Abstract
BackgroundDynamic pulmonary hyperinflation may develop in patients with chronic obstructive pulmonary disease (COPD) due to dynamic airway collapse and/or increased airway resistance, increasing the risk of volutrauma and hemodynamic compromise. The reference standard to quantify dynamic pulmonary hyperinflation is the measurement of the volume at end-inspiration (Vei). As this is cumbersome, the aim of this study was to evaluate if methods that are easier to perform at the bedside can accurately reflect Vei.MethodsVei was assessed in COPD patients under controlled protective mechanical ventilation (7 ± mL/kg) on zero end-expiratory pressure, using three techniques in a fixed order: (1) reference standard (Veireference): passive exhalation to atmosphere from end-inspiration in a calibrated glass burette; (2) ventilator maneuver (Veimaneuver): measuring the expired volume during a passive exhalation of 45s using the ventilator flow sensor; (3) formula (Veiformula): (Vt × Pplateau)/(Pplateau − PEEPi), with Vt tidal volume, Pplateau is plateau pressure after an end-inspiratory occlusion, and PEEPi is intrinsic positive end-expiratory pressure after an end-expiratory occlusion. A convenience sample of 17 patients was recruited.ResultsVeireference was 1030 ± 380 mL and had no significant correlation with Pplateau (r2 = 0.06; P = 0.3710) or PEEPi (r2 = 0.11; P = 0.2156), and was inversely related with Pdrive (calculated as Pplateau −PEEPi) (r2 = 0.49; P = 0.0024). A low bias but rather wide limits of agreement and fairly good correlations were found when comparing Veimaneuver and Veiformula to Veireference. Vei remained stable during the study period (low bias 15 mL with high agreement (95% limits of agreement from − 100 to 130 mL) and high correlation (r2 = 0.98; P < 0.0001) between both measurements of Veireference).ConclusionsIn patients with COPD, airway pressures are not a valid representation of Vei. The three techniques to quantify Vei show low bias, but wide limits of agreement.
Highlights
Dynamic pulmonary hyperinflation is defined as increased relaxation volume of the respiratory system at the end of a tidal expiration above the expected normal value [1]
The aims of the current study were to evaluate in patients with severe chronic obstructive pulmonary disease (COPD) under controlled mechanical ventilation: (1) if airway pressures (i.e., Pplateau and Intrinsic positive end-expiratory pressure (PEEPi)) are valid representations of volume at end-inspiration (Vei), and (2) if two methods to quantify Vei, which are easier to perform at the bedside, namely a simple physiology-based equation and the use of ventilator built-in equipment to measure Vei, could provide a valid alternative to its direct measurement
The main findings of our study can be summarized as follows: in invasively ventilated patients with acute exacerbation of COPD (1) Veireference is not significantly correlated with P EEPi, Pplateau or Peak airway pressure of the respiratory system (Ppeak). Veireference is inversely correlated with Driving pressure of the respiratory system (Pdrive); (2) Veireference is significantly correlated with Vei measured with the ventilator maneuver or when calculated using a physiology-based formula and has a low bias, but rather wide limits of agreement
Summary
Dynamic pulmonary hyperinflation is defined as increased relaxation volume of the respiratory system at the end of a tidal expiration above the expected normal value [1]. As highlighted by the word dynamic, dynamic pulmonary hyperinflation is a consequence of a discrepancy between the expiratory time constant and the expiratory time either adopted by the patient or set at the ventilator [1] It increases the risk of volutrauma and hemodynamic compromise, especially during invasive mechanical ventilation and should be monitored in both the intensive care unit (ICU) and operation theater [2]. As airway pressures (PEEPi, Pplateau) at a certain lung volume (e.g., Vei) depend on respiratory elastance, safe airway pressures do not necessarily reflect safe Vei. Dynamic pulmonary hyperinflation may develop in patients with chronic obstructive pulmonary disease (COPD) due to dynamic airway collapse and/or increased airway resistance, increasing the risk of volutrauma and hemodynamic compromise.
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