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Weaning
Overview
Weaning is the gradual withdrawal of ventilatory assistance with modifying spontaneous breathing and resting periods for respiratory muscles. When a patient shows an improvement as clinical indicator of disease resolution ,the weaning should be started as the patient is able to maintain airways opened with physiologically normal ventilation cycles. The close continuous monitoring of patient's ventilatory status should be accompanying the disease correction process. Weaning competency assessed by measurement of cardiovascular and respiratory functions to avoid the possibility of weaning complications.
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
Patient Who Will Tolerate Weaning[1]
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:
- respiratory rate>35 breaths/min for more than 5 minutes
- an oxygen saturation <90%
- heart rate >140 beats per minute
- a sustained change in the heart rate of 20%
- systolic blood pressure >180 mm Hg or <90 mm Hg
- increased anxiety or diaphoresis
After successful SBT there are some factors to be considered before removing the endotracheal tube :
- The ability to maintain the airways opened upon removing the tube
- Secretions quantity from airway
- The strength of cough
- Aequate mental status
Rapid Shallow Breathing Index[2]
As a predictor for successful weaning ,the RSPI is the frequency of respiration to tidal volume ratio (f/VT). It 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. 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 and thus weaning tend to have rapid (high frequency) and shallow (low tidal volume)breathing. Thus, they generally have a high RSBI.
The sensitivity is the probability that a patient who successfully weans will have an RSBI <105[2] breaths/min/L and the specificity is the probability that a patient who fails weaning will have an RSBI ≥105[2] 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 SBTs
- CHF
- PaCO2 >45 mm Hg after extubation
- More than one coexisting condition other than heart failure
- Weak cough
- Upper-airway stridor at extubation
- Age ≥65 yr
- 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.)
- Patient in medical, pediatric, or multispecialty ICU
- Pneumonia as cause of respiratory failure
References
- ↑ 1.0 1.1 McConville JF, Kress JP (2012). "Weaning patients from the ventilator". N Engl J Med. 367 (23): 2233–9. doi:10.1056/NEJMra1203367. PMID 23215559.
- ↑ 2.0 2.1 2.2 Yang KL, Tobin MJ (1991). "A prospective study of indexes predicting the outcome of trials of weaning from mechanical ventilation". N Engl J Med. 324 (21): 1445–50. doi:10.1056/NEJM199105233242101. PMID 2023603.