Capnography Interpretation?

Question

I'm looking for interpretation results for ETCo2 using Capnography. I have found alot of different values. One source said that <35 is respiratory alkalosis thus your hyperventilating for patient and >45 is respiratory acidosis thus hypoventilating. Please leave your source with your answers.

Answer 1

Both are correct. CO2 is an acid, and thus lowers the pH of the blood. 35-45 is the generally accepted range of normal for end-tidal and PaCO2.

During hyperventilation, CO2 is exhaled faster than normal to the point that the CO2 level by capnography or arterial gas drops below 35. Since the body is losing an acid, pH goes up (alkalosis).

During hypoventilation, not enough CO2 is being exhaled. The body therefore has too much acid - therefore pH goes down (acidosis).

I'm not leaving a source for two reasons: 1) this is general knowledge, not something I've looked up, and 2) you can google this on your own to find a good source for your homework.

Answer 2

It is widely accepted in medicine that the normal PCO2 for a normal person is 40 mm Hg. So, anything much below that (35 is a reasonable value) is respiratory alkalosis -- and does generally represent hyperventilation. The PCO2 of VENOUS blood (i.e. de-oxygenated blood) is considered 46 mm Hg, which is insufficient for perfusion of tissues, and is considered acidotic -- ARTERIAL blood (i.e. blood just leaving the heart and thus should be "fully" oxygenated by the lungs) PCO2 of above 45 mmHg would most likely be the result of hypoventilation. So, your source was correct in using those reference values.

You don't need a source for this, because these are universally-accepted physiological values.