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Chapter: Essential Anesthesia From Science to Practice : Applied physiology and pharmacology : Anesthesia and the lung

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Mechanics of ventilation

Spontaneous ventilation at rest involves generating negative intrathoracic pres-sure (by lowering the diaphragm and expanding the chest wall), causing air to be drawn into the lungs.

Mechanics of ventilation

Spontaneous ventilation at rest involves generating negative intrathoracic pres-sure (by lowering the diaphragm and expanding the chest wall), causing air to be drawn into the lungs. This requires that the upper airway remains patent. In the presence of an obstruction, e.g., tongue, mass, mechanical, we observe retrac-tions, particularly around the clavicles and the jugular notch and, in children, the intercostal spaces. An early sign is a tracheal tug, a little downward movement of the larynx with each inspiration. A reliable sign of airway obstruction, the tra-cheal tug signals the recruitment of accessory muscles to maintain gas exchange. Similarly, pulmonary cripples (advanced emphysema) and patients still partially paralyzed after anesthesia will show a tracheal tug. Hypoxemic patients weakened by drugs or muscle disease require immediate assisted ventilation with bag and mask and, if necessary, establishment of a patent airway.

At rest, exhalation should be passive and, if it is not, consider asthma or airway obstruction.


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