The correct answer is:

0 to rarely 5 cm H2O

Educational Objective:

Discuss the adjustment of standard ventilator settings for patients with obstructive respiratory failure.

Key Point:

The recommendation is to add little, if any, PEEP, e.g. 0 cm H2O or possibly 5 cm H2O. In the setting of asthma, extrinsic PEEP programmed into the ventilator settings further obstructs exhalation, which may further exacerbate the already greatly increased alveolar pressure, resulting in a tension pneumothorax soon after intubation.

Explanation:

The physiology behind the ventilation of patients with obstructive disease is complex. 

The main goal in asthma management is to use low respiratory rates and maximum expiratory times. To achieve this without a patient fighting the ventilator due to respiratory drive, the patient must remain completely sedated after intubation. In addition, it is important to resist the temptation to add a little PEEP to “stint open” the airway for inhalation. This does indeed facilitate inhalation, but it also obstructs exhalation, which is the patient’s greater challenge after intubation (since positive pressure ventilation can overcome inhalational obstruction, but passive exhalation cannot overcome exhalational obstruction.

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Pearl:

Classic Post-Intubation Error: manual positive-pressure hyperventilation (e.g. rapid bagging at a high rate and volume without complete refilling of the ambubag) after intubation kills patients with airway obstruction because it induces severe air trapping, high intrathoracic pressures, insufficient venous return, and cardiac arrest. The patient being increasingly “hard to bag” is a sign of this phenomenon.

References:

Seigel T. Mechanical Ventilation and Noninvasive Ventilatory Support. (Chapter 2) In: Walls R, et al. Rosen’s Emergency Medicine: Concepts and Clinical Practice. 9th ed., 2018: 25-33.e2