The Science Journal of the American Association for Respiratory Care

2003 OPEN FORUM Abstracts

THE UTILIZATION OF AIRWAY PRESSURE RELEASE VENTILATION FOR LUNG RECRUITMENT DURING SECONDARY ARDS

Stephanie Brown, RRT; Joseph Groller, RRT; Cheryl Justice, RRT; Chad Traub, BS, RRT; Kenneth Miller, MEd, RRT; Dr. Richard Strobel. Lehigh Valley Hospital Center, Allentown, PA

Introduction: Recent ventilatory management of ARDS has been centered on lung protection. The ARDS/Net ventilatory strategy has demonstrated a decrease in mortality compared to conventional strategies. One problem that can arise during ARDS/Net is the inability to recruit the lung quickly in severe ARDS, when a distending pressure has to be maintained for several seconds. Airway Pressure Release Ventilation utilizes both pressure and time to re-inflate and maintain inflation of de-recruited lung units. In our case presentation, we demonstrate the use of APRV to improve the P/F ratio and maintain lung inflation when ARDS/Net strategy fails.

Case review:
A twenty-two year-old male was admitted with the diagnosis of acute Pancreatitis. Within four hours of admission, the patient develop acute respiratory failure and required emergent intubation and mechanical ventilation. Post intubation the Pa02/FI02(P/F ratio) <100 torr and chest x-ray revealed bilateral diffuse infiltrates consistent with the diagnosis of ARDS. The ARDS/Net ventilatory strategy was implemented. Despite aggressive ventilator adjustments the patient continued to maintain a Sp02<85% and P/F ratio<100 torr. The decision was made to attempt lung recruitment by changing to Airway Pressure Release Ventilation (APRV). The P1 was set at 50cm/H20 for 5.5 seconds and P2 set at 0cmH20 for .8 second. Within two hours the P/F ratio increased to 200 torr and a repeat x-ray showed a decrease in the bilateral infiltrates with an increase in lung expansion. P1 was weaned by increments of 5cm/H20 every hour maintaining a release volume of 1000cc. Gas exchange stabilization was maintained with a P1 of 36cm/H20 and P1 time of 7.1 seconds. FIO2 was weaned down to 40%. The patient was then placed back on the ARDS/Net ventilatory strategy per physician preference. Within forty-eight hours after ARDS/Net implementation the P/F ratio decreased <200 torr and there was an increase in bilateral infiltrates and noted loss of lung volume, consistent with basilar atelectasis via cat scan. Ventilatory adjustments were made with no improvement in gas exchange. Prone positioning was instituted with minimal improvement in gas exchange. The patient was then placed back on APRV with a P1 of 45cm/H20 and P1 time of 5.5 seconds. Within four hours the P/F ratio improved to 200 torr and the chest revealed a decrease in infiltrates. P1 high was reduced to 30 cm/H20 without deterioration of the P/F ratio. APRV was maintained until liberation.

Discussion:
During the ARDS/Net clinical trials, there was a group of patients that "failed" the low tidal volume ventilatory strategy. One possible explanation was the lack of sustained mean airway pressure required to inflated collapsed lung units. By utilizing APRV as a recruitment tool, a high mean airway pressure can be achieved to facilitate recruitment of collapse lung units. By using time in conjunction with pressure, APRV can maintain lung inflation at a transpulmonary pressure that is consistent with lung protection. Furthermore, utilization of a short expiratory time maintains expiratory lung volume, thus prevents lung derecruitment. A clinical trial evaluating APRV as a recruitment tool in ARDS patients deserves consideration in the near future.

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