Bedside tip: How to wean with ASV®
The American Thoracic Society and the American College of Chest Physicians recently provided recommendations to help optimize liberation from mechanical ventilation in adult ICU patients (1). They suggest using a ventilator liberation protocol and performing spontaneous breathing trials (SBTs) with modest inspiratory pressure support (5-8 cmH2O). So how do we implement these recommendations using the Adaptive Support Ventilation (ASV) mode?
a) Screening the readiness-to-wean criteria
The following parameters are constantly screened and displayed in the Vent Status panel (2):
- For oxygenation: Oxygen and PEEP
- For CO2 elimination: Minute volume (MinVol) and pressure support above PEEP (Pinsp)
- For spontaneous activity: Rapid Shallow Breathing index (RSB) and percentage of spontaneous breathing (%fSpont)
You can set the thresholds yourself in configuration. The range of values in between (shown in light blue) is known as the weaning zone. In short-term ventilated patients, you can use these parameters as a guide for extubation. In long-term ventilated patients, the parameters indicate when you can consider performing an SBT.
When all the values are within this set range, the timer appears and shows you how long the patient has been in the weaning zone for. If a parameter moves out of the weaning zone for longer than two minutes, the timer will reset to 00:00.
Other non-respiratory weaning criteria also need to be screened at the bedside. These are:
- Absence of sedation or comfort sedation
- Patient awake or Coma Glasgow Score > 8 for brain-injury patients
- Absence or low dose of vasopressor drugs
- Patient able to cough when suctioning
If all these conditions are fulfilled, you can start an SBT.
b) Spontaneous breathing trial:
You can carry out an SBT in ASV by decreasing PEEP to 5 cmH2O and lowering the target minute volume (%MinVol) setting to reduce the pressure support as needed. If the pressure support on the current %MinVol setting is higher than 15 cmH2O, the %MinVol setting can be lowered first to 70% and then 25% to reduce pressure support gradually to 5-8 cmH2O for the SBT.
The patient should be monitored both clinically and using the Vent Status panel. Clinical monitoring includes neurological status, effort to breathe, heart rate, and arterial blood pressure. Respiratory monitoring includes SpO2, PetCO2, respiratory rate, and tidal volume. Patient exhaustion may lead to an increase in the respiratory rate with a small tidal volume, and cause an increase in pressure support according to the ASV algorithm.
If the patient remains stable for 30 minutes, you can consider extubation (3).
- Girard TD, Kress JP, Morris PE, Ouellette DR, Alhazzani W, et al. Official Executive Summary of an American Thoracic Society/American College of Chest Physicians Clinical Practice Guideline: Liberation from Mechanical Ventilation in Critically Ill Adults. Am J Respir Crit Care Med 2017;195(1):115-119.
- Ely W, Baker A, Dunagan D, Burke H, Smith A, Kelly P, et al. Effect on the duration of mechanical ventilation of identifying patients capable of breathing spontaneously. N Engl J Med 1996; 335: 1864-9.
- Esteban A, Alia I, Tobin M, Gil A, Gordo F, Vallverdu I, et al. Effect of spontaneous breathing trial duration on outcome of attempts to discontinue mechanical ventilation. Am J Respir Crit Care Med 1999;159:512-8.
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