Patient selection: ICU nonsurgical patients who are dependent on mechanical ventilation
Requirements:
(1) radial artery catheter for measuring oxygen saturation in the artery
(2) central venous catheter inserted in the jugular or subclavian vein for measuring oxygen saturation in the central venous blood
Measurements:
(1) arterial oxygen saturation in percent at baseline
(2) central venous oxygen saturation in percent at baseline
(3) arterial oxygen saturation in percent at 30 minutes into spontaneous breathing test
(4) central venous oxygen saturation in percent at 30 minutes into the SBT
difference between arterial oxygen saturation at baseline and at 30 minutes =
= (arterial oxygen saturation at baseline) - (arterial oxygen saturation at 30 minutes)
difference between central venous oxygen saturation at baseline and at 30 minutes =
= (central venous oxygen saturation at baseline) - (central venous oxygen saturation at 30 minutes)
oxygen extraction ratio at baseline in percent =
= ((arterial oxygen saturation in percent at baseline) - (central venous oxygen saturation at baseline)) / (arterial oxygen saturation at baseline) * 100%
oxygen extraction ratio at 30 minutes in percent =
= ((arterial oxygen saturation in percent at 30 minutes) - (central venous oxygen saturation at 30 minutes)) / (arterial oxygen saturation at 30 minutes) * 100%
difference in oxygen extraction ratio in percent =
= (oxygen saturation ratio at baseline) - (oxygen saturation ratio at 30 minutes)
where:
• The use of simple differences is based on Figure 2.
Findings associated with reintubation:
(1) difference in central venous oxygen saturation > 4.5% (decrease, odds ratio 49.5)
(2) difference in oxygen extraction ratio as a percent < -8% (increase, odds ratio 32)
Performance:
• The difference in central venous oxygen saturation had a sensitivity of 88%, specificity of 95% and area under ROC curve of 0.87.
• The difference in oxygen extraction ratio had a sensitivity of 95%, specificity of 63% and area under ROC curve of 0.85.
