The Science Journal of the American Association for Respiratory Care

2006 OPEN FORUM Abstracts

SYNCHRONIZING PHIGH AND PLOW DURING AIRWAY PRESSURE RELEASE VENTILATION IN A PEDIATRIC PATIENT

Keith R. Hirst RRT, Peter Betit RRT-NPS, David Heitz RRT-NPS, David A. Turner MD.  Children's Hospital Boston and Harvard Medical School, Boston, MA

Introduction: Airway pressure release ventilation (APRV) is a ventilator mode aimed at recruiting and maintaining lung volume, while preserving spontaneous ventilation1. In our center, APRV is applied with the AveaT ventilator (Viasys Healthcare, Palm Springs, CA). We report the use of this mode and the use of its synchronization features in the care of a 14 year-old male who developed ARDS.

Background:
The patient was a child with Bardet Biedl Syndrome admitted for suspected aspiration during induction for an endoscopy. The patient subsequently developed ARDS, and required high-frequency oscillatory ventilation (HFOV) and muscle relaxation due to worsening lung compliance and gas exchange. Over the 7 day HFOV course, gas exchange improved and the patient was transitioned to APRV in order to promote spontaneous ventilation. Initial APRV settings were; FIO2 0.6, PHIGH /PLOW of 25/0 cmH2O, and THIGH /TLOW 6.0/0.8 seconds, Paw 22 cmH2O.  At hour 36 of APRV the patient developed a pneumothorax, received a chest tube, and transitioned to PSV/PEEP of 10/8 cmH2O in order to minimize further barotrauma. Over the next 48 hours, the patient's gas exchange worsened and work of breathing increased. The mode was changed to SIMV-PCV + PSV with no improvement. In an attempt to avoid HFOV and the need for paralysis, a second trial of APRV was employed with the settings; FIO2 0.7, PHIGH/PLOW of 23/0 cmH2O, and THIGH /TLOW of 5.5/0.3 sec, Paw 22 cmH2O. During the transition to APRV, the patient became tachypneic, tachycardic, hypertensive, diaphoretic, and accessory muscle use was noted. The increase in work of breathing was presumed to be from under-recruited lungs and increases in PHIGH were attempted and were unsuccessful. The APRV synchronization features were added; 20% TLOW Synch for PLOW to PHIGH transition, and 5% THIGH Synch for PHIGH to PLOW transition. After these changes were made, work of breathing and RR subsequently decreased, and the patient appeared more comfortable. Blood pressure and heart rate returned to clinically acceptable levels, and there was no recurrence of air leak. Gas exchange improved over the next 9 days and the patient was transitioned from APRV settings of FIO2 0.45 PHIGH/PLOW 16/0 cm H2O THIGH/TLOW 10/0.7 sec, to PSV/PEEP of

12/8 cmH2O. The patient was successfully extubated 2 days later.

Discussion:
The addition of TLOW Synch and THIGH Synch in this case improved the patient / ventilator interaction during APRV. The APRV advanced settings of TLOW Synch and THIGH Synch are adjusted as a percentage of TLOW and THIGH   and are unique to the AveaT.  It is possible that the lack of improvement and the development of a pnuemothorax may have been avoided if the synchronization features were used in the initial APRV attempt.  Prior to this patient, we had not used this feature as part of our APRV settings.  This case has assisted us with further developing our APRV protocol, and we now routinely synchronize to improve patient/ventilator interactions.  Clinical trials are warranted to validate the benefits of synchronization during APRV.

1. Habashi N, Andrew P (2004). Ventilator strategies for posttraumatic acute respiratory distress syndrome: airway pressure release ventilation and the role of spontaneous breathing in critically ill patients. Curr Opin Crit Care 10(6):549.

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