Integrated Control of Ventilation Flashcards
How does respiratory acidosis occur in the event of hypoventilation?
- Decreased ventilation
- Increases PACO2 - hypercapnia.
- Increases H+ concentration in the blood
- Decreases pH (acidosis).
How does the body respond to acidosis?
- Chemoreceptors detect both the increased PACO2 and the decreased pH.
- Receptors signal to increase the respiratory rate.
decrease in ventilation which means more CO2 is removed from the alveoli which reduces the amount of CO2 in the blood resulting in blood pH decreasing
What are some causes of hypoventilation related to airway obstruction?
- asphyxia, chocking, etc.
- obstructive sleep apnoea
- increased airway resistance (as in asthma and COPD)
What are some causes of hypoventilation related to initiation of breathing?
- drug overdose (typically opioids)
- stroke
- neuromuscular problems
How does respiratory alkalosis occur in the event of hyperventilation?
- Increased ventilation rate.
- Decreases PACO2 - hypocapnia.
- Decreases the H+ concentration in the blood
- Increases the pH (alkalosis).
How does the body respond to alkalosis?
- Chemoreceptors detect the decreased PACO2 and the increased pH.
- Receptors signal to decrease the respiratory rate
What is metabolic acidosis?
- When the metabolic acid production exceeds excretion, or can occur due to insufficient HCO3- concentrations. Decreased pH
- Unless the PaCO2 changes in proportion with the HCO3- concentration (in the opposite direction), acidosis will occur.
What is the body’s response to metabolic acidosis?
- Respiratory compensation typically occurs almost instantly; however, may not be sufficient enough to prevent a disturbance in pH.
List some causes of metabolic acidosis.
LACTIC ACIDOSIS (EXERCISE)
LACTIC ACIDOSIS (SEPSIS)
DIABETIC KETOACIDOSIS
DIARRHOEA
RENAL FAILURE
Outline what occurs in lactic acidosis related to exercise
- Intense exercise
- Insufficient O2 delivery
- Increased lactic acid production
- Metabolic acidosis
- Subsequent respiratory compensation to reduce ‘oxygen debt’ and convert lactic acid
Outline what occurs in lactic acidosis related to sepsis. PART 1
- Infection
- Pathological immune response
- Septic shock
- Decreased O2 delivery (hypoxia)
Outline what occurs in lactic acidosis related to sepsis. PART 2
- Increased lactic acid production and decreased pH
- Metabolic acidosis
- Respiratory compensation to increase O2 delivery and increase lactic acid conversion
Outline what occurs in diabetic ketoacidosis.
- Increased fatty acid released from liver due to insulin deficiency
- Increased (acidic) ketone body production
Outline what occurs in diarrhoea
Decreased HCO3- absorption from the colon
Outline what occurs in renal failure
Decreased HCO3- reabsorption in proximal tubule
What is metabolic alkalosis?
- When metabolic acid excretion is excessive, or can occur due to excess HCO3- concentration. Increased pH
- Unless the PaCO2 changes with the HCO3- concentration, alkalosis will occur.
What is the body’s response to alkalosis?
Respiratory compensation typically occurs almost instantly - however may not be sufficient to prevent a disturbance in pH.
List some causes of metabolic alkalosis.
- DIURETICS: changes to H+ and CO3- concentration
- ANTACIDS: increase HCO3- consumption
- VOMITING: loss of H+ in stomach acid
Interpret these ABG results for acid-base disorders:
pH: 7.30 (7.35-7.45)
PaCO2: 4.0 (4.9 - 6.1)
[HCO3-]: 18 (22-30)
- pH is low, indicating acidosis.
- PaCO2 is low, indicating hyperventilation.
- Hyperventilation wouldn’t usually produce acidosis, so indicates respiratory compensation.
- [HCO3-] is low. This does produce acidosis, so it indicates metabolic acidosis.
This patient has metabolic acidosis with respiratory compensation.
Interpret these ABG results for acid-base disorders:
pH: 7.48 (7.35-7.45)
PaCO2: 3.0 (4.9-6.1)
[HCO3-]: 18 (22-30)
- pH is high, indicating alkalosis.
- PaCO2 is low, indicating hyperventilation.
- Produces alkalosis, thus indicating respiratory alkalosis.
- [HCO3-] is low. However, this doesn’t produce alkalosis, so this indicates metabolic compensation.
This patient has respiratory alkalosis with metabolic compensation.
Interpret these ABG results for acid-base disorders:
pH: 7.1 (7.35-7.45)
PaCO2: 8.0 (4.9-6.1)
[HCO3-]: 18 (22-30)
- pH is low, indicating acidosis.
- PaCO2 is high, indicating hypoventilation.
- Produces acidosis, indicating respiratory acidosis.
- [HCO3-] is low. This does produce acidosis, so it indicates metabolic acidosis.
The patient has mixed metabolic and respiratory acidosis.
What is blood pH proportional to?
Ratio of [HCO3-] to PaCO2
What are disruptions in pH homeostasis caused by?
From respiratory (CO2) or metabolic (HCO3-) dysfunction
What does acidosis involve?
Increased [H+] within the blood
What does acidosis activate?
Respiratory chemoreceptors
How are normal pHs restored after acidosis?
- Increase in CO2 removal
- Increases blood pH until normal level are re-established via negative feedback.
What does alkalosis involve?
Decreased [H+] within the blood
What does alkalosis decrease the activation of?
Decreased activation of respiratory chemoreceptors
How are normal pHs restored after alkalosis?
- Accumulation of CO2
- Decreases blood pH until normal level are re-established via negative feedback
Describe the pathway of alkalosis-induced vasoconstriction
- CO2 (via H+) acts as a vasodilator in blood vessels
- Hyperventilation so decrease in C02 and H+ levels
- Alkalosis causes vasoconstriction of cerebral arteries
- Reduced cerebral blood flow - causes headache, confusion
How do the lungs and kidney maintain blood pH homeostasis?
By regulating paCO2 and [HCO3-] respectively
How does anxiety lead to respiratory alkalosis?
- increased ventilation (tachypnoea) without increased metabolic demand
- hyperventilation
- decreased paCO2
- respiratory alkalosis
How does an increase in altitude lead to respiratory alkalosis?
- increased ventilation
- decreased CO2
- respiratory alkalosis
What is the effect of acidosis induced hyperkalaemia? PART 1
- pH decreases
- Greater concentration of H+ ions outside of cell compared to inside
- Reduced uptake of K+ ions through H+/Na+ followed by Na+/K+ exchange (indirect H+/K+ exchange)
- K+ concentration in blood rises since concentration gradient means K+ cannot enter cells
What is the effect of acidosis induced hyperkalaemia? PART 2
- Reduced potassium ion concentration within cells e.g cardiac pacemaker cells
- Symptoms include arrythmia
