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NBME 18 Answers

nbme18/Block 3/Question#45 (reveal difficulty score)
65 yo patient with lung region ...
Physiologic shunt ๐Ÿ” / ๐Ÿ“บ / ๐ŸŒณ / ๐Ÿ“–

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 +13  upvote downvote
submitted by โˆ—banana(18)

If you got all tangled up on this question like me:

anatomic dead space= conducting airways

Alveolar dead space= alveoli that are ventilated but not perfused (wiki)

physiologic dead space=anatomic dead space+ alveolar dead space

Po2: just no

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motherhen  When I get mixed up on dead space vs shunt, I anchor myself on the meaning of anatomic dead space: the parts of the airway that don't have associated blood vessels for gas exchange (nose, trachea, bronchi). From there I work backwards to what shunt means: blood vessels that don't have enough air. +1

 +4  upvote downvote
submitted by โˆ—regents(6)

Good memory tip: to remember dead space, think "dead people don't have any blood flow"--> lung areas that are NOT perfused

In this case, the lung region is well perfused. So the answer must be shunt.

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burak  what if I say "dead people don't have any air flow" ??? +4

 +0  upvote downvote
submitted by โˆ—sugaplum(487)

bnb video - ventilation and perfussion.
underventilated but well perfused = aspiration, mucus plug, atelectasis. this causes physiologic shunting.

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