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Reverted the previous edit but there should be a clear statement that the example values represent the normal values of bicarbonate and PCO2 at sea level. |
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===Buffer===
The decreased bicarbonate that distinguishes metabolic acidosis is therefore due to two separate processes: the buffer (from water and carbon dioxide) and additional renal generation. The buffer reactions are: <chem display=block>H+ + HCO3- <=> H2CO3 <=> CO2 + H2O</chem>
The [[Henderson-Hasselbalch equation]] mathematically describes the relationship between blood pH and the components of the bicarbonate buffering system: <math chem display=block>p\ce{H}=pK_\text{a}+\operatorname{\mathrm{Log}}\frac{\left[\ce{HCO3^-}\right]}{\left[\ce{CO2}\right]}\text{,}</math> where {{math|''pK''<sub>a</sub> ≈ 6.1}}. In clinical practice, the {{CO2}} concentration is usually determined via [[Henry's law]] from {{math|''P''<sub>a{{CO2}}</sub>}}, the {{CO2}} partial pressure in arterial blood: <math chem display=block>[\ce{CO2}] = 0.03 \times P_{\text{a}\ce{CO2}}\text{.}</math>
For example, blood gas machines usually determine bicarbonate concentrations from measured ''p''H and {{math|''P''<sub>a{{CO2}}</sub>}} values. Mathematically, the algorithm [[substitution (algebra)|substitutes]] the Henry's law formula into the Henderson-Hasselbach equation and then rearranges: <math chem display=block>\left[\ce{HCO3^-}\right]=0.03\cdot P_{\text{a}\ce{CO2}}\cdot 10^{p\ce{H}-pK_\text{a}}</math> At [[sea level]], normal numbers might be {{math|''p''H ≈ 7.4}} and {{math|''P''<sub>a{{CO2}}</sub> ≈ 40}}; these then imply <math chem display=block>\begin{align}
\left[\ce{HCO3^-}\right]&=0.03\cdot40\cdot10^{7.4-6.1} \\
&=24
\end{align}</math>
== Consequences ==
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