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Critical Care Medicine

Answer 2
  1. Reduce the respiratory rate. This patient most likely has severe air trapping with significant auto-positive end-expiratory pressure (PEEP)/intrinsic PEEP (iPEEP). iPEEP will reduce venous return and therefore also cardiac output and blood pressure. The resistance to expiration may result in significant iPEEP with hemodynamic compromise. The iPEEP and/or the exhaled tidal volumes must be measured in all patients to avoid significant air trapping. A low inspiratory-expiratory ratio (long expiration) should always be used. Permissive hypoventilation may be required in patients with severe airway obstruction. Extrinsic PEEP should be avoided in asthmatic patients because it has not been shown to increase alveolar ventilation; it may also increase air trapping. iPEEP can be diminished by either decreasing the ventilator rate or increasing the flow. The latter step, however, may increase the peak airway pressure. The low dynamic compliance results in high airway pressures with attendant risk of barotrauma.

    SUGGESTED READING
    1. Bonten MJ, Gaillard CA, Wouters EF, et al. Problems in diagnosing nosocomial pneumonia in mechanically ventilated patients: a review. Crit Care Med 1994;22:1683-91.

    2. Chiles C, Ravin CE. Radiographic recognition of pneumothorax in the intensive care unit. Crit Care Med 1986;14:677-80.

    3. Lamm WJ, Graham MM, Albert RK. Mechanism by which the prone position improves oxygenation in acute lung injury. Am J Respir Crit Care Med 1994;150:184-93.

    4. Pappert D, Rossaint R, Slama K, et al. Influence of positioning on ventilation-perfusion relationships in severe adult respiratory distress syndrome. Chest 1994;106:1511-6.

    5. Tuxen DV. Detrimental effects of positive end-expiratory pressure during controlled mechanical ventilation of patients with severe airflow obstruction. Am Rev Respir Dis 1989;140:5-9.

    6. Tuxen DV, Williams TJ, Scheinkestel CD, et al. Use of a measurement of pulmonary hyperinflation to control the level of mechanical ventilation in patients with acute severe asthma. Am Rev Respir Dis 1992;146(5 Pt 1):1136-42.

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