Abstract
BackgroundPendelluft, the movement of gas within different lung regions, is present in animal models of assisted mechanical ventilation and associated with lung overstretching. Due to rebreathing of CO2 as compared to fresh gas, pendelluft might reduce ventilatory efficiency possibly exacerbating patient’s respiratory workload during weaning. Our aim was to measure pendelluft by electrical impedance tomography (EIT) in patients who failed a spontaneous breathing trial (SBT).MethodsThis is an observational study conducted in a general intensive care unit of a tertiary-level teaching hospital. EIT signal was recorded in 20 patients while pressure support (PS) ventilation was progressively reduced from clinical level (baseline) to 2 cmH2O, as in an SBT; four ventral-to-dorsal lung regions of interest were identified for pendelluft measurement. A regional gas movement (> 6 mL) occurring in a direction opposite to the global EIT signal was considered diagnostic for high pendelluft.ResultsEight patients out of 20 (40%) were classified as high-pendelluft; baseline clinical characteristics did not differ between high- and low-pendelluft patients. At PS reduction, pendelluft and EtCO2 increased more in the high-pendelluft group (p < .001 and .011, respectively). The volume of gas subject to pendelluft moved almost completely from the ventral towards the dorsal lung regions, while the opposite movement was minimal (16.3 [10:32.8] vs. 0 [0:1.8] mL, p = .001). In a subgroup of patients, increased pendelluft volumes positively correlated with markers of respiratory distress such as increased respiratory rate, p0.1, and EtCO2.ConclusionsOccult pendelluft can be measured by EIT, and is frequently present in patients failing an SBT. When present, pendelluft increases with the reduction of ventilator support and is associated with increased EtCO2, suggesting a reduction of the ability to eliminate CO2.
Highlights
Pendelluft, the movement of gas within different lung regions, is present in animal models of assisted mechanical ventilation and associated with lung overstretching
Pendelluft is a phenomenon known as the pendular movement of gas between different lung regions; classically it is described during controlled mechanical ventilation when regional heterogeneity in time constants is present: after the tidal volume has been delivered, the gas moves from “faster” lung regions towards “slower” ones [4, 5]
Subjects Patients admitted to the general intensive care unit (ICU) of the University hospital San Gerardo (Monza, Italy) were screened for inclusion criteria: age > 18 years, assisted mode of ventilation (PS is the first choice in our unit), “ready to wean” evaluation by the attending physicians, failure of the standard spontaneous breathing trial performed in our ICU
Summary
Pendelluft, the movement of gas within different lung regions, is present in animal models of assisted mechanical ventilation and associated with lung overstretching. At the very beginning of inspiration, inflation of the dorsal regions due to uneven distribution of the negative pressure generated by the diaphragmatic pump resulted in a concomitant deflation of the ventral ones, consistent with a movement of gas within the lung (pendelluft). This phenomenon may induce overdistension of dorsal regions even in the presence of fully protective “global” ventilator settings. The gas subject to pendelluft moving within the lung will not contribute to gas exchange, possibly causing CO2 retention, resulting in wasted work of breathing and ventilatory inefficiency
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