Flail Chest

Published on 23/05/2015 by admin

Filed under Pulmolory and Respiratory

Last modified 23/05/2015

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Flail Chest

Anatomic Alterations of the Lungs

A flail chest is the result of double fractures of at least three or more adjacent ribs, which causes the thoracic cage to become unstable—to flail (see Figure 21-1). The affected ribs cave in (flail) during inspiration as a result of the subatmospheric intrapleural pressure. This compresses and restricts the underlying lung area and promotes a number of pathologies, including atelectasis and lung collapse. In addition, the lung also may be contused under the fractured ribs.

A flail chest causes a restrictive lung disorder. The major pathologic or structural changes of the lungs associated with flail chest are as follows:

Etiology and Epidemiology

A blunt or crushing injury to the chest is usually the cause of flail chest. Such trauma may result from the following:

image OVERVIEW of the Cardiopulmonary Clinical Manifestations Associated with Flail Chest

The following clinical manifestations result from the pathologic mechanisms caused (or activated) by Atelectasis (see Figure 9-8) and Consolidation (see Figure 9-9)—the major anatomic alterations of the lungs associated with flail chest (see Figure 21-1).

CLINICAL DATA OBTAINED AT THE PATIENT’S BEDSIDE

The Physical Examination

Vital Signs

Increased Respiratory Rate (Tachypnea)

Several pathophysiologic mechanisms operating simultaneously may lead to an increased ventilatory rate. These include the following:

Paradoxic Movement of the Chest Wall

When double fractures exist in at least three or more adjacent ribs, a paradoxic movement of the chest wall is seen. During inspiration the fractured ribs are pushed inward by the atmospheric pressure surrounding the chest and negative intrapleural pressure. During expiration (and particularly during forced exhalation), the flail area bulges outward when the intrapleural pressure becomes greater than the atmospheric pressure.

As a result of the paradoxic movement of the chest wall, the lung area directly beneath the broken ribs is compressed during inspiration and is pushed outward through the flail area during expiration. This abnormal chest and lung movement causes air to be shunted from one lung to another during a ventilatory cycle.

When the lung on the affected side is compressed during inspiration, gas moves into the lung on the unaffected side. During expiration, however, air from the unaffected lung moves into the affected lung. The shunting of air from one lung to another is known as pendelluft (Figure 21-2). As a consequence of the pendelluft, the patient rebreathes dead-space gas and hypoventilates. In addition to the hypoventilation produced by the pendelluft, alveolar ventilation also may be decreased by the lung compression and atelectasis associated with the unstable chest wall.

As a result of the pendelluft, lung compression, and atelectasis, the image ratio decreases. This leads to intrapulmonary shunting and venous admixture (Figure 21-3). Because of the venous admixture, the patient’s Pao2 and Cao2 decrease. As this condition intensifies, the patient’s oxygen level may decline to a point low enough to stimulate the peripheral chemoreceptors, which in turn initiate an increased ventilatory rate.