The Control of Breathing during Weaning from Mechanical Ventilation (12)

Thus, during mechanical ventilation with a volume preset mode, minute ventilation and PaCOz are as much determined by machine settings as they are dependent on the state of the respiratory controller. When the level of ventilatory support is progressively reduced, as is the case during weaning with IMV and/or PS modes, Ve and PaC02 become increasingly dependent on mechanical loads and the performance capacity of the respiratory pump. In accordance with this reasoning, patients whose lungs were ventilated in the assist control mode (subjects 4, 5, 9, 10, and 11) had C02MV tensions that were significantly lower than either C02RT or C02SB (4±3 and 8±3 mm Hg, respectively, p<0.05). Four patients in group 2    (subjects 6, 12, 13, and 14) whose lungs were ventilated in an IMV or PS mode had C02MV tensions that were between 4 and 8 mm Hg greater than at the end of a symptom-limited weaning trial. The latter observation is consistent with reports suggesting that mechanical ventilation with low IMV backup rates may mask the presence of respiratory pump failure by blood gas criteria.
The Determinants of C02RT
From this and previous studies, we know that the within-subject variability in C02RT is between 2 and 3    mm Hg, provided the measurement is standardized as described herein.

Category: Pulmonary Function | Tags: hypothesis, mechanical ventilation, respiratory distress, respiratory muscle