Session 12 - Shock Flashcards
What is the main cause of peripheral vascular disease?
-Partial occlusion of arteries due to atheromatous plaque
What is intermittent claudication?
- Intermittent calf pain due to limited bloodflow at rest causing downstream vasodilation
- Upon exercise vessels cannot dilate anymore and BF cannot be increased resulting in the accumulation of toxic metabolites
How does peripheral vascular disease present in the veins?
- Varicose veins
- Deep vein thrombosis
At what point does coronary artery occlusion become problematic?
->70% occlusion
At what point does coronary occlusion produce pain on rest?
-90%
What is the difference between stable angina and unstable angina?
-Unstable angina can be present at rest
How does unstable angina present differently from MI?
- Does not radiate as much
- Limited duration and smaller obstruction
What is the usual cause of progression from stable angina to unstable angina?
-Disruption of atherosclerotic plaque and thrombus formation
How is unstable angina separable from NSTEMI clinically?
-No detectable necrosis in unstable angina ie no cardiac enzymes or troponin elevation
What is the difference between NSTEMI and STEMI?
- STEMI is full thickness of myocardial wall
- NSTEMI is more limited
How is an STEMI different from STEMI on ECG?
-NSTEMI has ST depression
Describe the ECG changes of a STEMI
- ST elevation
- Pathological Q waves
- Twave inversion
When is a Q wave pathological?
-Greater then 1mm in width and 2 small squares in height
Define cardiac arrest
-Unresponsiveness associated with a lack of pulse due to the heart stopping or ceasing to pump effectively
What is asystole?
-Loss of electrical and mechanical activity
What is ventricular fibrillation?
-A form of cardiac arrest where there is asynchronous contraction of ventricles
What are the main causes of ventricular fibrillation?
- Following an MI
- Electrolyte imbalance
- Some arrythmias
Name an arrhythmia which develops to ventricular fibrillation
-Long QT syndrome and Torsades de pointes
What are the modes of treatment for cardiac arrect?
- Basic life support -> chest compressions and external ventilation
- Advanced life support -> defibrillation
- Adrenaline
How does defibrillation work in ventricular fibrillation?
- Electrical current delivered to the heart
- Depolarises all the cells and puts them into refractory period
- Allows coordinated electrical activity to restart
How does adrenaline help treat cardiac arrest?
- Increases total peripheral resistance
- Enhances myocardial function
What is the equation to calculate MABP?
-COxTPR
What are the two groups of causes of shock?
- Decrease CO
- Decrease TPR
Define shock
-Circulatory collapse when the arterial blood pressure is too low to maintain adequate perfusion
What are the three causes of decreased CO leading to shock?
- Mechanical -> pump cannot fill
- Pump failure
- Loss of blood volume
What is the main cause of a decrease in peripheral resistance?
-Excessive vasodilation
Name the 3 types of shock due to falls in CO
- Cardiogenic shock
- Mechanical shock
- Hypovalaemic shock
Define cardiogenic shock
-Acute failure of the heart to maintain cardiac output
What are the main causes of cardiogenic shock?
- Following MI due to damage to LV
- Serious arrhythmias
- Acute worsening HF
How is the CVP effected in cardiogenic shock?
-Can be normal or raised as heart fills but fails to pump effectively
What are the main issues in cardiogenic shock?
- Drop in arterial BP
- Poor perfusion to coronary arteries -> makes pump failure worse
- Poor perfusion to kidneys -> oliguria
What are the main causes of mechanical shock?
- Cardiac tamponade
- Pulmonary embolism
What is a cardiac tamponade?
- Blood or fluid build up in pericardial space
- Restricts filling of the heart -> limits end diastolic volume
What are the clinical features of mechanical shock?
- High central venous pressure
- Low arterial blood pressure
Is the electrical activity of the heart effected in mechanical shock?
-No
Describe the effect of a pulmonary embolus occluding a large pulmonary artery
- Pulmonary artery pressure high
- RV cannot empty
- High CVP
- Reduced flow to left heart
- Limits filling of heart
How could you tell the difference clinically between mechanical shock caused by cardiac tamponade and that caused by PE?
- PE will have chest pain and dyspnoea
- Cardiac tamponade will have muffled heart sounds
What is hypovolaemic shock?
-Shock caused by a reduced blood volume
What is the most common cause of hypovolaemic shock?
-Haemorrhage
Over what % loss does hypovolaemic shock occur?
-20%
What are the clinical signs of hypovolaemic shock?
- Tachycardia
- Weak pulse
- Pale skin
- Cold, clammy extremities
Besides haemorrhage, name 2 other causes of hypovolaemic shock
- Severe burns
- Severe diarrhoea or vomiting and loss of Na+
What decompensative mechanism occurs in hypovolaemic shock?
- Peripheral vasoconstriction impairs tissue perfusion
- > tissue damage due to hypoxia
- > release of chemical mediator causes vasodilation and TPR falls
- > AP falls dramatically
- > Vital organs no longer pefused
What is distributive shock?
-Shock caused by profound peripheral vasodilaiton
Name 2 types of distributive shock
- Anaphylactic
- Toxic
What causes toxic shock?
- Septicaemia caused by endotoxins being released by circulating bacteria causes profound vasodilation
- Dramatic fall in TPR followed by a fall in AP as CO cannot compensate
What are the clinical signs of toxic shock?
- Tachycardia
- Warm, red extremities
How is CO attemted to be increased in toxic shock?
- Drop in AP detected by baroreceptors
- Increased sympathetic output
- Heart rate and SV increased
In toxic shock, if vasoconstriction is stimulated by the sympathetic nervous system, why does vasodilation occur?
-Vasoconstrictor effect overridden by mediators of vasodilation
What is the cause of anaphylactic shock?
- Severe allergic reaction causes release of histamine from mast cells
- Histamine is a powerful vasodilator which causes a dramatic fall in TPR
- Dramatic drop in BP which cannot be overcome by sympathetic response
Why do people in anaphylactic shock have difficulty breathing?
-Mediators also cause bronchoconstriction and laryngeal oedema
What are the clinical signs of anaphylactic shock?
- Difficulty breathing
- Collapsed
- Rapid heart rate
- Warm red extremities
Define hypertension
-Consistent BP over 140/90
What are the three key sites of BP regulation?
- Kidneys
- Heart
- Vasculature
What are the possible consequences of longstanding hypertension?
- LV hypertrophy and risk of HF
- Risk of arterial disease
- > coronary arteries (MI/angina)
- > cerebral (stroke)
- > renal (kidney failure)
What are the two main causes of poor regional perfusion?
- Arterial occlusion
- Venous congestion
