الفهرس 
Chapter one: anatomical and physiological considerations of respiratory system.Only 14 pages are availabe for public view
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Abstract
Despite promising scientific advances, non-ventilatory strategies for ALI/ARDS remain elusive. The best evidence is for minimizing pulmonary oedema via fluid restriction when appropriate. Recruitment maneuvers (RMs) can be defined as voluntary strategies to increase the transpulmonary pressure (PL) transiently with the goal to reopen those alveolar units that are not aerated or poorly aerated but reopenable. The consequence of this should be the induction of lung recruitment. This strategy can be performed by using the conventional ICU ventilator or the high frequency oscillation device in the supine or prone positions. Recruiting the lung is a ventilatory strategy that can prevent Ventilator-induced lung injury (VILI). This benefit may result from two mechanisms. The first is the increase in the aerated lung mass, which contributes to minimize the lung heterogeneity and to increase the size of the lung. The second is the prevention of the repeated opening and closure of the terminal respiratory units RMs have probably long been used mostly to improve oxygenation, which is a good thing if this improvement results from or is associated with lung recruitment. However, the global effect of RM is actually a balance between positive effects (reduction in ventilator induced lung injury VILI, improvement in oxygenation) and negative effects (increase in VILI, hemodynamic impairment). from this balance, one can expect favorable or poor outcome of the patient. Several factors are involved in the response to RMs in terms of oxygenation, lung recruitment, or hemodynamics. Type of ARDS, This is a major factor because ARDS is highly heterogeneous by nature, both within patients and between patients. The separation between focal and not focal ARDS has been largely accepted. Separated ARDS patients into focal and not focal morphological patterns from the CT scan and studied the effect of applied RM maneuvers before and after open lung ventilation, namely a high PEEP. After the RM, the oxygenation remained unchanged in the focal ARDS whilst it is improved in the not focal ARDS pattern. Most importantly, in the focal pattern after the RM, the lung over distension is markedly increased. Once RM was released, the over distension remained above its level before RM. In sharp contrast in the not focal ARDS pattern, the recruited volume markedly increased and was greater than the concomitant over distension with the RM. After the RM, the over distension went back to its baseline level but the recruited volume remained higher than its pre-RM level. This result was extended by Grasso. Who investigated the effect of a single high PEEP in three experimental ARDS in pigs: 1) Surfactant depletion with massive derecruitment and no inflammation. 2) Oleic acid-induced ARDS with massive lung edema and no inflammation. 3) And hydrochloride acid-induced ARDS characterized by massive inflammation. The RM did promote recruitment but also over distension in the most anterior parts of the lungs in the three ARDS models, making the lungs more heterogeneous than before the RM application. Furthermore, the over distension, and hence the lung heterogeneity, was maintained after RM release. The morphological lung heterogeneity was associated with a marked functional heterogeneity because the elastance of the recruited parts of the lungs was significantly greater than in the control animals and than that of the baby lung in each ARDS model. This result is very important to keep in mind when RM is used. Another criterion to separate ARDS patients is the severity of the lung injury. where as it is difficult to accurately and precisely define what severe ARDS is, the paraquat (dipyridylium) model of ARDS in rats is useful in this purpose because the lung histomorphometry findings are different with the dose of paraquat administered. The intra peritoneal injection of 20 mg/kg paraquat induces alveolar collapse and interstitial oedema whilst a greater dose of 25 mg/kg promotes an additional alveolar oedema. Therefore, low dose of paraquat induced moderate ARDS whilst with high dose of paraquat severe ARDS would follow. Santiago found that a single self-induced injury (SI) induced a significantly greater magnitude of over distension endothelial and epithelial alveolar cells injury, and apoptosis to the lungs and kidneys in severe than in moderate paraquat-induced ARDS in rats. Lung perfusion; Lung perfusion is a critical determinant of oxygenation.
The mechanism of this finding was that: 1) the RM did not recruit the dorsal part of the lungs in which there was a massive loss of aeration, and 2) redistributed the pulmonary blood flow toward them. Therefore, the intrapulmonary shunt increased in these dependent parts of the lung leading to oxygenation worsening In 22 patients with ARDS, it WAS FOUND THAT half was responder in terms of oxygenation after a single high PEEP and the other half was not. The explanation was that the chest wall elastance was greater in the non-responders than in responders, and hence, more pressure dissipated into the chest wall and less pressure was available to distend the lung in the non-responder than in the responder group.