Question about shock and head Trauma

[EDAC]

I was thinking about this today while driving home from class, we are in the bleeding and shock area of our studies now. We were discussing Hypovolemic shock and skin signs and BP, we were told if PT is in Hypovolemic shock BP would begin to fall, OK. Now what if the same PT also had significant blunt head trauma? With head trauma BP will go up, correct? If that is the case how will BP react to a intercrainial bleed and profuse bleeding in other areas of the body? In other words if you have a head bleed, and hypovolemic shock will the BP go up or down, I would assume down, but did not have time to ask the question in class today. Would the most significant of the two affect the pt blood pressure more than the other?
Sorry if it is a stupid question, but I'm just trying to take it all in and go in the right direction.

I hope this is the appropriate forum for this question.

 

[Melclin]

I don't think its a stupid question, but my god they are doing you a disservice, by simplifying it that much and superimposing such basic knowledge over very little AnP. I've always hated it when teachers simplify things to the point of just basically being wrong. Doesn't happen to much in university now thankfully, but I remember it well. Now I'm sure others will come along and school you much better and probably rant a little about education, so I won't say too much, I am just a student myself.

I think the interaction probably depends very much on how serious each is (what stage of shock, what type of trauma, level of ICP). It's very much more complicated than saying shock = low BP, TBI = high BP, so which wins.

My simplified understanding of TBI issues, given that I haven't specifically done the trauma or advanced management units yet, is that you want to keep the blood pressure, or more specifically the mean arterial pressure (MAP) up to overcome increased ICP to keep the cerebral perfusion pressure up to prevent ischemia. I think I remember hearing that a MAP of between 100 and a 150 was desirable, but I've seen a lot of other ranges as well (90-130 comes to mind).

CPP= MAP - ICP(or JVP if its higher than the ICP)

Hypertension is the body's way of forcing blood into the brain to overcome the the increased ICP. Whether or not this was effected significantly by hypovolaemia would depend on how bad the hypovolaemia was I suppose. I have heard that the bradycardia of cushing's triad is caused by the exhaustion of certain catecholamines. If thats true, those hormones are also necessary for compensating for shock, so I imagine that being hypovolaemic would profoundly impair the pt ability to perfuse their brain and vice versa. In any case, they draw on similar resources, so I would think that the two together, would increase the progression of each other (the shock makes the TBI worse, faster and vice versa). Eg, the BP would go up, probably quite high (compensation for shock and HTN associated with ^ICP) then crash down, with dire results.

Like I said, I only have a thin, theoretical understanding of the issue, so I'd be interested to see if what I've said is true, both theoretically and in practice.

 

[BruceD]

I was thinking about this today while driving home from class, we are in the bleeding and shock area of our studies now. We were discussing Hypovolemic shock and skin signs and BP, we were told if PT is in Hypovolemic shock BP would begin to fall, OK. Now what if the same PT also had significant blunt head trauma? With head trauma BP will go up, correct? If that is the case how will BP react to a intercrainial bleed and profuse bleeding in other areas of the body? In other words if you have a head bleed, and hypovolemic shock will the BP go up or down, I would assume down, but did not have time to ask the question in class today. Would the most significant of the two affect the pt blood pressure more than the other?
Sorry if it is a stupid question, but I'm just trying to take it all in and go in the right direction.

I hope this is the appropriate forum for this question.

Forgive me, I am tired...

If I read your question correctly:
Because you state your patient is already in hypovolemic shock, it means that the body is not able to compensate for the lost volume. The only way the BP will rise is to correct the underlying condition.

tc
-B

 

[Shishkabob]

The cranium can only hold so much blood, which is why you see Cushings Triad. So when you have a cranial bleed, AND a large bleed somewhere else on the body, blood, like any other fluid, goes to the path of least resistance.

Sure, BP could raise at first due to the cranial bleeding, but eventually there will be no blood to do the raising, because it will be gone, and as such the BP will be falling.

 

[ResTech]

As Melclin said and from my own experiences, the EMT-B programs do students a great disservice when teaching shock. Hopefully I will be able to break it down and clarify it for ya since your instructor seemed to be very vague on the subject of Shock.

In hypovolemic shock states, the B/P will not begin to drop until the patient has lost a very considerable amount of volume... as in the range of >25-30% (give or take given the patients age and state of compensatory mechanisms). With a decreased amount of blood circulating in the body, there is less blood being returned to the heart (decreased preload) which does not stretch the heart muscle as much causing a significant decrease in the force of contraction (Starlings Law) which causes a decreased blood pressure.

It is also important to note that at the very earliest detection of a decreased fluid volume by the body (sensed by barorecepters), the body is going to activate its compensatory mechanisms to maintain blood pressure and perfusion. So at first, the patient is going to have a normal or maybe even a slightly elevated blood pressure due to the compensatory mechanisms. But once these compensatory mechanisms reach their limit and begin to fail, then you will start to see a drop in blood pressure.

You should be able to see that a drop in blood pressure is a LATE sign of shock and unless the patient has a massive wound and they are dumping blood to the ground like a rainy day, don't expect to see a low blood pressure right away.

What you want to be looking for are these signs which are a part of the compensatory mechanisms:

Tachycardia - from sympathetic stimulation (catacholamine release). First line attempt by the body to maintain perfusion and cardiac output/blood pressure.

Tachypnea - also an early sign - caused by the body's detection of an increase in acid production (acidosis). Resp rate increases to rid the body of CO2 and increase intake of O2.

Pale, Cool, Clammy Skin - caused by sympathetic stimulation. The catacholamine release (epi/norepinephrine) cause blood to be shunted away from non-essential body regions and directed to the body core. This shunting results in reduced blood supply to the skin causing it to appear pale and cold. The clamminess (moistness) of the skin also comes from the norepinephrine. Also, an early sign.

Mental Status Changes - maybe very vague, but the slightest decrease in perfusion to the brain will cause a person to have a change in mental status - usually anxiety, anxious, can become combativeness if severe hypoxia. This is a pretty early sign as well.

Nausea - caused by the shunting of blood from the non-essential areas (stomach/intestines) to the body core.

Thirst - hormones are released that cause the sensation of thirst to signal a person to consume fluids to replace lost fluid volume. I wanna say the ADH hormone and Aldosterone... someone correct me if I am wrong.

"Narrowing" Pulse Pressure - a diagnostic sign that many providers do not understand or ignore. Pulse pressure is simply the difference between the systolic and diastolic pressures (just subtract the two) that directly indicates the degree of peripheral vascular resistance or vasoconstriction. In shock, usually the systolic will remain the same or begin to drop while the diastolic will begin to rise. This indicates the degree of compensation by the body and tells you that the body is vasoconstricting and is compensating. A B/P of 102/88 is considered narrow with a pulse pressure of 14.

All too often EMT's know the signs to look for but they have no clue what is happening inside to cause these signs. I feel its important to have that understanding. I was not all inclusive but it gives a good explanation.

As far as the head injury and blood pressure goes..... it all depends. Most head injured patients are not gonna be hypotensive unless they also have other traumatic injuries. They are gonna be normotensive or hypertensive. If you have a head injured patient that is hypotensive, start looking for signs of fluid loss or consider this patient to be very seriously head injured as hypotension in the head injured patient is a very ominous sign.

The brain injured patient becomes hypertensive to increase perfusion to the brain as a protective reflex as Melcin has explained. Blood pressure is largely dependent on the amount of volume you have in your body. If you lose a lot of blood, the body is not gonna be able to increase the pressure as it would like to help perfuse the brain. So I would say hypovolemia is gonna drop the pressure despite having a serious brain injury.

Sorry so long!

 

[EDAC]

Thank you very much

Wow, excellent information, thank you very much. I agree we just always just seem to touch on and skim through indepth information. I seems that the emt-b educational reguirements do not require us to have a deep understanding of medical knowledge, just enough to get by. I am usually not satisified and therefore am usually seeking further indepth knowledge to get a better understanding of what we are studying at the time.

I am trying to become better educated but my other classes don't start until after the EMT course is over, I am starting Med. Terminology, A&P, and Biology in August, so hopefully the information I gained in the EMT course, will be better applied once I have the other foundation courses completed.

Again thanks for the information, it was very helpful.

 

[MrBrown]

Excellent information! I was going to put in my two cents but wasn't overly sure of the answer so I thought best if I sat back and listened.

 

[Shishkabob]

Thirst - hormones are released that cause the sensation of thirst to signal a person to consume fluids to replace lost fluid volume. I wanna say the ADH hormone and Aldosterone... someone correct me if I am wrong.

You are (somewhat)correct.


The body senses lower levels of fluid, so it releases both ADH (Anti-diuretic Hormone) and Aldoseterone. ADH basically tells the kidneys not to absorb water, thereby keeping more fluid in the blood vessels. Aldosterone tells the body to re-absorb sodium, and water follows sodium, so with the reabsorption of sodium, more fluid is brought back.

Along with that sodium comes thirst.



ADH is also the drug known as "Vasopressin" which as the name implies, constricts vessels in high doses, thereby also increasing BP.

 

[Shishkabob]

Something else shock related that basics should read up on... the Renin-Angiotensin system


(image taken from wiki, but it explains it)

 

[ResTech]

I knew I was pretty close and on the right track... thanks for the clarification...

 

[Melclin]

I missed the Renin-Angiotensin pathway lecture last year and the lecture notes didn't make a bit of sense. The 'Shock' wiki, got me going, I just about would have nosed dived if I hadn't have had that wiki to teach me the basics before I went onto the more complex stuff.

That diagram was in my study notes summary for exam prep. Best diagram I could find on the R-A tensin pathway B) One of the exam question for TEN marks was 'Describe the renin angio tensin pathway, its effects and its role in homeostasis using diagrams if you wish'. Got a HD in that subject. Thanks wiki

Wiki is the best gate way resource for medical stuff. Of course, its best not to rely on it to be right about the details, but its great for students to jump from link to link, to get a nice simple overview of how things all fit together.

 

[ResTech]

That diagram looks intimidating to me and I understand the Renin-Angiotensin-Aldosterone system...lol.

Its not that complicated to understand though really...

 

[Foxbat]

ADH basically tells the kidneys not to absorb water, thereby keeping more fluid in the blood vessels.

As far as I understand, it tells the kidneys to reabsorb more water (from DCT).

 

[Shishkabob]

As far as I understand, it tells the kidneys to reabsorb more water (from DCT).

Semantics.


Either way you phrase it, it tells the kidneys to make less urine.

 

[Melclin]

Yes, the less water going to urine, the more there is to make up the blood volume.
ADH doesn't (to my knowledge) affect how much water the kidney's filter out of the blood stream, but it increases the permeability of the absorbing bits of the kidney so that more water is reabsorbed back into the blood stream. It also stimulates another chemical pathway (Na+ and K+ transporty something or other) to the same affect.