Integrated control of ventilation Flashcards
What is blood pH proportional to and what can excessive changes result from?
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).
What is acidosis due to and at what pH?
pH<7.35
-CO2 is high or HCO3- is low
What is alkalosis due to and at what pH?
pH>7.45
-CO2 is low or HCO3- is high
What type of acidosis is it if CO2 is high?
Respiratory acidosis
What type of acidosis is it if HCO3- is low?
Metabolic acidosis
What type of alkalosis is it if CO2 is low?
Respiratory alkalosis
What type of alkalosis is it if HCO3- is high?
Metabolic alkalosis
What does an increase in ventilation do to PaCO2 and pH?
↑Ventilation = ↓ PaCO2 = ↑ pH
What does a decrease in ventilation do to PaCO2 and pH?
↓Ventilation = ↑ PaCO2 = ↓ pH
What does a decrease in HCO3 excretion do to [HCO3-] and pH?
↓ HCO3 excretion = ↑ [HCO3-] = ↑ pH
What does an increase in HCO3 excretion do to [HCO3-] and pH?
↑ HCO3 excretion = ↓ [HCO3-] = ↓ pH
When does respiratory acidosis occur?
Respiratory acidosis occurs when ventilation is
insufficient relative to the metabolic demands of the body (in terms of metabolic CO2 production)
What must happen to HCO3- excretion in the event of chronic hypoventilation?
In the event of chronic hypo-ventilation, HCO3- excretion must
decrease to maintain normal pH.
What are the steps invovled in respiratory acidosis?
- Decrease in ventilation
- Increase in PaCO2
- Increase in PaCO2(hypercapnia)
- Increase in [H+] which results in decrease in pH(acidosis)
- Results in decreased HCO3- excretion. An increase in chemoreceptor feedback, increase in respiratory rate.
-However a pathology prevents normal reflex increase in ventilation
What happens in anxiety in terms of hyperventilation?
- Anger triggers panic attack
- Leads to increased ventilation(tachypnoea) without increased metabolic demand
- Hyperventilation leads to decreased PaCO2
- This leads to respiratory alkalosis
What happens when there’s an increase in altitude?
- At sea level, Patm is approx 100kPa
-100kPa x 21% O2 is approx 21kPa, CO2 is approx 0kPa - At 8000ft, PAtm is approx 75kPa
-75kPa x 21% O2 is approx 15 kPa, CO2 is approx 0 kPa - This leads to an increase in alveolar ventilation to try and maintain normal PAO2 and PaO2(via hypoxic drive)
- This leads to increased ventilation which decreases PaCO2
- Ultimately causing respiratory alkalosis
When does metabolic acidosis occur?
Metabolic acidosis occurs when metabolic acid
production is excessive and/or [HCO3-] is deficient
What occurs immediately in metabolic acidosis?
Respiratory compensation (↑ventilation) occurs almost instantly, and attempts to return pH back to normal range. However, if
patients have simultaneous respiratory pathology, this may not be possible)
What is lactic acidosis(sepsis) a cause of and how does it work?
Infection
↓
Pathological immune response
↓
Septic shock
↓
↓oxygen delivery to tissues (hypoxia)
↓
↑Lactic acid production & ↓pH
Respiratory compensation to ↑O2
delivery and ↑lactic acid conversion
What does diabteic ketoacidosos cause and how does it work?
-Causes metabolic acidosis
↑ fatty acid release from
liver due to insulin deficiency
=
↑ (acidic) ketone body
production
What does renal failure cause and how?
Renal failure causes metabolic acidosis
-Decreased HCO3- reabsorption in proximal tube
What does diarrhoea cause and how?
Causes metabolic acidosis
-Decreased HCO3- in absorption in colon
When does metabolic alkalosis occur?
Metabolic alkalosis occurs when metabolic acid
excretion is excessive and/or [HCO3-] becomes
excessive
What will occur in compensation for metabolic alkalosis?
Respiratory compensation (↓ventilation) attempts to return
pH back to normal range.
What can diuretics cause and how?
Can cause metabolic alkalosis
-Changes to H+ and HCO3- reabsorption
What can antacids cause and how?
Can cause metabolic alkalosis
-Increase H+ consumption
What can vomiting cause and how?
Can cause metabolic alkalosis
-Loss of H+ in stomach acid
What are the steps that occur in acidosis-induced hyperkalemia?
- Acidosis occurs due to increased extracellular [H+]
- This leads to decreased H+ concentration gradient
- This leads to decreased H+ excretion which leads to decreased H+-Na+ exchange which leads to decreased Na+-K+ exchange.
- This causes a decrease in Na+-K+ exchange which leads to a decrease K+ absorption
- This results in K+ accumulation in serum which leads to hyperkalemia
- This ultimately causes cardiac arrhythmias and muscle weakness
What occurs in alkalosis induced cerebral vasoconstriction?
o CO2 (via H+) acts as a vasodilator in blood vessels (cerebral
arteries particularly sensitive)
o Hyperventilation = ↓CO2 and ↓H+ (alkalosis)
o Alkalosis causes vasoconstriction of cerebral arteries
o ↓ cerebral blood flow = headache, lightheadedness, confusion, seizures
What are the causes of acidosis?
Hypercapnia (hypoventilation)
↑ Lactic acid (spesis)
↑ Ketone bodies (diabetes)
↓ Kidney acid excretion (renal failure)
↓HCO3- reabsorption (renal acidosis)
Diarrhoea (loss of HCO3- from gut)
What are the effects of acidosis?
Tachypnoea
Muscular weakness
Headache
Confusion, Coma
Cardiac arrhythmia
Hyperkalaemia
What are the compensatory mechanisms for acidosis?
- Hyperventilation (↓PaCO2,
respiratory compensation) - ↓ HCO3- excretion (renal
compensation)
What are the causes of alkalosis?
Hypocapnia (hyperventilation)
Vomiting (loss of H+ in HCl)
↑ kidney acid excretion (diuretics)
↑ alkalotic agent consumption
(antacids, NaHCO3
What are the effects of alkalosis?
Bradypnoea
Muscular weakness, cramps, tetany
Headache, Nausea
Lightheadedness, confusion, coma
Cardiac arrhythmia
Hypokalaemia
