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Tracheal pressure was measured through an air filled catheter introduced down the endotracheal tube, positioned 2 cm distal to the tube tip, and connected to the ventilator, to obtain alveolar pressure.

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Signals of arterial blood pressure, pressure at the airway opening, and air flow were read by transducers (Becton Dickinson, Sandy, UT, USA), connected to an A/D card (MP 100 Biopac Systems, Santa Barbara, CA, USA), acquired at 200 Hz and analyzed with Acknowledge ® software (Biopac Systems, Santa Barbara, CA, USA). Pressure at the airway opening was measured using a connecting tube with lateral aperture connected between the endotracheal tube and the pneumotachograph. MeasurementsĪir flow was measured using a small volume pneumotachograph (PN 281637, Hamilton medical AG, Bonaduz, Switzerland). FiO 2 was increased to 1 at the end of animal preparation. Carotid artery was cannulated with an 8.5 Fr catheter. Right jugular vein was cannulated with a 3-lumen 8.5-Fr catheter for drug administration. Muscle relaxation was obtained with pancuronium bromide. kg -1, inspired fraction of oxygen (FiO 2) 0.21, zero end-expiratory pressure, and RR adjusted to achieve normocapnia using Engström Carestation ® ventilator (General Electric Healthcare, Madison, WI, USA).Pigs were anesthetized with propofol and fentanyl, tracheotomized and mechanically ventilated in volume-controlled mode, with constant inspiratory flow, V T 10 mL This study was approved by our Institutional Review Board for the care of animal subjects (Comité d’experimentation animale de l′université Lyon I), and carried out in 14 pigs (28 ± 2 kg). The aims of this study were to evaluate (1) the reliability of EELV WI-WO measurement at variable PEEP and V T, at high RR and FiO 2 during experimental ARDS, using CT as a reference and (2) the trending ability of WI-WO technique to detect change in EELV associated with PEEP and V T variations. įurthermore, the WI-WO technique is particularly suitable for repeated EELV assessment, and hence to identify EELV trends, but has never been formally validated for this purpose. Such ventilatory settings may have insufficiently challenged the validity of this technique, which requires a constant inhomogeneity in alveolar gas throughout the measurement, and may be less precise at FiO 2 greater than 0.7. kg -1 in the upper range of current experts’ recommendations for ARDS management.Validation of this technique has been previously performed in mechanically ventilated patients using computed tomography (CT) as gold standard, but at relatively low PEEP levels (5 cm H 2O), low fraction of inspired oxygen (FiO 2) and respiratory rate (RR), and with tidal volume ( V T) 8 ± 1 mL End-expiratory lung volume measurement by the nitrogen washin-washout technique (EELV WI-WO) is available at the bedside from an ICU ventilator, and may help titrating PEEP during mechanical ventilation of ARDS patients. The reliability of the WI-WO technique is critically dependent on ventilatory settings, but sufficient to accurately detect EELV change greater than 200 mL.Īcute respiratory distress syndrome (ARDS) is characterized by a major decrease in lung aerated volume. Diagnostic accuracy was good for detection of absolute EELV changes above 200 mL (AUC = 0.79). Concordance rate of EELV changes between consecutive measurements was fair (79%). Bias between methods was greater at high PEEP, and further increased when high PEEP was combined with low V T. Limits of agreement for bias were ☓98 mL.

ResultsĮELV WI-WO underestimated EELV CT with a non-constant linear bias, as it decreased with increasing EELV. EELV WI-WO and EELV CT were determined after ARDS onset, at variable PEEP and V T. kg -1) were finally applied at optimal PEEP.Optimal PEEP was selected during a decremental PEEP trial, based on best compliance, best EELV WI-WO, or a PEEP-FiO 2 table. MethodsĪRDS was induced in 14 piglets by saline lavage. The aims of this study were (1) to evaluate the reliability of EELV WI-WO measurements at different PEEP and V T during experimental ARDS and (2) to evaluate trending ability of EELV WI-WO to detect EELV changes over time. Validation of this technique has been previously performed using computed tomography (EELV CT), but at mild PEEP levels, and relatively low fraction of inspired oxygen (FiO 2), which may have insufficiently challenged the validity of this technique. End-expiratory lung volume measurement by the nitrogen washin-washout technique (EELV WI-WO) may help titrating positive end-expiratory pressure (PEEP) during acute respiratory distress syndrome (ARDS).

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