Weaning with end-tidal CO2 and pulse oximetry.

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.