Master the board step 3

Master the Boards: USMLE Step 3
Basic Science Correlate
Mechanism of “Cephalization” of Flow
The bases or bottom of the lungs are generally more “full” of blood because
of gravity. As fluid builds up in the lungs, it fills the vessels from the bottom to
the top, like a cup filling with water. This moves the fluid toward the head, a
process called “cephalization.”
Mechanism of Dobutamine, Imamrinone, and Milrinone
Imamrinone and milrinone are phosphodiesterase inhibitors. They increase
contractility and decrease afterload as vasodilators, yielding much the same
effect as dobutamine. Dopamine increases contractility, but dopamine’s alpha-1
agonist activity causes vasoconstriction. This increases afterload.
Mechanism of Respiratory Alkalosis in CHF
Fluid overload causes hypoxia. Hypoxia causes hyperventilation.
Hyperventilation decreases pCO 2 . Decreased pCO 2 causes alkalosis. Hence,
hypoxia causes respiratory alkalosis.
Cases of pulmonary edema
and myocardial infarction
should be placed in the
intensive care unit.
Digoxin is never the
right answer as an acute
treatment for pulmonary
edema. Digoxin can be
used to slow the rate of
atrial fibrillation.
CCS Tip: On CCS, the order in which the tests and treatments are written on
the screen does not matter, as long as they are written at the same time. Pulmonary
edema is the perfect example of a CCS in which all the tests should be ordered at
the same time as the treatment.
Further Management
The vast majority of patients with pulmonary edema will respond to preload
reduction alone to control the acute symptoms.
In a small number of patients, acute management with a positive inotrope
will be necessary. There is no evidence that any positive inotrope or contractility
inducing agent will lower mortality. They are also the answer on a CCS case
of pulmonary edema when furosemide, oxygen, nitrates, and morphine are
given and the patient is still short of breath after the clock is moved forward.
Positive Inotropic Agents Used Intravenously in the Intensive Care Unit
Dobutamine (drug of choice)
Inamrinone
Milrinone
These are used as further management of acute
pulmonary edema cases after the clock is moved forward
30–60 minutes and there is no response
to preload reduction.
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