What do we mean by Weaning ?
Weaning from ventilator comprises 2 separate aspects:
1. Liberation from the ventilator and the mechanical support
2. Removal of the artificial airway.
Identifying patients suitable for Weaning
Many studies show that a spontaneous breathing trial (SBT) is a good method of identifying patients ready to be weaned from mechanical ventilation. This is commonly done using a pressure support ventilation (PSV) mode or a T-piece trial. If the patient can maintain gas exchange at minimal levels of pressure support (usually 5 to 10 cm H2O) or when on the T-piece, the feasibility of weaning from mechanical ventilator support can be assessed.
Weaning Indices
Multiple criteria have been used to assess readiness to wean.
- Subjective criteria include tachypnoea, diaphoresis, haemodynamic stability, delirium, and other signs of increased work of breathing.
- Integrated indices include the compliance, resistance, oxygenation, and pressure index; the simplified weaning index; and the rapid shallow breathing index (RSBI).
- Many studies have demonstrated the validity of the RSBI (respiratory rate/tidal volume) on T-piece in terms of predicting successful weaning;
What is the best ventilator mode to wean on ?
4 modes for weaning in patients who experienced respiratory distress during a 2-hour spontaneous breathing trial: synchronized intermittent mandatory ventilation (SIMV; mandatory rate gradually reduced), PSV (pressure support gradually reduced), daily multiple T-piece trials, and a daily single T-piece trial.
They found the mean duration of ventilation in the SIMV group was 5 days, versus 4 days for the PSV group and 3 days for both T-piece groups. They concluded that, in this study, the T-piece spontaneous breathing trial patients weaned more quickly than the PSV group, who weaned more quickly than the SIMV group.
Difficult Weaning
Factors responsible for difficult weaning may be grouped under the following headings:
Respiratory
Poor lung compliance (e.g., oedema, consolidation, fibrosis, atelectasis, pulmonary secretions)
Poor chest wall compliance (e.g., pleural effusion, obesity)
Increased resistive load (e.g., bronchoconstriction, dynamic hyperinflation in COPD, blocked artificial airway, airway swelling or obstruction)
Neuromuscular
- Decreased central respiratory drive (e.g., coma, obesity hypoventilation syndrome, myxoedema)
- Decreased airway reflexes (e.g., toxin- or drug-related, bulbar neurological dysfunction) c. Neuromuscular weakness (e.g., critical illness, neuromyopathy, myasthenia)
Neuropsychiatric
Delirium, anxiety, sleep disturbance
Metabolic
Hypokalaemia, hypophosphataemia, hypomagnesaemia
Cardiac failure
Long-Term and Prolonged Mechanical Ventilation
Some patients may simply never wean from mechanical ventilation. Up to 50% of difficult-to-wean patients require prolonged ventilation. According to a National Association for Medical Direction of Respiratory Care Consensus Conference, prolonged mechanical ventilation should be defined as the need for more than 21 consecutive days of mechanical ventilation for more than 6h/d.
Successful weaning in prolonged mechanical ventilation constitutes complete liberation from mechanical ventilation (or a requirement for only nocturnal NIV) for 7 consecutive days.
The previously described clinical review also highlights that there is no evidence-based time limit for when further attempts at weaning can be declared futile. Similarly, there are also no evidence-based guidelines to inform decisions as to whether withdrawal of or continued use of potentially lifelong ventilator support is the correct course of action. Decisions such as these should clearly involve the wider interdisciplinary team; the patient, where possible; and the patient’s family. Input from a palliative care team may add significant value for the patient and their family.
Continuing the weaning process in an alternative environment may become appropriate depending upon the individual patient’s physiological needs. There are advantages to providing ongoing weaning and ventilator support in other environments, not only for the patient, in terms of the special expertise and access to medical and nonmedical therapies that may not be universally available, but also for the demands on the critical care unit where the patient may be moved from.
What is the role of Tracheostomy in Weaning ?
Tracheostomy may be advantageous for an individual patient. Mechanically ventilated patients may no longer require any sedation after insertion of a tracheostomy and thus may avoid some of the complications and disadvantages of long-term sedation and may be weaned more rapidly.
Patients with marginal respiratory mechanics may be weaned quickly after tracheostomy because of lower airway resistance, especially if respiratory rates are high.
The ability to eat orally, the ability to communicate, and the enhanced mobility after tracheostomy can provide psychological well-being and help weaning in prolonged mechanical ventilation. In addition, the ability to receive physical therapy and use mobility aids can aid the recovery of respiratory and skeletal muscle strength.
Conclusion
Failure to wean may result in prolonged ventilation in specialized respiratory care units outside an ICU which are called now LTVU (long term ventilation unit).
Weaning from mechanical ventilation remains an evolving domain of intensive care where more research is required to clarify unsettled terrains.
In the meantime, as with many aspects of healthcare, there appears to be a role for a protocol-based, multidisciplinary approach with an emphasis on getting the basics right by minimizing sedation, using daily sedation holds, and maximizing early nutrition and mobility.
Prolonged mechanical ventilation carries multiple complications which could be avoided if these kind of patients were referred to specialized LTVUs for weaning trials by applying based-evidence weaning protocols
