This study evaluated the physical parameters, lactatemia, glycemia, and tolerability in canines with pyometra and sepsis who underwent hyperbaric oxygen therapy (HBO₂). Eighteen female dogs were randomly assigned to two groups: the hyperbaric group (HG) (three sequential sessions of HBO₂ [O₂ with 2 ATA for 45 min] after ovariohysterectomy) and the control group (CG) (ovariohysterectomy). Glycemia and lactatemia were measured at admission (T0), 1 hour after the end of the surgical procedure (T1), 24 hours (T2), 48 hours (T3), and 72 hours (T4) after surgery. Physical assessments were conducted at the same times, except for HG, which was assessed before and after each HBO session. There was no difference between the groups in relation to the physical parameters evaluated; however, rectal temperature was reduced in the group subjected to HBO₂. We observed an increase in lactate at T0 and T2, and a reduction at T3 and T4 in both groups. We did not identify changes in blood glucose levels. HBO₂ is acceptable and safe, but may reduce rectal temperature, although hypothermia can be expected in dogs with pyometra following the surgical procedure. Lactate may take up to 48 hours to begin, but it does not appear to be linked to prognosis or length of stay.