Identifying lung overdistention during mechanical ventilation by using volume‐pressure loops

Abstract

We measured the pulmonary mechanics of 23 mechanically ventilated neonates. Airway pressures, inspiratory and expiratory flows were simultaneously measured. Values for respiratory system mechanics were then derived from these data by using a personal computer and a special software program. Volume-pressure (V-P) loops and respiratory system compliance values were determined for representative mechanical breaths. Twelve infants had normal-appearing V-P loops. Eleven had V-P loops characteristic of lung overdistention, showing decreasing changes in volume with progressive increases in pressure. To quantify this visual observation, we determined the change in compliance during the last 20% of inspiration (C20). We then compared this value to the total compliance value for the entire breath (C) using the ratio C20/C. Mean values for C, C20, and C20/C were compared for the two patient groups. Total respiratory system compliance values were similar. C20 values were decreased in those patients with V-P loops showing overdistention. C20/C values were significantly decreased in those patients with V-P loop evidence of overdistention. Patients with V-P loop evidence of overdistention all had C20/C values less than 0.8. Those with normal-appearing V-P loops all had C20/C values greater than 1.0. The C20/C ratio appears to effectively quantitate visual V-P loop evidence of lung overdistention during mechanical ventilation.

Weaning Preterm Infants from Mechanical Ventilation

“…Continuous monitoring of V T in newer mechanical ventilators can therefore be used to wean PIP. Although the effects of V T monitoring on weaning have not been fully evaluated, it can facilitate detection of lung overdistension and consequently lead to weaning of PIP [17] . Retrospective data suggest less air leaks and intraventricular hemorrhage among infants in whom V T was kept within normal limits compared to those not monitored [18] .…”

Postnatal Changes in Pulmonary Mechanics and Energetics of Infants with Respiratory Distress Syndrome following Surfactant Treatment

“…Even though there is an immediate signifi cant improvement in pulmonary mechanics from surfactant-replacement therapy for RDS, these mechanical changes are apparent only during spontaneous respiration and can be masked if measurements are made during mechanical ventilation [4,10,11,27] . Bedside evidence of respiratory barotrauma can be due to driving pressure-induced overdistension, volume-induced overdistension (high FRC due to excessive airfl ow or inadvertent PEEP), measurements of large V T ( 1 8.5 ml/kg) or actual evidence of high or low FRC.…”

“…Though improvement in oxygenation and gas exchange were readily apparent, improvement in C L was only evident after the tidal volume (V T ) overdistension was controlled [3,4] . The apparent increase in FRC following surfactant replacement was also confounded by lung overdistention during ventilation [5,6] .…”

Precision of continuous neonatal ventilator respiratory mechanics is improved with selected optimal respiratory cycles

“…V T is determined as the maximal volume provided during the cycle. C20/C is calculated as [(V T −V 0.8 Pmax )/ (P max −0.8 P max )]/Cdyn, according to Fisher et al [7]. Cdyn and V T are adjusted for body weight.…”

“…Results are discarded if they do not attain a good enough fit, if leak exceeds 20% and in case of high spontaneous respiratory activity. The ratio between compliance during the last 20% of inspiration and total compliance (C20/C) is a lung overdistension index [7]. C20 is computed by the ventilator as C20=(V T inspiration −V T at 80% of inspiration )/(0.2×peak pressure) [6].…”