What bronchiolitis symptoms should I watch out for that warrant a hospital visit?

Difficulty breathing. Bronchiolitis tends to be more severe in children under 1 year of age, babies born early, or children with underlying medical problems. One worrisome sign is retractions, when a baby is breathing so hard that s/he is pulling at her/his skin and you can see the ribs as s/he breathes. Any hard, fast breathing, flaring of the nostrils, or high fever over 3 days should also be checked by your doctor.
Respiratory Distress. Respiratory distress (shortness of breath) can be a sign that your babies bronchiolitis has gotten more serious. Typically this means that they are breathing faster (tachypneic), breathing harder and sucking in the muscles between their ribs and under their ribs (retracting), making a noise with breathing out (wheezing/grunting), and flaring their nostrils. Dehydration would be another symptom.
Respiratory distress. Working hard to breathe, breathing more than 60 times per minute, and having difficulty breathing so that she cannot comfortably feed are all signs that she should be seen as soon as possible and may need hospitalization. If she develops wheezing or retractions (sucking in under neck or between ribs when breathing in) she should also be seen as soon as possible.
Rapid breathing . Bronchiolitis is an infection of the lungs caused by several viruses, including RSV and the flu. Most cases start with mild symptoms of runny nose and cough. Symptoms to watch out for that may need a visit to the hospital or your doctor include rapid breathing, retractions (the pulling-in of belly and chest muscles in an effort to breath), and paleness or cyanosis, a bluish tinge around the lips.
Trouble breath & eat. Trouble breathing-- gasping, pulling in ribs, breathing with belly muscles, or breathing with prominent caving in of ribs, or trouble taking a breast or bottle, or lethargy should all warrant contacting the pediatrician and visiting the ER in bronchiolitis.
Baby looks too sick. If a baby just looks too sick to a parent, then it's time to go to the hospital er, by ambulance if needed. If a baby with bronchiolitis was seen by a doctor and then cleared to be observed at home, the parents can look for any signs of worsening. Examples: baby no longer a nice pink color, baby more tired as hours pass, baby has trouble eating/swallowing, baby breathing >60 times a minute. . .
Apnea; cyanosis. Apnea refers to a period where someone stops breathing entirely for 20 seconds or more. Cyanosis refers to a bluish discoloration to the skin that happens when someone is hypoxic. Both are signs of severe respiratory compromise that can occur with bronchiolitis, and need to be emergently evaluated.
Blue lips. Or tugging in between the ribs or gasping for air all warrant an emergent visit.