PO2 - 2 Art: 714180-00K Rev. Date: 01-Aug-11
The reference ranges shown are for a healthy population. Interpretation of blood gas measurements depend
on the underlying condition (eg. patient temperature, ventilation, posture and circulatory status).
Clinical Significance
PO
2
(partial pressure of oxygen) is a measurement of the tension or pressure of oxygen dissolved in blood.
Some causes for decreased values of PO
2
include decreased pulmonary ventilation (e.g. airway obstruction
or trauma to the brain), impaired gas exchange between alveolar air and pulmonary capillary blood (e.g.
bronchitis, emphysema, or pulmonary edema), and alteration in the flow of blood within the heart or lungs
(e.g. congenital defects in the heart or shunting of venous blood into the arterial system without oxygenation
in the lungs).
sO
2
(oxygen saturation) is the amount of oxyhemoglobin expressed as a fraction of the total amount of
hemoglobin able to bind oxygen (oxyhemoglobin plus deoxyhemoglobin).
(X
3
+ 150X)
sO
2
=100
__________________
X
3
+ 150X + 23400
where X = PO
2
• 10
(0.48(pH-7.4)-0.0013(HCO
3
-25))
sO
2
is calculated from measured PO
2
and pH and from HCO
3
calculated from measured PCO
2
and pH.
However, this calculation assumes normal affinity of oxygen for hemoglobin. It does not take into account
erythrocyte diphosphoglycerate (2,3-DPG) concentrations which affect the oxygen dissociation curve. The
calculation also does not take into account the effects of fetal hemoglobin or dysfunctional hemoglobins
(carboxy-, met-, and sulfhemoglobin). Clinically significant errors can result from incorporation of such an
estimated sO
2
value for oxygen saturation in further calculations, such as shunt fraction, or by assuming the
value obtained is equivalent to fractional oxyhemoglobin.
Temperature “Correction” Algorithm
PO
2
is a temperature-dependent quantity and is measured at 37°C. The PO
2
reading at a body temperature
other than 37°C can be ‘corrected’ by entering the patient’s temperature on the chart page of the analyzer.
See section 12 ‘Procedure for Cartridge Testing’ in the i-STAT 1 System Manual or section 11 ‘Patient and
Control Sample Testing’ in the i-STAT System Manual for details. In this case, blood gas results will be
displayed at both 37°C and the patient’s temperature. The PO
2
at the patient’s temperature (T
p
) is calculated
as follows
3
:
Note: Patient temperature corrected results are only available on cartridges containing pH,
PCO
2
, and
PO
2
sensors.
Performance Characteristics
The performance characteristics of the sensors are equivalent in all cartridge configurations.
The typical performance data summarized below was collected in a health care facility by health care
professionals trained in the use of the i-STAT System and comparative method.
Precision data were collected in multiple sites as follows: Duplicates of each control fluid were tested in the
morning and in the afternoon on five days for a total of 20 replicates. The averaged statistics are presented
below.
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