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Unrecognized Imposed Resistive Work of Breathing Results in Inadequate Levels of Pressure Support Ventilation in Pediatric Patients with Respiratory Failure

Unrecognized Imposed Resistive Work of Breathing Results in Inadequate Levels of Pressure Support Ventilation in Pediatric Patients with Respiratory Failure

Anesthesiology Abstracts of Scientific Papers Annual Meeting: Abstract No. A-1397

Introduction: Mechanical ventilation with inadequate levels of PSV can contribute to respiratory muscle fatigue. This is especially true in children due to the resistance imposed by smaller diameter endotracheal tubes (ETT). Clinicians currently make ventilator adjustments based on airway pressure measurements obtained at the Y-piece (PY) of the ventilator circuit rather than the distal, intratracheal end of the ETT (PT). However, in healthy children PY underestimates the amount of negative airway pressure generated during spontaneous ventilation, which leads to an underestimation of WOBi.1 Underestimation of WOBi may, in turn, mislead clinicians as to the optimal level of PSV needed to nullify WOBi and avoid respiratory muscle fatigue. We hypothesized that, in children with respiratory failure a large amount of WOBi is unrecognized using PYdata and that this results in the administration of inadequate levels of PSV. Methods: Following IRB approval and parental consent, 22 pediatric ICU patients requiring ventilatory support for respiratory failure were enrolled in this prospective, observational study. All patients had previously been intubated with an ETT with a pressure measuring lumen embedded in its sidewall, which terminated at the tracheal end (Tyco:Mallinckrodt, St. Louis, MO). PY, tidal volume (VT), and peak inspiratory flow rate were measured by a flow-pressure sensor placed between the Y-piece and the ETT. PT was simultaneously measured from the side lumen of the ETT. Both pressure readings were directed to a bedside monitor (CP-100(R), Bicore Monitoring Systems, Irvine, CA) and pressure-volume loops created using PT and VT. WOBi was calculated for repeated spontaneous breaths as the area below the baseline pressure within the loop. The PSV level was documented for each patient at the time of the study. A PSV level that did not reduce WOBi to zero was considered inadequate. Data were analyzed with a repeated measures ANOVA and t-tests with alpha set at 0.05 for statistical significance. Results: The patients ranged in age from 10 days to 21 years and weighed an average of 26.4 kg. Twelve of the 22 children (54%) were determined to have inadequate levels of PSV as evidenced by increased WOBi (Figure). Two patients had particularly high levels of WOBi that was not appreciated clinically and were being inadequately treated with PSV. PY consistently underestimated WOBi compared with PTduring spontaneous breathing. Conclusions: The majority of critically ill children with respiratory failure in this study were found to be receiving PSV at levels insufficient to reduce their WOBi to zero. This is likely due to the fact that PY measurements underestimate patients' actual WOBi and adequate PSV is not prescribed. We recommend that PT be used to calculate WOBi in order to better apply PSV in pediatric patients with respiratory failure.

Accession: 036006343

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