Barotrauma is an important and potentially lethal complication of mechanical ventialtion.

Barotrauma is an important and potentially lethal complication of mechanical ventialtion. All physicians working with patients receiving mechanical ventialtion must be familiar with the different clinical manifestations of barotrauma, the recognition of these manifestations, and their management, Perhaps the greatest in number important aspect of management is the use of ventilatory strategies that may intercept or limit the development of barotrauma. This portion of the symposium will first review different protoplast that has only related to barotrauma, including single in kind type that has only lately been recognized (systemic gas embolism), and another protoplast that has only recently been attributed to barotrauma (diffuse lung injury). nearest the pathogenesis of these manifestations of barotrauma will be reviewed as this underlies the rational of newer ventilatory stratgies.

CLINICAL MANIFESTATIONS

Extra-alveolar Gas

The most numerous widely recognized from of barotrauma is the vicinity of extra-alveolar air. The strict definition of this phenomena is that gas readys in different tissue spaces after rupturing from alveoli.[1] Based forward work originally performed by Macklin and Macklin in the 1940s[2] it is although that gas in the alveoli first contentions across the boundary between the alveoli and the bronchovascular sheath. The gas then dissects within this sheath toward the mediastinum from which it decompresse [i]or[/i] part of to the other other fascial planes producing the radiographic and clinical manifestations of pneumothorax, subcutaneous emphysema, subpleural air pouchs pneumomediastinum, and pneumoperitoneum.

The incidence of pneumothorax in patients receiving mechanical ventilation is cited to be between 4 and 15 percent[3-7] although in patients with the adult respiratory distress syndrome (ARDS), status asthmaticus, and aspiration pneumonia, the incidence may be significantly higher.[4,7,8] Gammon and colleagues[7] lately published a study in which they retrospectively reviewed the films and medical records of 139 patients receiving ventilation in their ICU through a 10-month time period. While the incidence of pneumothoraces in the entire cluster was 14 percent, similar to earlier reports, the incidence in patients with ARDS was 60 percent while none was observ in patients with congestive heart failure or patients intubated for neurologic disease.[7]

The concatenations of a pneumothorax in a patient receiving positive squeezing ventilation can include impaired gas exchange, yet perhaps more importantly, adverse hemodynamic purports Intrathoracic extra-alveolar air may increase intrathoracic influence decreasing venous return to the right side of the heart. Compression of the lung and pulmonary sailing crafts may increase afterload to the right side of the heart, and geometric changes in the heart itself may decrease myocardial perfromance.[9,10] Studies in animals forward positive pressure ventilation demonstrate that there is an almost linear decrease in cardiac output as the bulk of an experimentally induced pneumothorax is increased.[10] A significant fall in cardiac output may be found without a corresponding decrease in oxygenation.[10] Therefore, changes in arterial kin gases may not be sensitive indicators of a hemodynamically important pneumothorax. These data also support the clinical maxim that on the same level a small pneumothorax must be evacuated in a patient receiving positive crushing ventilation as it may be causing hemodynamic purports or it could rapidly progres to single that would.

Unfortunately, it is difficult to make a radiographic diagnosis of a pneumothorax in succession portable x-ray films taken in the ICU setting.[1,11-15] The traditional radiographic hallmark of a pneumothorax--an apicolateral collection of air with the visceral pleura visible as a thin white line in the upper hemitihorax--may not be existing on portable supine films of patients with pneumothoraces. liberated air will often be located in the anterior costophrenic sulcus as this is the mostly superior portion of the pleural space in the supine patient.[12] In addition, associated lung disease may lead to different distributions of unrestrained air in the pleural sapce than in patients with relatively normal lungs[15] or to loculated gas collections if there is associated pleural disease.[13] "Les common" radiographic patterns for pneumothorax may, in fact, be the principally common findings in ICU patients. Tocino and colleagues[14] retrospectively determined the location of gas collections in succession the portable chest radiographs of patients in the ICU. The majority of pneumothoraces were located either in the anteromedial (38 percent) or subpulmonic (26 percent) areas. sole 22 percent of the pneumothoraces were located in the traditional apicolateral location. For this reason, the clinician must be alert to wily radiographic signs of pneumothoraces in these other locations: (1) relative hyperlucency through the whole extent of the upper abdominal quadrants;[12,15] (2) discerning costophrenic angle (the deep sulcus sign);[11,16] and (3) the visualization of the anterior costophrenic sulcus that ensues in a curvilinear change in density through the upper quadrant.[12]

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