Principles of Measurement and Parameters
Page B-8
Operator’s Manual PiCCO
2
Version 3.1
4
Central venous oximetry
4.1
Principle
The PiCCO
2
measures central venous oxygen saturation (ScvO
2
) by spectrophotometry. Spectrophotometry
involves the use of light emitting diodes (LED) that produce light of various wavelengths in red and infrared
spectra. The light is transmitted to the blood through a fiberoptic in the probe, reflected off the red blood cells
and transmitted back through a separate fiberoptic to an optical module.
Figure 9: The principle of spectrophotometry
The wavelengths are selected in a way that the absorption characteristics of haemoglobin and
oxyhaemoglobin are different. Given both the amount of total haemoglobin and the amount of haemoglobin
bound to oxygen, oxygen saturation can be calculated.
4.2
Determination of ScvO
2
ScvO
2
reflects the oxygen saturation of the haemoglobin in the blood in the superior vena cava directly before
the right atrium. It is an early indicator of an imbalance between oxygen delivery and oxygen consumption.
Thus this parameter early indicates a threat to global tissue oxygenation.
Absolute Parameters
Parameter
Abbr.
Unit
Central Venous Oxygen Saturation
ScvO
2
(%)
4.3
Oxygen delivery and oxygen consumption: DO
2
and VO
2
Absolute Parameters
Indexed Parameters
Parameter
Abbr.
Unit
Abbr.
Unit
Oxygen delivery
DO
2
ml/min
DO
2
I
ml/min/m
2
Oxygen consumption
VO
2
ml/min
VO
2
I
ml/min/m
2
4.3.1
DO
2
DO
2
is the amount of oxygen provided to the tissue per minute. It depends on the flow (cardiac output), the
amount of haemoglobin in the blood and the arterial oxygen saturation.
4.3.2
VO
2
VO
2
is the amount of oxygen consumed by the tissue per minute.
