ABSTRACT
Details on approaches to weaning are presented in Chapter 18, but special considerations in patients with asthma and COPD deserve mention here. With asthma, patients rarely require prolonged weaning. Because they normally have good ventilatory mechanics once the acute asthma is reversed, they tolerate rapid extubation well. Asthmatic patients who are not heavily sedated rarely tolerate an endotracheal tube without developing bronchospasm. As a result, as soon as airways
resistance returns to near -normal levels, and ventilation and oxygenation can be maintained at low ventilator settings (FIO2 =0.4, pressure support or control levels of
10-15 cmH2O and VT values in the 6-10 ml kg –1 range), extubation should be
considered5. In contrast, COPD patients frequently require a very long weaning period because
of chronic airway obstruction, other organ system dysfunction, and a general state of debilitation35. These patients require a consistent, standardized weaning program
Figure 17.3 Measurement of auto-PEEP by expiratory port occlusion. Normally (see top panel), alveolar pressure is atmospheric at the end of passive exhalation. With severe airflow obstruction (see middle panel) alveolar pressure remains elevated (in this example at 15 cmH2O) and slow flow continues even at the end of the set exhalation period. The ventilator manometer senses nagligible pressure because it is open to atmosphere through largebore tubing and downstream from the site of flow limitation. With gas flow stopped by occlusion of the expiratory port at the end of the set exhalation period (see lower panel), pressure equilibrates throughout the lungventilator system and is displayed on the ventilatory manomete From: Pepe, P.E. and Marini, J. J. (1982) Occult positive end-expiratory pressure in mechanically ventilated patients with airflow obstruction; the autoPEEP effect. Am. Rev. Respir. Dis. 126: 166-170.
