S3P2Q7EA1

							Title: Pulmonary Contusions and Critical Care Management in Thoracic Trauma
Authors: Sutyak JP, Wohltmann CD, Larson J
Journal: Thoracic Surgery Clinics 17 (2007) 11-23.

Key Points
         •     Isolated blunt pulmonary contusion is rare and is more commonly part of multisystem trauma.
         •     Current therapy for blunt pulmonary contusion focuses on support of oxygenation and ventilation
         •     Care must be taken to avoid ventilator-associated lung injury.
         •     Prevention of infection and/or early diagnosis and treatment of infection is important to avoid prolonged hospitalization and
               increased morbidity.

Clinical Conclusions
           •   Current critical care for post-traumatic respiratory failure focuses on maintenance of adequate, not necessarily normal, lung
               function, avoidance of iatrogenic injury, treatment of infection, and patience.

Section Highlights
Introduction
          •    Early efforts to treat rib fractures and flail segments by external stabilization resulted in uncoordinated ventilation with resultant
               ventilatory shunting leading to respiratory failure.
          •    Selective positive pressure ventilation was introduced for pulmonary support, not for chest wall instability, and became the standard
                         1, 2
               therapy.
Pathophysiology of pulmonary contusion and ventilator-associated lung injury
          •    Following blunt force trauma to the chest, lacerations occur in the lung parenchyma which release blood and plasma that flood local
               alveoli.
          •    This results in perfusion without ventilation, increased intrapulmonary shunt fraction, reduced compliance, increased pulmonary
                                                                                              3
               vascular resistance, reduced CO2 elimination, and decreased oxygenation.
          •    These pathologic changes are not confined to the local zone of injury because in cases where the inflammatory response is of
               adequate magnitude, the result is diffuse pulmonary dysfunction with patches of normal functioning lung parenchyma interspersed
               with areas of fluid-filled nonfunctioning lung.
Support of pulmonary function
          •    Current treatment strategies focus on the support of oxygenation and ventilation until spontaneous healing can occur.
Noninvasive ventilation
          •    Noninvasive positive pressure ventilation (NPPV), which delivers positive pressure in the form of continuous positive airway pressure
               (CPAP) or bi-level positive airway pressure (BiPAP) is a safe and effective strategy for the treatment of acute or chronic gas-exchange
                       4-6
               failure.
Mechanical ventilation modes and lung protective strategies
          •    Introduction
                     o In pressure-cycled systems the pressure delivered is constant but the volume is dependent on changes in lung mechanics.
                     o In contrast, volume-cycled systems, which are the current standard by which most positive-pressure mechanical
                                                                                                                                                   7, 8
                            ventilation is delivered, function to deliver a constant, predetermined, alveolar volume regardless of lung mechanics.
                     o Low-volume and low-pressure ventilation is the current recommended strategy for patients with ARDS.
          •    Controlled mandatory ventilation
                     o Assist-controlled or controlled mandatory ventilation is a mode of positive pressure, volume-controlled ventilation which
                            provides a minimum rate of set tidal volumes regardless of patient effort.
          •    Intermittent mandatory ventilation
                     o Intermittent mandatory ventilation combines periods of assist-control ventilation with spontaneous breathing.
          •    Pressure-controlled ventilation
                     o In pressure-controlled ventilation (PCV), a pressure-limited breath is delivered at a minimum rate.
                     o Tidal volume is dependent on the peak pressure limit, inspiratory time, and compliance.
          •    Pressure-regulated volume control ventilation
                     o Pressure-regulated volume control ventilation is an A/C mode that combines volume ventilation with pressure limitation.
                     o This provides a decelerating inspiratory flow pattern that produces lower peak inspiratory pressure without compromising
                                     9
                            volume.
          •    Inverse ratio ventilation
                     o Inverse ratio ventilation may be used in combination with PVC to enact prolonged inspiratory times.
                     o PCV-inverse ratio ventilation delivers a pressure-limited breath designed to facilitate recruitment of collapsed alveoli and
                            prevent derecruitment.
          •    High-frequency oscillatory ventilation
                     o High-frequency oscillatory (HFO) ventilators generate low-amplitude proximal airway vibrations, analogous to acoustic
                            waveforms, which result in sub-dead space tidal exchanges at varying airway pressures.
                     o HFO has been used in the setting of acute lung injury and ARDS as both a primary and rescue mode.
          •    Nitric oxide
                     o Inhaled NO acts locally to increase cyclic GMP and relax vascular smooth muscle to reduce pulmonary vascular resistance.
          •    Prone positioning
                  o    Patients with respiratory failure have the most non-functioning alveoli in the posterior part of the lung so prone position
                       helps to redirect flow to the working alveoli.
        •    Independent lung ventilation
                 o Independent lung ventilation may be useful when a significant pathologic difference exists between lungs and parallel
                       ventilation fails.
        •    Ventilator-associated pneumonia
                 o Ventilator-associated pneumonia (VAP) is the most frequent complication related to mechanical ventilation, occurring in 9-
                                                                                                                10, 11
                       24% of patients with acute respiratory failure and accounting for 50% of ICU infections.
                 o Bronchoalveolar lavage with quantitative culture has improved the accuracy of diagnosis and specificity of antibiotic
                       therapy in VAP.


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