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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.

• Respiratory Criteria

1. PaO2>= 60 mm hg ( FiO2<40-50,PEEP<5-8cm H2O)
2. PaCo2 normal or base line
3. Pt 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

the criteria that predict the patient tolerance to weaning are

1. Tidal volume :5-7 ml/Kg
2. respiratory rate is :10-18 per minute
3. total ventilation:5-6 L /min
4. RR/Vt ratio :40-50/L
5. MIP ( maximum inspiration pressure )between 90- to -120 cm H2O

Rapid shallow breathing index

1. —RR/Vt ratio(normally 40-50/L)
2. —Threshold RR/Vt of approximately 100/L
3. —Predictive of successful weaning(below 105/L 80% success)
4. —Failure of weaning(above105/L 95% failure)

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