CR Revision 5 Flashcards
What determines the alveolar to arterial PO2 difference? [1]
What is usual Alveolar-arterial O2 difference not normally greater than? [1]
Shunting determines the alveolar to arterial PO2 difference
The normal A-a O2 difference is not normally greater than 1.3 kPa
How do you calculate normal aterial PaO2? [1]
Normal PaO2 = 13.6 – (0.044 x age in yrs) kPa
What is shunting (of the lungs)? [1]
What can shunting be caused by [1]
]
When an area of the lung is perfused but not ventilated. Blood is transported through the lungs without taking part in gas exchange
Can be caused by Arteriovenous malformations (AVMs)
What causes changes in oxygen dissociation curve?
Shifts to L → Lower oxygen delivery, caused by:
Low [H+] (alkali)
Low pCO2
Low 2,3-DPG
Low temperature
Label A & B [2]
A: Lung failure
B: Pump failure
Type 2 Respiratory Failure is an imbalance between which three factors? [3]
Imbalance between:
- Neural respiratory drive
- Load of resp. muscles
- Capacity of the resp. muscles
LEARN ! Name 4 reasons that could cause hypoventilation
Increased resistance as a result of airway obstruction (e.g.COPD)
Reduced compliance of the lung tissue/chest wall (e.g. pneumonia, rib fractures, obesity).
Reduced strength of the respiratory muscles (diaphragm) (e.g. Guillain-Barré, motor neurone disease)
Drugs acting on the respiratory centre reducing overall ventilation (e.g. opiates)
Name three consequences of CO2 retention [3]
State for each their clinical signs [3[
End-organ hypoxia
- Altered mental status
- Bradycardia and hypotension (late)
Haemoglobin desaturation
- Cyanosis
CO2 Retention
- Flap (asterixis): ask a patient to extend arms out, close eyes, should be able to hold for 30 secs
- Bounding pulse
What would be the threshold limit pulse ox saturation (SpO2) that is a critical threshold?
~94% is a critical threshold. Below this level a small fall in PaO2 produces a sharp fall in SpO2
If the SpO2 is >94% the the PaO2 should be >[]kPa
If the SpO2 is >94% the the PaO2 should be >10kPa
First line of treatment for respiratory failure? [1]
Oxygen
If giving oxygen therapy, what is SpO2 target?
94-98%
Avoid hyperoxia in patients recieving supplemental oxygen !
Which type of patients would require the following?
- Oxygen masks / nasal cannulae
- Face mask with reservoir bag
- Venturi mask
Oxygen masks, nasal cannulae
Patient with normal vital signs (post-op)
Face mask with reservoir bag
Higher O2 concentration needed (asthma attack, pneumonia, sepsis)
Venturi mask
Controlled treatment in long-term respiratory failure (COPD)
Describe how conduct oxygen therapy?
High flow Oxygen
Continuous oximetry should be started immediately
Monitor:
Vital signs
ABGs
What are the two main mechanisms that cause ischaemic stroke? [2]
- Thrombosis: The formation of a blood clot in an artery normally at the site of an atheroma or atherosclerosis.
- Embolism: An embolus blocks a downstream artery after originating from somewhere else in the body, usually having broken off from a thrombus.
Explain MoA of how atherosclerosis causes ischaemic stroke
Endothelial damage allows lipoproteins and monocytes to adhere to the vessel wall and enter the intima.
Monocytes differentiate into macrophages and engulf the lipoprotein and become known as foam cells.
Further accumulation of cholesterol and foam cells forms a fatty streak.
Foam cells release pro-inflammatory cytokines which leads to smooth muscle cell proliferation. and connective tissue to deposition in the fatty streak.
These changes form a fibrous cap over the lipid core.
A necrotic core can form due to the lack of capillaries.
Plaque rupture removes the endothelium which exposes the fibrous cap leading to thrombosis and occlusion of the artery
What is a watershed ischaemic stroke? [1]
Sudden BP drop by more than 40mmHg, then there is low cerebral blood flow = global ischaemia leading to ‘watershed infarcts’ in vulnerable areas of cortex between boundaries of different arterial territories
brain ischemia that is localized to the vulnerable border zones between the tissues supplied by the anterior, posterior and middle cerebral arteries
When is common to see watershed stroke?
Sepsis patients
What is the most important risk factor for Haemorrhagic stroke? [1]
Hypertension !
Whats the difference between Intracerebral haemorrhage vs Subarachnoid haemorrhage (SAH)?
Which causes a thunderclap headache?
Intracerebral haemorrhage is bleeding into the brain parenchyma: basal ganglia particularly effected
SAH is bleeding into the subarachnoid space. thunderclap headache
Which artery is most common to have a stroke in? [1]
Middle cerebral artery
Which drug classes would use for primary prevention of stroke? [3]
Control of which disease would allow prevention of stroke? [1]
Primary prevention:
- Cholesterol: statin
- AF: anticoagulation
- Good diabetic control
- BP: antihypertensives
What are the 3 overlying causes of cellular death in stroke? [3]
Mechanical compression
Cerebral Oedema
Excitotoxicity
Excitotoxicity of stroke
