5. Weaning from Ventilation

Question 1

OVERVIEW

Answer 1

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

Question 2

Classification of weaning by duration

Answer 2

“Simple” — ventilator discontinued after the first assessment

“Difficult” — ventilator discontinued from 2–7d after initial assessment

“Prolonged” — ventilator discontinued in >7d after initial assessment

Question 3

Weaning failure

Answer 3

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)

Question 4

APPROACH TO WEANING

Answer 4

Generally a two step process:

weaning parameters are assessed (‘wean screen’)
perform weaning trial
Screening for ventilator weaning should be performed daily

Question 5

GENERAL REQUIREMENTS (‘WEAN SCREEN’)

Answer 5

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

Question 6

MANAGEMENT TO AVOID DELAYED WEANING

Answer 6

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)

Question 7

MANAGEMENT TO AVOID DELAYED WEANING

Answer 7

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

Question 8

PREDICTORS OF WEANING FAILURE

Answer 8

advanced age

prolonged mechanical ventilation

COPD

increased minute ventilation

positive fluid balance

Question 9

TECHNIQUES OF WEANING

Answer 9

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

Question 10

PROTOCOLS AND AUTOMATIC FEEDBACK SYSTEMS

Answer 10

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”

Question 11

EVIDENCE

Answer 11

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.

Question 12

Grant et al, 2013

Answer 12

SC RCT from 2000 – 2010

Conclusion: SBT leads to more rapid liberation from ventilator than PSV; clinicians were slow to wean/ extubate