Lecture 20- Haemodynamic shock Flashcards
To control arterial BP
Cardiac output and peripheral resistance
Mean arterial BP=
CO xTPR
CO=
SV x HR
Therefore: Mean arterial BP=
SV x HR x TPR
Calculating maBP=
diastolic pressure + 1/3 pulse pressure
which organs will constrict blood vessels to maintain blood pressure (altered peripheral resistance)
heart
brain
Haemodynamic shock
Acute condition of inadequate blood flow throughout the body
- Catastrophic fall in aBP leads to circulatory shock
- Inadequate flow= vital organs not perfused
when thinking of the causes of shock think
BP= CO xTPR
fall in CO
- Mechanical- pump cannot fill properly e.g. hypertrophy
- Pump failure- arrhythmia
- Loss of blood volume- stabbing
fall in TPR
Excessive vasodilation e.g. sepsis
Shock due to fall in CO
Always a dramatic drop in arterial blood pressure.
1.Cardiogenic shock (pump failure)
2.Mechanical shock (obstructive)
3.Hypovolaemic shock
1.Cardiogenic shock (pump failure)
Ventricle cannot empty properly
1.Mechanical shock (obstructive)
Ventricle cannot fill properly
Cardiac tamponade
3.Hypovolaemic shock
Reduced blood volume leads to poor venous return
cardiogenic shock occurs when
- Acute failure of the heart to maintain CO- pump failure
- Heart is filling but not pumping properly
- Central venous pressure may increase
causes of cardiogenic shock
- Following MI- damage to left ventricle
- Due to serious arrhythmias
- Heart block
- Low heart rate
- Profound bradycardia
- Profound tachycardia
- Not enough time for the ventricles to fill in diastole
- Ventricular tachycardia
- Acute worsening of heart failure
effect of cardiogenic shock
- Poor perfusion of tissue
- Poorly perfused coronary artery
- Exacerbate the problem
- Kidney poorly perfused
- Will produce smaller amounts of dark urine
- May increase or decrease heart rate
mechanical shock due to
Restricted filling i.e. heart cant contract properly e.g. after a stab to the heart the blood that fills will increase pericardial fluid compressing it. No problem with emptying (continued electrical activity)
e.g. cardiac tamponade
cardiac tamponade
- Blood or fluid build up in pericardial space
- Restricts filling of the heart- limits end diastolic volume
- Affects left and right side of the heart
causes of mechanical shock
- High central venous pressure
- Low arterial blood pressure (shock)
- Reduction in stroke volume- reduces CO- reduce maBP
- Rapid heart beat
mechanical shock and pulmonary embolism
- Massive PE (most will be smaller and will not cause shock)
- Embolus occludes a large pulmonary artery
- Pulmonary artery pressure is high
- Right ventricle cannot empty
- Central venous pressure high
- Reduced return of blood to left heart
- Limits filling of the left heart
- Left atrial pressure is low
- Arterial pressure low- SHOCK
- Also chest pain and dyspnoea
How might an embolus reach the lung?
- Typically due to deep vein thrombosis
- Portion of thrombus breaks off (emboli)
- Travels in venous system to right side of the heart
- Pumped out via pulmonary artery to lungs
hypovolaemic shock occurs due to
reduced blood volume 9most commonly due to haemorrhage)
<20% blood loss
unlikely to cause shock
>20-30% blood loss
- signs of shock
30-40% blood loss
Substantial decrease in mean aBP and serious shock response
Severity of shock is related
to amount and speed of blood loss
during haemorrhage
- Venous pressure falls
- CO falls (starlings law)
- AP falls
- Detected b baroreceptors
-
Compensatory response
- Increase heart rate (chronotropy)and contractility (inotropy)
- Contractility- increase in slope
-
Compensatory response
Normally at the capillaries you get a small net movement of fluid out to the tissues…this then returns to the venous system via
the lymphatic drainage
In hypovolaemic shock this reverses
Internal transfusion
Increased peripheral resistances reduces the capillary hydrostatic pressure
Net movement of fluid into capillaries
Due to:
- Arterials constrict peripherally to maintains arterial blood pressure
- Downstream pressure is lower- in the capillariesà less fluid forced out due to hydrostatic pressure
signs of hypovolaemic shock in a patient
- Tachycardia
- Weak pulse
- Pale skin
- Cold, clammy extremities (sympathetic adrenergic sweating)
- Low central venous pressure
- Less blood in the system
Hypovolaemic shock can also due to:
- Severe burns
- Severe diarrhoea or vomiting and loss of Na+
Danger of decompensation
Peripheral vasoconstriction (shutdown) impairs tissue perfusion (to increase BP)
- Tissue damage due to hypoxia
- Release of chemical mediators- vasodilators
- TPR falls
- BP falls dramatically
- Vital organs no longer perfuses
- Multi system failure
long term responses to hypovolaemic shock
RAAS
ADH
If you get a 20% of blood volume loss–> restoration of body fluid volume in
3 days (if salt and water intake are adequate)
cardiac arrest is
- Unresponsiveness associated with lack of pulse
- Heart has stopped or has ceased to pump affectively
causes of cardiac arrest
- Asystole (loss of electrical and mechanical activity)
- Can get pulseless electrical activity (PEA)
- Ventricular fibrillation (uncoordinated electrical activity)
- Most common for of cardiac arrest
- Often following MI
- Or electrolyte imbalance
- Or some arrythmias (e.g. long QT and Torsades de Pointes)
treatment of cardiac arrest
- Basic life support- chest compression and external ventilation
- Advanced life support
-
Defibrillation
- Electric current delivered to the heart
- Depolarises all the cells at once- puts them into the refractory period
- Allows coordinated electrical activity of the heart
-
Adrenaline
- Enhances myocardial function
- Increases peripheral resistance
-
Defibrillation
distributive shocck
- Low resistance shock (normovolaemic- normal volume)
- Profound peripheral vasodilation- decrease TPR
- Blood vol= constant
*
what causes distributive shock
Toxic shock
Anaphylactic shock
toxic shock
- In response to sepsis- serious life-threatening response to infection
- Can lead to septic shock
- Endotoxins released by circulating bacteria
- Chemokines released in response to inflammatory response- profound vasodilation
- Dramatic fall in peripheral resistance, decrease in maBP
- Hypoperfusion of vital organs
- Also really leaky capillaries- reduced blood volume
- Increased coagulation and localised hypo-perfusion (fingers and toes)
