Effect of tidal volume and PEEP in ethchlorvynol-induced asymmetric lung injury

Kinetic Resolution of Acyclic Tertiary Propargylic Alcohols by NHC-Catalyzed Enantioselective Acylation

We report herein an efficient NHC-catalyzed kinetic resolution of acyclic tertiary propargylic alcohols that provides them in high to excellent enantioselectivity. This is the first example of kinetic resolution realized by enantioselective acylation. The recovered enantioenriched alcohols can be facilely converted into other valuable compounds such as densely functionalized tertiary alcohols and carbmates in high yields and excellent stereopurity. Density functional theory calculations were performed to determine the reaction mechanism and to understand the origin of enantiodiscrimination.

Asymmetrical Lung Injury: Management and Outcome

Among mechanically ventilated patients, asymmetrical lung injury is probably extremely frequent in the intensive care unit but the lack of standardized measurements does not allow to describe any prevalence among mechanically ventilated patients. Many past studies have focused only on unilateral injury and have mostly described the effect of lateral positioning. The good lung put downward might receive more perfusion while the sick lung placed upward receive more ventilation than supine. This usually results in better oxygenation but can also promote atelectasis in the healthy lung and no consensus has emerged on the clinical indication of this posture. Recently, electrical impedance tomography (EIT) has allowed for the first time to precisely describe the distribution of ventilation in each lung and to better study asymmetrical lung injury. At low positive-end-expiratory pressure (PEEP), a very heterogeneous ventilation exists between the two lungs and the initial increase in PEEP first helps to recruit the sick lung and protect the healthier lung. However, further increasing PEEP distends the less injured lung and must be avoided. The right level can be found using EIT and transpulmonary pressure. In addition, EIT can show that in the two lungs, airway closure is present but with very different airway opening pressures (AOPs) which cannot be identified on a global assessment. This may suggest a very different PEEP level than on a global assessment. Lastly, epidemiological studies suggest that in hypoxemic patients, the number of quadrants involved has a strong prognostic value. The number of quadrants is more important than the location of the unilateral or bilateral nature of the involvement for the prognosis, and hypoxemic patients with unilateral lung injury should probably be considered as requiring lung protective ventilation as classical acute respiratory distress syndrome.

Role of Positive End-Expiratory Pressure and Regional Transpulmonary Pressure in Asymmetrical Lung Injury

Rationale: Asymmetrical lung injury is a frequent clinical presentation. Regional distribution of Vt and positive end-expiratory pressure (PEEP) could result in hyperinflation of the less-injured lung. The validity of esophageal pressure (Pes) is unknown.Objectives: To compare, in asymmetrical lung injury, Pes with directly measured pleural pressures (Ppl) of both sides and investigate how PEEP impacts ventilation distribution and the regional driving transpulmonary pressure (inspiratory - expiratory).Methods: Fourteen mechanically ventilated pigs with lung injury were studied. One lung was blocked while the contralateral one underwent surfactant lavage and injurious ventilation. Airway pressure and Pes were measured, as was Ppl in the dorsal and ventral pleural space adjacent to each lung. Distribution of ventilation was assessed by electrical impedance tomography. PEEP was studied through decremental steps.Measurements and Results: Ventral and dorsal Ppl were similar between the injured and the noninjured lung across all PEEP levels. Dorsal Ppl and Pes were similar. The driving transpulmonary pressure was similar in the two lungs. Vt distribution between lungs was different at zero end-expiratory pressure (≈70% of Vt going in noninjured lung) owing to different respiratory system compliance (8.3 ml/cm H₂O noninjured lung vs. 3.7 ml/cm H₂O injured lung). PEEP at 10 cm H₂O with transpulmonary pressure around zero homogenized Vt distribution opening the lungs. PEEP ≥16 cm H₂O equalized distribution of Vt but with overdistension for both lungs.Conclusions: Despite asymmetrical lung injury, Ppl between injured and noninjured lungs is equalized and esophageal pressure is a reliable estimate of dorsal Ppl. Driving transpulmonary pressure is similar for both lungs. Vt distribution results from regional respiratory system compliance. Moderate PEEP homogenizes Vt distribution between lungs without generating hyperinflation.

Favorable outcome with early initiation of VV-ECMO for unilateral lung disease in children

Unilateral lung diseases such as unilateral pneumonia, trauma or pulmonary hemorrhage can cause profound hypoxemic respiratory failure necessitating mechanical ventilation. These disorders are characterized by marked asymmetry in lung mechanics, with the affected lung having a lower compliance compared to the healthier lung, and management involves complex strategies such as simultaneous independent lung ventilation. However, such strategies can be challenging in pediatric populations due to technical limitations, and also lead to ventilator induced lung injury. We report two unique cases that support the use of venovenous extracorporeal membrane oxygenation as an alternative strategy for management of unilateral lung disease in children.

PEEP has beneficial effects on inflammation in the injured and no deleterious effects on the noninjured lung after unilateral lung acid instillation

OBJECTIVE

In clinical lung injury areas of inflammation and structural alveolar alteration are unevenly distributed and interspaced between healthy or less injured lung areas. Positive end-expiratory pressure (PEEP) applied with mechanical ventilation (MV) may affect injured and healthy lung areas differently. We compared the effects of PEEP on the inflammatory response in injured and noninjured regions of the lung in an animal model of unilateral lung acid instillation.

SUBJECTS

Anesthetized, paralyzed, and ventilated rats.

INTERVENTIONS

Rats underwent left-endobronchial instillation with either hydrochloric acid or isotonic saline and were randomized 24 h later to MV using constant tidal volume (16 ml/kg) with either ZEEP, PEEP at 5 mmHg, or PEEP at 10 mmHg. After 4 h of MV the animals (n=9 or 10 per group) were killed and inflammatory markers assessed in left- and right-lung lavage fluid samples. In four additional animals per group differential lung perfusion was assessed.

RESULTS

Unilateral acid injury alone worsened oxygenation, decreased left-lung perfusion, and increased left-lung lavage neutrophil and macrophage counts and cytokine levels. MV with ZEEP further impaired oxygenation and further decreased left-lung perfusion in acid-injured animals. MV with high PEEP preserved oxygenation and significantly decreased left-lung lavage protein content and cell counts in acid-injured animals and had no deleterious effect on the right (noninjured) lung.

CONCLUSION

In this model of unilateral lung acid injury high PEEP attenuates the inflammatory cell response in the acid-injured lung, preserved oxygenation and has no deleterious effects in the opposite lung.

Unilateral lung injury

Mechanical ventilation is a supportive lifesaving therapy that can potentially cause lung injury if periodic alveolar overdistension, or cyclic collapse, and reopening occur. The use of a low tidal volume with moderate to high positive end-expiratory pressure improves the survival of patients with acute lung injury and acute respiratory distress syndrome. Positioning the patient with the "good lung down" and using differential ventilation with selective positive end-expiratory pressure are the two currently accepted ventilatory strategies to be applied in patients with severe unilateral lung injury. However, both have serious limitations in clinical practice. Lung injury may be rather inhomogeneous-confined to one lung or preferentially distributed toward the dependent lung areas. In unilateral lung injury, ventilatory strategies that allow recruitment of injured lung and that avoid overdistension of uninjured lung parenchyma should be applied. Experimental studies have shown that the use of selective tracheal gas insufflation and partial liquid ventilation facilitates low tidal volume with appropriate gas exchange while reducing cyclic lung stretch and shear stresses. Further studies are needed to determine future applications of these therapies in humans.

Selective tracheal gas insufflation during partial liquid ventilation improves lung function in an animal model of unilateral acute lung injury

OBJECTIVE

During unilateral lung injury, we hypothesized that we can improve global lung function by applying selective tracheal gas insufflation (TGI) and partial liquid ventilation (PLV) to the injured lung.

DESIGN

Prospective, interventional animal study.

SETTING

Animal laboratory in a university hospital.

SUBJECTS

Adult mixed-breed dogs.

INTERVENTIONS

In six anesthetized dogs, left saline lung lavage was performed until PaO(2)/FiO(2) fell below 100 torr (13.3 kPa). The dogs were then reintubated with a Univent single-lumen endotracheal tube, which incorporates an internal catheter to provide TGI. In a consecutive manner, we studied 1) the application of 10 cm H(2)O of positive end-expiratory pressure (PEEP); 2) instillation of 10 mL/kg of perflubron (Liquivent) to the left lung at a PEEP level of 10 cm H(2)O (PLV+PEEP 10 initial); 3) application of selective TGI (PLV+TGI) while maintaining end-expiratory lung volume (EELV) constant; 4) PLV+TGI at reduced tidal volume (VT); and 5) PLV+PEEP 10 final.

MEASUREMENTS AND MAIN RESULTS

Application of PLV+PEEP 10 initial did not change gas exchange, lung mechanics, or hemodynamics. PLV+TGI improved PaO(2)/FiO(2) from 189 +/- 13 torr (25.2 +/- 1.7 kPa) to 383 +/- 44 torr (51.1 +/- 5.9 kPa) (p <.01) and decreased PaCO(2) from 55 +/- 5 torr (7.3 +/- 0.7 kPa) to 30 +/- 2 torr (4.0 +/- 0.3 kPa) (p <.01). During ventilation with PLV+TGI, reducing VT from 15 mL/kg to 3.5 mL/kg while keeping EELV constant decreased PaO(2)/FiO(2) to 288 +/- 49 torr (38.4 +/- 6.5 kPa) (not significant) and normalized PaCO(2). At this stage, end-inspiratory plateau pressure decreased from 19.2 +/- 0.7 cm H(2)O to 13.6 +/- 0.7 cm H(2)O (p <.01). At PLV+PEEP 10 final, measurements returned to those observed at previous baseline stage (PLV+PEEP 10 initial).

CONCLUSIONS

During unilateral lung injury, PLV with a moderate PEEP did not improve oxygenation, TGI superimposed on PLV improved gas exchange, and combination of TGI and PLV allowed a 77% reduction in VT without any adverse effect on PaCO(2).

Application of tracheal gas insufflation to acute unilateral lung injury in an experimental model

In unilateral lung injury, application of global positive end-expiratory pressure (PEEP) may cause overdistension of normal alveoli and redistribution of blood flow to diseased lung areas, thereby worsening oxygenation. We hypothesized that selective application of tracheal gas insufflation (TGI) will recruit the injured lung without causing overdistension of the normal lung. In eight anesthetized dogs, left lung saline lavage was performed until Pa(O(2))/FI(O(2)) fell below 100 mm Hg. Then, the dogs were reintubated with a Univent single lumen endotracheal tube that incorporates an internal catheter to provide TGI. After injury, increasing PEEP from 3 to 10 cm H(2)O did not change gas exchange, hemodynamics, or lung compliance. Selective TGI, while keeping end-expiratory lung volume (EELV) constant, improved Pa(O(2))/FI(O(2)) from 212 +/- 43 to 301 +/- 38 mm Hg (p < 0.01) while Pa(CO(2)) and airway pressures decreased (p < 0.01). During selective TGI, reducing tidal volume to 5.2 ml/kg while keeping EELV constant, normalized Pa(CO(2)), did not affect Pa(O(2))/FI(O(2)), and decreased end-inspiratory plateau pressure from 16.6 +/- 1.0 to 11.9 +/- 0.5 cm H(2)O (p < 0.01). In unilateral lung injury, we conclude that selective TGI (1) improves oxygenation at a lower pressure cost as compared with conventional mechanical ventilation, (2) allows reduction in tidal volume without a change in alveolar ventilation, and (3) may be a useful adjunct to limit ventilator-associated lung injury.

Advances in conventional and innovative therapies for respiratory distress syndrome in children

Adult respiratory distress syndrome is a phenomenon encountered by many pediatric critical care nurses. Care of these complex patients is multifaceted and requires an in-depth understanding of pathophysiology and therapeutic intervention. Several innovative treatments are now available as biomedical and technical advances have evolved. Outcomes will improve as clinicians improve patient selection, identify therapeutic endpoints, and risk/benefits. This article addresses the current understanding of pathophysiology, innovative treatments, and nursing care issues.

Effect of two tidal volumes on oxygenation and respiratory system mechanics during the early stage of adult respiratory distress syndrome

PURPOSE

To study the effect of two tidal volumes on gas exchange, lung mechanics, and hemodynamics in 12 patients with acute respiratory distress syndrome (ARDS) within the first 72 hours of mechanical ventilation.

METHODS

Tidal volume (VT) was increased by 40% from the initial value at fixed positive end-expiratory pressure (PEEP) and matched minute ventilation by adjusting the respiratory rate (RR) of the ventilator. Initial VT and RR were 592 +/- 42 mL and 19 +/- 1 min-1, respectively. High VT amounted to 825 +/- 54 mL with a RR of 12 +/- 1 min-1.

RESULTS

We found that at high VT (1) the index of oxygenation increased from 0.22 +/- 0.03 to 0.32 +/- 0.04 (P < .001) with a parallel decrease in the right to left venous admixture from 0.26 +/- 0.02 to 0.23 +/- 0.02 (P < .001), and in the ratio of physiological dead space to tidal volume (VDS/VT) from 0.53 +/- 0.05 to 0.46 +/- 0.04 (P < .01), without impairment to hemodynamics and (2) respiratory system compliance improved significantly from 34.8 +/- 2.8 mL/cm H2O to 37.2 +/- 2.9 mL/cm H2O (P < .05). In 4 patients, we performed pressure-volume curves on PEEP with the ventilator finding an upward concavity reflecting progressive alveolar recruitment with increasing inflation volume in 3.

CONCLUSIONS

High-tidal ventilation in the early stage of ARDS improved gas exchange, suggesting recruitment during the inspiratory phase. However, the benefit of better oxygenation should be weighed against the potential risk of barotrauma induced at high VT.