Respiratory Flashcards
What are the 5 causes of hypoxaemia
reduced pi02 hypoventilation V/Q mismatch diffusion R-L shunt
How can drug induced collapse cause hypercapnia?
she has high co2 and has alveolar hypoventilation (this was due to narcotics reducing respiratory drive due to generalised cerebral depression after drug)
Spinal cord levels responsible for resp muscles?
anterior horn cells, major resp muscles - the spinal cord would be C3,4,5
3 main causes of hypercapnia
- Respiratory drive from brainstem - how much output is there causing you to breathe e.g heroin, morphine
- Neuromuscular transmission - need this to be intact, could be interrupted at any part of tract e.g C3,4,5, nerves exiting , could be effecting neuromuscular transmission, or something wrong with muscle
- Load (work of resp muscles) - resp muscles need to do two types of work - resistive work and elastic work, amount of work may be increased e.g lung disease or weight gain, also fatigue of muscle
3 main causes of hypercapnia
- decreased respiratory drive from brainstem- how much output is there causing you to breathe e.g heroin, morphine
- Neuromuscular transmission - need this to be intact, could be interrupted at any part of tract e.g C3,4,5, nerves exiting , could be effecting neuromuscular transmission, or something wrong with muscle, muscle weakness/fatigue
- Load (work of resp muscles) - resp muscles need to do two types of work - resistive work and elastic work, amount of work may be increased e.g lung disease or weight gain, also fatigue of muscle (lung elastic load increases)
Equation for A-a gradient
A-a gradient = 20- Pac0/0.8 - Pa02
How can we measure diffusion of gas ?
also can use exercise test
use CO because this binds to haemoglobin straight away so then we can tests its diffusion capability - is diffusion not perfusion limited, soluble, binds Hb
-often poor diffison can be masked until you try exercising as oxygen requirements increase so CO increases and if diffusion is imparied will not beable to get enough oxygen across membrane - time for rbc to travel the same distance will increase, so if problem wont get as much perfusion (graph of alveolar p02 vs time in capillary)
What does diffusion depend on?
3 reasons causing bad diffusion
- gas
- diffusion distance/thickness
- surface area
- haemoglobin
- capillary volume
-alveolar capillary block (increase fibrous tissue due to aspestos - thickened walls)
-loss of diffusing surface - emphysema
-Capillary volume / haemoglobin
pulmonary capillaries e.g if someone has pulmonary hypertension or embolism then will have abnormal diffusion thing, anaemia
Chronic obstructive pulmonary disease
-what is it
-FVC FEV1
-
airway limitation that is not fully reversible. The airway limitation is usually both progressive and associated with an abnormal inflammatory response of the lungs to noxious particles or gases
- Lower FVC and FEV1 - ratio is low
- get an inflammatory reaction to cigarette smoke and this causes damage to collagen and structure of lungs
- shortness of breath, cough, excess mucous production, reduced gas exchange
V/Q mismatch
what happens when you hyperventilate
- can only ventilate the normal compartment
- co2 and o2 saturation curves have very different shapes - which means we reduce content of CO2 but dont increase o2 much
- when you hyperventilate, then you get a decrease in co2 but not o2
- maintain pH by metabolic compensation, but can get worse V/Q
Worsening disease
-why is it bad to give oxygen ?
- unable to undertake compensatory hyperventilation
- increase paCO2 - ph is normalised by renal mechanisms
- dangers - high inspired o2, monitorign o2 saturatin
- bad to give o2 - because the only thing keeping ventilation going is the hypoxic drive due to low 02, so if this gets worse then will not get as much ventilation
what is dead space, and what is a shunt?
- Dead space is when there is no perfusion so get very low V/Q
- when there is a trapped alveolr, then cannot get ventilation, and have a shunt
How to test cause of V/Q mismatch vs a r-l shunt
if administer 100% oxygen and then measure pa02 would rise
- get not much improvement with a right to left shunt
- also would have normal lung function test
- widened A-a gradient
Why can some people go red when they are hypoxaemic?
-due to having erythropoietin because they are trying to stimulate more red blood cells to be made so that there can be more oxygen carrying
Advantages and disadvantages of FEV testing and peak expiatory flow
FEV
-reduced variability
-less effort dependent
-tight normal range - can distinguish between abnromal and normal easily
FEV1
-can classify between obstructive and restrictive lung disease
PEF - easy, cheap, effort dependent, high variability - not very good
