HY lecture notes:
Pericardial effusion + cardiac tamponade on ECG –> “electrical alternans” or “alternating amplitudes of QRS complexes.”
Cardiac tamponade is merely a pericardial effusion that has hemodynamic decompensation (low BP).
Cardiac tamponade always presents with Beck triad in questions –> JVD, hypotension, muffled heart sounds.
The acuteness of fluid accumulation is what determines whether a fluid collection around the heart is a tamponade or not. For instance, a stab wound or LV free-wall rupture (post-MI) can cause a low-volume accumulation of blood around the heart that is super-fast and hence can cause decompensation (tamponade), whereas, e.g., malignancy (lymphoma or breast cancer) could cause a slow-accumulating chylous or serosanguinous effusion that could be large volume but doesn’t cause tamponade.
Tx for effusions/tamponade = do echo first, then pericardiocentesis or pericardial window –> student says “wtf? No way that’s right. Pericardiocentesis or pericardial window is definitely the first answer.” It’s not. This is on one of the 2CK NBME forms (I think surgery), where they had pericardiocentesis or echo, and echo was next best step for tamponade. Apparently you have to view the fluid around the heart first, then do the intervention.
USMLE won’t put both pericardiocentesis and pericardial window as two separate answers for the intervention; it will be one or the other. On NBME 8 for 2CK pericardial window was an answer, but pretty much any other Q I’ve seen has been pericardiocentesis.
Acid-base disturbance in PE –> respiratory alkalosis –> low O2, low CO2, high pH, normal bicarb –> O2 diffuses slowly; CO2 diffuses quickly; so you require healthy lungs to get O2 in, whereas CO2 can adequately get out despite decreased perfusion (PE) or increased secretions/bronchoconstriction (asthma; acid-base disturbance is the same acutely). High RR means CO2 is low. Bicarb is normal because it’s too acute to change (requires minimum 12-24 hours to go down).
For any type of shock, USMLE wants you to know you can get lactic acidosis causing low bicarb. Super HY. Once again, can be any type of shock. If you see low bicarb/pH, that’s why –> decreased perfusion to vital organs –> increased ischemia –> increased anaerobic respiration –> lactic acid production.
Also, don’t pigeon-hole findings in vignettes. For instance, there’s a Q on one of the NBMEs where they give obvious septic shock (old guy has catheter in + fever + high leukocytes + low BP), but they say his extremities are cold and clammy. Answer was septic shock, not hypovolemic shock. Student says, “Wait, why the fuck is he cold and clammy then?” Yeah, weird. But this is my point about not pigeon-holing things.
After ABCs (airway, breathing, circulation), first answer is generally just giving simple fluids (normal saline; 0.9% NaCl or Ringer lactate).
But shock-specific drugs:
Anaphylactic –> IM epinephrine
Septic –> Norepinpehrine
Cardiogenic –> Dobutamine (beta-1 agonist) or Dopamine
Cardiogenic shock –> most important parameter is high PCWP (pulmonary capillary wedge pressure). If all else fails, don’t forget that for shock for the USMLE.
Cardiogenic shock: low VR, low CO, high TPR, high PCWP –> HR can be high or low –> bottom line is your heart can’t pump –> cardiogenic shock is the answer after an MI. It can sometimes occur after sepsis –> the way to differentiate is they’ll say “hazy lung fields and dilated heart” in the setting of sepsis, and the answer is dobutamine or dopamine.
Hypovolemic shock: low VR, low CO, high TPR, low PCWP
Anaphylactic and septic shock: high VR, high CO, low TPR, normal PCWP
Neurogenic shock: low VR, low CO, low TPR, normal PCWP
