Step 1: Pediatric ARDS is diagnosed using a combination of timing, oxygenation, imaging, and exclusion criteria rather than a single feature.
Step 2: Onset must be within 7 days of a known clinical insult, which makes option 1 a valid diagnostic criterion.
Step 3: The respiratory failure must not be fully explained by cardiac failure or fluid overload, so the clinician must assess and account for cardiac contributions such as left ventricular dysfunction. This makes options 2 and 3 part of the diagnostic evaluation.
Step 4: Because all the listed elements are part of arriving at the diagnosis, the recall key marks option 4, all of the above, as correct.