA
2 Navy Experimental Diving Unit, Panama City, FL, USA
3 Department of Kinesiology, Faculty of Medicine, Université Laval, Québec, Canada
4 Service de médecine hyperbare, Centre de médecine de plongée du Québec, Levis, Québec, Canada
5 DEEP Research Inc., Miami, FL, USA
6 Department of Hyperbaric Medicine, Virginia Mason Hospital, Seattle, WA, USA
7 InDEPTH Magazine, High Springs, FL, USA
8 CPC Inc., San Diego, CA, USA
9 Department of Anaesthesiology, University of Auckland, Auckland, New Zealand
10 Department of Anaesthesia, Auckland City Hospital, Auckland, New Zealand
11 Slark Hyperbaric Unit, North Shore Hospital, Auckland, New Zealand
Corresponding author: Professor Simon J Mitchell, Department of Anaesthesiology, University of Auckland, Private Bag 92019, Auckland, New Zealand
Keywords
Oxygen clock; Rebreathers; Risk; Seizures; Technical diving
Abstract
(Hoyt J, Murphy G, Pollock NW, Kernagis D, Bird N, Menduno M, Bright J, Mitchell SJ. Revised guideline for central nervous system oxygen toxicity exposure limits when using an inspired PO2 of 1.3 atmospheres. Diving and Hyperbaric Medicine. 2025 30 September;55(3):262−270. doi: 10.28920/dhm55.3.262-270. PMID: 40986922.)
Technical and scientific divers breathing gases delivering hyperbaric pressures of inspired oxygen may be at risk of developing cerebral oxygen toxicity which can manifest as a seizure with little or no warning. The principle preventative strategy is adherence to time limits based on inspired PO2 levels promulgated in 1991. These limits had their origins in US Navy studies of exposures to higher inspired PO2s than are typically utilised by modern divers. Indeed, the duration limits for inspired PO2s in the range typically utilised by technical divers (≤ 1.3–1.4 atm) have relatively little experimental provenance. Contemporary technical dives often involve decompression durations that result in breaches of these limits, and anecdotally, this common occurrence seems associated with a low risk of cerebral oxygen toxicity. A committee of experts recently sought experimental evidence that might support an adjustment to the recommended duration limits for typical technical dives. Such evidence exists only for an inspired PO2 of 1.3 atm, which is a common default in use of constant PO2 rebreather devices. The (1991) limit for a single exposure to an inspire PO2 of 1.3 atm is 180 min with a 24-hour maximum of 210 min. Recent studies provide reassurance that dives with an inspired PO2 of 1.3 atm consisting of up to 240 min of working dive activity followed by up to 240 min of resting decompression are associated with an acceptably low risk of cerebral oxygen toxicity. This recommendation was promulgated and endorsed at a recent workshop convened by the National Oceanographic and Atmospheric Administration (NOAA) involving technical and scientific divers.
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