Great discussion, but....KISS
I think the simple answer to a simple question was lost in the minutea of acid-base explanations, some of which are nothing more than complicated guesswork.
So, I will attempt the simple:
1) pH is a relative measurement of the ratio of hydrogen ions (H+) to hydroxide ions (OH-)
2) the pH scale is 1 to 14. 7 is neutral, in which the ratio of H+ to OH- is 1:1.
Anything below 7 is acid, higher in hydrogen ions. Anything above 7 is basic (alkylotic), higher in hydroxide ions.
3) Venous blood is relatively more acid than arterial blood due to the way in which carbon dioxide is carried in the venous serum, in the form of carbonic acid. The presence of lactic acid or pyruvate has very little to do with it. It is the accumulation of CO2 in the form of carbonic acid that is the major and overriding factor.
What you need to know is that, metabolic and/or respiratory issues that take the human organism outside of the narrow limits of 'normal' pH (7.35 - 7.45) can be critical and can be corrected...within limits. Outside of the correctable limits (6.5 - 7.65), recovery is doubtful. Acidosis is much more prevalent than alkylosis. As one's condition deteriorates, with decreased respiratory status and increased tissue catabolism, one becomes acidic.
That, my friend, is the VERY basic bare bones of pH blood chemistry. I am really sorry that your instructor is so ill educated. Unfortunately, at least in my observations of EMT/Paramedic certification/education programs in this country, we have people placed as instructors in courses about which they know only enough to get in trouble, generate myths, and pass on bad information. By the way, that's pretty much the status of many nursing instructors as well.
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