Usefulness of measures of Svo2, Spo2, vital signs, and derived dual oximetry parameters as indicators of arterial blood gas variables during weaning of cardiac surgery patients from mechanical ventilation

To determine whether combined use of the parameters of mixed venous oxygen saturation, arterial oxygen saturation obtained by pulse oximetry (Spo2), and vital signs correlated with arterial blood gas variables (ABGs) better than each individual variable during weaning of postoperative cardiac surgery patients from mechanical ventilation; and to evaluate the relationship of derived parameters: oxygen extraction index and ventilation/perfusion index (VQI), and ABGs. Secondary analysis of previous correlational study. The cardiac care unit in a large medical center in central Florida. Thirty postoperative coronary artery bypass graft patients being weaned from mechanical ventilation. After a change in ventilator settings during systematic weaning towards extubation, measurements of variables were taken during a 30-minute period. At 30 minutes, an ABG was drawn for comparison. Data were collected after two ventilator changes. A total of 57 data sets were used for analysis. By use of multiple regression analyses, statistically significant (p < 0.01) independent variables predicting pH and partial pressure of carbon dioxide were Spo2 and respiratory rate. The independent variable contributing to the model versus partial pressure of oxygen was Spo2. The oxygen extraction index did not correlate with ABGs; however, the VQI correlated significantly with all ABG variables except bicarbonate. The use of multiple parameters was no more useful in predicting ABGs than individual variables of Spo2 and respiratory rate. The derived VQI parameter correlated with ABGs. The use of VQI in conjunction with Spo2 and respiratory rate may assist in patient monitoring during weaning and reduce the number of ABGs needed.