Answer
problem ( 1 ) :
- Alkalosis .
- Respiratory.
- Compensated.
- one possible cause : Prolonged Hyperventilation.
problem ( 2 ) :
- Acidosis.
- Metabolic.
- Compensated.
- one possible cause : Renal Failure or Diabetic ketoacidosis.
Work Step by Step
Normal Blood gases & acid-base Data
PH : 7.36 - 7.44
PaCO2 : 36 - 44 mmHg.
PaO2 : 85 - 100 mmHg.
SBC ( Standard Bicarbonate HCO3 ) : 22 - 28 mEq/L
BE ( Base excess or deficit ) : +2.5 or -2.5 mEq/L
SaO2 : 95 - 100 %
How to interpret the Acid-Base data
1- look at the PH :
the change in PH is in the direction of the primary
change :
Acidosis ( decrease PH ).
Alkalosis ( increase PH ).
2- look at the PaCO2 :
- this reflect the respiratory component .
- if the PaCO2 is High- then there is Respiratory
Acidosis.
- if it is low - Respiratory Alkalosis.
3- look at the standard bicarbonate ( SBC ) & the
base excess ( BE ).
- these reflect the Metabolic component.
- if the SBC is low or the BE is negative ( i.e. there
is base deficit ) - then there is a Metablic
Acidosis.
- if the SBC is High & BE is positive - then there
is Metabolic Alkalosis.
4- Note that the primary abnormality goes with the
direction of the PH
- so,
* if PH was Acidic & the PaCO2 is High - then
it is a Respiratory Acidosis.
& * if the PH was Acidic & the SBC or BE are Low
- it is a Metabolic Acidosis. & so on.
5- now, evaluate also the state of oxygenation by
looking at the PaO2 & SaO2 in relation to FIO2 :
- if SaO2 is greater than 90% - Oxygenation is
adequate.
( Hypoxaemia may be the reason of Acid-Base
disturbances ).
Problem ( 1 ):
PH : 7.63
PCO2 : 19 mmHg
HCO3 ( SBC ) : 19.5 mEq / L
- the PH is alkaline ( above 7.44 ).
& PaCO2 goes with the PH i.e. is low too
so, this is a Respiratory Alkalosis but with
compensatory decrease amount of HCO3 in blood
by alkalinazation of the urine.
- examples of Respiratory Alkalosis: conditions of
prolonged hyperventilation as occurs in :
1- high attitude .
2- some psychosomatic cases .
3- meningitis & certain trauma of the brain.
4- prolonged voluntary hyperventilation.
Respiratory Alkalosis
- this disorder develops due to decreased CO2 blood
level ( PaCO2 ).
Compensation ( correction ) in Respiratory alkalosis
- there is renal correction only ( since the cause is
a resiratory disorder ).
- the CO2 decrease in the tubular cells, so H
secretion decreases allover the renal tubules leading
to :
1- incomplete HCO3 reabsorption in the PCTs &
the excess is excreted in the urine.
2- decreased addition of new HCO3 at the DCTs
& CDs.
3- Excretion of alkaline urine containing excess
HCO3.
4- Minimal excretion of acid phophates &
ammonium salts.
Accordingly, the blood HCO3 level decreases, & in
compensated cases, such decrease is proportional
to the decrease in CO2.
Problem ( 2 )
PH : 7.22
PCO2 : 30 mmHg.
HCO3 ( SBC ) : 12 mEq / L.
- the PH is Acidic ( below 7.36 ).
& the metabolic component HCO3 ( SBC ) is Acidic
( low )
so, this is Metabolic Acidosis
but with a compensatory hyperventilation that lowered
the PaCO2 to 30 mmHg.
- Examples of Metabolic Acidosis :
1- Renal Failure.
2- Shock, diarrhea & severe vomiting.
3- severe dehydration & starvation.
4- salicylate poisoning.
5- hypoxia.
6- diabetic ketoacidosis.
7- deficient secretion of aldosterone
e.g. in Addison s disease.
Metabolic Acidosis
- the disorder develops due to decreased HCO3 blood
level ( decrease SBC ).
Compensation ( correction ) of Metabolic Acidosis :
- there is both renal & respiratory correction:
1- Respiratory correction :
- the respiratory rate increase due to stimulation
of the Respiratory centre by the increase blood H .
- this washes CO2 in the expired air, thus its
blood level ( PaCO2 ) is decreased.
2- Renal correction :
this is more efficient than the Respiratory
correction but it is delayed & requires alonger
time.
