Four of nine patients in group 2 had signs and symptoms of weaning-induced respiratory distress at a C02SB, 4 to 8 mm Hg lower than C02MV. These patients had been mechanically ventilated using either an intermittent mandatory ventilation (IMV) mode or a pressure support (PS) mode with low backup rates and remained ventilator dependent 24 hours after our study.
Figure 3. The differences between arterial COs tensions (in mm Hg) between mechanical ventilation (COsMV) and spontaneous breathing (COsSB) are shown. Dark shaded bars (patients 1 through 5) represent observations in group 1. light shaded bars (patients 6 through 14) represent observations in group 2. Patients 4, 5, 9,10, and 11 were ventilated with volume preset ventilation in the assist control mode. The remaining patients were ventilated with intermittent mandatory ventilation or pressure support ventilation. Figure 4 shows a comparison of C02RT measurements before (abscissa) and immediately following (ordinate) the weaning trial in seven patients. Open and closed symbols identify paired data from patients in group 1 and group 2, respectively. C02RT measurements were reproducible within 2.0 ±1.0 mm Hg. Although the number of observations is small, there is no indication that the C02 responsiveness of the unloaded respiratory pump is altered shortly after a failed weaning attempt.
Figure 4. Identity plot of CO, recruitment threshold measurements obtained under identical experimental conditions before (prewean; ordinate) and after (postwean; abscissa) a weaning trial from seven patients. Open symbols represent data from patients in group 1; closed symbols, data from patients in group 2.