Weaning is the process by which the amount of respiratory support provided by the ventilator is reduced resulting in discontinuation of ventilation.
Each day it should be considered whether weaning can occur. This is important to minimize the risks of being invasively ventilated (e.g. VAP, ventilator associated pneumonia).
Even if not ready for weaning then it can still be considered whether some of the ventilatory settings can be changed to decrease support (e.g. decrease FiO2 or PEEP)
Weaning Process
Weaning may be gradual or abrupt.
Simply, gradual weaning can be by reducing the amount of pressure support (PS) provided by the ventilator, which requires the patient to do more and more of the work for themselves.
Abrupt processes when deemed ready include a spontaneous breathing trial (SBT).
This can involve using no (PS and PEEP 0) or minimal (PS and PEEP < 5 cm H2O) support for ~ 30 minutes. Signs of failure include elevated respiratory rate, reduced tidal volumes or minute ventilation, hypoxia, hypercarbia, tachycardia, and agitation or diaphoresis.
Pre-requisites for SBT
- Stable or resolving respiratory pathology or cause for intubation
- Low FiO2 (< 0.5) and PEEP (typically <8 cm H20)
- Appropriate PaCO2
- Haemodynamically stable
- Spontaneous mode of ventilation (e.g. CPAP – Pressure Support)
- Adequate conscious state and ability to protect airway
- No significant derangements to acid-base
Factors that might make weaning difficult
- Increased respiratory load
- Increased resistance: bronchospasm, secretions, small ETT
- Poor compliance: pneumonia, pulmonary oedema, pleural effusions, abdominal distension
- Increased ventilatiory demand: Sepsis (leading to hypermetabolism), PE, profound metabolic acidosis
- Decreased respiratory drive
- Sedatives, neurological insult
- Impaired neuromuscular function
- Neurological disorders, ICU acquired weakness, electrolyte or endocrine abnormalities
Extubation
Extubation is the physical process of removing the ETT.
Often in clinical practice (especially if the ventilatory period has been short e.g. post operatively) the nursing staff will do a lot of the weaning process for you and have successfully transitioned the patient to a spontaneous mode of ventilation and have asked if this patient is ready to extubate. Extubation assessment is similar to assessing a patient’s readiness to wean with a few additional factors to consider.
The most common approach to assessing readiness for extubation is an A,B,C,D,E approach:
- A: Able to maintain a patent airway following removal of ETT
- B: FiO2 < 0.4 with appropriate SpO2, PEEP 5 – 8 cm H2O, improving respiratory pathology
- C: Stable haemodynamic parameters
- D: Adequate mentation and pain control. Good weakness.
- E: Stable acid base and electrolytes
- Other: Time of day, ease of initial intubation, staffing availability, need for further procedures
- Is another modality of respiratory support following extubation such as NIV or High Flow required?
Cuff Leak
A cuff leak test may be done – this is looking for a change in expiratory tidal volumes (varying amounts reported in the literature – 110mls to ~10% of tidal volume) when the pilot balloon is deflated. Crudely this will be heard as a cuff leak – a “gurgly” noise.
If there is a significant leak then it implies minimal oedema (common post prolonged intubation) as air bypasses the ETT when the cuff is deflated (and therefore is not recorded as expired by the ventilator). If there is significant oedema there is no room to bypass even with the cuff deflated so all the expired air still passes through the ETT and is recorded as expired by the ventilator.
Post Extubation Stridor
If there is significant odema this can lead to stridor. Risk factors include: female sex, multiple intubations, trauma, agitation when intubated and prolonged intubation time.
Treatment depends on severity and includes oxygen, steroids, adrenaline nebuliser, NIV +/- reintubation.
References and Further Reading
LITFL: Weaning from Mechanical Ventilation