Circulatory physiology uk

					The SHOCK Of Your Life !




                                               1
          Dr Hora Ejtehadi; Dr Usama ALAlami
           Physiology

   Basic unit of life = cell
   Cells get energy needed to stay
    alive by reacting oxygen with
    fuel (usually glucose)
   No oxygen, no energy
   No energy, no life



                                      2
    Cardiovascular System

   Transports oxygen, fuel to cells
   Removes carbon dioxide, waste
    products for elimination from body

      Cardiovascular system must be able to
        maintain sufficient flow through
       capillary beds to meet cell’s oxygen
                  and fuel needs


                                              3
                     Flow = Perfusion




 Adequate Flow =                         Inadequate Flow =
Adequate Perfusion                      Indequate Perfusion
                                          (Hypoperfusion)



                     Hypoperfusion =
                         Shock

                                                        4
What is needed to maintain
perfusion?

   Pump Heart
   Pipes Blood Vessels
   Fluid Blood




                             5
How can perfusion fail?

   Pump Failure
   Pipe Failure
   Loss of Volume




                          6
Circulatory Shock
“Pathophysiologic state in which tissue perfusion is totally
inadequate to meet the oxygen or nutritional needs of the
cells”
Shock described as “momentary pause in the act of death”
Shock is not a disease entity in itself, but a response to some
assault or injury the body has experienced

Whatever the initiating event, the cause of death in irreversible
shock is microcirculatory failure and the subsequent depression of
cellular metabolism




                                                            7
Aerobic Metabolism
Aerobic Metabolism

                         6 CO2


  6 O2
                            6 H2O
            METABOLISM

  GLUCOSE                   36 ATP



                         HEAT (417 kcal)




                                           8
Anaerobic Metabolism
Anaerobic Metabolism


                        2 LACTIC ACID



 GLUCOSE   METABOLISM     2 ATP



                        HEAT (32 kcal)




                                         9
Anaerobic? So What?
Anaerobic? So What?
               Inadequate
                Inadequate
                 Cellular
                  Cellular
              Oxygenation
              Oxygenation


Inadequate
 Inadequate   Anaerobic
               Anaerobic     Lactic Acid
                             Lactic Acid
  Energy
   Energy     Metabolism
              Metabolism     Production
                              Production
Production
 Production


Metabolic
Metabolic                    Metabolic
                             Metabolic
              Cell Death!
              Cell Death!
 Failure
 Failure                     Acidosis
                              Acidosis

                                      10
Homeostasis is maintenance of
Homeostasis is maintenance of
balance
balance
 Requires proper functioning systems
 Requires proper functioning systems
  Cardiovascular
  Cardiovascular
  Respiratory
  Respiratory
  Renal
  Renal




                                        11
             Classification Of Shock


                           Shock


Neurogenic   Hypovolemic    Cardiogenic    Vasogenic


                                   Anaphylactic    Septic

                                                        12
Blood Volumes: A Reminder
Contraction = Systole, dilation = diastole

At the end of diastole, the ventricle should contain 135 ml of blood
(EDV)
The amount of blood remaining in the ventricle at the end of
systole = 65 ml (ESV)

The difference between these two volumes is the stroke volume
(SV) = 70 ml/beat

Cardiac output = Stroke volume x heart rate = 5 litres/min
MAP = CO x peripheral resistance
Monitoring of blood pressure is through baroreceptors in the
carotid sinus and aortic arch. Send impulses to cardiovascular
centre                                                  13
Frank-Starling Law Of The Heart
The heart normally pumps the blood returned to it

Therefore, the more blood that is returned to the heart
(venous return) the higher the EDV and therefore the higher
the stroke volume.

The extent of cardiac filling is referred to as the “preload”

It is called the preload, because it is the work load imposed on the
heart before contraction even begins




                                                                14
Factors Affecting The Pump
Factors Affecting The Pump

 Preload
 Preload
 Contractile force
 Contractile force
  Frank-starling mechanism
  Frank-starling mechanism
 Afterload
 Afterload




                              15
What Affects Blood Pressure?
What Affects Blood Pressure?

 ANS balance
 ANS balance
 Contractility
 Contractility
  Preload
  Preload
    Starling‟s law
    Starling‟s law
 Afterload
 Afterload




                               16
 Changes in Afterload and Preload
 Changes in Afterload and Preload
  Peripheral
  Peripheral
  vasoconstriction…
  vasoconstriction…

           peripheral vascular
           peripheral vascular
           resistance…
            resistance…


                  afterload…
                  afterload…

                         blood pressure.
                         blood pressure.
                                             17
 Changes in Afterload and Preload
 Changes in Afterload and Preload
  Peripheral
  Peripheral
  vasodilation…
  vasodilation…

           peripheral vascular
           peripheral vascular
           resistance…
            resistance…


                    afterload…
                    afterload…

                            blood pressure.
                            blood pressure.
                                                18
  Changes in Afterload and Preload
  Changes in Afterload and Preload
  fluid volume…
  fluid volume…


           preload…
           preload…


                   contractility
                   contractility
                   (Starling‟s Law)…
                    (Starling‟s Law)…

  blood pressure.
  blood pressure.         cardiac output.
                            cardiac output.
                                                19
  Changes in Afterload and Preload
  Changes in Afterload and Preload
  fluid volume…
  fluid volume…


           preload…
           preload…


                  contractility
                  contractility
                      (Starling‟s Law)…
                       (Starling‟s Law)…

  blood pressure.
  blood pressure.            cardiac output.
                               cardiac output.
                                                   20
Cardiogenic Shock

Pathophysiology

Disorders that can result in the acute deterioration of cardiac
function and can lead to cardiogenic shock include:

1)    Myocardial infarction
2)    Myecardial ischaemia

3)    Sustained arrhythmia

Autopsy studies have shown that cardiogenic shock is associated
with loss of more than 40% of the left ventricular myocardial
function

Mortality rate from cardiogenic shock is high (80%)
                                                        21
Symptoms

Clinical evidence of hypoperfusion (low cardiac output)

Low urine output

Cool extremities, ashen and cyanotic
Systemic hypotension ultimately develops (systolic pressure < 90
mm Hg and MAP decreases by 30 mm Hg)

Hypoperfusion propagates to tissues

Exertional dyspnea     or dyspnea at      rest, palpitations    and
generalized anxiety



                                                           22
Myocardial Pathology

Cardiogenic shock is marked by both systolic and diastolic
dysfunction

Patients who develop cardiogenic shock from acute MI
consistently have evidence of progressive myocardial necrosis
with infarct extension

The patients have multivessel coronary artery disease with limited
coronary blood flow reserve

Myocardial ischemia results in decreased myocardial compliance

This increases left ventricular filling pressure

                                                           23
    Myocardial Pathology In
      Cardiogenic Shock

Decreased coronary perfusion pressure


 Increased myocardial oxygen demand

Cardiogenic shock


                                      24
Cellular Pathology

Anaerobic glycolysis

Intracellular acidosis (Why?)

Myocyte membrane pump fails
Sodium and calcium accumulate intracellularely  myocyte
swelling

Lysosomes, nuclear membranes and mitochondria breakdown

Oxidative stress and eventual apoptosis




                                                     25
Reversible Myocardial Dysfunction

a)    Myocardial stunning

b)    Hibernating myocardium

Myocardial stunning represents postischemic dysfunction that
persists despite restoration of normal blood flow

Hibernating myocardium is a state of persistently impaired
myocardial function at rest

Hibernating myocardium occurs because of severely reduced
coronary blood flow

Hibernating myocardium improves with neovascularization

                                                          26
Cardiovascular Mechanics Of Cardiogenic
Shock

The left ventricle is able to eject less blood volume per beat

The stroke volume is decreased due to weakened ventricles

To compensate for the reduced stroke volume, venous return is
increased

The EDV increases

However, this creates a left ventricular diastolic filling pressure

This results in backflow from the left ventricle to the lungs

This causes pulmonary oedema (this explains dyspnea) 27
Due to low cardiac output (because of low stroke volume), the
tissues increase their oxygen extraction

This contributes to substantial arterial oxygen desaturation

Other Effects

Myocardial ischemia is further exacerbated by compromised
myocardial perfusion due to hypotension and tachycardia




                                                        28
Pancreatic Ischemia And Cardiogenic
               Shock
                Pancreatic Ischemia


           Proteolytic enzymes released


           Stimulate release of MTF/MDP


        Interfere with function of calcium ions


            Reduces cardiac contractility


        Reduce stroke volume/Heart rate/CO


                   Hypoperfusion


                 Cardiogenic shock                29
Causes Of Cardiogenic Shock: A Summary

1)     Systolic Dysfunction

Myocardial contractility is abated

Systolic dysfunction mainly due to MI

Another cause for systolic dysfunction is severe myocarditis

2)     Diastolic Dysfunction

Increased left ventricular diastolic chamber stiffness contributes to
cardiogenic shock

Caused by ventricular hypertrophy
                                                               30
Detrimental hen systolic contractility is also depressed
3)     Valvular Dysfunction

Acute mitral valve obstruction by means of a left atrial thrombus
results in decreased cardiac output

Aortic valve regurgitations reduce forward flow f blood and
increase EDV and pressure  aggravate shock

4)     Cardiac Arrhythmias

Bradycardia cause a reduction in cardiac output thereby
aggravating shock

5)     Greatly Increased Afterload

Aortic or mitral stenosis
                                                          31
Chest Radiography: A Useful Technique For
Diagnosis Of Cardiogenic Shock

Most patients with cardiogenic shock exhibit:

@     Interstitial pulmonary oedema

@     Cardiomegaly

@     Alveolar oedema




                                                32
 Cardiogenic Shock
 Cardiogenic Shock
 R.A.S.
  R.A.S.                                  Catecholamine
                                          Catecholamine
                       CO
                       CO
Activation
Activation                                   Release
                                              Release



                  Myocardial                      SVR
                                                   SVR
                  Myocardial
Volume/
Volume/           O2 demand
                   O2 demand
 Preload
 Preload                               O22
                                       O
                                     supply
                                      supply

                                               Peripheral
                                                Peripheral
    Impaired                                   & pulmonary
                                               & pulmonary
     Impaired                 Dyspnea
                              Dyspnea            edema
myocardial function
myocardial function                                edema
                                                     33
Hypovolemic Shock

Diminished blood volume

Due to excessive bleeding (haemorrhage)

Loss of fluids derived from the plasma (e.g. diarrhoea, excessive
urinary loss and extensive sweating)

Prominent in burns patients. Why?

a)     Increase blood viscosity  venous stasis

b)     Increased capillary permeability (plasma shifts          from
       intravascular compartments to interstitial space)

Plasma proteins lost  limit fluid return to capillary
                                                           34
Neurogenic Shock

“Generalized vasodilation caused by decreased vasomotor
tone”

Blood volume remains normal

However, the capacity of the blood vessels is increased
Venous return is therefore diminished

Cardiac output is reduced and so is tissue perfusion

Reduction in vasomotor tone can occur at the level of the
vasomotor centre (neurogenic shock) or at the level of the blood
vessels (Vasogenic shock)

                                                          35
Neurogenic shock is enhanced by conditions in which the
vasomotor tone is reduced:

@    Spinal anaesthesia

@    Direct damage to the vasomotor centre of the medulla
@    Altered functions of the vasomotor centre in response
     to low blood glucose levels (insulin shock)

@    Actions of tranquilizer, narcotic or sedative drugs

@    Spinal cord injury




                                                           36
                    Spinal shock
   Pre-ganglionic symp
   fibres




Symp. ganglia




                                   37
              Spinal shock
• Occurs typically minutes / hours after onset
  of spinal cord lesion
• May be associated with normal spinal X-
  ray: >10% in children, 2 – 3% in adults
  SCIWORA
• Often need MRI / CT scan to demonstrate
  lesion
• Severity proportional to level of lesion


                                             38
Neurogenic Shock
Neurogenic Shock
   Sympathetic Tone
   Sympathetic Tone             Vascular Tone
         Or                      Vascular Tone
          Or
 Parasympathetic Tone
 Parasympathetic Tone


                 Tissue
                 Tissue    Massive Vasodilation
                            Massive Vasodilation
                perfusion
                perfusion




   Cardiac Output
   Cardiac Output            SVR & Preload
                              SVR & Preload

                                              39
Anaphylactic Shock
Anaphylactic Shock

 “Container failure”
 “Container failure”
 Massive & systemic allergic reaction
 Massive & systemic allergic reaction
 Large release of histamine
 Large release of histamine
 Increases membrane permeability &
 Increases membrane permeability &
  vasodilation
   vasodilation




                                         40
Septic Shock

Also known as endotoxic shock

Results from widespread, overwhelming infections

1/3 of cases caused by gram-positive organisms such as
streptococci, pneumococci and staphylococci (50% mortality rate)

Gram-negative infections resulting in shock cause higher mortality
rates (75%) (E.Coli infections)

Patients at risk are:

@      Patients with indwelling catheters
@      Chronic debilitating disease
                                                           41
      Psychogenic Shock

   Simple fainting (syncope)
   Caused by stress, pain, fright
   Heart rate slows, vessels dilate
   Brain becomes hypoperfused
   Loss of consciousness occurs

    What two problems combine to produce
     hypoperfusion in psychogenic shock?

                                           42
Fluid
Fluid

 Must have adequate
 Must have adequate
  amounts of
   amounts of
  hemoglobin
   hemoglobin
 Must have adequate
 Must have adequate
  intravascular volume
   intravascular volume




                          43
Maintenance of Fluid Volume
Maintenance of Fluid Volume

 Renin-Angiotensin-Aldosterone system.
 Renin-Angiotensin-Aldosterone system.
  Works through kidneys to regulate balance
  Works through kidneys to regulate balance
   of Na+ and water.
   of Na+ and water.




                                         44
   Renin-Angiotensin-Aldosterone
   Renin-Angiotensin-Aldosterone
        Plasma
        Plasma                           Kidney
                                          Kidney
        volume
         volume
                  Detected by       (juxtaglomerular
                                     (juxtaglomerular
 &/Or                                   apparatus)
                                         apparatus)
         [Na+]
         [Na+]                                    Releases
                     Via ACE
                     (Angiotensin
                     Converting         Renin
                                        Renin
                     Enzyme)
                                        Converts

Angiotensin II…
Angiotensin II…
                          Angiotensin I… Angiotensinogen
                          Angiotensin I…
                                                          45
   Renin-Angiotensin-Aldosterone
   Renin-Angiotensin-Aldosterone
                              vasoconstriction
                              vasoconstriction          PVR
                                                         PVR
Angiotensin II…
Angiotensin II…
                                   thirst
                                   thirst

              ADH
              ADH
                                             Fluid
                                              Fluid
          (anti-diuretic
           (anti-diuretic                                   BP!
                                                            BP!
            hormone)                         volume
                                              volume
             hormone)


   Adrenal
   Adrenal
                  Releases                                 Na+
                                                           Na+
   cortex                        Aldosterone
                                 Aldosterone           reabsorption
    cortex                                              reabsorption
                                                              46
Disseminated Intravascular
Disseminated Intravascular
Coagulation
Coagulation
“A systemic thrombohemorrhagic disorder
 “A systemic thrombohemorrhagic disorder
    … with evidence of:
    … with evidence of:
1) Procoagulant activation
 1) Procoagulant activation
2) Fibrinolytic activation
 2) Fibrinolytic activation
3) Inhibitor consumption
 3) Inhibitor consumption
4) End-organ failure”
 4) End-organ failure”

               Bick, R.L. Seminars in Thrombosis and Hemostasis 1996

                                                               47
Pathophysiology of DIC
Pathophysiology of DIC

 Uncontrolled acceleration of clotting
 Uncontrolled acceleration of clotting
  cascade
  cascade
 Small vessel occlusion
 Small vessel occlusion
 Organ necrosis
 Organ necrosis
 Depletion of clotting factors
 Depletion of clotting factors
 Activation of fibrinolysis
 Activation of fibrinolysis
 Ultimately severe systematic
 Ultimately severe systematic
  hemorrhage
  hemorrhage

                                          48
Container
Container

 Vasculature is continuous, closed and
 Vasculature is continuous, closed and
  pressurized system
  pressurized system
 Microcirculation responds to local tissue
 Microcirculation responds to local tissue
  needs
  needs
 Blood flow dependent on PVR
 Blood flow dependent on PVR




                                        49
Fick Principle
Fick Principle

 Effective movement and utilization of O22
 Effective movement and utilization of O
  dependent on:
  dependent on:
  Adequate fio22
  Adequate fio
  Appropriate O22 diffusion into bloodstream
  Appropriate O diffusion into bloodstream
  Adequate number of RBCs
  Adequate number of RBCs
  Proper tissue perfusion
  Proper tissue perfusion
  Efficient hemoglobin „loading‟
  Efficient hemoglobin „loading‟



                                            50
Fick Principle
Fick Principle

 Perfusion = Arterial O22 Content --
 Perfusion = Arterial O Content
  Venous O22 Content
  Venous O Content
 Affected by:
 Affected by:
  Hemoglobin levels
  Hemoglobin levels
  circulation of RBCs
  circulation of RBCs
  distance between alveoli and capillaries
  distance between alveoli and capillaries
  pH and temperature
  pH and temperature



                                              51
         Offloading Oxygen in Tissues
         Offloading Oxygen in Tissues
                                                     oxyhemeglobin
                                    pH 7.4
             Remember:
             Remember:
             CO22 [H++]
             CO  [H ]
Saturation




                                                          pH 7.35




                                           pH shifts curve to right
                                          ••pHshifts curve to right
             deoxyhemeglobin                offloading’ to tissues
                                          ••‘‘offloading’to tissues



                               Pressure
                                                                 52
Causes of Inadequate Perfusion
Causes of Inadequate Perfusion
 Inadequate pump
 Inadequate pump
   Inadequate preload
   Inadequate preload
   Poor contractility
   Poor contractility
   Excessive afterload
   Excessive afterload
   Inadequate heart rate
   Inadequate heart rate
 Inadequate fluid volume
 Inadequate fluid volume
   Hypovolemia
   Hypovolemia
 Inadequate container
 Inadequate container
   Excessive dilation
   Excessive dilation
   Inadequate systematic vascular resistance
   Inadequate systematic vascular resistance

                                                53
Cellular Response to Shock
Cellular Response to Shock
 O2
 O2             Tissue
                 Tissue            Impaired cellular
                                     Impaired cellular
 use
  use           perfusion
                perfusion              metabolism
                                       metabolism

Anaerobic
 Anaerobic      Stimulation of
                Stimulation of           Impaired
                                          Impaired
metabolism
metabolism   clotting cascade &
              clotting cascade &          glucose
                                           glucose
                inflammatory
                 inflammatory               usage
                                            usage
                   response
                    response
  ATP
  ATP
synthesis
 synthesis
              Intracellular Na++
              Intracellular Na
                   & water
                   & water           Cellular edema
Na++Pump
Na Pump                              Cellular edema
 Function
 Function                            Vascular volume
                                     Vascular volume
                                                 54
Stages of Shock
Stages of Shock

 Compensated
 Compensated
 Uncompensated
 Uncompensated
 Irreversible
 Irreversible




                  55
Compensated Shock
Compensated Shock

 Defense mechanisms are successful in
 Defense mechanisms are successful in
  maintaining perfusion
  maintaining perfusion
 Presentation
 Presentation
  Tachycardia
  Tachycardia
  Decreased skin perfusion
  Decreased skin perfusion
  Altered mental status
  Altered mental status




                                    56
Uncompenstated Shock
Uncompenstated Shock

 Defense mechanisms begin to fail
 Defense mechanisms begin to fail
 Presentation
 Presentation
  Hypotension
  Hypotension
  Prolonged Cap refill
  Prolonged Cap refill
  Marked increase in heart rate
  Marked increase in heart rate
  Rapid, thready pulse
  Rapid, thready pulse
  Agitation, restlessness, confusion
  Agitation, restlessness, confusion



                                        57
Irreversible Shock
Irreversible Shock

 Complete failure of compensatory
 Complete failure of compensatory
  mechanisms
  mechanisms
 Death even in presence of resuscitation
 Death even in presence of resuscitation




                                       58

				
DOCUMENT INFO
Shared By:
Categories:
Tags:
Stats:
views:0
posted:3/23/2011
language:English
pages:58