Should PEEP Be Used in Airflow Obstruction?
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Abstract
Notes
Annotations
(7/9/2022, 5:14:43 PM)
“It is important to emphasize that there are three distinct forms of auto-PEEP:
- Auto-PEEP without lung distention.
- Dynamic hyperinflation without flow limitation
- Dynamic hyperinflation with flow limitation.
“When PEEP is added to the central airway of a passively ventilated patient with auto-PEEP, its effect on expiratory airflow and lung volume may depend on the presence and extent of flow limitation .” Go to annotation (Marini, 1989, p. 1)
“Because the detrimental hemodynamic effects of PEEP are associated with lung distention , the addition of PEEP should not cause hemodynamic deterioration until this critical value is exceeded.” Go to annotation (Marini, 1989, p. 2)
“PEEP not only sets the end-expiratory system pressure but also adds flow resistance ” Go to annotation (Marini, 1989, p. 2)
“raising the set level of end-expiratory pressure might ease the inspiratory workload by
- improving lung mechanics or
- by facilitating the off-loading of inspiratory work to the expiratory side.
The distention expected from PEEP (a function of chest compliance) will not occur if active contraction of the expiratory muscles drives the chest below the appropriate equilibrium volume. Although expiratory work is performed in opposing PEEP , inspiration is aided by the boost received as the expiratory muscles relax, allowing the chest to recoil outward to its equilibrium position. Such "work sharing " represents one potential mechanism by which the application of a low level of PEEP or CPAP could make a breathless patient with (or without) moderate airflow obstruction more comfortable (7). Unfortunately, dynamic airway collapse frustrates this work-sharing mechanism by rendering expiratory muscle contraction ineffective in speeding airflow. Yet, in those with tidal flow limitation, the addition of PEEP might still be helpful, not only by retarding flow but also by narrowing the end-expiratory gradient between alveolar and central airway pressure .” Go to annotation (Marini, 1989, p. 2)
“If adding PEEP narrows the end-expiratory difference between alveolar and central airway pressures d(Palv - Paw), the effective triggering sensitivity of the ventilator improves. Note that improved sensitivity and decreased work of breathing require that the added PEEP cause little increase in end-expiratory alveolar pressure and lung volume; for these patients, PEEP and auto-PEEP are not algebraically additive .” Go to annotation (Marini, 1989, p. 2)
“in patients with extensive dynamic small airway collapse, the addition of PEEP (or CPAP) less than the original levelof auto-PEEP will increase average end-expiratory Palv and lung volume by only a small amount, but narrow the Palv - Paw considerably. In such patients, low level PEEP can make breathing more comfortable without causing significant distention. In others - those without extensive flow limitation during tidal breathing or those in whom endexpiratory airway pressure exceeds Pem - additional PEEP will cause proportional increases in Palv, hyperinflation, and the attendant risks of barotrauma, hemodynamic compromise, and impaired inspiratory muscle activity.” Go to annotation (Marini, 1989, p. 2)
“The primary objective of PEEP in airflow obstruction is to improve the workload and relieve dyspnea ” Go to annotation (Marini, 1989, p. 2)
“there is a subset of patients with auto-PEEP whose problems relate primarily to flow limitation, dynamic airway compression, and dyspnea. In these, the application oflow levels of PEEP (as a rule less than the original level of autoPEEP) may relieve dyspnea by making the machine easier to trigger or the spontaneous breath easier to draw. It is also possible that some patients who have high levels of VE and modest airflow obstruction (but no flow limitation) would benefit by work sharing.” Go to annotation (Marini, 1989, p. 3)