The stem
You are working an evening shift in an ABEM-capable tertiary hospital emergency department — CT, ultrasound, and the full laboratory are in-house. Consultants, blood bank, OR, and ICU pathways are available when requested or activated. Your next patient is Chloe Bennett, a 16-year-old girl brought in by her mother with vomiting, tiredness, and 'breathing funny.' Her vitals are on the monitor. She is slumped in the chair and answers you slowly. How would you like to begin?
The examiner asks
- Why must you know the potassium before starting insulin, and what do you do if it is low-normal?
- How do you sequence fluids and insulin in this adolescent, and what cerebral-edema warning signs stop you?
Key teaching points
- Check the potassium before you start insulin, every time. Total-body potassium is depleted in every DKA even when the serum level looks normal, and insulin drives it down further. If K is below ~3.3, hold insulin and replace potassium first — this is the single most dangerous timing error in the case.
- DKA is fluids and insulin, not bicarbonate. Reserve bicarbonate for pH < 6.9 at most; it worsens hypokalemia and causes paradoxical CSF acidosis, and the gap closes on fluids and insulin alone.
- Kussmaul breathing and a fruity breath in a thirsty, polyuric teenager is new-onset type 1 until proven otherwise. Do not mistake the tachypnea for a primary respiratory problem.
Excerpt only. The full clinical case runs live with the AI examiner and ends with a full debrief.