Lung Volume Recruitment in Lambs during High-Frequency Oscillatory Ventilation Using Respiratory Inductive Plethysmography

Abstract

Monitoring lung volume is important in the treatment of acute hypoxemic respiratory failure. However, there are no tools available for lung volume measurement to guide ventilator management during high-frequency oscillatory ventilation (HFOV) and during dynamic changes in conventional ventilation (CV). We studied the performance of a new respiratory inductive plethysmograph (RIP) with modified software. We measured Delta changes in lung volume above end-expiratory volume (V(RIP)) during HFOV and studied whether changes in V(RIP) parallel changes in mean airway pressure. Calibration of the plethysmograph was made by serial injections of a known gas volume in six term (140 d gestation) and eight preterm (125 d gestation) lambs. Linear regression analysis of the relationship between injected gas volume and V(RIP) showed strong correlation (r(2) = 0.93-1.00 term animals, r(2) = 0.86-1.00 preterm animals). The pressure volume curves from the calibration with the injected gas volumes also correlated well with the pressure volume curves extrapolated from changes in V(RIP). Lung hysteresis was clearly demonstrated with RIP after changes in mean airway pressure during HFOV and after changes in positive end-expiratory pressure during CV. We conclude that measurements of lung volume in term and preterm lambs by use of modified RIP correlate well with changes in mean airway pressure during HFOV, with static pressure volume curves and with changes in positive end-expiratory pressure during CV. We speculate that this technique may provide clinically useful information about changes in lung volume during HFOV and CV. However, evaluation of the precision and chronic stability of RIP measurements over prolonged periods will require further studies.

Optimal mean airway pressure during high-frequency oscillatory ventilation determined by measurement of respiratory system reactance

“…Our study suggested that oxygenation requires significant heterogeneous derecruitment before appreciable change was observed. A lag in the oxygen response to volume loss from the previously recruited lung has been described in newly born term lambs (32) and pediatric lung disease piglet models receiving HFOV (24). In contrast, changes of X RS over time at a given P AW were very sensitive even to partial (i.e., dorsal) V L recruitment and derecruitment.…”

Regional tidal ventilation and compliance during a stepwise vital capacity manoeuvre

“…Titration of positive end-expiratory pressure (PEEP) after maximal lung expansion allows tidal ventilation to be applied near the deflation limb of the pressure-volume (P-V) envelope [3], and is associated with best compliance and gas exchange [4,5], less repetitive recruitment and derecruitment of lung units [6], and reduction in ventilatorinduced lung injury [7]. Benefits have also been noted in animal models equivalent in size to term human newborns [3,8]. Clinical trials of open lung ventilation have suggested a benefit of this strategy in adults with acute lung injury [9]; similar trials have yet to be conducted in neonatal or paediatric subjects.…”

Electrical impedance tomography can rapidly detect small pneumothoraces in surfactant-depleted piglets

“…CXRs are also not a reliable method of quantifying subtle changes in intra-thoracic volume during mechanical ventilation [33]. We conducted a pragmatic study and used RIP, which is the only non-invasive, commercially available bedside tool that can be calibrated with good correlation to a known volume [34] to determine changes in thoracic volume. Although RIP detected as little as 10 ml instillation of air, it cannot differentiate the location or cause of a volume change.…”