• D N Thrush, S W Mentis, and J B Downs.
• Department of Anesthesiology, University of South Florida College of Medicine, Tampa 33601.
• J Clin Anesth. 1991 Nov 1; 3 (6): 456-60.

Study ObjectiveTo 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.DesignProspective study comparing SpO2 and P(ET)CO2 to calculated arterial oxygen saturation (SaO2) and arterial carbon dioxide tension (PaCO2) obtained from blood gas analysis.SettingCardiac surgical intensive care unit at a university-affiliated hospital.PatientsTen patients requiring elective coronary artery bypass grafting (CABG) were studied in the postoperative period during weaning from mechanical ventilation.InterventionsContinuous monitoring of SpO2 and P(ET)CO2 was used to wean patients from mechanical ventilation.Measurements And Main ResultsThe 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.ConclusionsContinuous 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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