Measurement of occult Pendelluft by Electrical Impedance Tomography in difficult weaning patients undergoing assisted mechanical ventilation
CCCF ePoster library. Grassi A. 11/12/19; 283433; EP93
Dr. Alice Grassi
Dr. Alice Grassi
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Abstract
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ePoster
Topic: Retrospective or Prospective Cohort Study or Case Series

Grassi, Alice1,2; Coppadoro, Andrea3; Giovannoni, Cecilia2; Rabboni, Francesca2; Ormas, Valentina2, Eronia, Nilde3; Bronco, Alfio3; Foti, Giuseppe2,3; Fumagalli, Roberto2; Bellani, Giacomo2,3
1Department of Ansthesia and Pain Management, University Health Network, Toronto
2Department of Medicine and Surgery, University of Milan-Bicocca, Monza, Italy
3Department of Anesthesia and Intensive Care, San Gerardo Hospital, ASST Monza, Italy
 


Introduction: Pendelluft, the movement of gas from lung regions characterized by different time-constants, has been described in animal models of assisted mechanical ventilation and is associated with lung tissue overstretching [1]. Due to the different contents of O2 and CO2 as compared to fresh gas, pendelluft might also reduce ventilation efficiency. We hypothesized that increased patient's inspiratory effort might trigger the pendelluft phenomenon, exacerbating patient's fatigue. Electrical Impedance Tomography (EIT) is a non-invasive device that allows bedside study of regional ventilation [2] and could allow to detect and quantify the pendelluft phenomenon during weaning from mechanical ventilation.
Objective: To identify and measure pendelluft phenomenon by EIT in difficult to wean patients.
Methods: This is a monocentric observational study. Patients included in the study were older than 18 years old, were ventilated in Pressure Support Ventilation mode (PSV), were considered “ready to wean” (resolution of acute phase, PEEP ≤ 8cmH2O, FiO2 ≤ 40%, light or no sedation, no need for vasopressors) but failed a Spontaneous Breathing Trial (SBT, meaning that they did not tolerate a PSV level of 2cmH2O for at least 2 hours without signs of respiratory distress). Exclusion criteria were: known severe chronic obstructive pulmonary disease, pneumothorax, impaired respiratory drive due to cerebral lesions, pneumonectomy, bronchial bleeding, presence of pleural catheters and those factors which contraindicated EIT positioning (presence of pace maker, unstable vertebral fractures). EIT signal was recorded while level of PSV was progressively reduced from clinical level (baseline) to 2 cmH2O (or the lowest tolerable level); 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. The cut off chosen to define high pendelluft is the mean of pendelluft volume measured at baseline.
Results: Twenty difficult-to-wean patients undergoing PSV were enrolled. Eight patients out of 20 (40%) were classified as high-pendelluft; baseline clinical characteristics did not differ between high- and low-pendelluft patients. In the high pendelluft group, volume of pendelluft increased with the reduction of PSV, while it did not change in the low-pendelluft group (Figure 1). Correspondently, EtCO2 increased more in the high-pendelluft group (Table 1). The volume of gas subjected to pendelluft moved almost completely from the ventral towards the dorsal lung regions, while the opposite movement was minimal (Table 1). In a subgroup of patients, increased pendelluft volumes positively correlated with markers of respiratory distress such as increased respiratory rate, p0.1 and EtCO2 (Figure 2).
Conclusions: Occult pendelluft can be measured by EIT, and is frequently present in difficult to wean patients. When present, pendelluft increases with the reduction of ventilator support and is associated with ventilator inefficiency, possibly playing a role in weaning failure.
 


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  1. Yoshida T et al, Spontaneous effort causes occult pendelluft during mechanical ventilation. Am J Respir Crit Care Med 2013;188(12):1420-1427
  2. Frerichs et al, Chest electrical impedance tomography examination, data analysis, terminology, clinical use and recommendations: consensus statement of the TRanslational EIT developmeNt stuDy group. Thorax Jan;72(1):83-93
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