There's a lot of variation and not tons of data looking at readmission rates and criteria, but most places (including my ER) are using an asthma pathway to aid in management both in the ER and in patient (maybe you already are too). A score can be useful in looking whether to discharge the patient. Here's a link to the
AAP article regarding pathways.
An example of a pathway scoring sheet is
here (check the bottom of the page). And here's a reasonable
decision making tree that leaves you with a firm endpoint for discharge. This is
another from the Navy. Your best bet may be to sit down with some pediatricians or pulmonologists at your hospital and develop one of these trees that is acceptable in the ED setting.
Be warned that the pathway can be misleading and make patients seem better or worse than than their score may indictate. If you give someone enough albuterol, they'll eventually VQ mismatch and have artificially lower sats by pulse ox. The number doesn't bother me if they're otherwise doing well. In other words they're useful as a guideline but be sure to treat the patient and not a number. That site also mentions getting a blood gas if they're getting sicker, and I generally recommend against that on the idea that you're better off not knowing.
My personal criteria for discharge once admitted tends to encompass several things. No retractions or other signs of respiratory distress. Off of O2, q4 bronchodilators. I'm assuming that they'll have received oral steroids by now and will continue to do so for a total of 5 days (also note that after an initial dose of 2 mg/kg or oral steroids, they can go home on 1mg/kg for 4 more days). PFTs are less helpful to me, especially in the younger patients, say less than 5 years, who may not be able to give the necessary effort to make the test accurate.
In the ER setting, if the child has received a few treatments, early oral steroids, and has no symptoms at all after an hour or so, I'm okay to send them out as long as their parent can give q4 treatments at home. They may have a little wheeze, but how much I'm okay with depends on how they look (some may disagree with that). Needing magnesium, IV steroids or continuous bronchodiator means all bets are off though.
Historis of prematurity, chronic lung disease or previous intubations may change your criteria. And the pathway above is only for kids over 2 years of age. Below that it's very individualized.
Don't know if that helps or not, but it's generally how I handle things in the ER.
