Protocols of Weaning from Mechanical Ventilation in Critically Ill Adult Patients

Abstract

SUMMARY T he respiratory tract is the path of air from the nose to the lungs. The normal adult human lung weighs about 1000g and consists of about 50% blood and 50% tissue by weight. About 10% of the total lung volume is composed of various types of conducting airways and some connective tissue. The remaining 90% is the respiratory or gas exchange portion of the lung, composed of alveoli and supporting capillaries. It is divided into two sections: Upper Airway and the Lower Airway. Mechanical ventilation is indicated when the patient's spontaneous ventilation is not adequate to sustain life or when it is necessary to take control of the patient's ventilation to prevent impending collapse of other organ functions. Mechanical ventilation refers to any method of breathing in which a mechanical apparatus is used to maintain adequate, but not necessarily normal, gas exchange. The ultimate goal of mechanical ventilation is ventilator weaning. Weaning from mechanical ventilation can be defined as the process of abruptly or gradually withdrawing ventilator support. A series of stages was described in the process of weaning, from intubation and initiation of mechanical ventilation through initiation of the weaning effort to the ultimate liberation from mechanical ventilation and successful extubation. Determining when a patient is ready to wean continues to be a concern of clinicians and investigators. Premature attempts of weaning and extubation can be deleterious to patient physiologic and psychological well-being. A number of so-called weaning predictors have been introduced, the intent of which is to identify extubation readiness. Most predictors of weaning outcome focus on the ability to achieve or sustain a specific ventilatory parameter. Four conventional modes of discontinuing patients from MV are in general use: (a) trials of spontaneous breathing (SB) with or without the addition of CPAP, (b) PS, (c) SIMV, and (d) noninvasive positive-pressure ventilation. Although most physicians generally use one of first three modes alone, some have used them in combination. Mechanically ventilated patients are at high risk of mortality, not only from the primary condition for which they have been ventilated, but also from complications arising directly or indirectly from mechanical ventilation itself. Several of these complications are related to endotracheal intubation. Critically ill patients are often immunosuppressed and are susceptible to nosocomial pneumonia for a number of reasons. Those complications have been organized into peri-intubation complications, complications that can occur acutely at any stage during mechanical ventilation, delayed complications and difficult weaning. Prompt corrective action may be life saving if some of these complications occu