The Science Journal of the American Association for Respiratory Care
Background: Weaning patients from mechanical ventilators optimally includes making frequent ventilator adjustments in response to the patients' needs. The Siemens Servo 300A mechanical ventilator proposes to allow the ventilator to be interactive with the patient needs, incorporating both control and support modes. We undertook the following experiment to validate the Automode algorithms in an animal model. Method: We ventilated six spontaneously breathing piglets in Pressure Regulated Volume Control/Volume Support (PRVC/VS), Pressure Control/Pressure Support (PC/PS) and Volume Control/ Volume Support (VC/VS). The animal was attached to a computerized respiratory monitor that recorded and analyzed individual animal breaths for response time, effort of triggering and work of breathing. Data collection was begun with the animals breathing spontaneously in each support mode. Succinylcholine was administered, inducing apnea, allowing the ventilator to switch between the modes automatically. Data collection was continued before, during and after apnea to observe the apnea delay time, trigger response time and any significant pressure or volume variances of the Automode feature.
Results: We found no instances of failure of Automode to follow the predetermined algorithms. In each animal, there was a difference in both changes in pressure and most negative deflection of pressure by the animal during triggering in the post apnea phase (p<0.05). Response time in milliseconds for individual breaths was shorter from initial animal effort to most negative deflection of pressure during the post apnea phase (p<0.05). Total work of breathing was no different pre or post neuromuscular blockade during spontaneous breaths. Experience: It is our experience in the animal laboratory that Automode functioned as predicted.
Conclusions: We conclude that differences in response time and negative deflection of pressure, as an indication of animal effort, were due to continued weakness from the neuromuscular blocker. However, the ventilator continued to trigger despite decreased effort by the animal.