Siemens Rapidlab 1200, Руководство оператора, Страница: 54 / 448

1-34 Rapidlab 1200 Operator’s Guide: System Overview and Intended Use
02087462 Rev. V
Using this formula, a hydrogen ion concentration of 1 x 10
-7
mol/L has a pH value of 7.
Because pH is the negative logarithm, its value is inversely proportional to the actual
hydrogen ion concentration in a sample. Therefore, as the hydrogen ion concentration
decreases, the pH value increases. As the hydrogen ion concentration increases, the pH
value decreases.
The normal pH range of human blood is 7.35–7.45.
The Henderson-Hasselbalch equation describes how pH expresses the interaction of acid
and base in blood:
acid
base
pK pH log
+ =
where K is the dissociation constant, which describes the ability to release hydrogen ions.
Because K, and thus pK, is a constant, this equation can be used to demonstrate that pH is
proportional to the acid-base concentrations in blood:
acid
base
pH
α
Therefore, if base increases without a corresponding increase in acid, the pH rises, and if
acid increases without a corresponding increase in base, the pH decreases.
pH is clinically significant as a means of determining acid-base disturbances. Acid-base
disorders can result in several pathologic conditions. Acidosis (low pH) stems from either
respiratory failure (high
p CO
2
) or from metabolic causes (including ketoacidosis, lactic
acidosis, uremia, severe diarrhea, hypoaldosteronism, renal tubular disease, drug effects,
or poisoning from several specific agents). Alkalosis (high pH) stems from
hyperventilation (low
p CO
2
) or from metabolic causes (including excessive vomiting,
gastric drainage, drug effects, hyperadrenocorticism, potassium depletion, or excessive
alkali intake). Extreme abnormalities of pH reflect a potentially life-threatening
pathophysiologic state that must be corrected promptly.
6,7