2-month-old presenting to the ER with tachycardia, fussy, unable to eat

Case

Hi, I’m calling from the Children’s Emergency Room and I have a 6-week-old female that is having tachycardia at a rate of 210 beats per minute (bpm). Baby looks OK but is breathing a little fast and appears a bit mottled. The mother reports that she has not been eating all that well over the past 48 hours and has been fussy. She’s only had 3–4 wet diapers over the past 24 hours. There have been some sick contacts at home but not unexpected since we’re in the winter season. I’m thinking about giving a fluid bolus but wanted to check with you first. Thoughts?