Effects of Lung Injury and Abdominal Insufflation on Respiratory Mechanics and Lung Volume During Time-Controlled Adaptive Ventilation.

BACKGROUND: Lung volume measurements are important for monitoring functional aeration and recruitment, and may help guide adjustments in ventilator settings. The expiratory phase of APRV may provide physiologic information about lung volume based on the expiratory flow-time slope, angle, and time to approach a no-flow state (TExp). We hypothesized that expiratory flow rate would correlate with estimated lung volume (ELV), as measured using a modified nitrogen washout/washin technique in a large animal lung injury model. METHODS: Eight pigs (35.2±1.0kg) were mechanically ventilated using an Engström Carescape R860 on the APRV mode. All settings were held constant except the expiratory duration (TLow), which was adjusted based on the expiratory flow curve. Abdominal pressure was increased to 15mmHg in normal and Tween-injured lungs to replicate a combination of pulmonary and extrapulmonary lung injury. ELV was estimated using the Carescape FRC InView Tool. The expiratory flow-time slope and TExp were measured from the expiratory flow profile. RESULTS: Lung elastance increased with Tween-induced lung injury from 29.3±7.3cmH2O/L to 39.9±15.1cmH2O/L and chest wall elastance increased with increasing intra-abdominal pressures from 15.3±4.1cmH2O/L to 25.7±10.0cmH2O/L in the normal lung and 15.8±6.0cmH2O/L to 33.0±6.2cmH2O/L in the Tween-injured lung (p=0.39). ELV decreased from 1.90±0.83L in the Tween-Injured lung to 0.67±0.1L by increasing intra-abdominal pressures to 15mmHg. This had a significant correlation with a TExp decrease from 2.3±0.8s to 1.0±0.1s in the Tween-injured group with increasing insufflation pressures (ρ = 0.95) and with the expiratory flow-time slope, which increased from 0.29±0.06L/s2 to 0.63±0.05L/s2 (ρ = 0.78). CONCLUSIONS: Changes in ELV over time, and the TExp and flow-time slope, can be used to demonstrate evolving lung injury during APRV. Using the slope to infer changes in functional lung volume represents a unique, reproducible, real-time, bedside technique that does not interrupt ventilation and may be used for clinical interpretation.

Sustained vs. Intratidal Recruitment in the Injured Lung During Airway Pressure Release Ventilation: A Computational Modeling Perspective.

INTRODUCTION: During mechanical ventilation, cyclic recruitment and derecruitment (R/D) of alveoli result in focal points of heterogeneous stress throughout the lung. In the acutely injured lung, the rates at which alveoli can be recruited or derecruited may also be altered, requiring longer times at higher pressure levels to be recruited during inspiration, but shorter times at lower pressure levels to minimize collapse during exhalation. In this study, we used a computational model to simulate the effects of airway pressure release ventilation (APRV) on acinar recruitment, with varying inspiratory pressure levels and durations of exhalation. MATERIALS AND METHODS: The computational model consisted of a ventilator pressure source, a distensible breathing circuit, an endotracheal tube, and a porcine lung consisting of recruited and derecruited zones, as well as a transitional zone capable of intratidal R/D. Lung injury was simulated by modifying each acinus with an inflation-dependent surface tension. APRV was simulated for an inhalation duration (Thigh) of 4.0 seconds, inspiratory pressures (Phigh) of 28 and 40 cmH2O, and exhalation durations (Tlow) ranging from 0.2 to 1.5 seconds. RESULTS: Both sustained acinar recruitment and intratidal R/D within the subtree were consistently higher for Phigh of 40 cmH2O vs. 28 cmH2O, regardless of Tlow. Increasing Tlow was associated with decreasing sustained acinar recruitment, but increasing intratidal R/D, within the subtree. Increasing Tlow was associated with decreasing elastance of both the total respiratory system and transitional subtree of the model. CONCLUSIONS: Our computational model demonstrates the confounding effects of cyclic R/D, sustained recruitment, and parenchymal strain stiffening on estimates of total lung elastance during APRV. Increasing inspiratory pressures leads to not only more sustained recruitment of unstable acini but also more intratidal R/D. Our model indicates that higher inspiratory pressures should be used in conjunction with shorter exhalation times, to avoid increasing intratidal R/D.

Protective ventilation in a pig model of acute lung injury: timing is as important as pressure.

Ventilator-induced lung injury (VILI) is a significant risk for patients with acute respiratory distress syndrome (ARDS). Management of the patient with ARDS is currently dominated by the use of low tidal volume mechanical ventilation, the presumption being that this mitigates overdistension (OD) injury to the remaining normal lung tissue. Evidence exists, however, that it may be more important to avoid cyclic recruitment and derecruitment (RD) of lung units, although the relative roles of OD and RD in VILI remain unclear. Forty pigs had a heterogeneous lung injury induced by Tween instillation and were randomized into four groups (n = 10 each) with higher (↑) or lower (↓) levels of OD and/or RD imposed using airway pressure release ventilation (APRV). OD was increased by setting inspiratory airway pressure to 40 cmH2O and lessened with 28 cmH2O. RD was attenuated using a short duration of expiration (∼0.45 s) and increased with a longer duration (∼1.0 s). All groups developed mild ARDS following injury. RD ↑ OD↑ caused the greatest degree of lung injury as determined by [Formula: see text]/[Formula: see text] ratio (226.1 ± 41.4 mmHg). RD ↑ OD↓ ([Formula: see text]/[Formula: see text]= 333.9 ± 33.1 mmHg) and RD ↓ OD↑ ([Formula: see text]/[Formula: see text] = 377.4 ± 43.2 mmHg) were both moderately injurious, whereas RD ↓ OD↓ ([Formula: see text]/[Formula: see text] = 472.3 ± 22.2 mmHg; P < 0.05) was least injurious. Both tidal volume and driving pressure were essentially identical in the RD ↑ OD↓ and RD ↓ OD↑ groups. We, therefore, conclude that considerations of expiratory time may be at least as important as pressure for safely ventilating the injured lung.NEW & NOTEWORTHY In a large animal model of ARDS, recruitment/derecruitment caused greater VILI than overdistension, whereas both mechanisms together caused severe lung damage. These findings suggest that eliminating cyclic recruitment and derecruitment during mechanical ventilation should be a preeminent management goal for the patient with ARDS. The airway pressure release ventilation (APRV) mode of mechanical ventilation can achieve this if delivered with an expiratory duration (TLow) that is brief enough to prevent derecruitment at end expiration.

Unshrinking the baby lung to calm the VILI vortex.

A hallmark of ARDS is progressive shrinking of the 'baby lung,' now referred to as the ventilator-induced lung injury (VILI) 'vortex.' Reducing the risk of the VILI vortex is the goal of current ventilation strategies; unfortunately, this goal has not been achieved nor has mortality been reduced. However, the temporal aspects of a mechanical breath have not been considered. A brief expiration prevents alveolar collapse, and an extended inspiration can recruit the atelectatic lung over hours. Time-controlled adaptive ventilation (TCAV) is a novel ventilator approach to achieve these goals, since it considers many of the temporal aspects of dynamic lung mechanics.

Robotic-assisted thoracoscopic resection of anterior mediastinal cystic teratoma: a case report and literature review.

BACKGROUND: Mediastinal teratomas are rare tumors that frequently occur in the anterior mediastinum. The majority of these tumors are benign and slow growing. Due to their low malignant potential, the treatment for these tumors is surgical resection. More recently, the surgical management has shifted from invasive approaches such as a sternotomy to minimally invasive ones such as robotic-assisted thoracoscopic resections utilizing lung isolation ventilation. We present a rare case of a locally advanced mediastinal teratoma requiring resection, which was initially attempted thoracoscopically using double lung ventilation. CASE PRESENTATION: A 43 year-old female was found to have an anterior mediastinal mass during work-up for an intermittent cough in 2009. Chest imaging and biopsy at the time showed evidence of a cystic teratoma without concerning features. She underwent imaging surveillance until 2018, when repeat chest imaging showed increasing growth and worrisome radiologic features concerning for malignant degeneration. She underwent an elective robotic-assisted thoracoscopic resection utilizing double lung ventilation, but due to extensive involvement of the right lung, pericardium, superior vena cava, and right phrenic nerve the patient had to be repositioned and started on single lung ventilation mid-procedure to facilitate a safe and complete resection. CONCLUSIONS: Anterior mediastinal teratomas can be successfully removed by robotic-assisted thoracoscopic resections utilizing single lung ventilation. Though robotic-assisted thoracoscopic resection utilizing double lung ventilation can be effective in performing certain procedures such as lung wedge resections, thymectomy, pleural biopsies and minimally invasive cardiac procedures, it is limited in removing locally advanced mediastinal tumors.

Hemostatic shape memory polymer foams with improved survival in a lethal traumatic hemorrhage model.

Although there are many hemostatic agents available for use on the battlefield, uncontrolled hemorrhage is still the primary cause of preventable death. Current hemostatic dressings include QuikClot® Combat Gauze (QCCG) and XStat®, which have inadequate success in reducing mortality. To address this need, a new hemostatic material was developed using shape memory polymer (SMP) foams, which demonstrate biocompatibility, rapid clotting, and shape recovery to fill the wound site. SMP foam hemostatic efficacy was examined in a lethal, noncompressible porcine liver injury model over 6 h following injury. Wounds were packed with SMP foams, XStat, or QCCG and compared in terms of time to bleeding cessation, total blood loss, and animal survival. The hemostatic material properties and in vitro blood interactions were also characterized. SMP foams decreased blood loss and active bleeding time in comparison with XStat and QCCG. Most importantly, SMP foams increased the 6 h survival rate by 50% and 37% (vs. XStat and QCCG, respectively) with significant increases in survival times. Based upon in vitro characterizations, this result is attributed to the low stiffness and shape filling capabilities of SMP foams. This study demonstrates that SMP foams have promise for improving upon current clinically available hemostatic dressings and that hemostatic material properties are important to consider in designing devices for noncompressible bleeding control. STATEMENT OF SIGNIFICANCE: Uncontrolled hemorrhage is the leading cause of preventable death on the battlefield, and it accounts for approximately 1.5 million deaths each year. New biomaterials are required for improved hemorrhage control, particularly in noncompressible wounds in the torso. Here, we compared shape memory polymer (SMP) foams with two clinical dressings, QuikClot Combat Gauze and XStat, in a pig model of lethal liver injury. SMP foam treatment reduced bleeding times and blood loss and significantly improved animal survival. After further material characterization, we determined that the improved outcomes with SMP foams are likely due to their low stiffness and controlled shape change after implantation, which enabled their delivery to the liver injuries without inducing further wound tearing. Overall, SMP foams provide a promising option for hemorrhage control.

Mechanical Ventilation in Pediatric and Neonatal Patients.

Pediatric acute respiratory distress syndrome (PARDS) remains a significant cause of morbidity and mortality, with mortality rates as high as 50% in children with severe PARDS. Despite this, pediatric lung injury and mechanical ventilation has been poorly studied, with the majority of investigations being observational or retrospective and with only a few randomized controlled trials to guide intensivists. The most recent and universally accepted guidelines for pediatric lung injury are based on consensus opinion rather than objective data. Therefore, most neonatal and pediatric mechanical ventilation practices have been arbitrarily adapted from adult protocols, neglecting the differences in lung pathophysiology, response to injury, and co-morbidities among the three groups. Low tidal volume ventilation has been generally accepted for pediatric patients, even in the absence of supporting evidence. No target tidal volume range has consistently been associated with outcomes, and compliance with delivering specific tidal volume ranges has been poor. Similarly, optimal PEEP has not been well-studied, with a general acceptance of higher levels of F i O2 and less aggressive PEEP titration as compared with adults. Other modes of ventilation including airway pressure release ventilation and high frequency ventilation have not been studied in a systematic fashion and there is too little evidence to recommend supporting or refraining from their use. There have been no consistent outcomes among studies in determining optimal modes or methods of setting them. In this review, the studies performed to date on mechanical ventilation strategies in neonatal and pediatric populations will be analyzed. There may not be a single optimal mechanical ventilation approach, where the best method may simply be one that allows for a personalized approach with settings adapted to the individual patient and disease pathophysiology. The challenges and barriers to conducting well-powered and robust multi-institutional studies will also be addressed, as well as reconsidering outcome measures and study design.

Perioperative Intravenous Corticosteroids and Radiographic Prevertebral Soft Tissue Swelling in Anterior Cervical Fusion for Degenerative Disease.

OBJECTIVE: Prevertebral soft tissue swelling (PSTS) is a known complication of anterior cervical fusion (ACF). Prior studies have shown that perioperative steroids may reduce PSTS after ACF. We retrospectively evaluated the role of perioperative intravenous (IV) corticosteroid administration in minimizing radiographic PSTS measurements in patients undergoing ACF for degenerative disease. METHODS: Records of 100 consecutive patients undergoing ACF for degenerative disease (Current Procedural Terminology code 63075) from January 2010 through December 2012 by 2 orthopedic spine fellowship-trained surgeons at a single institution were retrospectively reviewed. Patients were included on the basis of specific criteria. They were then separated into comparison and IV steroid groups. Demographic and surgical data were collected. Last, measurements of PSTS, which included PSTS ratio and PSTS index (PSTSI), were obtained from plain radiographs preoperatively and at 3 postoperative time points. RESULTS: Eighty patients were included; 26 received IV steroids at the surgeon's discretion (12 intraoperatively, 11 postoperatively and 3 at both time periods). With the exception of a history of prior anterior cervical spine surgery (3.70% comparison vs. 23.08% IV steroid, P = 0.01), there was no statistically significant demographic characteristic. Furthermore, there was no statistically significant surgical characteristic. Last, there was no statistically significant difference between groups at any time point for either PSTS ratio at any level or PSTSI. CONCLUSIONS: There does not appear to be a role for perioperative IV steroid administration in minimizing radiographic PSTS in patients undergoing ACF for degenerative disease. The relationship between perioperative IV steroid administration and PSTS requires further investigation.