Improved Lung Aeration Research Articles

Effect of surfactant on regional lung function in an experimental model of respiratory distress syndrome in rabbit.

We assessed the changes in regional lung function following instillation of surfactant in a model of respiratory distress syndrome (RDS) induced by whole lung lavage and mechanical ventilation in eight anaesthetized, paralyzed, and mechanically ventilated New Zealand White rabbits. Regional specific ventilation (sV̇) was measured by K-edge subtraction synchrotron computed tomography during xenon washin. Lung regions were classified as poorly aerated (PA), normally aerated (NA), or hyperinflated (HI) based on regional density. A functional category was defined within each class based on sV̇ distribution (High, Normal, and Low). Airway resistance (Raw), respiratory tissue damping (G), and elastance (H) were measured by forced oscillation technique at low frequencies before and after whole lung saline lavage-induced (100 ml/kg) RDS, and 5 and 45 min after intratracheal instillation of beractant (75 mg/kg). Surfactant instillation improved Raw, G, and H (P < 0.05 each), and gas exchange and decreased atelectasis (P < 0.001). It also significantly improved lung aeration and ventilation in atelectatic lung regions. However, in regions that had remained normally aerated after lavage, it decreased regional aeration and increased sV̇ (P < 0.001) and sV̇ heterogeneity. Although surfactant treatment improved both central airway and tissue mechanics and improved regional lung function of initially poorly aerated and atelectatic lung, it deteriorated regional lung function when local aeration was normal prior to administration. Local mechanical and functional heterogeneity can potentially contribute to the worsening of RDS and gas exchange. These data underscore the need for reassessing the benefits of routine prophylactic vs. continuous positive airway pressure and early "rescue" surfactant therapy in very immature infants.

Spontaneously Breathing Preterm Infants Change in Tidal Volume to Improve Lung Aeration Immediately after Birth

To examine the temporal course of lung aeration at birth in preterm infants <33 weeks gestation. The research team attended deliveries of preterm infants <33 weeks gestation at the Royal Alexandra Hospital. Infants who received only continuous positive airway pressure were eligible for inclusion. A combined carbon dioxide (CO2) and flow-sensor was placed between the mask and the ventilation device. To analyze lung aeration patterns during spontaneous breathing, tidal volume (VT), and exhaled CO2 (ECO2) were recorded for the first 100 breaths. Thirty preterm infants were included with a total of 1512 breaths with mask leak <30%. Mean (SD) gestational age and birth weight was 30 (1) weeks and 1478 (430) g. Initial VT and ECO2 for the first 30 breaths was 5-6 mL/kg and 15-22 mm Hg, respectively. VT and ECO2 increased over the next 20 breaths to 7-8 mL/kg and 25-32 mm Hg, respectively. For the remaining observation period VT decreased to 4-6 mL/kg and ECO2 continued to increase to 35-37 mm Hg. Preterm infants begin taking deeper breaths approximately 30 breaths after initiating spontaneous breathing to inflate their lungs. Concurrent CO2 removal rises as alveoli are recruited. Lung aeration occurs in 2 phases: initially, large volume breaths with poor alveolar aeration followed by smaller breaths with elimination of CO2 as a consequence of adequate aeration.

Ventilated postmortem computed tomography in children: feasibility and initial experience.

Ventilated postmortem computed tomography (vPMCT) is associated with improved pulmonary imaging compared to standard PMCT in adults. We aimed to evaluate the feasibility of performing ventilated PMCT in children. Postmortem thoracic CT was performed before (PMCT) and after ventilation (vPMCT). We used a range of mouthpieces, including endotracheal tubes, bag and mask and laryngeal mask airway (LMA). Hounsfield units of the lungs at PMCT were measured for normal and abnormal lung areas, before and after ventilation. All patients underwent full conventional autopsy and histology. Twelve patients underwent ventilated PMCT, median age 52 days (range 3-304 days). Ventilated PMCT provided diagnostic lung images in all 12 cases, compared to only three unventilated PMCT examinations (p < 0.005). In all cases, ventilated PMCT improved the image quality of aerated lungs irrespective of the method used. Average lung Hounsfield units decreased significantly with ventilation from pre-vPMCT values (-134.1 ± 215.1 vs post-vPMCT -531.8 ± 190.1; p < 0.001). LMA with continuous positive pressure ventilation subjectively provided the best results. Ventilated PMCT significantly improves lung aeration in children and can aid recognition of areas of abnormality in paediatric lungs. Such advances will improve accuracy and uptake of imaging-assisted autopsies in children.

Palliative interventional pulmonology procedures in the incarcerated population with cancer: a case series.

Cancer is the second most common cause of death in incarcerated population and lung cancer is the most common cause of cancer death in this group. Inmates are excluded from most published surveys and research,thus the effectiveness of lung cancer palliation in this population is not known. To report the feasibility and safety of palliative interventional pulmonary procedures in inmates with cancer. Retrospective review of registry data from a single center. Inmate data on prospectively enrolled data registry (2009–2012) from the interventional pulmonology procedural registry at Virginia Commonwealth University was extracted and analyzed for safety and efficacy. Inmates with lung cancer and advanced malignancies with pleural or airway metastasis requiring airway debulking (mechanical/thermal), airway stenting, and tunneled pleural catheter (TPC) placement were included in the analysis. A total of 16 procedures were performed in 12 incarcerated patients. These included six TPC placements in six patients. Ten procedures were performed in seven patients with airway obstruction. These procedures included rigid and flexible bronchoscopy with mechanical (rigid and balloon dilation) and thermal (laser, argon plasma coagulation, and cautery) tumor debulking and dilation,airway stenting, and tracheostomy in one case. All six TPCpatients had immediate symptomatic relief and improved lung aeration on chest radiograph. Three of six patients had successful auto-pleurodesis. In the seven patients with airway obstruction, three patients reported symptomatic relief and one had resolution of post-obstructive pneumonia. No immediate- or long-term procedure-related complications were reported. Incarcerated patients with advanced malignancy may benefit from interventional pulmonology procedures with low complications. Palliative interventional pulmonology procedures in inmates should not be withheld solely on their incarceration status.

Spontaneous breathing with biphasic positive airway pressure attenuates lung injury in hydrochloric acid-induced acute respiratory distress syndrome.

It has been proved that spontaneous breathing (SB) with biphasic positive airway pressure (BIPAP) can improve lung aeration in acute respiratory distress syndrome compared with controlled mechanical ventilation. The authors hypothesized that SB with BIPAP would attenuate lung injury in acute respiratory distress syndrome compared with pressure-controlled ventilation. Twenty male New Zealand white rabbits with hydrochloric acid aspiration-induced acute respiratory distress syndrome were randomly ventilated using the BIPAP either with SB (BIPAP plus SB group) or without SB (BIPAP minus SB group) for 5 h. Inspiration pressure was adjusted to maintain the tidal volume at 6 ml/kg. Both groups received the same positive end-expiratory pressure level at 5 cm H2O for hemodynamic goals. Eight healthy animals without ventilatory support served as the control group. The BIPAP plus SB group presented a lower ratio of dead space ventilation to tidal volume, a lower respiratory rate, and lower minute ventilation. No significant difference in the protein levels of interleukin-6 and interleukin-8 in plasma, bronchoalveolar lavage fluid, and lung tissue were measured between the two experimental groups. However, SB resulted in lower messenger ribonucleic acid levels of interleukin-6 (mean ± SD; 1.8 ± 0.7 vs. 2.6 ± 0.5; P = 0.008) and interleukin-8 (2.2 ± 0.5 vs. 2.9 ± 0.6; P = 0.014) in lung tissues. In addition, lung histopathology revealed less injury in the BIPAP plus SB group (lung injury score, 13.8 ± 4.6 vs. 21.8 ± 5.7; P < 0.05). In hydrochloric acid-induced acute respiratory distress syndrome, SB with BIPAP attenuated lung injury and improved respiratory function compared with controlled ventilation with low tidal volume.

Higher levels of unsupported spontaneous breathing improve lung aeration and redistribute perfusion in experimental acute lung injury

Higher levels of unsupported spontaneous breathing improve lung aeration and redistribute perfusion in experimental acute lung injury

Ventilation heterogeneity: small length scales, big challenges

the distribution of regional ventilation is heterogeneous in normal lung and increases dramatically under pathological conditions. This has been demonstrated both in humans and in animal models using a number of different imaging techniques. General anesthesia and mechanical ventilation can

Lung aeration changes after lung recruitment in children with acute lung injury: A feasibility study

There are several adult studies using computed tomography (CT-scan) to examine lung aeration changes during or after a recruitment maneuver (RM) in ventilated patients with acute lung injury (ALI). However, there are no published data on the lung aeration changes during or after a RM in ventilated pediatric patients with ALI. To describe CT-scan lung aeration changes and gas exchange after lung recruitment in pediatric ALI and assess the safety of transporting patients in the acute phase of ALI to the CT-scanner. We present a case series completed in a subset of six patients enrolled in our previously published study of efficacy and safety of lung recruitment in pediatric patients with ALI. RM using incremental positive end-expiratory pressure. There was a variable increase in aerated and poorly aerated lung after the RM ranging from 3% to 72% (median 20%; interquartile range 6, 47; P = 0.03). All patients had improvement in the ratio of partial pressure of arterial oxygen over fraction of inspired oxygen (PaO(2) /FiO(2)) after the RM (median 14%; interquartile range: 8, 72; P = 0.03). There was a decrease in the partial pressure of arterial carbon dioxide (PaCO(2)) in four of six subjects after the RM (median -5%; interquartile range: -9, 2; P = 0.5). One subject had transient hypercapnia (41% increase in PaCO(2)) during the RM and this correlated with the smallest increase (3%) in aerated and poorly aerated lung. All patients tolerated the RM without hemodynamic compromise, barotrauma, hypoxemia, or dysrhythmias. Lung recruitment results in improved lung aeration as detected by lung tomography. This is accompanied by improvements in oxygenation and ventilation. However, the clinical significance of these findings is uncertain. Transporting patients in early ALI to the CT-scanner seems safe and feasible.

Effects of positive end-expiratory pressure on anesthesia-induced atelectasis and gas exchange in anesthetized and mechanically ventilated sheep

To evaluate the effects of 10 cm H(2)O of positive end-expiratory pressure (PEEP) on lung aeration and gas exchange in mechanically ventilated sheep during general anesthesia induced and maintained with propofol. 10 healthy adult Bergamasca sheep. Sheep were sedated with diazepam (0.4 mg/kg, IV). Anesthesia was induced with propofol (5 mg/kg, IV) and maintained with propofol via constant rate infusion (0.4 mg/kg/min). Muscular paralysis was induced by administration of vecuronium (25 microg/kg, bolus IV) to facilitate mechanical ventilation. After intubation, sheep were positioned in right lateral recumbency and mechanically ventilated with pure oxygen and zero end-expiratory pressure (ZEEP). After 60 minutes, 10 cm H(2)O of PEEP was applied for 20 minutes. Spiral computed tomography of the thorax was performed, and data were recorded for hemodynamic and gas exchange variables and indicators of respiratory mechanics after 15 (T(15)), 30 (T(30)), and 60 (T(60)) minutes of ZEEP and after 20 minutes of PEEP (T(PEEP)). Computed tomography images were analyzed to determine the extent of atelectasis before and after PEEP application. At T(PEEP), the volume of poorly aerated and atelectatic compartments was significantly smaller than at T(15), T(30), and T(60), which indicated that there was PEEP-induced alveolar recruitment and clearance of anesthesia-induced atelectasis. Arterial oxygenation and static respiratory system compliance were significantly improved by use of PEEP. Pulmonary atelectasis can develop in anesthetized and mechanically ventilated sheep breathing pure oxygen; application of 10 cm H(2)O of PEEP significantly improved lung aeration and gas exchange.

The Impact of Spontaneous Ventilation on Distribution of Lung Aeration in Patients with Acute Respiratory Distress Syndrome: Airway Pressure Release Ventilation Versus Pressure Support Ventilation

In this study, we sought to determine which mode, airway pressure release ventilation (APRV) or pressure support ventilation (PSV), decreases atelectasis more in patients with acute lung injury/acute respiratory distress syndrome (ARDS). This was a retrospective study in the intensive care unit. Between 2006 and 2007, we identified 18 patients with acute lung injury/ARDS who received either APRV or PSV and had a helical computed tomography scan twice in 3 days. Computed tomography data from the APRV and PSV groups (n = 9 each) were analyzed for 3-dimensional reconstruction and volumetry. Aerated lung regions (normally aerated, poorly aerated, nonaerated, and hyperinflated) were identified by their densities in Hounsfield units. The Pao(2)/Fio(2) ratio and alveolar-arteriolar oxygen gradient after ventilation were improved in both groups (P = 0.008); however, the improvements in the APRV group exceeded those in the PSV group when delivered with equal mean airway pressure (P = 0.018 and 0.015, respectively). Atelectasis decreased significantly from 41% (range, 17%-68%) to 19% (range, 6%-40%) (P = 0.008) and normally aerated volume increased significantly from 29% (range, 13%-41%) to 43% (range, 25%-56%) (P = 0.008) in the APRV group, whereas lung volume did not change in the PSV group. Spontaneous ventilation during APRV improves lung aeration by decreasing atelectasis. PSV for gas exchange is effective but not sufficient to improve lung aeration. These results indicate that APRV is more efficient than PSV as a mode of primary ventilatory support to decrease atelectasis in patients with ARDS.

3 Level Ventilation: the First Clinical Experience

Considering the issues of artificial ventilation (AV) in non-homogenous pathological lung processes (acute lung injury (ALI), acute respiratory distress syndrome (ARDS), pneumonia, etc.), the authors applied the three-level lung ventilation to a group of 12 patients with non-homogenous lung injury. Three-level ventilation was defined as a type (modification) of AV whose basic ventilation level was produced by the modes CMV, PCV or PS (ASB) and add-on level, the so-called background ventilation was generated by two levels of PEEP. PEEP (constant) and PEEPh (PEEP high) with varying frequency and duration of transition between the individual levels of PEEP. Objective: to elucidate whether in cases of considerably non-homogenous gas distribution in acute pathological disorders, three-level ventilation (3LV) can correct gas distribution into the so-called slow bronchoalveolar compartments, by decreasing the volume load of the so-called fast compartments and to improve lung gas exchange, by following the principles of safe ventilation. Results. 3LV was applied to 12 patients with severe non-homogenous lung injury/disorder (atypic pneumonia and ARDS/ALI) and low-success PCV ventilation after recruitment manoeuvre (PaO2 (kPA) /FiO2 = 5—6). There were pronounced positive changes in pulmonary gas exchange within 1—4 hours after initiation of 3LV at a fPCV of 26±4 breaths/min-1 and PEEPh at a fPEEPH of 7±2 breaths/min-1 with a minute ventilation of 12±4 l/min. 3LV reduced a intrapulmonary shunt fraction 50±5 to 30±5%, increased CO2 elimination, with PaCO2 falling to the values below 6±0.3 kPa, and PaO2 to 7.5±1.2 kPa, with FiO2 being decreased to 0.8—0.4. Lung recruitment also improved gas exchange: with PEEP=1.2±0.4 kPa, static tho-racopulmonary compliance (Cst) elevated from 0.18±0.02 l/kPa to 0.3±0.02 l/kPa and then to 0.38±0.05 l/kPa. Airways resistance (Raw) decreased by more than 30%. Improved lung aeration was also estimated as a manifestation of gas distribution with a long time constant. After 5±1-day 3LV, the patients were switched to PS ventilation; after gradually reduction of ventilation maintenance, they were disconnected from a ventilator and transferred to a specialized unit. Conclusion. The small study group made it impossible to statistically assess outcomes; the clinical results are not at least contrary to the results of theoretical mathematic simulation of 3LV in mathematical and physical models. 3LV as compared with PCV applied within the first 2—4 hours of AV improved lung gas exchange. It can be a promising mode of ventilation for the lungs afflicted by a diffusive non-homogenous pathological process. Key words: artificial ventilation, three-level ventilation, acute lung injury, acute respiratory distress syndrome.

Spontaneous breathing improves lung aeration in oleic acid-induced lung injury.

Experimental and clinical studies have shown reduction in intrapulmonary shunt with improved oxygenation by spontaneous breathing with airway pressure release ventilation (APRV) in acute lung injury. The mechanisms of these findings are not clear. The authors hypothesized that spontaneous breathing results in better aeration of lung tissue and that improvement in oxygenation can be explained by these changes. This hypothesis was studied in a porcine model of oleic acid-induced lung injury. Two hours after induction of lung injury, 24 pigs were randomly assigned to APRV with or without spontaneous breathing at a positive end-expiratory pressure of 5 cm H(2)O. Hemodynamics, spirometry, and end-expiratory lung volume by nitrogen washout were measured at baseline, after 2 h of lung injury, and after 2 and 4 h of mechanical ventilation in the specific mode. Finally, spiral computed tomography of the chest was performed at end-expiratory lung volume in 22 pigs. Arterial carbon dioxide tension and mean and end-inspiratory airway pressures were comparable between settings. Four hours of APRV with spontaneous breathing resulted in improved oxygenation compared with APRV without spontaneous breathing (arterial oxygen tension, 144 +/- 65 vs. 91 +/- 50 mmHg, P < 0.01 for interaction time x mode), higher end-expiratory lung volume (786 +/- 320 vs. 384 +/- 148 ml, P < 0.001), and better aeration. End-expiratory lung volume and venous admixture were both correlated with the amount of lung reaeration (r(2) = 0.62 and r(2) = 0.61, respectively). The results support the hypothesis that spontaneous breathing during APRV improves oxygenation mainly by recruitment of nonaerated lung and improved aeration of the lungs.

Surfactant nebulization versus instillation during high frequency ventilation in surfactant-deficient rabbits.

Surfactant nebulization improves lung function at low alveolar doses of surfactant. However, efficiency of nebulization is low, and lung deposition seems to depend on lung aeration. High frequency ventilation (HFV) has been shown to improve lung aeration. We hypothesize that the combination of HFV and surfactant nebulization may benefit lung deposition of surfactant and consequently, lung function. The aim of this study was to compare the effect of surfactant nebulization versus instillation during HFV on lung function, surfactant distribution, and cerebral blood flow. Therefore, severe respiratory failure was induced by lung lavages in 18 rabbits. HFV was applied: frequency = 8 Hz, mean airway pressure = 12 cm H2O, amplitude = 100%, fraction of inspired O2 = 1.0. Technetium-99m-labeled surfactant (Alveofact, 100 mg/kg of BW) was nebulized or instilled (n = 6 each). Six other rabbits did not receive surfactant (control, HFV only). We found that after instillation partial arterial O2 tension increased from 7.0 kPa (95% confidence interval, 6.3-8.0 kPa) to 34 kPa (16-51 kPa), and during nebulization from 7.0 kPa (6.0-9.0 kPa) to 46 kPa (27-58 kPa). Partial arterial CO2 tension decreased after instillation from 6.1 kPa (5.3-7.1 kPa) to 4.8 kPa (3.9-5.6 kPa), and during nebulization, after an initial rise, it decreased from 6.3 kPa (5.3-7.4 kPa) to 4.9 kPa (4.4-5.6 kPa). Both treatments resulted in nonuniform distribution. Surfactant deposition after nebulization was 9.8%. Instillation resulted in a drop of mean arterial blood pressure of 17% (8-31%), and an even more pronounced drop in cerebral blood flow of 39% (18-57%). Nebulization did not affect blood pressure. Cerebral blood flow decreased with a maximum of 27% (10-37%). We conclude that surfactant nebulization during HFV improves lung function in rabbits with severe respiratory failure, without improving distribution, but with less effects on blood pressure and cerebral blood flow, when compared with surfactant instillation.

PRECIPITOUS CIRCULATORY COLLAPSE IN THE IMMATURE NEWBORN FROM SHUNTING ACROSS THE DUCTUS ARTERIOSUS

Sudden, unexplained circulatory collapse occurring after successful initial resuscitation of the extremely immature newborn has been attributed to massive intracranial hemorrhage. Our failure to find pathologic confirmation in three such infants led to a prospective attempt to define alternative mechanisms. Ten consecutive infants between 24 and 26 weeks gestation were resuscitated, placed on ventilators and followed serially with aortograms and differential blood gases and blood pressures. Four could not be resuscitated. After initial stabilization of the six remaining infants, leg pressures were higher than arm pressures and aortograms revealed no left to right shunt. Coincidental with rising PaO2 and radiographic evidence of improved lung aeration, leg blood pressures fell to levels equal to or lower than arm pressures in 5/6 infants. Aortograms revealed massive left to right shunts with minimal distal aortic flow. Only 1/5 had a murmur. Intractable aciemia and cardiovascular collapse occurred within 1 to 6 hours of the fall in leg pressures. 4/5 Infants died. Only two had significant intracranial hemorrhage. Sudden massive ductal shunting in the immature newborn can cause precipitous circulatory collapse in the absence of intracranial hemorrhage. The ability of the extremely immature newborn to survive in the extrauterine environment may depend on early closure of this low resistance shunt.