gas transport, control of ventilation & ABGS Flashcards
(60 cards)
how is oxygen transported in the blood?
-bound to haemoglobin - 98%
-dissolved in plasma 2%
how is CO2 transported in the blood?
-bicarbonate -92%
-bound to Hb -3%
-dissolved in plasma 5%
what are the 3 different receptors that control ventilation in the lungs?
-mechanoreceptors
-irritant receptors
-chemoreceptors
how do mechanoreceptors control ventilation?
-respond to stretch during inflation
-a very large inflation can lead to critical stretch of the lung parenchyma (alveoli) causing the herni bruer reflex
where are the mechanoreceptors found in the resp system?
-bronchial smooth muscle, trachea and visceral pleura
how do irritant receptors work on controlling ventilation?
-respond to irritants such as cigarette smoke, dust allergens or secretions
-they cause a change in respiratory depth or frequency and induce a cough, sneeze or bronchospasm
why are chemoreceptors important in controlling ventilation?
-they constantly sample arterial blood to maintain resp gases and PH within normal range
what is the function of the central chemoreceptors (in the brainstem)?
-their function is to sense increased H+ concentration in the CSF
what are the peripheral chemoreceptors most sensitive to?
low pO2 in the arterial blood
describe the normal cycle of control of ventilation in a patient with a slight increased pCO2 level in blood and CSF?
-increased pco2 will stimulate the central chemoreceptors In medulla
-this stimulates the inspiratory muscles
-increases the respiratory rate
-removes more co2 from the body
-decreases PCO2
-decreases chemoreceptor stimulation
what is respiratory failure?
a clinical condition that happens when the resp system fails to maintain its main function, which is gas exchange
-ie Pa02 is reduced (lower than 60mmHg) and or paCO2 is raised (ie above 50mmHg)
-classified into type 1 or type 2
what is type 1 resp failure?
-hypoxemia
- low levels of oxygen (below 60mmHg) with normal or subnormal paCO2
-gas exchange is impaired at the level of he alveolo-capillary
what are examples of type 1 resp failure?
-covid 19
-severe pneumonia
the lungs can still excrete CO2 / ie get rid of it
what is type 2 respiratory failure?
-hypoxemia (pa02 is less than 60mmHg)
-hypercapnia - raised PaC02 levels (higher than 50mmHg)
-common in COPD patients
describe the hypoxic drive theory
- in normal healthy people, elevated CO2 will drive respiration
-but in COPD pts, they will have chronically high CO2 levels
-in some pts, their chemoreceptors have become desensitised to the elevated CO2
-therefore, in these patients it is the decreased O2 (hypoxia) that drives respiration
what is a risk if you give a COPD patient too much oxygen therapy?
-it can blunt their hypoxic drive
-therefore, there respiration will begin to slow causing further rise in CO2 levels and potential loss of consciousness
what SP02 levels are acceptable for people with COPD?
between 88-92%
describe v/q mismatching w/ the administration of oxygen therapy
-poorly ventilated alveoli cause the body to redistribute blood flow - alveolar vasoconstriction
-administering O2 will cause vasodilation
-alveoli are still poorly ventilated but are now better perfused - causing a V/Q mismatch
describe the haldane effect
-describes how the binding of oxygen to haemoglobin affects the binding and release of carbon dioxide (CO₂) in the blood.
- how the deoxygenation of blood increases its ability to carry CO2
what is hypoxia?
reduced level of tissue oxygenation
what is hypoxemia?
it is defined as a decrease in the partial pressure of oxygen in the blood
give an example of when a patiet can develop hyoxemia without hypoxia?
if there is a compensatory increase in Hb level and cardiac output - therefore more O2 can get to the tissues
what can cause hypoxaemia (low levels of o2 in blood)?
-respiratory depression
-resp muscle weakness
-obstructive airway diseases
-pulmonary oedema
-acute resp distress syndrome
alveolar collapse
-pneumothroax
what are examples of treatment hypoxemia?
-supplemental oxygen
-physio - positioning, clearance of secretions
-non invasive ventilation etc
-mechanical ventilation - sedated - eliminates the metabolic cost of breathing
