The Science Journal of the American Association for Respiratory Care

1997 OPEN FORUM Abstracts

INCREASE IN MEASURED AUTO-PEEP WITH THE APPLICATION OF FLOW TRIGGERING. A PEDIATRIC CASE STUDY.

James E. Martin BS, RRT, CPFT, Kay Urmetz, RRT, CPFT, Kelli Chronister RRT, Rashed Durgham MD, John Pope MD, Departments of Pulmonary Services, and Pediatrics, MetroHealth Medical Center, Cleveland, OH

INTRODUCTION: Incomplete exhalation between delivered breaths results in pulmonary gas trapping. The term auto-PEEP has been used to describe this condition. Physiologic consequences of trapped gas may result. We report such changes when auto-PEEP is elevated during mechanical ventilation of a pediatric patient. CASE SUMMARY: A 6 y/o, 16 Kg. former 24-week preemie with a history of BPD and tracheostomy was seen in the pediatric clinic for retractions, wheezing, and increased tracheal secretions for the previous 48 hours. Physical examination revealed RR 36, HR 160, Temp 39° C, bilateral wheeze with decreased air exchange, marked accessory muscle use, and SpO_{2} 91- 93% on .30 FIO_{2}. Chest radiograph was remarkable for hyperinflation with perihilar bronchial thickening without infiltrates. The patient was directly admitted to the PICU for fever and respiratory distress. Supportive therapy included albuterol 2.5 mg Q2, intal 20 mg Q6, IV antibiotic, antipyretics, and 30% heated humidified oxygen. Within 24 hours, the patient was transferred to the general pediatric floor. On day 2, the patient's pulmonary status worsened and was readmitted to the PICU and started on albuterol 20 mg/hr (1.25 mg/Kg/hr), atrovent 250 mcg Q6, solumedrol Q6. During the course of the next two days, the therapy was increased to albuterol 40 mg/hr (2.5 mg/Kg/hr), with the addition of continuous terbutaline infusion. The decision was made to recannulate the patient with a cuffed trach tube and provide mechanical ventilator assistance. Volume ventilation with a Nellcor Puritan Bennett 7200ae ventilator was initiated with patient effort controlled with doxacurium and ativan. Three days after initiation of ventilator support, the doxacurium was discontinued resulting in increased bronchospasms, airway leak, and a reduction in both exhaled tidal volume and SpO_{2}. With a gross airway leak, the patient was changed to pressure control ventilation and subsequently re-paralyzed. There was a marked reduction in exhaled volumes. Airway graphics demonstrated obstructed expiratory flow consistent with gas trapping. A static auto-PEEP of 6 cm H_{2}O was measured using the ventilator software package. Given this patient's history of chronic airway obstruction and previous demonstration of this problem, the 6 L/m base triggering flow was discontinued. A repeat auto-PEEP measurement of 2 cm H_{2}O was obtained. To confirm the differences of auto-PEEP with and without flow triggering, the measurements were repeated the next day with the same results. In addition, with the flow triggering on, the expired tidal volumes were reduced from 140 ml to 50 ml with a decline in pulse oximetry from 93% to 88%. No additional flow was introduced into the circuit that would bias the measurements. DISCUSSION: With this pediatric patient experiencing severe obstructed expiratory flows, flow triggering using a base flow of 6 L/m resulted in an elevation of auto-PEEP, a reduction in expired tidal volumes, and desaturation as measured by pulse oximetry. Although this may be an isolated incident, the option of using flow triggering on chemically paralyzed pediatric patients with severe expiratory airflow should be reviewed with each individual case.

OF-97-042

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