Evaluation of Intensive Care Mechanical Ventilator Response Time During Varying Levels of Inspiratory Effort

Abstract

Objective: Mechanical ventilators must be responsive to a patient's variable inspiratory demand. Responsiveness is one attribute used to compare these expensive, but necessary lifesaving devices. Under varying levels of inspiratory effort, triggering performance was compared between the Maguet Servo-i and Respironics Esprit ventilators. Methods: The Ingmar ASL 5000 Breathing Simulator was used to provide normal respiratory mechanics (compliance of 50 mL/cm H2O; resistance, 3 cm H2O/L/s; spontaneous rate of 15 breaths/min) and inspiratory muscle pressures of 10, 15, and 20 cm H2O for 5-minutes each. The simulator was connected to each ventilator with the same settings (pressure support (PS) of 10 cm H2O; positive end-expiratory pressure (PEEP) of 0; and, a trigger flow of 3 L/min). Trigger response time, time from spontaneous effort (SoE) to a minimum pressure (Pmin), and the maximum pressure drop during triggering were collected. Results: The Esprit ventilator trigger response time and time from SoE to a Pmin decreased under conditions of increased inspiratory effort. The Servo-i trigger response time and time from SoE to Pmin increased with rising inspiratory muscle pressure. Both ventilators demonstrated a greater maximum pressure drop during triggering with each increase in inspiratory muscle pressure. However, for an inspiratory muscle pressure of 15 and 20 cm H2O, the drop in pressure was much larger for the Servo-i. Conclusions: Both ventilators are suitable for clinical use, however, the Respironics Esprit ventilator demonstrated a better response to a high ventilatory demand. A potential reason for this is the greater peak inspiratory flow rate (PIFR) capability of the Esprit ventilators. The Esprit's internal flow generator is a turbine and seems to be capable of a faster initial flow than the pneumatic flow design of the Servo-i.