Guest Post: Adam's explaination of pKa that will leave you wondering why you didn't read this before that one test you had to take last year.

Adam, seen here looking both patriotic and holier-than-thou.
Leave it to an SRNA to multitask!

What the heck is pKa? Back in the Fall last year I made the mistake of explaining pKa to Amy.  Ever since then she has been asking me to write a post to help others grasp this concept.  I would love to sit here and pretend that this is an altruistic exercise, but the truth is that I continually get these questions wrong on exams and am writing this post as much for my own benefit as anyone else's.  So here it goes…

Figuring out pKa questions is easier if we remember one rule and ask two questions.  The rule to remember is: pKa DOES NOT equal pH.  We will get to the questions a little later. pH and pKa are related, but totally different….kind of like Stephan and Alec Baldwin.  Put simply pKa is a quality that drugs have.  It is the pH at which the drug is 50% ionized and 50% unionized. Ionization is important because drugs that are ionized cannot cross lipid membranes.  If they can’t cross lipid membranes they can’t get to their sites of action.  The site of action might be the brain, or a nerve axon, or whatever.  So ionization is bad.  The nonionized portion of the drug is the portion that crosses the lipid membrane and gets to the site of action.  This is the portion of the drug that “works”, therefore the nonionized part is good.

I’m gonna go way back in the memory banks here and bring back some basic chemistry.  Remember how acids and bases behave?  Acids donate H+ and bases accept them.  (H+) + (OH-) <==> HOHWhen acids and bases are mixed together they are in a constant flux of ionization (which is bad).  But, if we mix a base in a basic environment or an acid in an acidic environment ionization doesn’t happen; there is nothing there to donate an H+ to and nothing there to accept one.  The drug is less ionized (or more nonionized), which is good.

This brings us to the first question we need to ask:  Is the drug we are examining an acid or a base?  Examples of basic drugs are local anesthetics and opioids; some of our acidic drugs are the barbiturates. 

So let’s pretend we are dealing with the basic drug lidocaine, whose pKa is 7.74.  So at a pH of 7.74 there is exactly 50% ionized lidocaine and 50% unionized.  Is this drug an acid or a base?  A base, like we just talked about. 

This brings us to our second question:  Are we placing our drug into a relatively more acidic or basic environment compared to the drugs pKa?  What is normal body pH?  Anyone, anyone…Bueller…7.4.   So, if we put this basic drug which is 50/50 at a pH of 7.74 into a relatively more acidic environment (body pH is 7.4, therefore relatively more acidic than 7.74) will we get more ionized or unionized drug?  I really hope you all said more ionized. 

Let’s deal with an acidic drug, like the barbiturates. The pKa of methohexital is 7.92.    So, we know this is an acidic drug that is 50/50 at a pH of 7.92.  Now we inject that into the body with a relatively more acidic pH of 7.4, will there be more ionized or nonionized drug?  Please say more nonionized. 

Did anyone notice that this acidic drug had a pKa greater than 7.0?  This is an excellent example of our #1 rule: pKa DOES NOT equal pH.

On exams I always find it super helpful to draw it out.  Here are some extreme examples (Click on each to enlarge):



2010 Joint Committee Meeting Review

Chicago was wonderful!  I spent two days meeting some of the "movers and shakers" of the AANA.  We worked hard, played hard, and ate well.  In reference to that last point, I'd like to note that the only photo I took while in the Windy City was of the Chicago style stuffed pizza from Giordanos that I had delivered to my hotel room on Friday evening after arriving at the hotel.  I think it's clear where my priorities lie.

That isn't a pizza... THIS is a pizza!

We kicked off the weekend on Saturday morning with a group breakfast, followed by a presentation led by Bernd Schmit, who is originally from Germany, enjoys a good steak, and also happened to pen the book Big Think Strategy: How to Leverage Bold Ideas and Leave Small Thinking Behind.  He did an amazing job of getting everyone in the room to participate in the discussion and to consider major ways in which we could improve our organization and profession.

 

After the conclusion of Mr Schmit's talk, each committee met to begin reviewing and checking off important items on our individual agendas.  We (members of the Education Committee) reviewed the items covered in the previous meeting before moving on to upcoming issues.  Discussions included the state of nurse anesthesia programs (growth rate of programs, growth rate of clinical sites, and numerical data on the education section of the AANA website to gauge future interest in programs) and the strategic organizational goals and objectives of the AANA Education Committee.  My committee is responsible for putting on or contributing to a number of meetings such as the Assembly of School Faculty (which takes place every February, this year's will be located in Orlando), the Financial Issues Workshop, the New Program Administrator's Workshop, and the Annual Meeting.  Thus, we spent the majority of our time together discussing the proposed agendas for each and making changes based on the evaluations submitted by the previous year's participants.  (I can honestly say that your comments are taken into consideration - so keep those evals coming!)

As a new member of the Education Committee, some of the information that was discussed was a bit "over my head" as it pertained more to educators than to students.  However, at any mention of SRNAs, everyone in the room looked to me for my input.  I was even able to make a few suggestions for the 2012 Assembly of School Faculty that made it onto the proposed agenda!  I felt as though my opinion was solicited and respected and that I, as a student, had a voice in the organization.  Some of the student-related topics that were discussed included improvements to the student section of the AANA website (which, by the way, will be undergoing a major overhaul in the near future as the AANA is well aware of the fact that the website falls short on a number of levels.) and revising the campaign requirements for those running for the position of Student Representative to the Education Committee in the future in an effort to level the playing field and provide more clarity to those interested in running.

All in all, the Joint Committee Meeting in Chicago made for a very exciting weekend and I was so thrilled to have the opportunity to represent my fellow SRNAs at the Education Committee meetings.  I'm also very excited about the upcoming week, as my classmate Adam will be offering a guest post in an attempt to explain the mysterious and ever-elusive concept of pKa.  Prepare your brain for the massive onslaught of knowledge coming its way!


Not that kind of pKa...

I'm more excited than the Pointer Sisters...


... Because I leave in just a few hours for the fabulous city of Chicago, where I will meet my fellow AANA Education Committee members (as well as members of each AANA committee) for a weekend-filled series of meetings!  I'm looking forward to getting to know the members of my committee, seeing how the organizational decision-making process works, and learning about the issues affecting us all as students.  I'll be sure to give you all an update upon my return!  

The other thing I'm excited about?  I was recently promoted from "girlfriend" to "fiancee"!  The only downside is that my betrothed did entirely too good of a job on the ring and now I can't stop staring at my left hand.  I would venture to say that newly engaged females are the least productive human beings on the planet.

KPEP

My classmate Lashaunda (of paralytic dosing fame) just passed along another study aid which I liked and thought might be of help to other SRNAs who read this blog.  Not only will this post enable you remember the doses of the following sedatives, but I can now officially claim that this website isn't completely useless!  Double win.

KPEP 1, 2, 0.3, 4

Ketamine 1mg/kg
Propofol 2mg/kg
Etomidate 0.3mg/kg
Pentothal 4mg/kg

Flow Volume Loops

We are currently studying respiratory anatomy, physiology, and associated disease states.  My buddy Adam, who apparently has entirely too much time on his hands*, found a cool website covering flow volume loops and emailed the link to the rest of our class.  So, from Adam, to me, to you: enjoy!

http://www.spirometrie.info/fvc.html

* Says me, who maintains a blog in between classes, clinical obligations, and happy hours.  Glass houses, Amy.  Glass houses.

Image via here]