Arterial blood gasses and acid base regulation Flashcards
what is pO2
partial pressure of oxygen
- Indicates how much oxygen is dissolved in the arterial blood, and if it is particularly low it can suggest inadequate gas exchange in the lungs
what is pCO2
partial pressure of carbon dioxide
- This variable indicates how much CO2 is dissolved in arterial blood, and if it is particularly high can suggest inadequate gas exchange in the lungs
what is base excess?
conc of bases (predominantly bicarbonate) compared with expected conc.
An exact match is ‘0’, an excess base is positive and base deficit is negative
in arteries: what are the PaO2, SaO2 and PaCO2 levels?
PaO2 >10kPa
SaO2 >95%
PaCO2: 4.7-6.0kPa
in veins what are the PaO2, SaO2 and PaCO2?
PaO2: 4.0-5.3kPa
SaO2= 75%
PaCO2= 5.3-6.7
why is there not much of a difference in SaO2 between arteries and veins?
despite massive decrease in PaO2, SaO2 is not far decreased due to the sigmoidal shape of the oxygen dissociation curve
what is the calculation to convert H+ to pH?
pH= -log[H+]
what is a base?
anionic (-ve changed ion) molecule capable of reversibly binding proteins (to reduce amount that are free)
what is the relationship between acid and base at equilibrium?
H2O + CO2 H2CO3 H+ + HCO3-
what is CO2 flux?
net amount of CO2 being produced
CaCO2 minus CvCO2
mL/dL-1 x50 = mL CO2/Min-1
what is most of the acid produced cleared by?
lungs
how does the body respond to changes in acidity
blood had a buffering capacity that can react almost immediately to imbalances
what other organ can compensate to acid/ base other than lungs
changes in HCO3- and H+ retention/secretion in kidneys can stimulate a low compensatory response to pH
what are the normal pH levels?
7.35-7.45
what are normal PaCO2 levels?
4.7-6.4 kPa
what are normal BE levels?
-2 to 2
what are the normal PaO2 levels?
10 - 13.5 kPa
what is the acid-base status in respiratory and metabolic disorders?
what is the consequence of hypoventilation?
uncompensated respiratory acidosis
what is the consequence of hyperventilation?
uncompensated respiratory alkalosis
what is the consequence of diarrhoea?
uncompensated metabolic acidosis
what is the consequence of vomiting?
uncompensated metabolic alkalosis
what is the compensation for respiratory acidosis?
secretion HCO3- from kidneys
what is the compensation for respiratory alkalosis?
inhibition of HCO3- secretion and HCO3- absorption in CD
what is the compensation for metabolic acidosis?
hyperventilation
what is the compensation for metabolic alkalosis?
hypoventilation
