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Weaning

Overview

Weaning of mechanical ventilator is gradual withdrawal of ventilatory support through utilization of a variety of ventilator modes, periods of total spontaneous ventilation, and appropriate rest periods for muscle unloading. Discontinuation of mechanical ventilation should occur as soon as the patient is able to protect his/her airway and sustain a physiologically-competent minute ventilation while important indicators of disease show resolution. The plan of weaning is not static but requires continual reassessment so that the particular ventilatory needs of the patient are met while the disease process is corrected. Bedside measures of cardiopulmonary function aid in the assessment of weaning fitness; these should not take the place of careful bedside observation and "hands-on" care, however. Patients should not be allowed to fatigue during weaning trials, and interventions to ensure an adequate nutritional status and good bronchial hygiene should be applied.

Criteria for Spontaneous Breathing Trial (SBT)

Trials of spontaneous breathing assess a patient’s ability to breathe while receiving minimal or no respiratory support. To accomplish this, ventilators are switched from full respiratory support modes such as volume-assist control or pressure control to ventilatory modes such as pressure support, continuous positive airway pressure (CPAP), or ventilation with a T-piece (in which there is no positive endexpiratory pressure). Ideally, a trial of spontaneous breathing is initiated while the patient is awake and not receiving sedative infusions. The typical readiness criteria for SBT are:

• Respiratory Criteria

1. PaO2>= 60 mm hg ( FiO2<40-50,PEEP<5-8cm H2O)
2. PaCo2 normal or base line
3. the Patient able to initiate inspiratory effort

• Cardiovascular Criteria

1. No evidence of myocardial ischemia
2. HR<140/min
3. BP normal without vasopressor or minimal vasopressor support
4. Adequate mental status :arousable/GCS.13

• Absence of correctable comorbid conditions

1. Patient is afebrile
2. No significant electrolytes abnormalities

Patient who will tolerate Weaning

For a spontaneous-breathing trial to be successful, a patient must breathe spontaneously with little or no ventilator support for at least 30 minutes without any of the following:

1. respiratory rate>35 breaths/min for more than 5 minutes
2. an oxygen saturation <90%
3. heart rate >140 beats per minute
4. a sustained change in the heart rate of 20%
5. systolic blood pressure >180 mm Hg or <90 mm Hg
6. increased anxiety or diaphoresis

Rapid shallow breathing index

DEFINITION — The rapid shallow breathing index (RSBI) is the ratio of respiratory frequency to tidal volume (f/VT). As an example, a patient who has a respiratory rate of 25 breaths/min and a tidal volume of 250 mL/breath has an RSBI of (25 breaths/min)/(.25 L) = 100 breaths/min/L. Patients who cannot tolerate independent breathing tend to breathe rapidly (high frequency) and shallowly (low tidal volume). Thus, they generally have a high RSBI. • The RSBI was originally measured using a hand-held spirometer attached to the endotracheal tube while a patient breathed room air for one minute without any ventilator assistance.

maximum inspiratory pressure

It 's used as —Evaluation of diaphragm and other muscles of inspiration , —Normal values usually are (-90 to -120 cm H2O) —Threshold -20 cmH2O —Identifying Pts who will not tolerate SBT —Below threshold(less negative than -20)no successful weaning —Above threshold(more negative than -20)40% did not wean