Integrated control of ventilation Flashcards
Respiratory acidosis or alkalosis occurs when a change in respiratory function causes a disturbance in pH
what is blood pH proportional to?
what is it called when pH is low? High?
what happens when one system is dysfunctional?
explain how the different systems can change the pH
As blood pH is proportional to the ratio of HCO3- to CO2, excessive changes may result from respiratory (CO2) or metabolic (HCO3-) dysfunction (↓pH = acidosis, ↑pH = alkalosis).
If one system is dysfunctional, other system will try to compensate and bring pH back to normal e.g respiratory acidosis by hyperventilation -> the metabolic system will try to compensate by inducing metabolic alkalosis
↑Ventilation = ↓PaCO2= ↑ pH ↓Ventilation = ↑PaCO2= ↓ pH ↓ HCO3 excretion = ↑[HCO3-] =↑ pH ↑ HCO3 excretion = ↓[HCO3-] =↓pH (unless PaCO2 or HCO3 changes proportionally, in the opposite direction)
Respiratory acidosis
what causes the increased pH?
Low pH accompanied by high PaCO2 is termed respiratory acidosis, as hypoventilation is responsible for the increase in CO2 levels and decreased pH
↓ventilation
↓
↑PACO2
↓
↑PaCO2 (hypercapnia)
↓
↑[H+] = ↓pH (acidosis)
Respiratory acidosis - what happens in the case of chronic hypo-ventilation?
what happens if no chronic hypo-ventilation?
In the event of chronic hypo-ventilation, HCO3- excretion must decrease to maintain normal pH.
↓HCO3 excretion by kidney as the renal system will detect there is a decrease in pH therefore try to retain bi-carbonate in the body -> as it is alkaline so up pH
Also, there will be an increased chemoreceptor feedback to increase repsiratory rate hence increase ventilation
If any pathology affects this, it’ll cause chronic respiraotry acidosis/hypoventilation
Respiratory alkalosis
what causes this and the high pH?
High pH accompanied by low PaCO2 is termed respiratory alkalosis, as hyperventilation is responsible for the decrease in CO2 levels and increased pH
↑ventilation
↓
↓PACO2
↓
↓PaCO2 (hypocapnia)
↓
↓[H+] = ↑pH (alkalosis)
Respiratory alkalosis - what happens in the case of chronic hyper-ventilation?
if not chronic hyper-ventilation?
In the event of chronic hyperventilation, HCO3- excretion must increase to maintain normal pH.
↑HCO3 excretion by kidney as a means to lower pH
Also, there will be an decreased chemoreceptor feedback to decrease repsiratory rate hence decrease ventilation
Causes of hyperventilation: anxiety
what does anxiety cause?
what reflex follows up on this?
why isnt this sufficient enough to bring the breathing rate down?
Anxiety trigger → panic attack ↓ Increased ventilation (tachypnoea) without increased metabolic demand ↓ Hyperventilation → Decreased PaCO2 ↓ Respiratory alkalosis
the reflex in a healthy person will still be there hence decreased chemoreceptor feedback and decreased respiratory rate
BUT because of the strength of the kind of emotional stimulus + anxiety panic attack, it isn’t suffiecient to bring breathing rate down so breathing rate remains high
Intervention for anxiety attack
why does this intervention work?
classic intervention is to get the person to breathe into a paper bag -> inspiring expired air will recycle the co2 + keep in body rather than expel into the environment
Hence you will breathe in more co2 and keep more co2 in body
therefore correct co2 previously lost + correct alkalosis
Causes of respiratory alkalosis: altitude
what happens at higher altitude? how does body accomodate to this and effect of this?
At sea level, PAtm ≈ 100kPa
100kPa x 21% O2 ≈ 21kPa, CO2 ≈ 0kPa
↓
At 8000ft, PAtm ≈ 75kPa
75kPa x 21% O2 ≈ 15kPa, CO2 ≈ 0kPa
↓
↑ alveolar ventilation to try and maintain normal PAO2 & PaO2 (via hypoxic drive)
↓
Increased ventilation = ↓PaCO2
↓
Respiratory alkalosisHigher altitude - what happens if breathing at normal rate?
why? and effect of this?
If breathing normally, individual will become hypoaemic due to decreased pressure gradient in the alveoli
This will be detected by peripheral chemoreceptors (hypoxia + less o2) hence there will be increased alveolar ventilation by hypoxic drive to maintain normal level of o2
How to avoid respiratory alkalosis with increased altitude?
To avoid respiratory alkalosis, try to ascend at a relatively low rate
Compensatory mechanisms in body e.g. renal system can excrete more HCO3 to compensate for the increase in pH
metabolic acidosis
what causes the low pH? (3 things that can do this)
what is the compensatory reflex and how does it recognise it?
Low pH accompanied by low [HCO3-] is termed metabolic acidosis, as excessive metabolic acid production and/or increased excretion of HCO3- is responsible for the decreased pH
𝑝𝐻∝(↓[𝐻𝐶𝑂3− )/〖𝑃𝑎 𝐶O2 )
↓absorption or ↑excretion of HCO3- OR Addition of H+ (reacts with available HCO3-)
Unless PaCO2 changes in proportion with [HCO3-] (in the opposite direction), acidosis (↓pH) will occur.
Respiratory compensation (↑ventilation) occurs almost instantly, and attempts to return pH back to normal range (impacts the levels of co2 in CSF and central/peripheral chemo recptors separately inducing a reflex compensation)
Metabolid acidosis - correction pathway
Excessive acid production and/or insufficient [HCO3-]
↓
↑[H+] = ↓pH (acidosis)
↓
↑Chemoreceptor feedback
↓
↑Respiratory rate
↓
Respiratory compensation (↑ventilation)
↓
↓PaCO2Causes of metabolic acidosis: Lactic acidosis (sepsis)
Infection ↓ Pathological immune response ↓ Septic shock ↓ ↓oxygen delivery to tissues (hypoxia) ↓ ↑Lactic acid production & ↓pH
Respiratory compensation to ↑O2 delivery and ↑lactic acid conversion
Causes of metabolic acidosis: other
3 other causes?
which of the 3 parameters do they relate?
Diabetic ketoacidosis
↑ fatty acid release from liver due to insulin deficiency =↑ (acidic) ketone body production
Diarrhoea (e.g. decreased HCO3- absorption in colon)
Renal failure (e.g. decreased HCO3- reabsorption in proximal tubule)
Metabolic alkalosis
what causes this? 3 things
compensatory reflex?
High pH accompanied by high [HCO3-] is termed metabolic alkalosis, as reduced metabolic acid production or reduced excretion of HCO3- is responsible for the increased pH
𝑝𝐻 ∝ (↑𝐻𝐶𝑂3− )/(𝑃𝑎 𝐶𝑂2)
Removal of H+ (less reacts with available HCO3-)
↑absorption or ↓excretion of HCO3-
Unless PaCO2 changes in proportion with [HCO3-] (in the opposite direction), alkalosis (↑pH) will occur. Respiratory compensation (↓ventilation) attempts to return pH back to normal range.
