Theory; Respiratory Failure Flashcards
Why is surfactant important in gaseous exchange?
The oxygen dissolved into the surfactant in the alveoli in order to travel through alveolar wall to capillaries
How do co2 and o2 move between the alveoli and capillaries at the same rate?
O2 I has a bigger gradient but is less soluble
Co2 is more soluble but has a smaller gradient
When is gaseous exchange occurring by “diffusion” and when by “bulk flow”?
alveoli to capillary = diffusion
Capillary to tissue = bulk flow
How does o2 get from alveoli to capillary? (The pathway)
Alveoli -> Diffuses into surfactant -> alveolar wall -> capillary wall -> plasma -> rbc and haemoglobin
How does o2 get from capillary to tissue? (The pathway)
O2 diffuses through rbc wall -> plasma -> capillary wall -> tissue membrane -> mitochondria
Why is the oxygen disassociation curve normally an S?
The first oxygen molecule binds slower to haemoglobin. The next two can bind more easily but the fourth is again hard to bind
What 3 things is essential for respiratory function
Brain - control
Lungs - exchange organ
Chest wall, diaphragm, neuromuscular - R PUMP
What is respiratory failure
Inadequate gaseous exchange by respiratory system:
Co2 and o2 cannot be kept within normal parameters so arterial blood isn’t adequately oxygenated causing hypoxia and hypoxaemia and ventilation is too poor to eliminate co2 resulting in hypercapnia
What is hypoxaemia
Resp system fails to oxygenate arterial blood adequately
What is hypoxia
Failure to provide the body with enough oxygen or to ventilate well enough to eliminate co2
How do you diagnose respiratory failure
Arterial blood sample and partial pressure of o2 and co2
What is hypercapnea
Too much co2 in the blood stream
Normal co2 partial pressures in arterial blood
PaCO2 = 4.7 - 6kpan (35-45 mmHg)
Normal o2 partial pressure in arterial blood
PaCO2 = 10.7-13.3kpa (80-100mmHg)
What is acute vs. Chronic respiratory failure? And one example of both
Acute: mins to hours
Pneumonia
Chronic: days
COPD
What is type 1 respiratory failure?
Fail to maintain o2 levels in arterial blood
Failure to oxygenate
Hypoxaemia
ABG: Pa02 <8kpa
PaCO2 normal or low
Co2 can be low as peripheral chemoreceptors stimulate more breathing as response to hypoxaemia to try provide more oxygen but they’re just blowing out more co2
What is type 2 respiratory failure
Resp pump fails to ventilate
Failure to eliminate co2
Hypoxaemia and hypercapnia
ABGs: Pa02 <8kpa
PaCO2 higher >6.6kpa
How does hypoxaemia manifest
O2 sats (saO2) <90%
PaO2 <8kpa
What are 4 causes/ types of hypoxaemia
Hypoxic hypoxaemia: V/Q mismatch
Ischaemic hypoxaemia: V/Q mismatch
Anaemia hypoxaemia
Toxic hypoxaemia
Describe hypoxic hypoxaemias 4 causes
Diffusion problem!!
- Blood flow through unventilated lungs [SHUNTING] so vq mismatch
- COPD
- PF
- CF
- PNEUMONIA
- SPUTUM RETENTION - Acute bronchoconstriction
- ASTHMA - Problem transferring o2 across membrane; gas exchange across thickened membrane
- PF
- CARDIAC DISEASE ( HF, CongestiveCF, PO as diffusion is limited across resp membrane) - Insufficient o2
- altitude
What is the law relating to alveolar o2 exchange
Ficks law
Surface area X difference in concentration
————————————
Diffusion distance
(Lung SA, partial gas pressures, resp membrane thickness)
What would cause ischaemic hypoxaemia
Inadequate blood flow through lung
- PE
- pulmonary trauma
- destruction of pulmonary vascukature in COPD
What causes anaemia hypoxaemia
Reduction in carrying capacity if blood
- blood loss
- sickle cell crisis
- anaemia
What causes toxic hypoxaemia
Difficulty utilising oxygen
- inhalation burns and smoke
- CM poisoning
- cyanide poisoning
