Abstract
Background:
Atelectasis results when alveoli collapse and is prevalent in approximately 90% of patients undergoing some period of anesthesia. (1-4) The pathophysiological effects of atelectasis include decreased lung compliance and decreased gas exchange capacity, leading to lung injury. (5) Current strategies to minimize atelectasis in these patients are centered around an ‘open lung’ approach that relies on PEEP to maximize alveolar patency. (6) Our research group is investigating the use of transvenous phrenic nerve stimulation to provide controlled diaphragm contractions to maximize alveolar patency. Compliance is a measure of the elastic resistance of a system and correlates with the number of patent alveoli. (7) It can be measured dynamically, while flow is occurring, reflecting the pressure exposure of the alveoli as they are stretching. (7, 8) This describes pathological changes indicating the potential risk for ventilator-induced lung injury in sedated patients.
Methods:
A preclinical, semi-blinded study was conducted using large pigs, mechanically ventilated for 12 h post oleic acid-induced lung injury. This is an accepted preclinical model of ARDS. (9) The MV group received lung-protective volume control ventilation at 8 mL/kg (n = 6). Transvenous diaphragm neurostimulation (TTDN), delivered on every breath in synchrony with volume control ventilation at 8 mL/kg was delivered to the MV+TTDN group. The strength of diaphragm contraction targeted a reduction in ventilator pressure-time product of 15-20% during inspiration (n = 6) as previously published. (10) Dynamic compliance was measured by electrical impedance tomography at baseline, post achievement of lung injury, and hourly for 12 h. Statistical analysis of the repeated measures over time used a linear mixed model. Fixed effects were time, TTDN dose and TTDN dose interaction with time. Random effect was subjects. Data is reported as median with interquartile ranges. Ethics approval was obtained from the local REB.
Results:
The dynamic compliance was significantly higher after 12 h post oleic-acid-induced lung injury in the MV+TTDN group compared to the MV group (75 mL/cm H2O (51-90) vs. 31 mL/cm H2O (25-36). The dynamic compliance was significantly affected by both TTDN (P = 0.002) and TTDN over time (P = 0.002).
Conclusions:
Negative-pressure-assisted ventilation, comprised of transvenous diaphragm neurostimulation during inspiration in volume control ventilation, improves dynamic compliance in a preclinical model of ARDS.
Dynamic Compliance as Measured by EIT over Time
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