ABGs Flashcards
Which of the two systems is the most powerful compensator of metabolic inbalances?
Metabolic
What is the normal pH range?
7.35-7.45
At what level does the optimal level of acid/base dissociation occur?
K
Why is the bicarbonate the main buffer system in the body?
There is dual control via volatile gas (CO2) and renal control of bicarb and H+
Name 5 other buffers in the body
NB - 3 main categories
BBS, Hb, intracellular protein, plasma proteins, phosphate,
What is the Henderson-Hasselback equation?
pH = pKa (6.37) + logHCO3-/0.03xpCO2
How do you work out HCO3 levels?
Derive from HH equation, you can’t get it from the ABG directly.
What is the base excess?
amount of moles os stron acid required to back titrate 1 litre of blood to correct pH….finish…
Normal pCO2 levels?
4.5 - 5.8kPa
Normal pO2 levels?
11-13 kPa
Normaly HCO3- levels
22-28
Normal base excess?
-2 to +2 mmol/L
Normal anion gap?
10-14
Normal chloride levels?
98-107
Name 2 potential causes of a primary respiratory alkalosis?
PE, pneumonia
What are normal Na+ levels?
135-145
What is main cause of primary metabolic alkalosis?
Loss of acid in vomiting
What is the anion gap? And which anions are the cause of it?
The unmeasured anion gap
(because blood tests measure most cations but only a few anions)
Na+ - (Cl- + HCO3-)
The unmeasured anions are intracellular (and??)
How do you correct the anion gap for albumin?
Corrected AG = AG + [0.25 x (40 - [alb])]
CAUSES of high AG metabolic acidosis
…
Normal causes normal AG metabolic acidosis
….
When would you look at the anion gap?
If the patient is acidotic but CO2 seems to be normal ?
Why does someone who is bicarb wasting have a normal anion gap?
Bicarb wasting
How long does respiratory compensation take?
Begin in minutes, complete in 12-24 hours
What are the two components of metabolic acidosis?
Cellular and renal
How long does cellular compensation take?
Minutes to hours
How long does renal compensate take?
3-5 days
What is the alveolar-arterial gradient?
The difference between the calculated pO2 and the measured arterial pO2.
What is arterial pO2?
Function of ventilation and fractional inspired concentration of O2 (FiO2)
What is the A-a gradient affected by? (3)
Altitude
Inspired oxygen percentage
Rate of respiration
What are the causes of hypoxia with a normal A-a gradient?
Hypoventilation
Subnormal PiO2
What are the causes of hypoxia with a raised A-a gradient?
V/Q mismatch
Shunt
Dead space
Low cardiac output states
Why can’t a shunt be corrected with 100% oxygen?
The alveoli units are STILL not being perfused. The same fraction of deoxygenated blood continues to circulate the system.
What is carpo-pedal spasm?
2 signs?
….??
Acutely hypocalcaemic signs due to increasingly negative charge due to hypocapnia
Why is breathing into a paper bag helpful for those hyperventilating?
They rebreathe their own CO2, reduces their hypocapnia
When should you be considering A-a gradient?
Hypoxia
What is the most common ECG finding for a PE?
Sinus tachycardia
What are normal potassium levels?
3.5-5 mmol/L
Normal creatinine levels?
70 - 150 micromol/L
Normal urea levels?
2.5 - 6.7 mmol/L
Normal eGFR?
> 90
What are the biggest risks when plasma electrolytes are dangerously abnormal?
(2 main categories)
Cardiac arrhythmias CNS events (eg seizures)
When should you be REALLY worried about Na+ levels?
155 mmol/L
When should you be REALLY worried about K+ levels?
6.5 mmol/L
When should you be REALLY worried about Ca+ levels? (corrected)
3.5 mmol/L
When should you be REALLY worried about glucose levels?
20 mmol/L
When is hypoxia severe?
<8.0kPa
When is pH dangerously acidotic?
<7.1
When are haemoglobin levels dangerously low?
<70g/l
When are platelets dangerously low?
< 40x10^9/L
What concentration of neutrophils would you expect in meningitis?
> 1 neutrophil/ mm^3
What biochemical features would you find in dehydration? (3)
And two other features of patient?
Incr urea (moreso than creatinine) Incr albumin Incr haemocrit Decr urine volume Decr skin turgor
What are the two major biochemical pictures of abnormal kidney function?
Low GFR
Tubular dysfunction
How does low GFR appear biochemically?
Incr urea Incr creatine Incr K+ Incr H+ Incr urate Incr phosphate Incr anion gap
Mem aid
CHUK A PU (up)
Decr
Bicarbonate, urine output (oligouria)
What are the causes of low GFR?
Early acute oliguric renal failure
Chronic kidney disease
If low GFR is caused by chronic kidney disease, what else is found biochemically?
Decr Hb
Incr PTH
Renal bone disease