ΔMAPINSP, maximum deviation of mean airway pressure from continuous distending pressure during inspiration; ΔMAPEXP, maximum deviation of mean airway pressure from continuous distending pressure during expiration.
Therefore, having concluded that upstream microvascular pressure might be an important cofactor in the development of VILI, we next addressed the question of how the number of ventilatory cycles occurring over a timed interval influences the rate of edema formation or severity of histologic alterations when maximum, minimum, and mean airway pressures are held identical.
ΔMAPINSP is the maximum deviation from the mean airway pressure during inspiration, and ΔMAPEXP is the maximum deviation from the mean airway pressure during expiration.
CDP = continuous distending pressure; HFOV = high-frequency oscillatory ventilation; MAP = mean airway pressure; ΔMAPEXP = maximum deviation from the mean airway pressure during expiration; ΔMAPINSP = maximum deviation from the mean airway pressure during inspiration; PETT = pressure at end tracheal tube; PTM = transmural pressure; VT = tidal volume; WOB = work of breathing.
The ventilatory strategy employed was permissive hypercapnia (target pO2 ≥ 60 mmHg, pH > 7.25) with limitation of peak inspiratory pressure (Pplat < 35 cm H2O) while employng elevated mean airway pressure to ensure maximum lung volume recruitment (PEEP above the lower inflection point on PV curve).
At TLC, mean airway diameters were only 87.0% and 76.1% of maximum for the aerosol and locally challenged airways respectively (Figure 1B).
In addition, at 45 cm H2O, mean airway diameter was only 87.0%±6% and 76.1% ±7%of maximum for the aerosol and locally challenged airways, respectively, indicating that even at the maximal inflation airways were still not fully dilated with either challenge.
The SensorMedics 3100B HFO ventilator used generates a mean airway pressure by a continuous fresh gas flow, with a maximum of 60 l minute-1.
In the heavily sedated and paralyzed patient, the continuous distending pressure can be titrated up the inflation limb (to recruit) and down the deflation limb (to find the least pressure required to keep the lungs open) of the static pressure volume curve, which often allows substantial reduction of mean airway pressures [ 2, 12, 13] while reducing hemo-dynamic side effects to a maximum.
