Abstract
Background:
Patient effort during AMV is measured by esophageal pressure change (ΔPes) as a signifier of Pmus. Proper esophageal balloon placement requires close correspondence between ΔPes and airway pressure change (ΔPaw) during an occlusion test (ie, Baydur Maneuver). Because ΔPaw is the accepted standard for estimating ΔPmus, we reasoned that introducing an airway occlusion at end expiration to measure ΔPaw during the subsequent patient-triggered inspiration might be a practical, noninvasive way to assess inspiratory effort. We evaluated how closely clinician Pmus measurements using EMP reflected that generated by a breathing simulator under various conditions of inspiratory effort and breathing modes.
Methods:
Spontaneous breathing was simulated using an Ingmar ASL-5000 (Ingmar, Pittsburgh, PA) with a compliance of 80 mL/cm H2O and resistance of 5 cm H2O/L/s. The breathing pattern was f of 20 breaths/min at 3 ΔPmus levels reflecting mild, moderate and high effort (5, 10, 15 cm H2O) using a 20% pressure rise, 10% hold and 10% decay (inspiratory time or Ti: 1.2 s). The test series consisted of 15 breaths/Pmus. A PB-980 ventilator (Medtronics, Minneapolis, MN) was used with 3 modes: continuous positive airway pressure (CPAP: 5 cm H2O), pressure support ventilation (PSV: Δ15/5 cm H2O), and volume control ventilation (VCV: tidal volume: 500 mL, f: 15 breaths/min, peak flow: 60L/m, Ti: 0.9s, positive end-expiratory pressure: 5 cm H2O). Trigger sensitivity was set at 3 L/min. For each condition (and after allowing 5 min of practice), 5 clinicians measured Pmus using the ventilator's negative inspiratory force function during expiration and releasing the pause-hold as soon as a negative deflection in ΔPaw was observed on the scalar waveform. An average of 24 breaths per observer was used for each condition. Multiple comparisons used one-way ANOVA and Tukey Kraemer post-test. Bland Altman analysis was done during passive VCV comparing plateau to lung pressure with a 1.5-s pause. Alpha was set at 0.05.
Results:
EPM closely approximated simulated Pmus for all mild and moderate Pmus conditions for CPAP and PSV (Table). Under VCV at moderate and high effort EPM estimates of Pmus deviated from measurements made on CPAP and PSV. However, most comparisons were within parameters suggested by Bland-Altman analysis (ie, PB-980 Pressure bias -1.7 cm H2O (95% CI: -1.5 to -1.8 cm H2O).
Conclusions:
EPM is a feasible, noninvasive technique to assess breathing effort during AMV.
† P< 0.001 compared to VCV. View all access options for this article.
ΔPmus (set)
CPAP
PSV
VCV
P (ANOVA)
5 cmH2O
4.0 ± 0.2†
4.0 ± 0.2†
4.2 ± 0.4
< 0.001
10 cmH2O
8.9 ± 0.4†
8.9 ± 0.3†
7.5 ± 0.8
< 0.001
15 cmH2O
13.3 ± 0.5†
13.3 ± 0.6†
12.1 ± 0.8
< 0.001
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