11. Acid-Based Regulation Flashcards
What is the partial pressure of oxygen on the arterial side of circulation?
> 10kPa
What is the partial pressure of oxygen on the venous side of circulation?
5.3kPa
What is the saturation of O2 on the arterial side of circulation?
> 95%
What is the saturation of O2 on the venous side of circulation?
~75%
What is the partial pressure of CO2 on the arterial side of circulation?
4.7-6.4kPa
What is the partial pressure of CO2 on the venous side of circulation?
6.1kPa
Define Alkalaemia
Refers to higher than normal pH of blood
Define Acideaemia
Refers to lower than normal pH of blood
Define Alkalosis
Describes circumstances that will decrease [H+] and increase pH
Define Acidosis
Describes circumstances that will increase [H+] and decrease pH
What did the Pitts and Swan experiment show?
The blood has enormous buffering capacity that can react almost immediately to imbalances in the pH
How do you calculate pH?
-log10[H+]
What is the unit for H+
Eq/L –> equivalence per litre
Equivalence system basically counts the charges. H+ = 1 eq. There is barely any [H+] in the blood
Where are the two categories of acids?
Respiratory acid (CO2 = carbonic acid) Metabolic acid (Pyruvic acid, lactic acid)
Which category of acid is greater?
Respiratory acids are greater - most of the acid produced is from CO2
What Henderson-Hasselbalch equation
pH = pK + log10 ([HCO3-]/[CO2])
What is arterial and venous pH?
Arterial pH = 7.4
Venous pH = 7.36
What are the basic guidelines of PaO2?
>10kPa = normal 8-10kPa = mild hypoxaemia 6-8kPa = moderate hypoxaemia <6kPa = severe hypoxaemia
What are the compensatory mechanisms to changes in pH?
RAPID compensatory response to change CO2 elimination and therefore alter pH - Changes in ventilation
SLOW compensatory response response to increase/decrease pH - Changes in HCO3- and H+ retention/secretion in the kidenys
An acidaemia will need…
an alkalosis to correct
An alkalaemia will need…
an acidosis to correct
What is the physiological optimum pH?
7.4
What is standard tidal volume?
500ml
What is standard breathing rate?
12 breaths per minute
What does hypoventilation cause?
A lower than normal pH
Higher than normal PaCO2
Normal base excess - Bicarbonate concentration is correct for the PaCO2
Uncompensated Respiratory Acidosis
What does the body do in response to uncompensated respiratory acidosis?
There will be a need to reduce H+
1) The body will produce more HCO3- from erythrocytes
2) The kidneys will absorb more HCO3-
What does hyperventilation cause?
Higher than normal pH
Lower than normal PaCO2
Normal base excess
Uncompensated Respiratory Alkalosis
What does diarrhoea cause?
Lower than normal pH
Normal levels of PaCO2
Lower than normal base excess - Loss of HCO3- in diarrhoea
Uncompensated Metabolic Acidosis
What does vomiting cause?
Higher than normal pH - loss of H+ in vomit
Normal levels of PaCO2
Higher than normal base excess - HCO3 is high compared to H+
Uncompensated Metabolic Alkalosis
