Weaning is the process of liberating a patient from mechanical ventilation.
Mechanical ventilation can often be necessary in critical illness, but is associated with significant complications. Once the need for it has resolved, it is therefore desirable to discontinue its use. In many cases this will be straightforward, but in some cases can be very challenging.
Simple weaning - progression from initial attempt at weaning to successful extubation at first attempt. Difficult weaning - when the initial attempt at weaning has failed, requiring up to 3 spontaneous breathing tests (SBT) or 7 days (from the first attempt) to achieve successful weaning. Prolonged weaning - when the attempts at weaning take over 3 SBT attempts or over 7 days.
Process of Weaning
In general, a progressive step wise approach can be seen in the weaning process:
Treatment of respiratory compromise
Suspicion of readiness for weaning
Assessment of suitability
Spontaneous breathing trial
In some cases there will be respiratory failure following extubation, and reintubation will be needed.
Readiness to wean In general, there will be a number of features that may indicate that a patient is ready for weaning of the respiratory support. This is generally when there is improvement of the pathology that led to the requirement for ventilatory support, and the clinical features will reflect this e.g. the difference between ventilation for short acting overdose vs severe pneumonia. Examples for pneumonia may include reducing sputum load, improving inflammatory markers.
More general features may include:
Low/acceptable respiratory parameters
P/F ratio >150 mmHg
Airway reflexes intact
Not excessive vasopressor/inotropic support
When this clinical picture becomes apparent, it should hopefully trigger consideration of whether the patient is ready for weaning.
Optimisation As can be well appreciated, some of these factors may be open to optimisation. Whilst some of these may only be appropriate once a decision has been made to attempt weaning, some should be regularly considered in ventilatory patients.
Areas for consideration may include:
Treatment/resolution of bronchospasm
Treatment of secretions e.g. hypertonic saline nebs
Optimal sizing of artificial airway (to minimise resistance)
Appropriate ventilatory settings e.g. adequate PEEP
Appropriate treatment of underlying cardiac pathology e.g. heart failure
Avoidance/treatment of delirium
Degree of sedation
Avoid abdominal distension
Optimise nutritional state
Correct electrolyte disturbances
Assessment of suitability Whilst the above factors may trigger suspicion, a more detailed assessment of the patient can give some predictive information of the chances of success. These can provide more objective measurements on the ongoing respiratory demands of the patient, and of their likely ability to meet these. Parameter include:
Minute ventilation < 10L/min
Tidal volume > 5ml/kg
Not excessive tachypnoea - RR < 30/mins
Rapid shallow breathing index < 105 (calculated as RR/TV)
Respiratory muscle strength
Able to generate maximal inspiratory pressure < -20 cmH20
The failure to meet some of these parameters may suggest that the patient will struggle with the removal of ventilatory support.
Weaning Once the above steps have been undertaken, it is usually appropriate to start the ‘attempt’ at weaning. There are generally 2 approaches:
Trial of unassisted breathing - if successful, extubation
More gradual weaning process
Gradual reduction in ventilatory support
Interspersed periods of unassisted breathing/reduced support
Trial of Unassisted Breathing
This may itself take several different forms:
Replacement of ventilator with T-piece
Maintenance of PEEP
Tube compensation mode
It is frequently referred to as a spontaneous breathing trial.
These different options take into account the ‘abnormal’ ventilation that may still be present due to the presence of an endotracheal tube. Continuing to provide PEEP may help to reduce the decruitment of the patient’s lungs. Tube compensation mode is available on some ventilators to provide a calculated degree of ventilatory support to offset the increased resistance that arises from the narrower and longer than usual airway. This continued mild support is probably preferable to full removal and use of a T-piece. The cases where this might be less beneficial is in the case of pathology which may get a lot of benefit e.g. heart failure, and thus potentially mask features that would suggest failure.
In these cases, an observation period of 30 minutes is generally described. This period is to assess how well the weaning is being tolerated, with longer periods appearing to provide little additional information.
Features that may indicate failure are essentially those that show that the additional respiratory effort is too much for the patient to sustain:
RR > 35 bpm
Desauration - SpO2 < 90%
Noticeable increased work of breathing
Tachycardia - >140 bpm or a rise of > 20%
Hypertension - SBP > 180 mmHg
Hypotension - SBP < 90 mmHg
In this case, it usually means that the patient is not yet suitable for weaning or extubation. Next steps may include:
Review of optimizable factors
Gradual reduction in ventilatory support
Repeat SBT at another time e.g. daily
Gradual Reduction in Support
This approach is to allow a more gradual recovery of the patient’s respiratory strength so that they will eventually be able to have the ventilatory support withdrawn.
With one approach there is a gradual reduction in some of the parameters of ventilatory support over a period of time. With a ventilation mode that allows the patient to breathe for themselves, this reduces the work of the ventilator and increases the work of the patient. An example may be to progressively decrease the pressure support being provided with each breath.
Another approach is to intersperse periods when the patient is breathing independently, but then going back on the ventilator in a planned manner. As with a SBT, this may include with PEEP still applied or just with a T-piece. The ventilator-free windows can start very small e.g. 10 minutes, and then be steadily increased.
There may be patients in whom weaning is difficult. Some formal definitions are described above, with categorisation as difficult (up to 3 SBTs or 7 days) or prolonged (over this). This should be a trigger to look for modifiable factors that may be contributing, as described above. Some commonly overlooked ones include:
Resistance from airway circuit
A more extensive investigation of possible causes may be prompted by weaning difficulty.
The difficulty in weaning should also prompt a review of strategy. Some considerations for ongoing weaning trials:
Optimal ‘resting’ between SBTs
There may be cases where mechanical ventilation is prolonged and weaning attempts have been unsuccessful. There is likely a role for tracheostomy in some of these patients. Whilst there are definite risks to performing a tracheostomy, there are a number of benefits from a respiratory perspective. Tracheostomies are discussed elsewhere.
In some cases, a very prolonged weaning process may be needed. Some specialist centres for weaning exist in the UK which can provide specialist care for those patients with prolonged weaning processes.
NIV The use of NIV (prophylactically or as a rescue) may be considered as an option for patients that have been extubated. The concept is that it can continue to help optimise some of the mechanics of breathing and reduce the work, thereby providing additional support to patients with borderline reserve.
The evidence for a weaning approach is challenging. There does seem to be trial evidence that the use of an at least daily SBT improves the time until the patient is off the ventilator.
Subira https://www.thebottomline.org.uk/summaries/icm/subira/ This trial aimed to look at the difference between the use of longer, more demanding spontaneous breathing trial (non PS for 2 hours) compared with less demanding trials (8cm/H20 PS for 30 mins). The results favoured the less demanding trial, with better success for extubation and several other outcomes.
Reconnect https://www.thebottomline.org.uk/summaries/icm/reconnect/ This looked at whether resting a patient on IMV after a SBT before extubation is beneficial. This study suggested that it did improve a number of outcome, including reintubation rate. There were some challenges with the study design, including differences in SBT duration and the clear lack of blinding.
The use of tracheostomies for respiratory weaning is one of the indications for percutaneous tracheostomy insertion on the ICU. The topic of tracheostomies, including indications, is covered in more detail in other notes. They do allow a notably different approach to the weaning process which will be covered in more detail here.
Sedation Part of the role of tracheostomies in weaning is their increased comfort (after initial insertion). The absence of material passing through the vocal cords allows reduction in sedation if otherwise possible. Once there is stability after tracheostomy insertion there is usually scope for reduction or hold of sedation.
Cuff Management The role of the cuff may have less of a role in patients that are weaning than in those who are acutely requiring advanced respiratory support. The protective function may be able to be superseded by the patient’s own capacities whilst a degree of leak can be compensated for in patients without severe mechanical support demands. Indeed, the belief that an inflated cuff protects against aspiration and pneumonia pathologies seems incorrect, perhaps actually opposite. There may therefore be a role in deflating the cuff to help with the weaning process. Advantages may include:
Ability to vocalise
More effective swallowing
There is some limited evidence that this translates into improved clinical outcomes, in terms of faster weaning (Whitmore et al). Work by Pryor and collegaues have suggested it is usually well tolerated, even if instigated in a single step rather than episodic periods. They suggested positive predictive factors inludedm medical stability, respiratory stability and suitable secretion management. Negative predictive factors included high secretion load, reduced conscious level, poor cough and older age.
Tube Selection Alteration of the type of tracheostomy tube may also help with weaning. These tend towards the effects of maximising the function of the patient’s own upper airway. Two common approaches include:
Cuffless tracheostomy tubes
These both have the effects of providing less occlusion of the trachea and therefore more effective use of their own airway.