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Causes of errors
In the pulse oximeter, adequate waveform implies
the reliability. Always check the plethysmograph or
bar graph for noises and disturbances. When
noises or disturbances occur, check the probe
connection or patient condition. The following are
the main causes of errors in arterial oxygen
saturation measurement.
Abnormal hemoglobin
Besides oxygenated hemoglobin and reduced hemoglobin, there are carboxyhemoglobin (COHb) and
methemoglobin (MetHb). They do not carry oxygen and are called abnormal hemoglobin. Normally,
carboxyhemoglobin is about 1%. Methemoglobin is abundant in neonates, but it decreases to a negligible
level as they grow. When abnormal hemoglobin has increased due to carbon dioxide poisoning or
methemoglobinemia, a measurement error occurs. For those suffering from these conditions,
2-wavelengh pulse oximeter can not be used.
Venous pulsations
When the sensor is secured tightly with tape, the venous pulsations may be also detected and the lower
arterial oxygen saturation is obtained.
Low perfusion
When peripheral circulation disorder exists, pulses enough to detect the arterial oxygen saturation can not
be obtained. Do not secure the sensor too tightly with tape or do not place the probe at the same location
for a long period of time.
A pulse oximeter does not require calibration. Check the performance using the optional checker
periodically.
Plethysmograph
Pulse bar graph
