Shock Flashcards
What is shock?
Shock is inadequate perfusion to the organ tissues which leads to organ injury
What leading factor ofen causes shock?
Hypotension- the blood pressure falls to levels too low to maintain adequate perfusion to the tissues
What equation is used to work out mean arterial blood pressure? How does each factor represent a cause of shock?
MABP= CO X SVR
Systemic vascular resistance falls with vasodilation and decreased circulating volume. Cardiac output falls with decreases in stroke volume or heart rate. A number of different causes can therefore be applied to this equation to cause shock.
What is stroke volume dependent on?
Preload- the venous return to the heart
Contractility- the pumping action of the myocardium
How can the causes of a decreased cardiac output be divided?
Decreased preload
Decreased contractility
Decreased rate or increased rate (too fast for filling)
What is the equation for cardiac output?
CO= SV X HR
What is the equation for SV?
EDV- ESV
What is another name for the end diastolic volume?
Preload
What is starling’s law?
Increased the EDV increases the contractility of the myocardium and therefore increases SV
Force of ventricular contraction is dependent on the length of the ventricular muscle fibres in diastole- greater filling= greater stretching of the fibres
What factors increase EDV?
Increasing venous return
Increased central venous pressure
What 5 factors affect venous return to the heart?
Blood volume Skeletal muscle pump action Gravity Venous tone Respiratory pump
At rest around 60-70% of the blood volume is found within the venous circulation and this therefore represents a large pool of blood that can be used to increase EDV.
What is the preload?
The load of blood to the heart at the end of diastole. This is the EDV.
Due to starling’s law, increases in preload increase the stretch on the muscle fibres which in turn generates greater forces of contraction and greater stroke volumes.
What is the afterload?
The load against which the heart must contract to eject the stroke volume.
Aortic or pulmonary artery pressures are the most important in determining this.
Pressure is determined by volume and compliance, compliance reduces with increased vascular tone.
What are some causes of a decreased preload/EDV?
Compression of SVC- Tension Pneumothorax
Compression of heart chambers- Pericardial Tamponade
Reduced effective circulating volume- Haemorrhage, Dehydration
What are some causes of cardiogenic shock?
Congestive heart failure
MI
Arrhythmia
What are some causes of shock that cause shock through reduced SVR?
Anaphylaxis
Sepsis
Neurogenic shock (loss of sympathetic vasoconstriction on peripheral vascular tone)
What investigation can confirm the presence of shock?
Lactate- this can be obtained rapidly via an ABG or VBG
What are some signs of end organ perfusion?
Altered mental status, agitation, confusion- cerebral hypoxia
Low urine output- Renal hypoperfusion
Prolonged CRT- Decreased skin perfusion
What immediate action can be done to investigate for causes of shock/haemorrhage in ED?
FAST Scan
H- Heart, ventricular function and presence of tamponade
I- Inferior Vena Cava for volume status and CVP indication. If dilated it is high and if flat or collapsed it is low.
M- Morrison’s Pouch- Hepatorenal Recess and check other areas in the abdomen and pelvis for any bleeding
A- Aorta- Look for AAA signs and potential for bleeding
P- Pneumothorax
What pH change is likely to be seen on an ABG in a shocked patient?
Metabolic acidosis due to the lactate and anaerobic metabolism involved
How can the causes of hypovolemic shock be divided?
Hemorrhagic- Bleeding
Non-Haemorrhagic- GI Losses, Vomiting, Diarrhoea, Renal Losses, DKA, Diabetes Insipidus, Dehydration, Third Spacing
What are some causes of non-hemorrhagic shock?
GI Losses- Vomiting, Diarrhoea
Renal Losses- DKA, Diabetes Insipidus
Third Spacing- Burns, Pancreatitis
Dehydration
Outline the basic management for shock
Resus First- Fluids, Blood etc.
Treat the underlying cause
If cause of shock is haemorrhage what needs to be given?
You replace what is lost, therefore use blood products, if they’re bleeding give them blood
Replace in a 1:1:1 ratio of Packed Red Cells, Plasma and Platelets
What scan can indicate deficiencies in blood clotting rapidly?
TEG Scan
Above what level is a lactate concerning and indicative of shock?
Above 2
