ABG's - page 2
I have an ABG question - sorry if it seems simple, but I'm having trouble researching it.... Any of the hospitals I have worked at always sent back an HCO3 level with the rest of the gas numbers.... Read More
Jul 17, '03Would it be obtuse to say there is nothing like the old uro-swan? Don't get me wrong, real swans are great during the first few hours with a fresh heart, but soon enough everything becomes relative.
At my hospital (Creighton University Medical Center, Omaha), we use Baxter continuous CO monitors. When I was in school, 3 years ago, I was told that soon swan-ganz catheters would become obsolete. I wouldn't totally agree, but I do believe that your senses are much more valuable than calculations.
Jul 17, '03Tenesema
I had this very discussion with a colleague at work In reference to a patient, as we had significantly different CI over a shift. It all came down to wether or not dry weight was being used, and no two people could seem to agree on which to use.
Jul 17, '03Speaking of dry weight....we have been having this discussion a lot at work lately. Do you use the dry weight to calculate gtt rates for pressors and sedatives that are run in mcg/kg/min? We had a big debate about it and finally found our policy which is dry weight...we use it for CI too. Just wondering how everyone else does it!
Jul 17, '03you guys are going to hate my argumentative nature today hehe
but pressors and sedatives really shouldn't be based on weight at all... you should titrate them in to effect... of course you start low, and work your way up... for a big reason (the weight based recommendations are all from the pharmacy companies and have no real researched value) - most pressors and sedatives have little to do with weight: ie 1) pressors: somebody who is adrenally insufficient or extremely septic may need more per weight than somebody who has had a dose of spinal 2) sedatives: somebody who is an IVDA/ETOH may need more than you or me....
my point is that there is a lot of clinical judgement in anesthesia... and a blatant example is how i use NEO (phenylephrine): i run it in a microdripper (NOT on a pump) and i open or close the flow based on what i need for pressuer.... now of course in an ICU setting that isn't feasible, so pumps are fine - but you can see that weight doesn't come into play.... i think the only time it may be appropriate to incorporate weight is when you are unsure of the initiating/starting dose: and then just start conservatively
Now the exception for this: neonatal or pedi patients - those absolutely need to be weight based primarily because overdose is sooo ridiculously easy...Last edit by Tenesma on Jul 17, '03
Jul 17, '03I tend to disagree, you can titrate with a pump or a microdripper, but you do not have finite control over the microdripper and in some cases this can make a difference. I can see a scenario where I would be over/under shooting my target a lot longer if I were dripping it in (probably not with neo, but certainly with some other drugs such as nipride, or pressor wise vasopressin). I also would be concerned that if something else occurred, I might lose track of the drip and run out or continue running at a rate I would not normally want to run at. Granted it would have to be a pretty big something, but...things happen.
In conclusion, I think from a safety perspective there is no good reason to microdrip something in, when there are pumps readily available and easy to use.
Jul 17, '03i agree with you ABSOLUTELY about pumps being way better than drips - primarily because things do happen and you do lose your focus.... but it is an example of how weight plays no role...
Jul 18, '03I guess since I have only been practicing for the last ten years or so, I have been accustomed to looking at the HCO3. I'm sure I could calculate it if it was not provided and/or I did not have a set of lytes. It just seems so much easier to have it printed out.
I have to continue to disagree... I find HCO3 levels a valuable indicator of the degree of my patient's metabolic acidosis, and the effectiveness of my therapies.
Regarding CI, I was educate to believe that it was more accurate than CO. The agruement used of course, was that a CO of 4 in a 7 foot tall 300 lb football player would not be adequate and might indicate cardiac failure, whereas, this would be the low end of normal for the average 70kg male. I still think this argument has some validity.
I've never really conisdered the accuracy of BSA. Although I think your examples related to amputations give me something to think about, I think the argument in general is not all that good. The majority of patients do NOT have amputations, and just because BSA would not be accurate in these patients, this does not mean that it is not accurate in all patients. Can you provide me with any other evidence that BSA is an invalid concept?
Jul 18, '03I sincerely did not imagine this post would get so much attention or spark such a discussion! After a few nights in the unit between this post and my original, here are some thoughts:
1) After another look at Marino's chapter on Acid-Base Interpretations, I am becoming more inclined to see where Tenesma is coming from. It is a bit of a paradigm shift for me, because ANY reference to ABG interpretation I have encountered included evaluating the HCO3 as a parameter. However, I am beginning to understand the concepts a little better (and I thought I knew them so well..... ), and I can see how one can become practiced in using the standard measured values (pH/pCO2/pO2) alone, especially as an anesthesia provider, which I am not.
2) That having been said, perspective is important. If you're standing in the SICU/MICU/CCU at 3 am wondering where your patient is going....it probably doesn't hurt to have some more information to help you make decisions. I get a bicarb from the lab, I don't have to spend time doing algebra, as someone put it. I can check the anion gap, do an AG excess/HCO3 ratio, get mixed venous gases or even venous gases. If the patient has any blood left, we can get even more information.....
3) Garbage In, Garbage Out (GIGO) is a good rule of thumb to remember. Information is only as good as the raw data used to get the info. Indexing cardiac outputs is a very appropriate way (IMHO) to normalize the information; it creates a level playing field. But, Tenesma's point is well taken - how good is the data used to get the CI, in this case the BSA? How accurate is it? (I still think if we measure to the end of the stump, and are not weighing the missing legs, our BSA calc may be right... ). Our information is only as good as the data we collect. I find trending more important than individual values. (and in the limited time frame in the OR, you probably don't have a lot of time to trend...).
4) Lastly, looking at the actual patient is probably a good idea......I know this is obvious to you, and wouldn't mention it, except I think it's germaine to the discussion. We all know that relying more heavily on monitors and lab print outs than assessing our patients is a pitfall any provider can fall into, and most do fall into at some point or another, albeit until all hell breaks loose with the patient.
Anyway, thanks for the good discussion (and please don't stop!) It helps me to check my thinking, and I always learn something from board here.