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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)

Spontaneous Breathing trials assess patient’s ability to breathe without or with the least

respiratory support. In order to accomplish this, ventilators'  modes are switched

from full respiratory support 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). Typically, the patient is awake and not sedated during a trial of spontaneous breathing is initiated while the

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. The sensitivity is the probability that a patient who successfully weans will have an RSBI <105 breaths/min/L and the specificity is the probability that a patient who fails weaning will have an RSBI ≥105 breaths/min/L. The positive predictive value is the probability of successfully weaning when the RSBI is <105 breaths/min/L and the negative predictive value is the probability of failing weaning when the RSBI is >105 breaths/min/L.

Risk Factors For Unsuccessful Weaning

1. Failure of two or more consecutive spontaneous-breathing trials
2. Chronic heart failure
3. Partial pressure of arterial carbon dioxide >45 mm Hg after extubation
4. More than one coexisting condition other than heart failure
5. Weak cough
6. Upper-airway stridor at extubation
7. Age ≥65 yr
8. APACHE II score >12 on day of extubation(Acute Physiology and Chronic Health Evaluation (APACHE II)range from 0 to 71, with higher scores indicating greater impairment.)
9. Patient in medical, pediatric, or multispecialty ICU
10. Pneumonia as cause of respiratory failure