I'm a soon to be PGY3 who is planning on a career in pulmonary/critical care. What you need to know depends on what the level of expectations are during your rotation. For new interns, the most important areas to feel somewhat familiar with prior to your start in the MICU are:
1. Sepsis and its resuscitation -> fluids, initial pressor choice and when to initiate a 2nd, when to consider PRBC transfusions, when to consider dobutamine, when to consider steroids, when to consider activated protein C
2. Sepsis and its source -> how to investigate for sources, what to culture, what emperic coverage should you initiate, does your hospital have an antibiotic algorhythm or not, etc
3. Hypercarbic Respiratory Failure -> what are its causes, how do you treat it, RR and Vt and how to approach a vent, non-invasive ventilation choices
4. Hypoxic Respiratory Failure -> causes, approaches, non-invasive and invasive vent, role of PEEP and FiO2
5. Sedation and Analgesia in the ICU -> get a handle on what your ICU likes to use: propofol, versed, fentanyl, ativan, etc; daily interruption of sedation for spontaneous ventilation trials
6. Mechanical Ventilation: what are plateau pressures, peak pressures, auto-Peep, bucking the vent, etc
7. Decompensated Cirrhosis: severe encephalopathy, variceal bleeding, sbp, hepatorenal syndrome, hepatopulmonary syndrome, portopulmonary HTN
8. Fulminant Hepatic Failure: what's the differential, what initial labs should you send, what to watch for clinically
8. DIC - ddx and treatment
9. Prophylaxis: DVT, GI, Catheter related infections, Delirium, myopathy, etc
there's lots more. Personally, I think the ICU is a great place to start. You'll get your jitters out early and will be more comfortable with sick patients early in your intern year. It's a great place to practice a lot of internal medicine, without the pain of working your ass of to place someone. Have a great time!