Weaning with end-tidal CO2 and pulse oximetry
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Updated: Aug 9, 2026
Expired CO2 Measurement in Intubated or Spontaneously Breathing Patients from the Emergency Department
Published on: January 29, 2011
D N Thrush1, S W Mentis, J B Downs
1Department of Anesthesiology, University of South Florida College of Medicine, Tampa 33601.
Study Objective:
To determine whether continuous measurement of arterial oxyhemoglobin saturation (SpO2) and end-tidal carbon dioxide (P(ET)CO2) can be used to wean patients safely and efficiently from postoperative mechanical ventilation after cardiac surgery.
Design:
Prospective study comparing SpO2 and P(ET)CO2 to calculated arterial oxygen saturation (SaO2) and arterial carbon dioxide tension (PaCO2) obtained from blood gas analysis.
Setting:
Cardiac surgical intensive care unit at a university-affiliated hospital.
Patients:
Ten patients requiring elective coronary artery bypass grafting (CABG) were studied in the postoperative period during weaning from mechanical ventilation.
Interventions:
Continuous monitoring of SpO2 and P(ET)CO2 was used to wean patients from mechanical ventilation.
Measurements And Main Results:
The patients were weaned from mechanical ventilation in an average time of 6.5 +/- 1.5 hours (mean +/- SD). A plot of SaO2 versus SpO2 indicated a high correlation (r = 0.84) with sensitivity (100%) for hypoxemia (SaO2 less than 90%). P(ET)CO2 was a good indicator of PaCO2 (r = 0.76); its sensitivity to detect hypercarbia (PaCO2 less than 45 mmHg) was 95%. The gradient between SpO2 and SaO2 was not significantly affected by the weaning process, but the PaCO2-P(ET)CO2 gradient decreased significantly as the ventilator rate was decreased (p less than 0.001). The weaning process was discontinued on four separate occasions because of metabolic acidosis. Ninety-five percent of arterial blood samples confirmed the weaning recommendations based on the continuous monitoring of SpO2 and P(ET)CO2.
Conclusions:
Continuous monitorin of SpO2 and P(ET)CO2 can be used to wean patients safely and effectively after CABG when adjustment of minute ventilation compensates for an increased PaCO2-P(ET)CO2 gradient during controlled ventilation.
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