Marrow emboli have been identified in the lungs of patients, leading to the term fat embolism syndrome, but ARDS may also develop in the absence of fracture marrow emboli. Studies have demonstrated the release of free fatty acids, cytokines, and other inflammatory cascade molecules into the blood stream, which produces characteristic pulmonary changes: congestion, atelectasis, venous and capillary engorgement, and interstitial edema. These pulmonary changes prevent the exchange of oxygen across the alveolocapillary membrane, resulting in profound systemic hypoxia. As a consequence, the patient becomes progressively more hypoxic and may die if the disorder is not treated aggressively. When ARDS is suggested, arterial oxygen tension should be determined. The severity of hypoxemia necessary to make the diagnosis of ARDS is defined by the ratio of the partial pressure of oxygen in the patient’s arterial blood (Pao2) to the fraction of oxygen in the inspired air (FIo2). In ARDS, the Pao2/FIo2 ratio is less than 200.
Great debate exists among the trauma community regarding the best methods of reducing the incidence of ARDS that follows multiple-injury trauma. This has led to the term damage control orthopaedics, which refers to the theory that surgical management of patients should be staged to minimize the systemic effects of the patient sustaining subsequent iatrogenic trauma (i.e., surgery). Because patients with multiple injuries are already “primed” for systemic inflammation due to their injuries, clinicians must be mindful to not perform nonemergent procedures before medical optimization of the patient. Clinical evidence demonstrates that ARDS can be prevented, or at least minimized, by mobilizing the patient early and avoiding prolonged bed rest and traction. These precautions require immobilization of fractures as soon as possible after the injury. Intramedullary nailing of all long bone (especially femur) fractures should be performed in less than 24 hours from injury if possible. This reduces the risk of fat embolism syndrome, ARDS, and other medical complications such as large amounts of blood loss from unreduced fractures. This is particularly important in patients with multiple injuries. Intramedullary long bone fixation allows the patient to be mobilized immediately after fracture fixation, minimizing bed rest and eliminating the need for skeletal traction.
If promptly recognized and treated vigorously, the pulmonary changes of ARDS are possibly reversible. Failure to treat the patient aggressively may be fatal. Treatment focuses on correcting the hypoxemia and maintaining arterial oxygen tension greater than 70 mm Hg until the pulmonary lesions resolve. This essentially consists of improving oxygenation by way of utilizing positive end-expiratory pressure (PEEP) to drive sufficient oxygen across the alveolocapillary membrane for adequate arterial oxygenation. Treatment may be required for 2 days to multiple weeks, depending on the severity of the pulmonary lesions. If oxygen delivered with a facemask does not restore the arterial oxygen tension to the desired level, mechanical ventilation with a closed system should be instituted. Even at this stage, fracture fixation to allow mobilization of the patient combined with vigorous respiratory therapy may help reverse the pulmonary insufficiency.
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