gas transport, control of ventilation & ABGS Flashcards
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
how is hypoxemia classified?
-mild - 90-94%
-moderate -75-89%
-severe-75%
what are examples of clinical features of hypoxia?
-SOB
-cyanosis (blue or purple discolouration)
-arrhythmias
-peripheral vasodilation
-systemic hypotension
-hypoventilation
where is a blood sample taken for ABGs?
taken from the radial artery located in the wrist
what 2 sets of information can be obtained from ABGs?
-blood oxygenation
-blood acid-base balance
what is the purpose of ABG’s?
-evaluate acid-base status
-evaluate oxygenation status
-evaluate adequacy of ventilation
-to monitor pt
-to evaluate treatment
what are the 5 components of ABG’s?
-PH
-PaCO2
-PaO2
-HCO3
-SaO2
what is the normal PH of blood?
7.35-7.45
what are the normal levels of CO2 in arterial blood? In kPa ?
-4.6-6kPa
what are the normal levels of oxygen in the blood in kPa?
-10.6-13.3kPa
what are normal levels of HCO3 in arterial blood in mmol/L?
22-26mmol/L
what are normal SaO2 levels?
95-100
define PH
the measure of H+ ions in the blood
what is a blood PH below 7.35 termed?
acidotic
what is a blood PH above 7.45 termed?
alkalotic
what does BE stand for?
base excess
what are the 2 buffering systems in the body to keep the blood PH as close to 7.4 as possible?
-the resp system and dissolved CO2
-the renal system - dissolved bicarbonate (HCO3) produced by the kidneys
what its an very important chemical equation in terms of HCO3-, H+, CO2 and H20?
CO2+ H20== H2CO3= HCO3- + H+
what impact does the resp system have on the important chemical equation?
- it manipulates the CO2 levels
-increasing or decreasing the RR does this
how does the renal system impact the chemical equation?
it produces or retains HCO3- by eliminating hydrogen ions
what are the 4 possibilities outside the normal range for ABG results?
-respiratory acidosis
-respiratory alkalosis
-metabolic acidosis
-metabolic alkalosis
describe respiratory acidosis
- clinical disturbance due to alveolar hypoventilation
-production of CO2 occurs rapidly, and failure of ventilation promptly increases the partial pressure
why can resp acidosis happen?
-airway obstruction eg COPD, asthma
-depression of resp centre - eg sedatives etc
-pulmonary disorders eg fibrosis, ARDs
-neuromuscular disorders eg MND
what are examples of symptoms of resp acidosis?
-rapid, shallow respirations
-decrease in BP
-headache
-increase HR or CO
-muscle weakness
what would respiratory acidosis look like on ABG results?
-PH would be lower than 7.35
-PaCO2 would be increased
-HCO3 would be normal (no metabolic compensation)
describe respiratory alkalosis
-a clinical disturbance due to alveolar hyperventilation
-leads to decreased partial pressure of CO2
what can cause resp alkalosis?
-pain
-anxiety
-PE
-aspiration
-pneumonia
-hyperthyroidism
what are examples of symptoms of resp alkalosis?
-seizures
-deep rapid breathing
-hyperventilation
-tachycardia
-normal or low BP
-lethargy and confusion
-nausea and vomiting
how would resp alkalosis look like on a ABG?
-PH is high or above 7.45
-paCO2 is decreased !!
what is metabolic acidosis?
- a process where blood PH is low due to increased production of H+ by the body without enough HCO3- to neutralise it
why can metabolic acidosis occur?
- can occur due to gain of acid or loss of base
GAIN OF ACID
-increased H+ formation eg lactic acidosis
-decreased H+ exception eg renal failure
-ingestion of acid eg poisoning
LOSS OF BASE
-loss of bicarbonate
-eg dehydration ,and diarrhoea
what are examples of symptoms of a pt with metabolic acidosis?
-headache
-low BP
-muscle twitching
-warm or flushed skin
-decrease muscle tone
-hyperventilation
what does metabolic acidosis look like on an ABG?
-PH is decreased
-HCO3- decreased
what is metabolic alkalosis?
results from hydrogen ion loss or excessive intake of alkaline substances
how can metabolic alkalosis occur?
-GAIN OF BASE
- alkali administration eg sodium bicarbonate
LOSS OF ACID
-loss of H+ ions eg vomiting, NG suctioning
-shift of H+ ions into intracellular space eg hypokalemia
what are examples of symptoms associated with metabolic alkalosis?
-restlessness
-compensatory hypoventilation
-tachycardia
-confused
-loss of consciousness
-muscle cramps
what does metabolic alkalosis look like on an ABG?
-PH is high
-HCO3 is increased
