Despite mixed results in studies the guidelines from the Undersea and Hyperbaric Medical Society are liberal in their recommendations for hyperbaric treatment:
The UHMS currently recommends HBO2 treatment of individuals with serious CO poisoning, as manifest by transient or prolonged unconsciousness, abnormal neurologic signs, cardiovascular dysfunction, or severe acidosis.
UptoDate has similar recommendations and suggests cutoffs for carboxyhemoglobin levels above which hyperbaric treatment should be administered. Their suggestion is 25%, or 20% in pregnancy.
A policy statement from the American College of Emergency Physicians cites the conflicting evidence, notes that hyperbaric oxygen is a therapeutic option, and comes short of a definitive recommendation.