When the researchers assessed changes in the two measures in sequential ABGs, they found that the magnitude of change in SaO2 in the cyanotic range was substantially larger than the magnitude of change in PaO2. In serial ABGs, PaO2 and SaO2 often changed in opposite directions on the same ABGs.

This means that “a patient believed to be worsening on the basis of PaO2 may frequently have improved based on SaO2, and vice versa,” the researchers noted. Given these findings, “we believe that measured SaO2 provides a superior assessment of oxygenation in cyanotic patients,” the researchers said.

“I think it might be a good idea for experts to write a guideline around this, as this study suggests that there may be best practices in the assessment of oxygenation,” Dr. Kheir said. “One practical implication that we are considering is a change in the ‘critical lab call’ from a PaO2 threshold to an SaO2 threshold.”

The work is a “pretty elegant study” with conclusions that are not overstated, Dr. Jerry J. Zimmerman, a pediatric clinical care expert at Seattle Children’s Hospital and University of Washington School of Medicine, told Reuters Health by email.

“This is an important issue for infants with cyanotic heart disease who are frequently critically ill before surgical intervention,” said Dr. Zimmerman, who was not involved in the study.

He noted it wasn’t clear if the authors adjusted for type of hemoglobin (fetal versus adult) or just concentration of hemoglobin. “Fetal and adult hemoglobin bind oxygen quite differently, and the concentration of both are changing dynamically with normal development as well as with transfusion,” he said.

Ultimately, what is most important in terms of “assessment of oxygen” is determining if oxygen delivery is adequate, Dr. Zimmerman added.

“If oxygen delivery is inadequate, either by low arterial oxygen content or low cardiac output, an oxygen debt ensues that can be measured by increasing lactate (reflecting anaerobic metabolism) or . . . low central venous hemoglobin oxygen saturation (reflecting increased tissue oxygen saturation),” he said.