Shock Flashcards
Describe the features of cardiogenic shock.
ACUTE failure of heart to maintain cardiac output (chronic = heart failure)
Occurs after MI, acute worsening of heart failure, or serious arrhythmias (tachy/bradycardia)
Heart fills but cannot pump effectively
- CVP is normal/raised
- coronary arteries & renal arteries poorly perfused
Define circulatory shock. What are the two mechanisms by which this can occur?
SHOCK = acute condition of inadequate bloodflow
- circulatory: dramatic fall in ARTERIAL blood pressure
Mean arterial BP = Cardiac Output x Total Peripheral Resistance
Therefore can occur by a reduction in cardiac output/total peripheral resistance
Reduced cardiac output:
- cardiogenic shock (pump failure - ventricle cannot empty properly)
- mechanical shock (obstructive - ventricle cannot fill properly)
- hypovolaemic shock (reduced blood volume -> reduced venous return)
Reduced total peripheral resistance (distributive shock)
- toxic shock syndrome (septicaemia)
- anaphylaxis
Describe the features of mechanical shock.
Occurs due to cardiac tamponade
CARDIAC TAMPONADE = blood/fluid builds up in pericardial space -> restricts filling of heart -> limits end-diastolic volume
note: pericardial effusion called cardiac tamponade when heart function is adversely affected
- affects both sides of the heart
- high CVP (distended JVP)
- continued electrical activity
- can be due to massive PE -> occludes pulmonary artery -> right ventricle cannot empty -> high CVP -> reduced return of blood to left heart -> limits filling of left heart -> low atrial & arterial pressure
note: catheter in pulmonary artery = same pressure as in left atrium as catheter occluded flow in small vessels, so blood backs up from left atrium
note: left atrial pressure is raised due to compression of the heart
Describe the features of hypovolaemic shock.
Reduced blood volume (most likely due to haemorrhage)
Compensatory mechanism:
- tachycardia, positive inotropy, peripheral vasoconstriction, venoconstriction
- internal transfusion: increased peripheral resistance -> reduced capillary hydrostatic pressure -> net movement of fluid into capillaries –> raised blood volume
Can also occur due to severe burns, vomiting, diarrhoea, or loss of sodium
DECOMPENSATION:
Hypoxia -> vasodilators released -> total peripheral resistance falls -> multi-system failure
- cold extremities
- rapid, thready pulse (reduced systolic BP)
Give blood + electrolytes + crystalloid (increase oncotic pressure & reduce tissue fluid formation)
Determine volume to infuse by checking CVP via central line (until CVP rises into upper half of the normal range)
Describe toxic shock syndrome (septicaemia).
Circulating bacteria release endotoxins (& body releases inflammatory mediators e.g. alpha-TNF, leukotrienes in response)
Widespread vasodilatation & capillary leakage
Cardiac output increases to try and compensate for reduced total peripheral resistance
note: effect of vasodilation overrides vasoconstriction due to sympathetic stimulation
- red, warm extremities
- tachycardia
- fast, bounding pulse
Treatment: give crystalloid to increase blood volume & antibiotics to treat bacterial infection
Describe anaphylaxis.
Severe allergic reaction causes release of histamine from mast cells & basophils (increases capillary permeability, bronchoconstriction, vasodilatation) + prostaglandins, leukotrienes, cytokines, kinins
Vasodilation (despite symp. activation)
+ bronchoconstriction
+ laryngeal oedema
- red warm extremities
- tachycardia
- difficulty breathing
- fast, bounding pulse
Treat with adrenaline (vasoconstriction at high conc.)
note: initial increase in cardiac output due to increased symp., but then decreases due to capillary leakage
How would you treat cardiac tamponade?
Pericardiocentesis
Insert needles up and left under the xiphisternum (base of sternum) to avoid damaging the coronary vessels
