HY lecture notes:
What is PCWP? –> equal to left atrial pressure; if you stick a catheter through the venous circulation all the way back to the right heart, and then into the pulmonary circulation, and then into a distal pulmonary capillary such that it can’t go any farther, the pressure reverberations are said to best reflect those of the left atrium. The USMLE is obsessed with PCWP. You need to know it is increased not just in cardiogenic shock, but also in left heart pathology of any kind (e.g., mitral regurg, MI, LVH, etc.).
Need to know low bicarb in patient with dehydration (or any type of shock) –> answer = lactic acidosis –> decreased perfusion to vital organs –> decreased oxygen delivery –> increased anaerobic respiration –> increased lactic acid.
Hypovolemic shock arrows: CO down, VR down, TPR up, PCWP down (or normal).
Cardiogenic shock arrows: CO down, VR down, TPR up, PCWP up.
Septic + anaphylactic shock arrows: CO up, VR up, TPR down, PCWP normal.
Neurogenic shock + adrenal crisis arrows: CO down, VR down, TPR down, PCWP normal.
First answer for Tx of shock on USMLE? –> manage ABCs, but fluids is what they want –> normal saline (0.9% NaCl, or Ringer lactate).
After fluids:
Tx of anaphylactic shock? –> IM epinephrine.
Tx of septic shock? –> norepinephrine.
Tx of cardiogenic shock? –> dopamine or dobutamine.
Difference between epinephrine and norepinephrine binding? –> Epi binds alpha 1, alpha 2, beta 1, and beta 2; NE does not bind beta 2.
What does that matter? –> beta 2 agonism opens the lungs so is ideal in anaphylaxis. In addition, beta 2 dilates peripheral arterioles, and this is not preferred in septic shock because we need strong peripheral vasoconstriction to maintain BP. Alpha 1’s main effect is to constrict vessels peripherally, so for septic shock, NE is used because we get strong alpha 1 without beta 2 – i.e., just strong vasoconstriction.
