A New Lung Mechanics Model and Its Evaluation with Clinical Data

Acute Respiratory Distress Syndrome (ARDS) is a major cause of morbidity and has a high rate of mortality. ARDS patients in the intensive care unit (ICU) require mechan-ical ventilation (MV) for breathing support, but inappropriate settings of MV can lead to ventilator induced lung injury (VILI). Those complications may be avoided by carefully optimizing ventilation parameters through model-based approaches. In this study we introduced a new model of lung mechanics (mNARX) which is a variation of the NARX model by Langdon et al. A multivariate process was undertaken to deter-mine the optimal parameters of the mNARX model and hence, the final structure of the model fit 25 patient data sets and successfully described all parts of the breathing cycle. The model was highly successful in predicting missing data and showed minimal error. Thus, this model can be used by the clinicians to find the optimal patient specific ventilator settings.

Driving pressure in mechanical ventilation:A review

Driving pressure(ΔP)is a core therapeutic component of mechanical ventilation(MV).Varying levels ofΔP have been employed during MV depending on the type of underlying pathology and severity of injury.However,ΔP levels have also been shown to closely impact hard endpoints such as mortality.Considering this,conducting an in-depth review ofΔP as a unique,outcome-impacting therapeutic modality is extremely important.There is a need to understand the subtleties involved in making sureΔP levels are optimized to enhance outcomes and minimize harm.We performed this narrative review to further explore the various uses ofΔP,the different parameters that can affect its use,and how outcomes vary in different patient populations at different pressure levels.To better utilizeΔP in MV-requiring patients,additional large-scale clinical studies are needed.

Effects of continuous tracheal gas insufflation during pressure limited ventilation on pulmonary surfactant in rabbits with acute lung injury

Background Pulmonary surfactant dysfunction may contribute to the development of ventilator induced lung injury （VILI）. Tracheal gas insuffiation （TGI） is a technique in which fresh gas is introduced into the trachea and augment ventilation by reducing the dead space of ventilatory system, reducing ventilatory pressures and tidal volume （VT） while maintaining constant partial arterial CO2 pressure （PaCO2）. We hypothesised that TGI limited peak inspiratory pressure （PIP） and VT and would minimize conventional mechanical ventilation （CMV） induced pulmonary surfactant dysfunction and thereby attenuate VILI in rabbits with acute lung injury （ALI）. Methods ALI was induced by intratracheal administration of lipopolysaccharide in anaesthetized, ventilated healthy adult rabbits randomly assigned to continuous TGI at 0.5 L/min （TGI group） or CMV group （n=8 for each group）, and subsequently ventilated with limited PIP and VT to maintain PaCO2 within 35 to 45 mmHg for 4 hours. Physiological dead space to VT ratio （VD/VT）, dynamic respiratory compliance （Cdyn） and partial arterial O2 pressure （PaO2） were monitored. After ventilation, lungs were analysed for total phospholipids （TPL）, total proteins （TP）, pulmonary surfactant small to large aggregates ratio （SA/LA） in bronchoalveolar lavage fluid （BALF） and for determination of alveolar volume density （Vv）, myeloperoxidase and interleukin （IL）-8. Results TGI resulted in significant （P〈0.05 or P〈0.01） decrease in PIP [（22.4±1.8） cmH20 vs （29.5±1.1） cmH2O], VT [（6.9±1.3） ml/kg vs （9.8±1.11） ml/kg], VD/VT [（32±5）% vs （46±2）%], TP [（109±22） mg/kg vs （187±25） mg/kg], SA/LA （2.5±0.4 vs 5.4±0.7）, myeloperoxidase [（6.2±0.5） U/g tissue vs （12.3±0.8） U/g tissue] and IL-8 [（987±106） ng/g tissue vs （24±3） mN/m] of BALF, and significant （P〈0.05） increase in Cdyn [（0.47±0.02） ml·cmH2O^-1·kg^-1 vs （0.31±0.02） ml·cmH2O^-1·kg^-1], PaO2 [（175±24） mmHg vs （135±26） mmHg], TPL/TP （52±8 vs 33±11） and Vv （0.65±0.05 vs 0.44±0.07） as compared with CMV. Conclusions In this animal model of ALI, TGI decreased ventilatory requirements （PIP, VT and VD/VT）, resulted in more favourable alveolar pulmonary surfactant composition and function and less severity of lung injury than CMV. TGI in combination with pressure limited ventilation may be a lung protective strategy for ALI.