Episode 26: When Oxygen Becomes the Problem — Hyperoxia, Oxidative Injury, and Smarter Oxygen Targets

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In this episode, Dr. Lance Wheeler, DVM, DACVECC tackles the therapy we reach for most reflexively and titrate least carefully - oxygen, and what happens when the dose we give exceeds the dose the patient actually needs. Drawing from Chapter 8 of Small Animal Critical Care Medicine (3rd edition) by Duana McBride, and weaving in the 2023 New England Journal of Medicine review "Oxygen Therapy Part 2 - Indications and Toxicity" by Wemple et al., Lance reframes oxygen as a dose-dependent drug rather than a benign intervention and walks through a practical, structured framework for recognizing and avoiding oxidative harm: how 90 to 95 percent of oxygen is safely reduced to water while roughly 5 percent forms reactive oxygen and nitrogen species, the superoxide to hydrogen peroxide cascade and the Fenton, myeloperoxidase, and peroxynitrite pathways branching off it, how lipid peroxidation and DAMP release turn oxidative injury into a self-amplifying inflammatory cycle, and why the xanthine oxidoreductase system fires within 10 to 30 seconds of reperfusion. He then moves into the organ-by-organ consequences and the numbers that actually change bedside decisions, including absorption atelectasis and surfactant impairment in the lung, hyperoxic vasoconstriction and falling cardiac output, cerebral blood flow and traumatic brain injury, ventilated targets of SpO2 88 to 92 percent and PaO2 55 to 80 mm Hg, the FiO2 0.5 anchor below which clinical pulmonary oxygen toxicity is generally absent, hyperbaric oxygen therapy at 1.5 to 3.0 atmospheres absolute and its CNS toxicity risk, and where antioxidants genuinely fit. Along the way, he integrates the veterinary evidence, including 2021-2025 studies on hyperbaric oxygen adverse events across 2,792 treatment sessions, dietary antioxidants in dogs and cats, and N-acetylcysteine in Babesia gibsoni infection, and closes with a high-yield rapid-fire board review covering every key number worth memorizing.

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