Interpreting blood gas values
Assessing acid–base disorders
Assessing acid–base disorders involves examining the pH, PaCO 2 and
HCO3:
● pH – a low pH (7.4) indicates a tendency towards acidosis, a high pH
(7.4) indicates a tendency towards alkalosis.
● PaCO2 – an increase in PaCO2 leads to acidosis, a decrease to alkalosis.
● HCO3 – an increase in HCO3 leads to alkalosis, a decrease to acidosis.
Assessment
1. Establish whether the patient’s pH is acidotic, alkalotic or normal.
2. If the pH is acidotic establish whether this is due to:
– increased PaCO2 – indicating respiratory acidosis
– decreased HCO3 – indicating metabolic acidosis.
3. If the pH is alkalotic establish whether this is due to:
– decreased PaCO2 – indicating respiratory alkalosis
– increased HCO3– indicating metabolic alkalosis.
4. If the pH is within normal range the original abnormality can be
identified by comparing the pH to the PaCO2 and the HCO3.
Assessing acid–base disorders
Assessing acid–base disorders involves examining the pH, PaCO 2 and
HCO3:
● pH – a low pH (7.4) indicates a tendency towards acidosis, a high pH
(7.4) indicates a tendency towards alkalosis.
● PaCO2 – an increase in PaCO2 leads to acidosis, a decrease to alkalosis.
● HCO3 – an increase in HCO3 leads to alkalosis, a decrease to acidosis.
Assessment
1. Establish whether the patient’s pH is acidotic, alkalotic or normal.
2. If the pH is acidotic establish whether this is due to:
– increased PaCO2 – indicating respiratory acidosis
– decreased HCO3 – indicating metabolic acidosis.
3. If the pH is alkalotic establish whether this is due to:
– decreased PaCO2 – indicating respiratory alkalosis
– increased HCO3– indicating metabolic alkalosis.
4. If the pH is within normal range the original abnormality can be
identified by comparing the pH to the PaCO2 and the HCO3.
