Why are crystalloids better > pressors ?

[IVAN HRONEK]

Let me try to reply to keep the ball rolling:
 
The way I look at it is the pressors would save administration of crystalloid, espec. beneficial in TBI e.g.
You're right, in some of the animal studies they did decrease perfusion/cardiac output. The idea is to follow the "delayed resuscitation philosophy" with keeping the crystalloid volume low prior to control of bleeding. 
 
Which pressor: again, you're right: one animal study compared phenylephrine to vasopressine and got similar results. Levophed also did similar job. One difference is the effect on the heart - Levophed has some beta 1 effect and may cause more tachycardia than appropriate. Phenylephrine and Vasopressine are pure vasoconstrictors and so fulfil this role best. A lot of studies have been done with Vasopressine and so it is better known and can be used in follow-up human studies easier.
 
Vasopressin dose: 40 U is the CPR dose, right. I agree with you Mike, again, I can't see myself shooting a big blous dose to a patient without starting with smaller doses and yes, I think titration to effect is best, definitely, as with perhaps any drug.
 
CVP: yes, most vasoconstrictors also squeeze the large veins, but I think this would be a transient effect.
The kidneys are more affected by hypotension as GF is entirely dependent on the filtration pressure. Once you raise the BP, urine stats flowing again, like it has been shown with Levophed before. We are talking short-time use here, prior to control of bleeding and transfusion, which are the definitive therapy. A more common complication is skin ischemia, I saw digital ischemia in a pt. who was on it for > 7 days, splanchnic ischemia has also been shown to exist in the animal studies.
 
Where the idea comes from: I think saving crystalloids, when I see myself giving > 10 L of crystalloid and see the anasarca hapenning in front of my eyes, I start hating myself.  I agree with you once again - the BP is not a good diagnostic endpoint, CO is better, SvO2 better still, as is acidosis or lactate, however people say these all are general and not regional (e.g. brain or kidney ischemia) monitors. If you mean to say that pts. with an OK BP can be in deep trouble, I agree. 
 
I think here we would be trying to temporize and hope the kidneys, the muscles, skin and the splanchnic organs can take some temporary ischemia from the vasoconstriction due to the hemorr. shock as well as to that due to the vasopressor and we would keep perfusing the brain and the heart, that's what the body does by itself in these situations anyway.
 
What I don't understand is why crystalloids help - they do not increase oxygen delivery meaningfully..
but they keep the BP and CO, - is that useful for the body ?? Why ?
 
What if we just keep up the BP and not the CO - by using pressors ??  (now I am questioning the dogma).
Would patients become more acidotic and have low SvO2 more than with crystalloids ?
 
Thanks also for considering my question, yours, Ivan
 



> Date: Sun, 5 Aug 2007 17:56:32 -0700> From: medic0947969 at yahoo.com> To: trauma-list at trauma.org> Subject: pressors in trauma, wasn't the world once flat?> > Thanks everyone for the replies to my earlier questions on theraputically reduced SBP.> > Prior to signing up for this list I raised the question about using pressors in trauma and to say I was met with resistence would be a kind understatement. But here is my madness.> > Pressors are used all the time in trauma, but nobody realizes it. How often in the OR or while sutering is epi used to constrict vasculature to help control bleeding? It seems to me, all the time. I would stipulate that cutting or suturing causes trauma. Maybe a controlled trauma or over a small area. But still a pressor used for bleeding control. (not to raise CVP)> > Now it was brought up on this list to use vasopressin. Stepping away from the TBI for a second, from cardiogenic shock of nontraumatic origin to spinal trauma, pressors are indicated; If not to aid in perfusion, then for what? I understand the dogma of no pressors comes from the idea that the pressor does not help CVP and therefore is contraindicated because the increase in BP gives a false impression of tissue perfusion. But from a common sense point of view, back to TBI, you are not trying to raise CVP, you are trying to raise MAP. So why would the pressor not work? Unfortunatly I don't know the answers to the following questions. Please can anyone tell me: > > Which pressor? Why vasopresson over levofed or any other? Obviously some work differently than others, but I do not know why the focus is on Vasopressin.> > What doses are being considered and why? It seems to me using 40 units of vasopressin might be too much on a pt with a pulse, but what is the reasoning for the dose being used or is it titrated to effect? > > The other side of the coin is by raising MAP with a pressor do you impact CVP? Are any other organs or systems negatively impacted? i.e. the kidneys?> > Does this idea simply come from the idea that in a cold, diaphoretic patient we might look at the BP reading and forget we treat patients not monitors?> > Thanks for taking time to consider this.> > Mike> > KMATTOX at aol.com wrote:> > In a message dated 8/5/2007 4:30:51 P.M. Central Daylight Time, ih7 at msn.com > writes:> > if the ICP is increased, you need to keep the MAP 60 mm higher so the blood > flows forward through the brain> > > I would agree with that, but would plead that it is NOT crystalloid fluids > which should be used to achieve that MAP. Remember that most of the studies > of the past 30-40 yrs were in patients that had 3 liters (or more) challenge > of crystalloid prior to any surgeon, especially neurosurgeon, seeing them. > The ICP increase is a complex compartment syndrome and much of our > traditional urban legend therapy actually iatrogenicly contributed to the spiraling > increase in ICP. > > I am delighted to see the direction of the discussions on this web site, and > do believe that it is going to lead to a whole new wave of research. > > k> > > > ************************************** Get a sneak peek of the all-new AOL at > http://discover.aol.com/memed/aolcom30tour> --> trauma-list : TRAUMA.ORG> To change your settings or unsubscribe visit:> http://www.trauma.org/index.php?/community/> > > > ---------------------------------> Be a better Heartthrob. Get better relationship answers from someone who knows.> Yahoo! Answers - Check it out. > --> trauma-list : TRAUMA.ORG> To change your settings or unsubscribe visit:> http://www.trauma.org/index.php?/community/