The Science Journal of the American Association for Respiratory Care

2004 OPEN FORUM Abstracts


Paul Luehrs RRT, Kara McKilvain RRT, Zach Frazier RRT CoxHealth Respiratory Care Springfield, MO.

INTRODUCTION: Airway Pressure Release Ventilation (APRV, Drager) has gained in popularity over the past several years as a mode of mechanical ventilation. APRV, a style of inverse-ratio ventilation, is most commonly used to support hypoxemic respiratory failure patients. The majority of published information regarding APRV references the Drager Evita and the Puritan Bennett 840 (BiLevel) ventilators. The MAQUET (formerly SIEMENS) Servo i has the capabilities of performing APRV using BiVent mode. We compared our use of APRV in the BiVent mode to the Evita published information.

METHODS: The Servo i BiVent mode allows the practitioner to set independent inspiratory (P High) and expiratory (PEEP) pressure settings. Time spent in each phase is controlled by adjusting inspiratory (T High) and expiratory (T PEEP) time. These set times determine the I:E ratio and the frequency of pressure releases. In the severely hypoxemic patient, the T High and T PEEP are adjusted to produce an inverse ratio that results in a higher mean airway pressure (MAP). The goal of the inverse ratio is to inflate the lungs to a set peak pressure (P High) and periodically release the pressure to a set PEEP, for a short time (T Peep), in order to allow for exhalation of CO2 while trapping air and preventing alveolar derecruitment. A randomly selected group of intubated, acutely hypoxemic respiratory failure patients (n=11) were placed on the Servo i in the Bivent mode with a mean P High of 26 cmH2O (24-28), set PEEP 0, mean T High of 4.5 s (3.0-5.5), mean T PEEP of 0.4 s (0.2-0.7). The percent of peak expiratory flow (%PEF) where T High began was monitored and recorded every two hours. Manipulations in T PEEP were made in order to maintain a %PEF between 25% and 75% in an attempt to keep the PaO2/FiO2 >300.

RESULTS: The mean P High of 27 and mean T PEEP of 0.35 s resulted in a mean %PEF of 51. These settings resulted in an average MAP of 25 cmH2O. We applied an average PS above P High of 3 cmH2O to achieve an average total respiratory rate of 22 breaths/min.

DISCUSSION: Upon initiating the BiVent mode on the Servo i, we found differences between the reported APRV settings on a Drager Evita ventilator and the needed BiVent settings on the Servo i. We analyzed a random group of patients on the Maquet Servo i BiVent mode in the various intensive care units. The demographic data between the two groups comparing age, gender, patients with acute lung injury or acute respiratory distress syndrome, and the number of extrapulmonary organ systems in failure, were all found to be similar. In order to maintain adequate oxygenation, the Servo i requires a shorter T PEEP (0.4 s), compared to 0.7 s on the Drager. We maintained a set Peep of 0. We used a low level of PS (3 cmH2O) above P High, and a moderate T High (4.5 s) to encourage spontaneous breathing. With all patients, we adjusted the P High to maintain adequate oxygenation and ventilation.

CONCLUSIONS: APRV using the Servo i BiVent mode required shorter T PEEP. BiVent allows settings to be monitored and adjusted to achieve adequate P/F ratios and successfully meet ventilation requirements for hypoxic respiratory failure patients.

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