Acid-Base balance and Blood Gas Analysis Flashcards
what is the normal H+ and pH in body
35-45 nmol/L
pH 7.35-7.45
how are H+ ions produced
metabolism- oxidation of sulfur-containing amino acids/proteins, ketogenesis, ATP hydrolysis
CO2 produces weak acid H2CO3
write a note on bicarbonate buffer system
balances carbonic acid (H2CO3), bicarbonate (HCO3-) and carbon dioxide.
carbonic anhydrase catalyses CO2 to H2CO3 which in turn dissociates to form HCO3- and H+
what are some acids HCO3- helps to neutralise
lactic acid, ketone bodies
what bases can H2CO3 neutralise
urea via protein catabolism
how do kidneys regulate bicarbonate
secretion of H+ ions in urine, or reabosorption of HCO3 ions into plasma
Aldosterone
Bicarbonate generation
write a note on metabolic acidosis
is a decreased blood bicarbonate conc and a decreased blood pH caused by:
1. inc metabolic production: lactic acidosis, ketoacidosis
2. ingestion of organic acids (methanol, aspirin, cyanide)
3. reduced renal excretion (decreased acid excretion and decreased HCO3 reapsorption) in CKD
write a note on metabolic alkalosis
inc blood bicarb conc, inc blood pH casued by:
1. primary (conn’s syndrome) or secondary aldosteronism (decreased renal blood flow)
2. loss of hydrogen ions via vomiting, loss of HCL, hyponatraemia, hypokalaemia)
write a note on resp acidosis
decreased blood pH and inc conc of carbon dioxide caused by hypoventilation via drug use, neuromuscular disorders such as Guillain-Barré syndrome, asthma, COPD
write a note on resp alkalosis
elevated blood pH and decreased conc of carbon dioxxide by hyperventilation i.e at high altitudes
what is the anion gap
quantity difference between cations and anions in bodily fluid. magnitude of the difference can measure metabolic acidosis
AG = Na+ -(Cl + HCO3)
the total number of cations should be equal to number of anions so electric charge is neutral
what happens in terms of metabolic acidosis with elevated anion gap
HCO3- is converted to H2CO3 or is consumed by buffering acids
can be caused by:
1. metabolism: lactic acidosis, ketoacidosis
2. ingestion of organic acids
3. reduced renal excretion in CKD
which all consume bicarb- lowering the conc
what causes acidosis with normal anion gap
build up of chloride ions that result in hyperchloremic acidosis
what causes acidosis with reduced anion gap
multiple myeloma (inc conc of anionic paraproteins), hypoalbuminaemia, concomitany retention of anions (CL of HCO3)
metabolic acidosis clinical findings?
low pH, low ctCO2, low bicarb, low pCO2, Ag might be up
compensatory mech = hyperventilation
metabolic alkalosis lab findings
pH up, ctCO2 up, bicarb up, pCO2 up
compensation mech = lungs, hypoventilation, kidneys- decrease reabsorption of HCO3, decrease H+ secretion
resp acidosis lab data
pH down, ctCO2 up, HCO3 up, pCO2 up
compensatory mech = kidneys increase reabsorption of HCO3 and increase H+ secretion
respiratory alkalosis lab findings
pH up, ctCO2 down, HCO3 down, pCO2 down
compensatory mech = kidneys decrease reabsorption of bicarb, decrease H+ secretion
what is BGA
blood gas analysis - measures o2, CO2, pH
sample taken from arterial blood from radial artery or sometimes femoral or arterial catheter
commonly taken in ICU and pulmonary wards
what is the principle of the BGA
measures blood gas tension values of:
1. arterial partial pressure of O2 (PaO2)
2. arterial partial pressure of carbon dioxide (paCO2)
3. blood pH
4. arterial O2 saturation
how can BGA be analysed
calculations, nomograms, rules of thumb
what is the henderson hasslebach eqn for bicarb sys
pH = 6.1 + log (HCO3-/(0.03 x PCO2))
how to calculate HCO3 conc
0.03 x pCO2 x 10 ^(pH - 6.1)
