clinical questions/help please

Nitecap · Jan 27, 2006

I was asked the following shadowing questions during a shadowing experience. Can I get some feedback and let me know if I am on the right track or not.
1. Explain dead space in the lungs?
after during research my understanding of it is parts of the respiratory tract that doesnt take part in gas exchange. put reading the physiologic explanation it states gas volume of the alveoli that are not functional b/c of absent or poor flow through capillaries. Now can deadspace be catagorized as both function
2. what is shunting?
my explanation of this after doing some research is basically a small percent of the cardiac output that bypass the lungs and enter the pulmonary vein through the bronchial tree. Now b/c this bypass the lungs is that portion still considered oxygenated blood returning to pulmnary vien? I know this may sound like a stupid question but I am trying to comprehend it all. from my understanding co2 and o2 exchange takes place in the alveoli which is located in the broanchial tree. correct me if I am wrong. why is this shunting important. I want to make sure I am not missing the point.
3. last how does blood get back to the heart.
without looking this up my first thought is the area of low and high pressure. I am not sure how it works.
thanks in advance for your response. I am working on 3 as I surf..

1-Say we have a some sort of micro emboli in the lung that occludes some pulm caps. The associated alveoli may still be ventilated ( may have a volume of inspired gases in them) but since there is not perfussion the gas is not diffusing into the caps so basically its a waste. You have just increased your dead space.

Also there is anatomical deadspace which is your conducting airways for bronchial divisions 1-16. These airways merely carry gas to and fro areas that participate in x change. There is also alveolar deadspace which is in the senario in numer 1. These were once functioning but may not be participating in x change d/t to a pathology say PE.

So a PE is increased vent, but no perfusion leading to a V/Q mismatch will be greater value.

Anatomical + alveolar deadspace = physiologic deadspace.

You have to account for deadspace when ventilating a pt. A rough estimate in spontaneous breather no ETT is approx 2/3 alveolar vent and 1/3 deadspace vent. An intubated is 1:1 with deadspace increasing d/t tubes ect so you must give the pt their alveolar vent needs as well as what ever deadspace to ventilate as well

2-As far as shunting goes it depends on what type of shunt. There is physiologic shunting with some of the CO not taking part in x change (about 2%). This bld is not oxygenated but is a really small percent.

You may have a large shunt with say a Vent septal defect that totally bypass pulm circ or smaller ones. If a lung is atelectatic then it is down and not ventilated though bld is still perfussing the caps around the down area. So you are correct that if there is a true shunt the bld will not be oxygenated. Hence though you put the pt on Fio2 of 100% it will not increase sats or PaO2 b/c there is no ventilation to drive the o2 across.

3-What do you mean how does bld get back to the Heart? The venous system of course. Are you trolling?

rose234 · Jan 27, 2006

Thank you nitecap that was very helpful. Question # 3 I knew it was the venous system but I thought the answer was too simple. So of course I was looking for something more indepth. He caught me there.