User's Manual

i15 Blood Gas and Chemistry Analysis System User Manual Parameters
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Chapter 12 Parameters
12.1 pH
pH reflecting the acid-base status of a patient is the negative logarithm of the hydrogen ion
concentration.
pH is measured by potentiometry with a pH selective membrane electrode. The concentration of
hydrogen ions is determined by the measured potential through the Nernst equation.
If test results are inconsistent with the clinical assessment, the sample should be analyzed again
with a new test cartridge.
12.1.1 Intended Use
The pH test is intended for the quantification of pH in arterial, venous, or capillary whole blood
samples.
pH is an important clinical indicator to assess the acid-base imbalance caused by pathologic
conditions, such as ventilatory dysfunction and renal inadequency. The reasons for abnormal
blood pH values are:
 primary bicarbonate deficit - metabolic acidosis
 primary bicarbonate excess - metabolic alkalosis
 primary hypoventilation - respiratory acidosis
 primary hyperventilation - respiratory alkalosis
12.1.2 Traceability
pH values assigned to calibrant and controls are traceable to NIST standards.
12.1.3 Temperature Correction
pH is a temperature dependent quantity which is measured at 37°C on the system. The pH value
can be corrected to the patient’s temperature other than 37°C. Patient temperature can be entered
on the Enter Patient Information screen during each patient sample test.
The pH at the patient’s temperature is calculated as follows:
pH (T) = pH – [0.0147 + 0.0065(pH – 7.4)] (T – 37)