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 +2  (nbme20#24)

Another quick way to think of this is through the formula: pH = HCO3/CO2. Since pH is low and HCO3 is low, CO2 must also be low.

 +1  (nbme20#42)

Vomiting blood and cool skin indicates this is a type of hypovolemic shock. To understand shock, remember that 1) BP = TPR x CO 2) CO = SV x HR 3) SV = EDV - ESV In hypovolemic shock, you are losing fluid, so stroke volume is decreased and end diastolic volume is decreased. Decreased EDV means that the "filling volume" is decreased, which also means the preload will be decreased (https://www.cvphysiology.com/Cardiac%20Function/CF007). Also, skin is cool because you're decreasing SV --> decreased CO --> Ang II/ADH/etc is released to vasoconstrict increaseing resistance. Since there is increased resistance, there is less blood flow causing skin to be cold/clammy.

hello  Patient in hypovolemic shock - the clues are low BP and COOL skin. Hypovolemic shock is caused by fluid loss. The patient has decreased preload b/c of fluid loss, i.e. there is decreased blood volume returning to heart --> thus decreased preload.

Subcomments ...

Legionella is common causes of pneumonia superimposed on chronic obstructive pulmonary disease.

asapdoc  Im pretty sure so is strept pneumoniae +2  
usmleuser007  COPD is also exacerbated by Viral infection: Rhinovirus, influenza, parainfluenza; and Bacterial infection: Haemophilus influenzae, Moraxella catarrhalis, Streptococcus. however, the questions gives a hint that it may be legionella = "weekend retreat" which may be associated with this infection +2  
loopers  From FA 2017 pg 139: Legionnaires’ disease—severe pneumonia (often unilateral and lobar A ), fever, GI and CNS symptoms. Common in smokers and in **chronic lung disease.** +1  
kentuckyfan  I also believe that the other attendees showed signs of pontiac fever, which is another hint they tried to get at. +2  
luke.10  i did it wrong and chose influenza virus since it is most common infection in COPD but the clue in the Question is that the other attendee didnt get sick since in legionella there is no person to person transmission +  
endochondral   but in Uworld s. pneumo is one of the most common bacterial exacerbation of COPD legionella wasn't even mentioned. How do we rule out s. pneumo ? +3  
nala_ula  maybe because in children s.pneumo causes otitis media? +  
smc213  Another hint made in the Q stem is the location being rural Pennsylvania.... Legionnaires disease was first discovered by the outbreak in 1976 at a convention held in Philadelphia, Pennsylvania. Not sure why I know this fact... +4  
hpsbwz  Biggest hint towards legionella to me was that they all were at a residence hall... i.e. where there'd be air conditioners and such. +4