Page 551 - Clinical Application of Mechanical Ventilation

Weaning from Mechanical Ventilation 517

Learning Objectives

After studying this chapter and completing the review questions, the learner
should be able to:

Define weaning success, weaning in progress, and weaning failure.
List, describe, or calculate the weaning criteria for assessing ventilation,
oxygenation, pulmonary reserve, and pulmonary measurements.
Calculate and interpret the rapid shallow breathing index (RSBI).
Describe the following weaning procedures: spontaneous breathing trial,
SIMV, pressure support ventilation, and other partial ventilator support.
List the indicators of weaning failure.
List the causes of weaning failure.
Differentiate withholding and withdrawing of mechanical ventilation.

INTRODUCTION

Weaning is the process of withdrawing mechanical ventilatory support and transfer-
ring the work of breathing from the ventilator to the patient. In most cases, weaning
may be accomplished rapidly from full ventilatory support to unassisted spontaneous
breathing.
Many patients can tolerate an abrupt termination of ventilatory support; this
would include those who have been on the ventilator for a relatively short time
(usually no more than 1 to 2 days) and who have also regained normal cardiopul-
monary function. Examples include patients recovering from postanesthesia, drug
overdose, and status asthmaticus.
For other patients, successful weaning requires a more gradual withdrawal of me-
chanical ventilatory support. Generally, the longer the patient has been on mechani-
cal ventilation, the more gradual the weaning process should be. The process of grad-
ually reducing mechanical ventilatory support must be individualized and the weaning
process may take from days to weeks or even months. Indeed, some patients become
ventilator-dependent and may not be able to maintain adequate ventilation without
mechanical assistance. Examples of these patients include high cervical spine injury,
traumatic brain injury, and some neuromuscular diseases.

DEFINITION OF WEANING SUCCESS AND FAILURE

The ability to breathe spontaneously is the criterion to gauge the success or failure of
The process of gradu-
ally reducing mechanical weaning attempts. Weaning success means that a patient is able to maintain sponta-
ventilatory support must neous breathing for a prescribed period of time. This usually leads to termination of
be individualized for each
patient. mechanical ventilation. Weaning failure generally means that a patient is returned to
mechanical ventilation after a period of unsustained spontaneous breathing.

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