MECHANICS OF BREATHING AND PEEP

Introduction

Although it is the most ubiquitous form of ventilatory support, positive end expiratory pressure (PEEP) remains a large area of confusion for most physicians. For a start, the term PEEP is an anachronism, as the positive pressure is actually applied throughout the respiratory cycle ans is more correctly termed “continuous positive airway pressure (CPAP)”; during this discussion, I will use these terms interchangeably.

There are three purposes to using PEEP: 1) To prevent derecruitment, by returning the functional residual volume to the physiologic range. 2) To protect the lungs against injury during phasic opening an closing of atelectatic units. 3) To assist cardiac performance, during heart failure, by increasing mean intrathoracic pressure. This tutorial focuses on the rational for the pulmonary uses of PEEP. In the end there is one clear message: low lung volumes are bad!

Learning Objectives:

1. To explore the physiologic rational behind the use of PEEP

2. ·To discuss the therapeutic use of PEEP in hypoxemia.

3. ·To discuss the “open lung” approach to mechanical ventilation

4. ·To explore the concept of recruitment maneuvers.

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