respiratory failiure Flashcards
define type 1 respiratory failure
hypoxic, lung failure
define type 2 lung failiure
pump failure, hypercapnic
to be classified as having hypoxaemia what does your PaO2 have to be
PaO2 < 8kPa
what are the causes of hypoxaemia
vq mismatch, aveolar hypoventialation, impaired diffusion, low partial pressure of inspired oxygen, anatomical shunt
what is the most common cause of aterial hypoxaemia
vq mismatch, it’s the most critical factor
does the v/q ratio change depending on the region
Regions of high ventilation should have high blood flows i.e. base of lung Regions of low ventilation should have low blood flows i.e. apex of lung Inadequate gas exchange occurs when regional VA /Q << 1 or VA /Q >> 1
what is dead space
ventilation is there but no gaseous diffusion can occur due to poor perfusion
what is shunt
poor ventilation but good perfusion
name the reflex mechanisms in lung that keep v/q as close to 1 as possible in healthy lungs
hypoxic pulmonary constriction
how does lung disease cause hypoxia and hypercapnia
In lung disease there is an imbalance
between VA and Q resulting in
hypoxaemia and hypercapnia
define hypercapnia
PaCO2 > 6.0kPa
partial pressure of carbon dioxide in arteries equals
VCO2(co2 produced in body tissues) divided by aveolar ventilation
what is more important for hyypercapnia ventilation or oxygen
Adequate alveolar ventilation is
essential to maintain carbon dioxide
homeostasis
what determines aveolar ventilation
Alveolar ventilation is determined by
respiratory rate and tidal volume
Why do some patients develop
hypercapnia on oxygen therapy?
Worsened VA
/Q matching due to attenuation
of hypoxic pulmonary vasoconstriction. more oxygen causes vasoconstricted areas of lung to dilate spreading blood flow to areas of lung that are bad.
• Decreased binding affinity of haemoglobin for
CO2 (Haldane effect)
• Decreased VE
