IOD Acid Base Balance Flashcards
What does it depend on?
relative balance between acid production and excretion
carbon dioxide production and excretion (respiration)
hydrogen ion production and excretion (renal)
Balance?
carbonic acid
(volatile)
15,000 mmol/Day
non-carbonic acids
(non-volatile)
80 mmol/Day
out
lungs-15000
kidneys-80
for every fall in pH of 0.3…
H+ conc doubles
compensation
Attempt to return acid / base status to normal
1 Buffering –
Bicarbonate buffer in serum, phosphate in urine (for excretion)
Skeleton
Intracellular accumulation/loss of H+ ions
2. Compensation
Diametric opposite of original abnormality
Never overcompensates
Delayed and limited
3. Treatment
By reversal of precipitating situation
speed of resp comp?
Respiratory compensation for a primary metabolic disturbance can occur very rapidly Kussmaul breathing (respiratory alkalosis) in response to DKA
speed of metabolic comp?
Metabolic compensation for primary respiratory abnormalities take 36-72 hours to occur
requires enzyme induction from increased genetic transcription and translation etc
No compensation seen in acute respiratory acidosis such as asthma
Requires more chronic scenario to include compensation mechanism
metabolic acidosis?
more H made than excreted
comp-more bicarb retained and more CO2 removed-kussmaul breathing
resp acidosis?
more CO2 made than excreted-
comp-more bicarb retained and CO2 removed
bicarb regeneration?
more carbonic acid made H made and removed in tubules bicarb made and reabsorbed more K/Na pump-more sodium in Less ATP means Na/K pump doesn't work-less excretion of K-hyperkalaemia
ABG measurable parameters?
Measured parameters
pH electrode permeable to H+ ions
pCO2 CO2 electrode
PO2 02 electrode
All other parameters are calculated or derived by the blood gas machine software
ABG errors?
Errors in blood gas analysis are dependent more on the clinician than on the analyser
Trust POCT policy: Trained & competency tested before given password
pitfalls of ABG?
Expel air Mix sample Analyse ASAP Plastic syringes OK at room temp for ̴ 30mins Ice not required Ensure no clot in syringe tip
Need to collect blood anaerobically into a heparinsed blood gas syringe or capillary – NO air bubles (to prevent loss of CO2 from blood into air
K+ result may not be valid if haemolysed sample – but YOU WILL NOT KNOW!
order of interpretation?
pO2 – remember to check FiO2
pH – ? Normal or does it show an acidosis or alkalosis
pCO2 – primary respiratory or compensatory response
HCO3 – metabolic component
resp acidosis?
CO2 retention
Compensation is metabolic alkalosis
resp alkalosis?
increased CO2 loss
Compensation is metabolic acidosis
