Ventilator-induced lung injury (VILI) is a significant risk for patients with acute respiratory distress syndrome (ARDS). Management of the ARDS patient 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 PaO2/FiO2 ratio (226.1±41.4mmHg). RD↑OD↓ (PaO2/FiO2 = 333.9 ± 33.1 mmHg) and RD↓OD↑ (PaO2/FiO2 = 377.4 ± 43.2 mmHg) were both moderately injurious, while RD↓OD↓ (PaO2/FiO2 = 472.3±22.2mmHg; 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.
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.
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.
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