ABG Flashcards
ABG measurement give indication of
- ventiliation
- gas exchange
- acid-base status
Fi02
‘fraction of inspired o2’ which is the amount of oxygen that a patient is receiving
respiratory drive
- brain
- centeral (in the brainstem) and peripheral (in the heart) chemoreceptors
- mechanoreceptors is the lungs/chest wall (smooth muscle)
- other factors- pain/fear affect rate and depth
partial pressure
air moves in when
- Air moves in when air pressure inside the lungs is less than that in the atmosphere.
- Air moves through a concentration gradient
partial pressure
air moves out
- Air moves out when the pressure inside the lungs is greater than the pressure outside.
- Air moves through a concentration gradient
inhalation
- PP
- how is it achieved
- pressure in alveoli must be lower than atmospheric pressure for air to flow into the lungs
this is achieved by increasing the pressure in the lungs
increase in volume of the lungs mechanics
- Achieved by contraction of the diaphragm and external intercostals. As the diaphragm contracts it flattens thus increasing the vertical diameter of the thorax.
- As the external intercostals contract, the ribs elevate (bucket handle movement) thus increasing the anterior posterior and lateral diameters of the chest wall.
- As the size of the thoracic cavity increase, the volume increases and the pressure decreases. Air continues to flow as long as there is a pressure difference
- This inverse relationship is known as Boyle’s Law.
If someone doesn’t have the ability to change their lung volumes i.e. contract their muscles
- they cannot achieve adequate ventilation.
- (weak – weaning patient; fatigued – pt working hard for a long time; lack of innervation – SCI or progressive NMD)
- OR they could have abnormal MSK eg kyphoscoliosis
exhalation
- occurs due to the elastic recoil of the chest wall and lungs - doesn’t normally involve any muscle contraction.
- as muscles relax the size of thoracic cavity decreases –> volume decreases–> alveolar pressure increases
exhalation pressure
when the pressure inside the lungs is greater than the pressure in the atmosphere
factors affecting exhalation ihalation
- airway patency
- air flow
- respiratory drive
- skeletal structure
- muscle function
- BMI
obstructed airway can be affected by eg
sputum
bronchospasm
resp drive can be affected by
- GCS
- medication - opioids
- muscular dystrophy conditions
- Severe kyphosis or kyphoscoliosis affects chest wall biomechanics
skeletal structure affects breathing
overuse of muscles to fatigue them- need to build the muscles back up so theres no exhaustion of respiratory muscles to the point they cant ventilate themselves
obesity affects breathing by
increased subcutaneous fat lungs stay the same size but there’s an increased load on their lungs which makes it a lot harder to take in breaths
partial pressure definition
pressure exerted by each individual gas in a mixture of gases (air)
- gas diffuses down a pressure gradient (from high to low)
ficks law of diffusion
The rate of diffusion is proportional to the surface area and concentration difference and is inversly proportional to the thickness of the membrane
efficient diffusion needs
- a concentration gradient, a large surface area and a thin membrane.
- Large surface area created by the millions of alveoli.
Any disease state that can reduce the number of functioning alveoli will affect the surface area e.g. sputum, collapse, conditions such as emphysema
other factors affecting diffusion
- Other factors affecting diffusion – thickened membrane between alveoli e.g. fibrosis
- Bullae- big areas in lungs with lost lung tissue reduce surface area- affecting oxygenation
oxygen transport in blood
- 2% in plasma
- 98% RBC
oxygen heamoglobin dissociation curve
- Partial pressure is high in the capillaries in the lungs and so almost all of the Hb is saturated with O2
- Areas where partial pressure is low e.g. capillaries supplying the tissues of the body, Hb will release it’s O2 and therefore supply the cells with O2 for respiration.
