Lecture 8 Shock

From Iusmphysiology


Contents

[edit] Cardiovascular Shock

  • The term shock is used incorrectly in most situations.
  • Definition: inadequate perfusion of the body such that oxygen use declines.
    • The cells become anaerobic
  • We fix it with lots of things we know alla bout.
  • Then we worry about decomnpensation and death dispite our effort.

[edit] Objectives

  • What is the general definition of the term “shock?” How can a patient be entering into shock yet have a near normal arterial pressure?
  • What are the four broad categories of pathophysiological conditions which can lead to shock? What is the fundamental primary problem in each broad category of these forms of shock?
  • How do each of the following physiological systems help to compensate for cardiovascular problems during shock?
    • Sympathetic nervous system
    • Endocrine system
      • Antidiuretic hormone
      • Renin-angiotensin system
      • Cortisol release
  • How does recovery of water from interstitial space and cells help to compensate for shock-like states? Which of the capillary forces falls and which is used to recover water? What happens to the hematocrit?
  • How will you estimate that the decompensatory phase of shock has begun based on each of the following and what is your physiological basis for your decision?
    • Increasing hematocrit
    • Decreasing vascular resistance
    • Decreasing stroke volume despite increasing central venous pressure
    • Decreasing urine formation despite ample hydration

[edit] I. Shock - Inadequate perfusion of the body such that oxygen usage declines

  • There used to lions, tigers, and bears and mammoths that caused shock.
    • People got trounced and then lived!
  • Now there are cars.
  • We also have tornadoes.
  • How do we deal with the shock?
  • We have the baroreceptors and many hormones.
  • There are multiple kinds of shock.

[edit] The issue of arterial pressure during shock

  • See hypovolemic shock

[edit] Types of shock

[edit] Hypovolemic shock
  • This may be called "shock at near normal arterial pressure"
  • Usually in young healthy poeple
  • These pts have great CV systems: can lose lots of volume and still generate high cardiac output and high resistance.
  • But high resistance will cost the gut, liver, kdiney, skin, and some skeletal muscle to go into definition of shcok: anaerobic b/c of lack of perfusion.
  • Something has put them into shock.
  • We want a measure of how well their body is responding:
    • Reperfusion
    • Urine formation (kidney function test)
    • Neck vein collapsed?
    • Ultrasound to see if heart is being filled and is pumping ok
  • Saline can be given to resuscitate.
  • This type of shock could be hypovolemic
  • Causes: bleeding, vomitting (most common cause), lack of water intake (common in elderly and babies when they don't feel well), diarrhea
  • Treatment:
    • Give liquid part of blood like saline or plasma
    • Serious states require real blood.
[edit] Cardiogenic shock
  • Cardiac contractility has gone wrong for some reason
  • Sympathetics are tyring to raise contractility and heart rate
  • Causes: bad arrythmias, MI,
    • Poor conduction at AV node causing decreased heart rate and decreased cardiac output
    • Atrial tachycardia causing poor filling of ventricle and decreased cardiac output
    • Valve issues: regurgitation decreases cardiac output
    • Chest trauma: breathing is poor, pump inside the pump isn't helping fill the heart. furthermore the heart is physically damaged a bit like a small MI
  • Treatment:
    • Fix the heart if you can
    • If you can't fix the heart, start heart failure treatment (more later)
[edit] Peripheral collapse
  • This is a pretty routine problem: dilation of the artiioles and venules
  • Causes
    • Allergies:
      • Too much histimine release from mast cells
      • Breathing goes down, bp drops
    • Bacterial septicemia
      • Bacteria in the blood at high enough levels that ednothelial cells make NO with inducible NOS
      • Vascular resistance is real low
      • Veins aren't constricted
      • Can't fill heart
      • Don't have a sufficient resistance against pumping of heart

[edit] Neurogenic shock

  • This is a loos of the sympathetic nervous system control or a loss of neural ventilation control
  • There is a big drug problem in the US.
    • Most drugs that are troublesome are good at knocking out ventilation.
  • The neuro control center and the sympathetic control center in the brain are side-by-side so when one goes off line so does the other.
    • Therefore, contractility, heart rate, arterial resistance and venous constriction are all impaired
  • Causes:
    • Brain trauma / infection
      • Trauma because there isn't enough blood flow to sympt to fire fast
    • Depressant drugs
    • Alcohol
      • By the time someone passes out from alchol they are at about 80% of the dose required to kill you.
      • Closer to reality than you think.
      • At this point, sympathetic nervous system is in trouble


  • stopped here on 01/27/11 at 12PM.
  • started here on 01/28/11 at 9AM.


  • We won't be tested harder than the objectives.
  • Know why the answers to the clinical questions are wrong and right because they may be rewritten.


  • recall shock:
    • Brain can go bad from a bump or meds causing sympathetics to go bad
    • Myocardial contractility or valve or rythm can go wrong
    • Toxins or infection can cause anaphylatic shock
    • Blood volume can drop: diarrhea, hemmorage, etc.

[edit] II. Compensatory Mechanisms used to restore the arterial blood pressure and cardiac output

  • How do you fix shock?
  • Hard to fix the brain; sorry.
    • Might give Epi
  • Heart attack
    • Usually the remaining part can compensate
  • Peripheral resistance
  • Endocrine copensation:
    • Hypothal releases antidiuretic hormone
      • Stimulates thirst, helps kidney retain water, vasoconstricts
    • Renin-angiotensin system
      • Angiotensin 2 activates aldosterone at the medulla, and retains K and Na in kdiney
    • Cortisone
      • Cortisol is stimualted to be released from cortex
      • Potentiates norepi
      • Amino acids are released

[edit] Reabsorb water from the interstitial space and take water from cells

  • Low arterial pressure to reduce capillary pressure
  • If arterial resistance elevated, even lower capillary pressure
  • Colloidal osmotic pressure of plasma pulls in the interstitial water
  • Results of water reabsorption from the tissue
    • There is only so much saline you can give to increase blood pressure before you're diluting the blood too much. 
 (a). Gain 500-1000 ml of water for plasma 
 (b).  Dilute the red blood cells, hematocrit falls, viscosity falls 
    (c).  Dilute the plasma proteins with water, colloidal osmotic        pressure falls and the reabsorption of water is limited

[edit] Flow chart

  • Most people who go into shock live.
  • At some point, not much can save you: the decompensatory phase.
  • Blood flow is so low that organs cannot get oxygen so they go into anearobic metabolism.
  • Anearobic metabolims will cause leakage, relaxation, and ischemia
  • This will make everything worse: decrease in blood volume, decreases vascular resistance, and decreased contractility of the heart.
  • Other effects in decompensatory:
    • reabsorption of water from tissue begins to fail
    • water loss to tissue will begin to increase red cell hematocrit
    • venous congestion leads to elevated capillary pressure
    • Vascular smooth muscle overwhelmed by vasodilators in tissue
      • relaxation and decreased resistance
      • diminished response to norepinephrine
    • Kidney failure - the body becomes toxic
      • Kidney doens't have enough pressure to filter correctly.
      • Kidneys need stuff going through tubules for kidney to be healthy
      • If kidney cannot get rid of water and you give saline, then the liquid will just go straight into the tissue
    • Heart problems in deocmpe
      • Stroke volume goes down
      • Contractility goes down
      • We can keep fluids up to keep central venous pressure up (12 mmHg)
        • So shcok pts don't die of low venous pressure
      • Arterial pressure goes down because of contractility issues
      • Tissues that don't have enough oxygen release all cytes of bad things like cytokines and necrosis factors.
      • These interfere with heart regulation and decrease contractility

[edit] Clinical Example

  • Blood loss
  • Heart rate is high
  • No chest pain
  • EF is 0.4 (should be 0.6 or 0.7, even with low blood volume)
  • A. could be
    • This is the answer
  • B. not likely (look at the heart rate, the sympathetics are doing what they should)
  • C. could happen but EKG says it's something worse, witht he heart
  • D. could be happening (in low bp and shock, there is excessive clotting; so the clot could have gotten bigger; probably wouldn't generate EKG problems, though)
  • E. this wasn't really mentioned, she might be better with blood, but most pts like this don't get blood


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