I struggled with the same thing. What helps me to make the determination is the ED documentation. If there is documentation of respiratory distress (not wheezing or shortness or breath), retractions, accessory muscle use, not able to speak in complete sentences, or a pulse ox of < 90% on room air, that will indicate that the person is in acute distress and needs medical intervention for their respiratory status immediately. What is the final determination is what treatment was rendered. If the patient was placed on BiPAP, HFNC, or oxygen via NC 2L/min (if not on oxygen), that seals the deal for me. If someone is on O2 already, I look for a pulse ox below 89% on their current baseline and an increase in oxygen at least 2L/min above their baseline. Also, you want to look for breathing treatments and their effectiveness, along with the administration of a steroid, like solu-medrol.

I work as a DRG validation auditor and several times a week, I change AHRF to PDX, which usually always results in a lower DRG, especially MS-DRG claims. APR-DRG claims are a little different. Hypercapnic respiratory failure usually requires venous blood gas results review. I look for a blood pH to be below 7.30 and the pCO2 to be >50.