Abstract
BackgroundWhether spontaneous breathing (SB) should be used in early acute respiratory distress syndrome (ARDS) is questioned because it may cause ventilator-induced lung injury (VILI) by tidal high strain/stress and recruitment/derecruitment (R/D). However, SB has shown beneficial effects when used appropriately. We hypothesized that high levels of positive end-expiratory pressure (PEEP), during assisted SB, would prevent tidal R/D, reducing ventilatory variation and respiratory rate while potentially increasing transpulmonary pressure (PTP). The aim was to test this hypothesis in experimental mild ARDS during continuous SB using neurally adjusted ventilator assist (NAVA) and uninterrupted computed tomography (CT) exposure.MethodsMild experimental ARDS (PaO2/FiO2-ratio of 250) was induced in anesthetized pigs (n = 5), ventilated using uninterrupted NAVA. PEEP was changed in steps of 3 cmH2O, from 0 to 15 and back to 0 cmH2O. Dynamic CT scans, ventilatory parameters, and esophageal pressure were acquired simultaneously. PTP and R/D were calculated and compared among PEEP levels.ResultsWhen increasing PEEP from 0 to 15 cmH2O, tidal R/D decreased from 4.3 ± 5.9 to 1.1 ± 0.7% (p < 0.01), breath-to-breath variability decreased, and PTP increased from 11.4 ± 3.7 to 29.7 ± 14.1 cmH2O (R2 = 0.96).ConclusionThis study shows that injurious phenomena like R/D and high PTP are present in NAVA at the two extremes of the PEEP spectrum. Willing to titrate PEEP to limit these phenomena, the physician must choose the best compromise between restraining the R/D or PTP.
Highlights
Acute respiratory distress syndrome is characterized by epithelial dysfunction, pulmonary edema, and lung collapse, causing hypoxemia (Bernard et al, 1994), whose treatment has its mainstay in mechanical ventilation using low tidal volume (TV) (Acute Respiratory Distress Syndrome Network Brower et al, 2000)
Mean TV during spontaneous breathing (SB) and neurally adjusted ventilator assist (NAVA) increased from 52 ± 45 ml at positive end-expiratory pressure (PEEP) 0 cmH2O to 338 ± 176 ml at PEEP 15 cmH2O (p < 0.01)
The results presented in the experiments reported here indicate that beyond all of the limitations bound to an animal experiment, a potential track for future research is to investigate the possibility of governing SB activity by titrating the applied PEEP
Summary
Acute respiratory distress syndrome is characterized by epithelial dysfunction, pulmonary edema, and lung collapse, causing hypoxemia (Bernard et al, 1994), whose treatment has its mainstay in mechanical ventilation using low TVs (Acute Respiratory Distress Syndrome Network Brower et al, 2000) In recent times, it has been questioned whether SB should be allowed during ARDS or other types of lung injury. During ARDS, in relation to the necessities of gas exchange, the patient often needs a high minute ventilation that can be achieved by increasing breathing frequency and/or TV The latter phenomena may cause considerably high tidal PTP swings, generated by a combination of effects by the diaphragm activity and the delivery of pressure from the ventilator (Yoshida et al, 2012). The aim was to test this hypothesis in experimental mild ARDS during continuous SB using neurally adjusted ventilator assist (NAVA) and uninterrupted computed tomography (CT) exposure
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