Acid base balance 2 - acidosis and alkalosis Flashcards
what is the** respiratory response** to acidosis (ie increase in CO2 in blood)?
- the acidic blood stimulates the medullary respiratory centre in brain
- the brain increases the speed and depth of breathing
- an increase in ventilation increases the amount of CO2 exhaled which decreases the CO2 in the blood and therefore increases the PH (ie PH is more alkaline)
What is the** respiratory response** to alkalosis?
- alkalosis - decrease in CO2 in blood - PH = alkaline
- the rate and depth of breathing** reduces**
- therefore there is a** reduction in CO2 eliminated ** and increase in CO2 in fluids
- therefore a decreased ventilation decreases the amount of CO2 exhaled which **increases CO2 in blood and therefore PH is more acidic **
What is the** definition of acidosis**?
rememeber - PH value is important
- A PH below 7.35
what are the 2 types of acidosis?
- respiratory
- metabolic
what is the definition of alkalosis?
- PH above 7.45
what is respiratory / metabolic acidosis or alkalosis dependent on?
the **ratio **of HCO3- : PCO2
what are examples of symptoms associated with acidosis?
- depressed CNS
- coma
- disorientated
what are examples of symptoms associated with alkalosis?
- hyperexcitability of CNS
- spasms, tetany and convulsions (uncontrollable muscle contractions)
What are the axis’ of the davenport diagram?
- on the Y axis - there is the plasma concentration of HCO3-
- on the X axis, there is the PH
what does the davenport diagram describe?
- This diagram describes the relationship between [HCO3-], PH and PCO2
On the davenport diagram, if the [HCO3-] is raised, what occurs?
if the [HCO3-] is raised, the PH increases (ie more alkaline)
on the davneport diagram, if the [HCO3-] is decreased, what occurs?
if the [HCO3-] decreaes, the PH decreases (more acidic)
what are examples of causes of respiratory acidosis?
- hypoventilation - depression of respiratory centre (not breathing fast enough)
- asphyxia (eg when airway is physically blocked)
- asthma
- severe emphysema (sacs in lungs are damaged)
Is there an increase or decrease in PCO2 for respiratory acidosis?
- increase in PCO2
what happens to the ratio of HCO3-:PCO2 and the PH during respiratory acidosis?
both decrease
what is important to note about the [HCO3-] when the PCO2 rises?
whenever the PCO2 rises, the [HCO3-] must also increase to some extent because of the dissociation of the carbonic acid produced
what are the compensatory responses to respiratory acidosis?
lungs + kidney
- hyperventilation initially- decreases CO2 as more is eliminated and increases PH - more alkaline
- kidney responds by conserving HC03- which moves the ratio back up toward its normal level
what are the causes of respiratory alkalosis?
- increased elimination of CO2
- hyperventilation
- emotion - anxiety - panic attacks
- high altitude
- lung diseases eg asthma
is there a decrease or increase in PCO2 in respiratory alkalosis?
a decrease in PCO2
what happens to the PH and HC03-:PCO2 ratio in respiratory alkalosis?
- increase in PH - ie more alkaline
- increase HCO3-:PCO2 ratio
what are the compensatory responses to respiratory alkalosis?
- hypoventilation which increases CO2 and decreases PH
- kidney excretes HCO3- and restores the ratio of HCO3-: PCO2
what is metabolic acidosis?
- ‘metabolic’ means a primary change in HCO3-
- the ratio of HCO3-:PCO2 falls and therefore depresses the PH
what are the causes of metabolic acidosis?
- the HCO3- may be lowered by the accumulation of acids in the blood eg in uncontrolled diabetes mellitus or after tissue hypoxia (lactic acid)
what are the compensatory response to metabolic acidosis?
- the respiratory compensation - hyperventilation - which decreases CO2 as more is eliminated
- PH is increased - more alkaline
what is metabolic alkalosis?
- increase in HCO3- raises the HCO3:PCO2 ratio and therefore increases the PH
what are examples of the causes of metabolic alkalosis?
- excessive ingestion of alkaline substances
- acidic urine - from drugs like diuretics
what are the **compenasatory responses **to metabolic aklalosis?
- hypoventilation - occasionally
- this increases CO2 as less is eliminated and decreases PH
- kidney also excretes HCO3- and restores ratio of HCO3:PCO2