Dynamic oxygen assessment techniques enable determination of anesthesia's impact on tissue

Tissue oxygenation is well understood to impact radiosensitivity, with reports demonstrating a significant effect of breathing condition and anesthesia type on tissue oxygenation levels and radiobiological response. However, the temporal kinetics of intracellular and extracellular oxygenation have never been quantified, on the timescale that may affect radiotherapy studies. C57BL/6 mice were anesthetized using isoflurane at various percentages or ketamine/xylazine (ket/xyl: 100/10 mg/kg) (N = 48). Skin pO₂ was measured using Oxyphor PdG4 and tracked after anesthetization began. Oxyphor data was validated with relative measurements of intracellular oxygen via protoporphyrin IX (PpIX) delayed fluorescence (DF) imaging. Ex vivo localization of both PdG4 Oxyphor and PpIX were quantified. Under all isoflurane anesthesia conditions, leg skin pO2 levels significantly increased from 12-15 mmHg at the start of anesthesia induction (4-6 minutes) to 24-27 mmHg after 10 minutes (p < 0.05). Ketamine/xylazine anesthesia led to skin pO2 maintained at 15-16 mmHg throughout the 10-minute study period (p < 0.01). An increase of pO2 in mice breathing isoflurane was demonstrated with Oxyphor and PpIX DF, indicating similar intracellular and extracellular oxygenation. These findings demonstrate the importance of routine anesthesia administration, where consistency in the timing between induction and irradiation may be crucial to minimizing variability in radiation response.