Читать книгу Respiratory Medicine - Stephen J. Bourke - Страница 91
Review of acid/base balance
ОглавлениеCO2 dissolves in H2O and forms carbonic acid (H2CO3), which dissociates into H+ and HCO3 – in a constant relationship:
Table 3.1 Normal values for arterial blood gases whilst breathing normal room air at sea level
| pH | 7.35–7.45 |
| PCO 2 | 4.5–6.0 kPa, 34–45 mmHg |
| PO 2 | 11–14 kPa, 83–105 mmHg |
| Actual bicarbonate (aHCO 3 – ) | 22–26 mmol/L |
| Standard bicarbonate (sHCO 3 – ) | 22–26 mmol/L |
| Base excess | –2 to +2 mmol/L |
| Oxygen saturation | 96–98% |
Thus:
As [H2CO3] directly relates to the partial pressure of CO2:
In other words, for a given concentration of bicarbonate, PCO2 has a direct linear relationship with [H+] (and thus an inverse relationship with pH, which is the negative logarithm of [H+]).
Similarly, for a given PCO2, there is a direct relationship between [HCO3 –] and pH.
These relationships can be represented graphically (Fig. 3.9).
