Healthy lungs tolerate repetitive collapse and reopening during short periods of mechanical ventilation

The possible occurrence of lung damage if alveolar units are allowed to collapse and reopen breath by breath during mechanical ventilation with normal tidal volumes was investigated. Anaesthetised, paralysed, open chest rabbits were subjected to either intrathoracic negative (NEEP; n=6) or positive (PEEP; n=6) end-expiratory pressure during volume controlled mechanical ventilation. Both experimental settings were preceded by a 30 min control period and followed by a 30 min recovery period during which a PEEP of 0.2 kPa was maintained. Pao₂ and pulmonary compliance deteriorated significantly in the NEEP group during the experimental period and compared to ventilation with PEEP. Partial restoration of lung mechanics and blood gases was achieved during the recovery period. After an alveolar recruitment manoeuvre, this recovery was complete. Lung clearance studied by depositing an aerosol of technetium-99m-labelled diethylenetriamine pentaacetate (^99mTc-DTPA) in the alveoli, was significantly faster during ventilation with NEEP compared to the PEEP group ( P =0.0002) as well as the control period ( P = 0.0029). It did not recover completely during the recovery period but remained significantly faster. light microscopic histology was normal in both groups with no evidence of inflammation or epithelial disruption. We conclude that previously healthy rabbit lungs show only a transient disturbance of lung mechanics and blood gases with repetitive collapse and re-expansion. The integrity of the alveolar rnicrostructure is preserved. The disturbance in the alveolo-capillary permeability persists and may indicate surfactant related alveolo-capillary barrier dysfunction.     

Positive end-expiratory pressure prevents atelectasis during general anaesthesia even in the presence of a high inspired oxygen concentration

BACKGROUND: General anaesthesia impairs the gas exchange in the lungs, and moderate desaturation (SaO2 86-90%) occurred in 50% of anaesthetised patients in a blinded pulse oximetry study. A high FiO2 might reduce the risk of hypoxaemia, but can also promote atelectasis. We hypothesised that a moderate positive end-expiratory pressure (PEEP) level of 10 cmH2O can prevent atelectasis during ventilation with an FiO2 = 1.0. METHODS: Atelectasis was evaluated by computed tomography (CT) in 13 ASA I-II patients undergoing elective surgery. CT scans were obtained before and 15 min after induction of anaesthesia. Then, recruitment of collapsed lung tissue was performed as a "vital capacity manoeuvre" (VCM, inspiration with Paw = 40 cmH2O for 15 s), and a CT scan was obtained at the end of the VCM. Thereafter, PEEP = 0 cmH2O was applied in group 1, and PEEP = 10 cmH2O in group 2. Additional CT scans were obtained after the VCM. Oxygenation was measured before and after the VCM. RESULTS: Atelectasis (> 1 cm2) was present in 12 of the 13 patients after induction of anaesthesia. At 5 and 10 min after the VCM, atelectasis was significantly smaller in group 2 than group 1 (P < 0.005). A significant inverse correlation was found between PaO2 and atelectasis. CONCLUSIONS: PEEP = 10 cmH2O reduced atelectasis formation after a VCM, when FiO2 = 1.0 was used. Thus, a VCM followed by PEEP = 10 cmH2O should be considered when patients are ventilated with a high FiO2 and gas exchange is impaired.     

A new treatment modality for unilateral athelectasis: Recruitment maneuver with endobronchial blocker

Atelectasis is a commonly seen complication during the post-operative period in intensive care units. The treatment of atelectasis depends on the underlying cause. We aimed to share our experience on the treatment of right total atelectasis in our intensive care unit applied with the help of the endobronchial blocker.     

Is radiological appearance of lower respiratory tract infection due to respiratory syncytial virus a predictor of clinical outcome?

Objective: Respiratory syncytial virus (RSV) lower respiratory tract infection is the most common viral infection in childhood. RSV-infected infants demonstrate various radiographic findings. The aim of the study is to evaluate whether assessment of radiological characteristics of lower tract infection due to RSV may be a predictor of clinical outcome in newborns.

Methods: The study included 36 newborn infants hospitalized for lower tract infection. In order to detect RSV, RSV Respi-Strip (Coris Bioconcept Organization) test kits were used on admission. Chest X-rays and clinical characteristics of the study group were reviewed.

Results: Of 36 patients hospitalized for lower tract infection from October 2012 to April 2013, 18 (50%) newborns were infected with RSV. The study included 36 neonates. Patients with RSV-positive infants at admission had greater need for respiratory support, supplemental oxygen and prolonged stay in the NICU. Newborns with an atelectasis pattern on admission chest radiograph had greater at RSV-positive infants.

Conclusion: Chest radiological patterns with lower respiratory tract infection in newborn infants due to RSV are a predictor of clinical outcome.     

Antagonism of leukotriene receptors and administration of a 5-lipoxygenase inhibitor do not affect hypoxic vasoconstriction

The role of leukotrienes in hypoxic vasoconstriction remains controversial. Our previous study using the lipoxygenase inhibitor BW 755C in dogs failed to show a substantive role for leukotrienes in hypoxic vasoconstriction. To clarify further the role of leukotrienes, we designed 3 protocols. In the first protocol, we examined the effects of LTD₄ boluses on the pulmonary circulation in 6 anesthetized dogs. LTD₄, 1 μg/kg, (a large dose relative to other species) produced no detectable constriction of the pulmonary artery, while systemic vascular resistance increased 41±17% (SD), left atrial pressure rose 3.5±1.5 mmHg, and cardiac output fell 18±8%. Two leukotriene receptor antagonists, LY171883 and L-648051, decreased these effects by more than 50%. In the second protocol, we tested these antagonists in 7 anesthetized, paralyzed, closed-chest dogs with acute left lower lobe atelectasis. Two manifestations of hypoxic vasoconstriction were examined: shunt fraction (as an inverse indicator of regional constriction in response to local hypoxia) and the pulmonary pressor response to global alveolar hypoxia (as an index of general hypoxic vasoconstriction). During normoxia before administration of the inhibitor, shunt fraction, measured using an SF₆ infusion, was 25±7%. The pulmonary pressor response to hypoxia, defined as the increase in pulmonary end-diastolic gradient (PDG) produced by 10% O₂ inhalation, averaged +10.5±3.6 mmHg. The increase in pulmonary vascular resistance (PVR) with hypoxia was +2.4±1.7 mmHg/L/min. Then, during normoxia, 1 of the 2 antagonists was administered. Shunt fraction was unchanged (26±4%; p=0.5). The pressor response to hypoxia was slightly less but remained substantial (the increase in PDG with hypoxia was +7.9±2.8 mmHg; p<0.05; the increase in PVR was +1.8±1.2 mmHg/L/min, p<0.10). In the third protocol we gave RG 5901, a relatively specific 5-lipoxygenase inhibitor, to 5 dogs with lobar atelectasis. The indices of hypoxic vasoconstriction were not affected by RG 5901. Shunt fraction was 29.5±8.1% before and 27.0±7.4% after RG 5901 (p>0.05). The pressor response to hypoxia was + 8.9±2.1 mmHg before and +8.7±3.7 mmHg after RG 5901 (p>0.05). We conclude that in dogs, hypoxic vasoconstriction does not appear to be mediated by leukotrienes.     

Ultrasound of the Pleurae and Lungs

The value of ultrasound techniques in examination of the pleurae and lungs has been underestimated over recent decades. One explanation for this is the assumption that the ventilated lungs and the bones of the rib cage constitute impermeable obstacles to ultrasound. However, a variety of pathologies of the chest wall, pleurae and lungs result in altered tissue composition, providing substantially increased access and visibility for ultrasound examination. It is a great benefit that the pleurae and lungs can be non-invasively imaged repeatedly without discomfort or radiation exposure for the patient. Ultrasound is thus particularly valuable in follow-up of disease, differential diagnosis and detection of complications. Diagnostic and therapeutic interventions in patients with pathologic pleural and pulmonary findings can tolerably be performed under real-time ultrasound guidance. In this article, an updated overview is given presenting not only the benefits and indications, but also the limitations of pleural and pulmonary ultrasound.     

不同剂量氨溴索对实验性肺不张炎症因子及影像学的影响

目的探讨不同剂量氨溴索（ambroxol,AMB）对实验性肺不张炎症因子及影像学的影响。方法将雄性实验用中国小型猪随机分成肺不张组（M组6只）、AMB处理组（T组18只）及对照组（C组6只）。其中T组又随机分成30、60及90mg/Kg剂量的AMB处理的T30、T60及T90组,每组均为6只。M及T组小型猪的右主支气管下端在纤支镜下置入镍钛合金封堵器,T组小型猪在放入封堵器当天即予相对应的AMB剂量静脉注射,每8h注射1次,每3dCT检查肺部确定肺不张的形成,在肺不张形成后的第3天,3组动物均处死,收集右下肺组织行炎症因子TNF-α、IL-1β和IL-10检测。结果M组和T组呈典型的肺不张CT改变。各组肺组织匀浆中TNF-α、IL-1β和IL-10水平的表达差异均有统计学意义（均P＜0.05）。与C组比较,M组和T组TNF-α、IL-1β水平明显升高（均P＜0.01）;与M组比较,T组TNF-α、IL-1β水平明显下降（均P＜0.01）;T60组和T90组与T30组比较差异均有统计学意义（均P＜0.01）,但T60组和T90组间无统计学差异。与C组比较,M组和T组IL-10表达显著下降（均P＜0.01）;与M组比较,T组IL-10水平明显升高（均P＜0.01）;但不同治疗剂量3组之间无统计学差异。与C组比较,M组和T组CT值均有显著提高（均P＜0.01）,但M组和T组间CT值无统计学差异;与M组比较,T组肺不张面积显著减小（均P＜0.01）,肺不张占单侧肺面积比T90组明显低于T30组（P＜0.01）,但T30和T60,T60和T90之间并无统计学差异。结论大剂量AMB能抑制实验性肺不张的炎症因子TNF-α、IL-1β的表达,提升IL-10的表达,能减小肺不张面积。