Metabolic Acidosis Flashcards
Between what pHs is intracellular pH maintained?
7.0 and 7.3
How does metabolic acidosis occur?
- Loss of CO2 drives formation of H+ into H2O
- Therefore, you become acidotic if have a lot of H+ and can’t blow off enough CO2
How does respiratory acidosis?
If you can’t blow off enough CO2, the equation goes in the other direction, increasing H+
What is the primary disturbance in metabolic acidosis?
Decreased bicarbonate
What is the primary disturbance in metabolic alkalosis?
Increased bicarbonate
What is the primary disturbance in respiratory acidosis?
Increased pCO2
What is the primary disturbance in respiratory alkalosis?
Decreased pCO2
What is the compensatory response in metabolic acidosis?
Decreased pCO2
What is the compensatory response in metabolic alkalosis?
Increased pCO2
What is the compensatory response in respiratory acidosis?
Increased bicarbonate
What is the compensatory response in respiratory alkalosis?
Decreased bicarbonate
What is the definition of metabolic acidosis?
A low arterial blood pH in conjunction with a reduced serum bicarbonate concentration
Why is it important to detect metabolic acidosis?
- Acidic environment associated with lots of significant medical conditions
- Metabolic acidosis → increased mortality
- Easy identified and potentially correctable
What is metabolic acidosis not?
A diagnosis → it is a sign of something else you need to diagnose
What is the anion gap due to?
Not measuring many anions (many proteins) → measure fewer anions than cations, causing an anion gap (even though we know it is equal
What are the measured cations?
Na+ and K+
What are the measured anions?
HCO3- and Cl-
What does an increased anion gap indicate?
An increase in the concentration of anions other than chloride or bicarbonate
What is the equation showing that plasma is always electroneutral?
Measured cations + unmeasured cations = measured anions + unmeasured anions
Why does low bicarbonate mean an increased anion gap?
Bc there is a higher concentration of an unmeasured anion
What happens during normal anion gap acidosis?
- Have lost bicarbonate but chloride has compensated
- Bicarbonate loss but chloride reabsorption
What are causes of normal anion gap acidosis?
1) GI losses of bicarbonate → diarrhoea, surgical drains/fistulae
2) Renal losses of bicarbonate → renal tubular acidosis
What is the mnemonic to remember for increase anion gap acidosis?
GOLDMARK
What are causes of increased anion gap acidosis?
1) Glycols (ethylene, propylene) - antifreeze
2) Oxyproline
3) L-lactate (common when sick)
4) D-lactate (common when sick)
5) Methanol
6) Aspirin
7) Renal failure
8) Ketoacidosis
What is lactic acidosis?
The result of lactic production in anaerobic respiration
When does lactic acidosis happen?
In any form of shock
What is ketoacidosis?
The result of ketone production from fat metabolism when cells can’t take up glucose
What are ketones?
Unmeasured anions
What are the main causes of ketoacidosis?
Diabetes, alcohol and starvation
What are the most common causes if increased anion gap?
Lactic acidosis and ketoacidosis
Describe taking ABGs
- Commonly use radial artery or femoral artery
- Can be painful
- Low resistance
- Don’t need vacuum
- BP pushes plunger up and fills up syringe on its own
What is the desired range of pCO2?
4.5-6.0 kPa
What is the desired range of pO2?
10-13 kPa
What is the desired range of HCO3-?
24-26 mmol/L
What is the desired range of SpO2 (on ABG)?
96-100% (more accurate than finger probe)
What is the desired range of base excess?
+2 → -2
What does a low base excess (-3 or lower) indicate?
(Metabolic) acidosis
What does a high base excess indicate?
Alkalosis
What is the base deficit?
Same as base excess but opposite numbers
What H+ concentration is alkalosis?
H+ < 35 nmol
What H+ concentration is acidosis?
H+ > 45 nmol/L
What PaCO2 level indicates respiratory acidosis or respiratory compensation for a metabolic acidosis?
> 6.0 kPa/45 mmHg
What PaCO2 level indicates respiratory alkalosis or respiratory compensation for a metabolic acidosis?
< 4.7 kPa/35 mmHg
What HCO3- level indicates metabolic acidosis or renal compensation for a respiratory alkalosis?
< 22mmol/L
What HCO3- level indicates metabolic alkalosis or renal compensation for a respiratory acidosis?
> 26 mmol/L
When is acidosis/alkalosis truly compensated?
When you have normal pH
When is acidosis partially compensated?
When pH is higher than expected but still not normal
What do you need for respiratory compensation?
Capacity of lungs
In what case could you have mixed metabolic and respiratory acidosis?
In someone with COPD and CKD → pt might not be able to compensate for acute respiratory/metabolic acidosis
What does not happen with regard to compensation?
Over compensation
What is the normal anion gap range?
8-12 mmol/L
Which test is most important to do if you suspect diabetic ketoacidosis and why?
Urinalysis → bc can see ketones and glucose (compared to blood glucose)
Generally what should pO2 be?
10 less than the % you are breathing → so at sea level, 21% (11kPa)
Why do GI losses lead to metabolic acidosis with a normal anion gap and high chloride?
1) Chloride reabsorbed balances bicarbonate lost
2) No generation of extra acid e.g. lactate or ketones
Why does increased anion gap occur?
Production of acids which are also anions
