Mechanical ventilation of patients with acute lung injury

Novel therapeutic strategies for acute lung injury induced by lung damaging agents: the potential role of growth factors as treatment options

The increasing threat from terrorism has brought attention to the possible use of toxic industrial compounds (TICs) and other lung-damaging agents as weapons against civilian populations. The way in which these agents could be used favours the development of generic countermeasures. Improved medical countermeasures would increase survivability and improve the quality of recovery of lung damaged casualties. It is evident that there is a dearth of therapeutic regimes available to treat those forms of lung damage that currently require intensive care management. It is quite possible that mass casualties from a terrorist incident or major industrial accident involving the release of large quantities of inhaled TICs would place a severe burden on already scarce intensive care facilities. The development of effective pharmacological approaches to assist the recovery of casualties suffering from acute lung injury (ALI)/acute respiratory distress syndrome (ARDS) may improve the prognosis of such patients (which is currently poor) and would ideally be used as a means of preventing subjects from developing the pulmonary oedema characteristic of ALI/ARDS. Many promising candidate pharmacological treatments have been evaluated for the treatment of ALI/ARDS, but their clinical value is often debatable. Thus, despite improvements in ventilation strategies, pharmacological intervention for ALI/ARDS remains problematical. A new approach is clearly required for the treatment of patients with severely compromised lungs. Whilst the pathology of ALI/ARDS associated with exposure to a variety of agents is complex, numerous experimental studies suggest that generic therapeutic intervention directed at approaches that aim to upregulate repair of the damaged alveolar blood/air barrier of the lung may be of value, particularly with respect to chemical-induced injury. To this end, keratinocyte growth factor (KGF), epithelial growth factor (EGF) and basic fibroblast growth factor (bFGF) are emerging as the most important candidates. Hepatocyte growth factor (HGF) does not have epithelial specificity for lung tissue. However, the enhanced effects of combinations of growth factors, such as the synergistic effect of HGF upon vascular endothelial growth factor (VEGF)-mediated endothelial cell activity, and the combined effect of HGF and KGF in tissue repair should be investigated, particularly as the latter pair of growth factors are frequently implicated in processes associated with the repair of lung damage. Synergistic interactions also occur between trefoil factor family (TFF) peptides and growth factors such as EGF. TFF peptides are most likely to be of value as a short term therapeutic intervention strategy in stimulating epithelial spreading activities which allow damaged mucosal surfaces to be rapidly covered by epithelial cells.

Effects of mechanical ventilation on platelet microparticles in bronchoalveolar lavage fluid

INTRODUCTION

Mechanical ventilation (MV) is considered to contribute to lung injury. Platelet membrane-derived microparticles (PMPs) are procoagulant and participate in the inflammatory process. The bronchoalveolar space could, besides plasma, be a site of origin of these microparticles. We evaluated the presence of these PMPs and two prostaglandin-derived metabolites in bronchoalveolar lavage fluid (BALF) regarding their possible relation to MV.

MATERIALS AND METHODS

Before and after 1 h of MV, PMPs and prostaglandin metabolites were analyzed, in BALF from 14 anesthetized pigs, by flow cytometry and RIA, respectively. Tracheal mucus from five humans was analyzed for PMPs at extubation after surgery.

RESULTS

Activated PMPs and prostaglandin metabolites were present in all BALF samples. The time needed to count 5000 cellular events was prolonged six-fold after 1 h of mechanical ventilation (p<0.001). The relative content of PMPs was constant in all samples. The PMPs were thrombogenic, i.e. they were fibrinogen, p-selectin and von Willebrand factor positive. Lavage did not per se affect the period necessary to count 5000 cellular events. PMPs in human tracheal mucus were in the same range as in the pig after 1 h of MV aiming at a PaCO(2) between 5.0 and 5.5 kPa.

CONCLUSIONS

Activated PMPs are present in the pulmonary air-liquid interface. The prolongation of the time needed to count 5000 cellular events in BALF after MV indicates activation and adherence. Adherent microparticles bind neutrophils, which may aggravate pathological processes leading to pulmonary dysfunction. Evaluation of PMPs in BALF may be useful in evaluating strategies for lung-protective ventilator treatment.

Prone-position ventilation induces sustained improvement in oxygenation in patients with acute respiratory distress syndrome who have a large shunt

OBJECTIVES

Prone-position ventilation (PPV) induces acute improvement in oxygenation in many patients with acute respiratory distress syndrome (ARDS), with some maintaining their oxygenation even after they were returned to the supine position, but it is unclear what clinical factors determine the sustained oxygenation benefit. We hypothesized that patients with ARDS who have a larger shunt would have a better acute and sustained oxygenation response to PPV.

DESIGN

Prospective, nonrandomized interventional study.

SETTING

Medical and surgical intensive care units, university tertiary care center.

PATIENTS

Twenty-two consecutive patients, with ARDS with an average PaO2/FiO2 of 94, were administered PPV for 12 hrs followed by supine-position ventilation for 2 hrs.

MEASUREMENTS

Hemodynamic and gas exchange variables were monitored. The shunt was measured as venous admixture at an FiO2 of 1.0, and compliances of the respiratory system, lung, and chest wall were measured by the esophageal balloon technique before PPV, during PPV, and during subsequent supine-position ventilation.

MAIN RESULTS

Fourteen patients (64%) responded to PPV, with PaO2/FiO2 increasing by > or =20. These changes were associated with a decrease in chest wall compliance. Responders had significantly shorter time from ARDS to PPV, a lower baseline PaO2/FiO2, and a higher venous admixture. All responders maintained the improvement in oxygenation and had a greater respiratory system compliance after returning to the supine position. Time from ARDS to PPV and baseline lung injury score were negatively associated, whereas chest wall compliance, heart rate, and PaCO2 were positively associated with sustained improvement in oxygenation.

CONCLUSIONS

PPV induced acute and sustained improvement in oxygenation in many patients with ARDS. The sustained improvement is more significant if PPV is administered early to patients with a larger shunt and a more compliant chest wall. Measuring venous admixture and chest wall compliance before PPV may help select a subgroup of patients with ARDS who may benefit the most from PPV.

Ventilation and the critically ill parturient

Positive-pressure ventilation is the keystone in the management of pulmonary dysfunction in the critically ill. An increased understanding of both the benefits and hazards has led to a general consensus regarding the optimal techniques to ensure adequate gas exchange. Unfortunately, the same cannot be said for ventilation terminology which, due to a lack of standardization, lends itself to confusion. Pulmonary dysfunction in the parturient may arise from thoracic or extra-thoracic pathologies but both may be defined as acute lung injury. In its most severe form this constitutes acute respiratory distress syndrome. Acute lung injury results in reduced lung compliance and a marked decrease in the volume of functional lung. Ventilation strategies are now designed to recruit as much available lung tissue as possible while simultaneously minimizing the injurious effects of alveolar over-distension. Upon resolution of the underlying pathology mechanical ventilation may be withdrawn. Recent evidence suggests that this final stage need not be protracted, and if certain criteria are fulfilled, rapid weaning is feasible.

Pathophysiology and implications for treatment of acute respiratory distress syndrome

Acute respiratory distress syndrome is a complex group of signs and symptoms caused by direct or indirect lung injury. In spite of decades of research, it is still associated with a high mortality rate. Pathogenesis of this disease is related to alveolar endothelial and epithelial cell injury and associated release and sequestration of inflammatory mediators and cells, including cytokines and neutrophils, respectively. Pharmacologic interventions have been largely unsuccessful, and ventilation strategies to support oxygenation while limiting ventilator associated lung injury have not demonstrated any significant reductions in the mortality rate. However, novel therapies are in development, based on the knowledge of the pathologic processes of acute respiratory distress syndrome. In this article an overview of the disease process and mediator involvement is presented, followed by a review of pharmacologic and ventilation treatments currently in use or under study.

Acute lung injury and acute respiratory distress syndrome in sepsis and septic shock

Sepsis remains the leading cause of ARDS, and ARDS is still an often fatal condition. With our expanding knowledge of the pathobiologic mechanisms and the relationship between these two entities, early recognition, treatment, and prevention of sepsis may prevent or hasten recovery from ARDS. Understanding the biologic markers involved in the complex inflammatory response of sepsis and acute lung injury offers the possibility of future investigations to target treatment based on these mediators.

Pleural Disease in the Intensive Care Unit

Pleural disease itself is an unusual cause for admission to the intensive care unit (ICU). Pleural complications of diseases and procedures in the ICU are common, however, and the impact on respiratory physiology is additive to that of the underlying cardiopulmonary disease. Pleural effusion and pneumothorax may be overlooked in the critically ill patient due to alterations in radiologic appearance in the supine patient. The development of a pneumothorax in a patient in the ICU represents a potentially life-threatening situation. This article reviews the etiologies, pathophysiology, and management of pleural effusion, pneumothorax, tension pneumothorax, and bronchopleural fistula in the critically ill patient. In addition, we review the potential complications of thoracentesis and chest tube thoracostomy, including re-expansion pulmonary edema.