Calculated risk of pulmonary and central nervous system oxygen toxicity: a toxicity index derived from the power equation.

Abstract

The risk of oxygen toxicity has become a prominent issue due to the increasingly widespread administration of hyperbaric oxygen (HBO) therapy, as well as the expansion of diving techniques to include oxygen-enriched gas mixtures and technical diving. However, current methods used to calculate the cumulative risk of oxygen toxicity during an HBO exposure i.e., the unit pulmonary toxic dose concept, and the safe boundaries for central nervous system oxygen toxicity (CNS-OT), are based on a simple linear relationship with an inspired partial pressure of oxygen (PO2) and are not supported by recent data. The power equation: Toxicity Index = t2 × PO2c, where t represents time and c represents the power term, was derived from the chemical reactions producing reactive oxygen species or reactive nitrogen species. The toxicity index was shown to have a good predictive capability using PO2 with a power c of 6.8 for CNS-OT and 4.57 for pulmonary oxygen toxicity. The pulmonary oxygen toxicity index (PO2 in atmospheres absolute, time in h) should not exceed 250. The CNS-OT index (PO2 in atmospheres absolute, time in min) should not exceed 26,108 for a 1% risk. The limited use of this toxicity index in the diving community, after more than a decade since its publication in the literature, establishes the need for a handy, user-friendly implementation of the power equation.