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

Abstract

Background:The aims of the present study were (i) to characterize the relationship between mean airway pressure (P AW ) and reactance measured at 5 Hz (reactance of the respiratory system (X RS ) , forced oscillation technique) and (ii) to compare optimal P AW (P opt ) defined by X RS , oxygenation, lung volume (V L ), and tidal volume (V T ) in preterm lambs receiving high-frequency oscillatory ventilation (HFOV). Methods: Nine 132-d gestation lambs were commenced on HFOV at P AW of 14 cmH 2 O (P start ). P AW was increased stepwise to a maximum pressure (P max ) and subsequently sequentially decreased to the closing pressure (P cl , oxygenation deteriorated) or a minimum of 6 cmH 2 O, using an oxygenation-based recruitment maneuver. X RS , regional V L (electrical impedance tomography), and V T were measured immediately after (t 0min ) and 2 min after (t 2min ) each P AW decrement. P opt defined by oxygenation, X RS , V L , and V T were determined. results: The P AW -X RS and P AW -V T relationships were dome shaped with a maximum at P cl +6 cmH 2 O, the same point as P opt defined by V L . Below P cl +6 cmH 2 O, X RS became unstable between t 0min and t 2min and was associated with derecruitment in the dependent lung. P opt , as defined by oxygenation, was lower than the P opt defined by X RS , V L , or V T . conclusion: X RS has the potential as a bedside tool for optimizing P AW during HFOV. h igh-frequency oscillatory ventilation (HFOV) is used to treat severe neonatal lung disease and has the potential to reduce ventilator-induced lung injury when applied optimally (1,2). HFOV optimally applied aims to recruit the lung and subsequently reduce mean airway pressure (P AW ) to an optimal pressure (P opt ) that achieves optimal lung recruitment at the lowest distending pressure (open lung strategy) (3,4). However, identification and maintenance of P opt remains challenging, particularly in the newly born, whose lungs are in a highly dynamic state because of fluid reabsorption and establishment of functional residual capacity (5). The lack of appropriate tools for the bedside assessment and continuous monitoring of lung function in infants makes targeting of P opt even more difficult.Oxygenation, evaluated by monitoring oxygen saturation (Sp O2 ), is most commonly used for targeting P opt during HFOV in clinical practice (6). However, Sp O2 is an imperfect guide for P AW titration as it is relatively uniform over a wide range of airway pressures and volumes (7). Beginning with the observations of Suter et al. (8), the notion that lung mechanics can guide pressure settings during mechanical ventilation has been examined carefully. For conventional ventilation, a relationship between end-expiratory lung volume (V L ), recruitment, and tidal breath mechanics has been demonstrated repeatedly (9,10). During HFOV, the same theoretical considerations apply (3), but the best means of assessing the mechanics of the oscillated lung remains unclear.A promising approach to noninvasive bedside assessment of lung mechanics ...

An individualized approach to sustained inflation duration at birth improves outcomes in newborn preterm lambs

“…Arterial blood gases were performed at 5 min of life and every 15 min from birth. A 5-Hz oscillatory pressure was superimposed onto the ventilation waveform for 10 s on completion of the ventilation strategy at birth and immediately after every arterial blood gas sample to calculate lung mechanics using the forced oscillation technique (FOT) as described in Dellacà and colleagues (6,7,43).…”

“…Total respiratory system reactance (Xrs) and resistance (Rrs) were computed from FOT recordings (6). Xrs is a measure of the elastic and inertive characteristics of the respiratory system that has been shown to be an accurate indicator of lung recruitment in our preterm lamb model (43). Static respiratory system compliance (C rs) was determined from the PV curve (35).…”

Intratracheal atomized surfactant provides similar outcomes as bolus surfactant in preterm lambs with respiratory distress syndrome

“…The fetal thorax was then exteriorized and dried. Sixteen custom-built EIT electrodes were placed equidistant around the fetal chest using our previously described methodology (35,36). The EIT electrodes were connected to a Goe-MF II EIT system (CareFusion, Hoechberg, Germany), and a 10-s baseline recording of the unaerated lung made as a reference.…”

The interrelationship of recruitment maneuver at birth, antenatal steroids, and exogenous surfactant on compliance and oxygenation in preterm lambs

“…This approach is known to place ventilation on the deflation limb of the quasi-static pressure-volume relationship (31,33) and targets the region of optimal compliance (31)(32)(33)(34). Thus, it is not surprising that the OLV approach improved C dyn and oxygenation.…”

“…Finally, although pneumothoraces were not found in our study population, reports in similar preterm lamb studies (6,17), and some human studies of SI (18,19), illustrate that the interaction between applied pressure and air leak in the preterm lung is not well understood. Interesting, in the already-aerated lung, air leak has not been a feature of OLV strategies in human (31,33) and animal studies (32,34,35).…”