The Science Journal of the American Association for Respiratory Care

2008 OPEN FORUM Abstracts

IMPOSED WORK OF BREATHING ASSOCIATED WITH INADEQUATE MECHANICAL VENTILATOR FLOW RESPONSE

Nancy Craig1, Brian K. Walsh1, Gerhard Wolf2, Peter Betit1,2



INTRODUCTION: In patients with CDH we have employed a mechanical ventilation strategy that includes the preservation of spontaneous breathing and avoidance of ventilator induced lung injury. To accomplish this goal we utilize PRESSURE A/C mode with flow cycle (AVEA, Viasys, Palm Springs, CA). This mode provides a back-up rate in the event of apnea or inconsistent respiratory drive.

CASE SUMMARY: A full-term male was admitted with the diagnosis of L-CDH. He was stabilized on the PRESSURE A/C mode, and on DOL 4 underwent a primary repair of his diaphragmatic defect. On DOL 8 prior to a planned extubation the patient exhibited signs of an increased WOB, including paradoxical breathing, tachypnea, and retractions. Abnormalities in both inspiratory and expiratory flow tracings were observed. When the patient initiated a breath there was an initial scalped appearance in the inspiratory flow waveform and inspiratory pressure did not appear to reach peak until the end of the breath. The breath cycled into exhalation when the inspiratory time-limit was met.

Adjustments in both rise time and flow termination sensitivity did not change the patient's WOB or ability to control I:E. It appears that the demand valve was sluggish leading to flow starvation. The TCPL A/C mode with adjustable peak flow rate was then selected. This change met the patient's inspiratory flow requirements, lead to successful flow termination of the breath, and abated the WOB.

DISCUSSION: This case illustrates that despite ventilator technology advancements limitations exist. The RT was able to identify and correct a technology deficiency that lead to an imposed WOB. The speculated etiology of the increased WOB was a lack of demand flow response. Ventilator flow starvation may be associated with imposed WOB. In this case the ventilator failed to meet the patient's flow demand requirements despite maneuvers to maximize available flow. The use of graphics in this patient aided the RT in determining the source of the increased WOB. Without the use of graphics the WOB may have been attributed to a change in the patient's underlying condition, and may have lead to an unnecessary escalation of ventilator support and delayed extubation.