5. Weaning from Ventilation

Ventilator management should be aimed at getting the patient off ventilator support as rapidly as possible Weaning can be considered once the underlying process necessitating mechanical ventilation is resolving Weaning is the process of liberation from, or discontinuation of, mechanical ventilatory support (‘weaning’ per se is not always required, ‘liberation’ may be a better term!) Weaning comprises 40% of the duration of mechanical ventilation 20% to 30% of patients are difficult to wean from invasive mechanical ventilation

“Simple” — ventilator discontinued after the first assessment “Difficult” — ventilator discontinued from 2–7d after initial assessment “Prolonged” — ventilator discontinued in >7d after initial assessment

Weaning failure is defined as the failure to pass a spontaneous-breathing trial or the need for reintubation within 48 hours following extubation predicting success is important to reduce rates of reintubation reintubation is associated with a 7-11x increase in hospital mortality reintubation rates of 10 to 15% are typical for most well-run ICUs (a target of 0% is unrealistic and would lead to prolonged ventilation)

Generally a two step process: weaning parameters are assessed (‘wean screen’) perform weaning trial Screening for ventilator weaning should be performed daily

The ‘wean screen’ should be performed daily lung disease is stable/ resolving low FiO2 (< 0.5) and PEEP (< 5-8cmH2O) requirement haemodynamic stability (little to no inopressors) able to initiate spontaneous breaths (good neuromuscular function) This indicates patients suitable for a spontaneous breathing trial, those who pass also to be assessed for extubation

Optimize Respiratory Muscle Power nutrition avoid neuromuscular blocking drugs, decrease steroid use and other contributors to critical illness-induced weakness encourage spontaneous breathing but avoid exhaustion normal electrolytes normal FRC physiotherapy Decrease Respiratory Work sit up decrease respiratory demand: — decrease CO2: treat pyrexia, treat agitation, avoid overfeeding, minimise dead space — correct metabolic acidosis decrease resistance: large, short diameter ETT, treat disease, decrease WOB increase compliance: treat lung disease; decrease abdominal distention (chest wall factors are not usually reversible)

Optimise ventilatory drive stop sedation consider causes from the brain to the neuromuscular junction Increase oxygenation and carrying capacity sit up and avoid atelectasis correct anemia correct acid-base disturbance (shift in Hb-O2 dissociation curve) Address cardiac dysfunction removal of PPV may unmask LV dysfunction treat ischemia Address sputum clearance treat infection, chest physiotherapy, suction, bronchoscopy mucolytics are controversial

advanced age prolonged mechanical ventilation COPD increased minute ventilation positive fluid balance

TECHNIQUES OF WEANING Techniques include: gradual reduction in mandatory rate during intermittent mandatory ventilation gradual reduction in pressure support spontaneous breathing through a T-piece spontaneous breathing with ventilator on ‘flow by’ and PS=0 with PEEP=0

Protocols protocol-driven ventilator discontinuation procedures have clearly demonstrated that traditional “standard care” is often associated with significant delays in ventilator withdrawal in numerous studies, non–physician-run protocols consistently produce faster ventilator discontinuation times when compared to physician-run “usual care”

EVIDENCE Summary No predictor indices have been proven to be clinically useful for guiding ventilation weaning. Esteban et al (1995) showed that trials of spontaneous breathing (SBT) resulted in faster liberation from mechanical ventilation compared with weaning using PSV or IMV. Other studies have conflicted with this conclusion. There is no evidence that a gradual reduction of ventilation support accelerates the ventilator discontinuation process. Non–physician-run protocols consistently produce faster ventilator discontinuation times than usual care.

SC RCT from 2000 – 2010 Conclusion: SBT leads to more rapid liberation from ventilator than PSV; clinicians were slow to wean/ extubate