Blood Gases
This can be extremely confusing. The body tries to maintain homeostasis, so if, for instance, the animal gets a metabolic acidosis, it tries to compensate by inducing a respiratory alkalosis by hyperventilating.
In anaesthesia, an arterial sample is usually taken, mainly to check oxygenation (PO2) or respiratory depression (PCO2).
In intensive care, the blood taken may be arterial or venous, and is often to assess the degree of metabolic acidosis (ABE, SBE, HCO3 or SBC) to guide treatment (sodium bicarbonate).
Blood gas machines
These actually measure pH, PO2 and PCO2, then calculate a variety of other parameters.
What the numbers mean
The numbers for normal may vary a bit according to who you believe.
| variable | units | normal | interpretation |
|---|---|---|---|
| pH | 7.35 - 7.45 | Low - acidaemia, high - alkalaemia | |
| PO2 | mmHg kPa |
85 - 105 11.3 - 14 |
Low - hypoxaemia: give oxygen |
| PCO2 | mmHg kPa |
35 - 45 4.5 - 6 |
High - respiratory depression, respiratory acidosis: give IPPV Low - respiratory alkalosis, usually to compensate for metabolic acidosis |
| HCO3 | mmol/L (mM) |
22 - 26 | Low - metabolic acidosis; high - metabolic alkalosis |
| TCO2 | mmol/L (mM) |
25 - 30 | HCO3 plus PCO2 |
| ABE | mmol/L (mM) |
-5 - +3 | Low - metabolic acidosis: give NaHCO3 High - metabolic alkalosis |
| SBE | mmol/L (mM) |
-5 - +3 | Base excess standardised to a haemoglobin of 5g/dL. |
| sat | % | 85 - 98 | Low - hypoxic: give oxygen |
| SBC | mmol/L (mM) |
22 - 26 | Bicarbonate standardised to normal PCO2 to remove respiratory effects. |
