Chest
Clinical Investigations in Critical CarePatient-Ventilator Trigger Asynchrony in Prolonged Mechanical Ventilation
Section snippets
Materials and Methods
We screened 200 consecutive ventilator-dependent patients transferred to BRH for attempted weaning over an 18-month period. Initial assessments for TA were performed within 1 week of hospital admission. Patients were excluded if they had weaned by the time of assessment, or if they were in hemodynamically unstable condition, in which case they were reassessed once their conditions stabilized. The assessment was performed as follows: all patients were ventilated via tracheostomy tubes using
Results
Of the 200 patients screened, 26 were excluded. The remaining 174 patients had a median duration of mechanical ventilation prior to transfer of 29 (3 to 371) days. Nineteen of the 174 patients (10.9%) were found to have TA on initial assessment. In these 19 patients, the set tidal volume was 576±75 mL, inspiratory flow was decelerating with peak flow of 81.9 ±7.2 L/min, effective respiratory rate was 14.7±3.0 with all breaths patient triggered, and ineffective efforts constituted 45.2± 13.8% of
Discussion
TA has also been called patient-ventilator “dyssynchrony,”7 “desynchronization,”2 “mismatching,”8 and trigger failure.9 We prefer the term TA because it has been used in the pediatric literature, and because we consider TA to be one of several conditions in which there is lack of synchrony in the interaction between patient and ventilator (Table 3). We found a prevalence of 10.9% TA in patients in stable condition with PMV on transfer to our RWC. These patients were older, weaker, and had a
Conclusion
In patients with PMV, the observation of uncoupling of accessory respiratory muscle movement and onset of machine breaths is highly specific and probably sensitive in identifying TA. TA is associated with low respiratory pump output and high auto-PEEP. Ventilator factors contribute to reduced pump output with high levels of ventilator support, and increased auto-PEEP with high tidal volume; patient factors include severe pump failure and expiratory airflow limitation. TA can be eliminated by
ACKNOWLEDGMENT
The authors thank Catherine S. H. Sassoon, MD, for her expert and thoughtful criticism and advice in manuscript preparation.
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Presented in part at Weaning ’96: Weaning from Prolonged Mechanical Ventilation, Palm Springs, April 1996; and at the 62nd Annual Scientific Assembly of the American College of Chest Physicians, San Francisco, October 27–31, 1996.