Weaning from Mechanical Ventilation

OVERVIEW

• 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

DEFINITIONS

Classification of weaning by duration

• “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

• 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)

APPROACH TO WEANING

Generally a two step process:

• weaning parameters are assessed (‘wean screen’)
• perform weaning trial

Screening for ventilator weaning should be performed daily

GENERAL REQUIREMENTS (‘WEAN SCREEN’)

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.

MANAGEMENT TO AVOID DELAYED WEANING

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

PREDICTORS OF WEANING FAILURE

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

OBJECTIVE INDICES TO PREDICT SUCCESSFUL WEANING

See Indices that predict difficulty weaning

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

There is no evidence that a gradual reduction of ventilation support accelerates the ventilator discontinuation process.

PROTOCOLS AND AUTOMATIC FEEDBACK SYSTEMS

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”
• this is probably because physicians leading weaning strategies do not adhere to evidence-based guidelines and their availability may have been delayed

Automated feedback systems

• Multiple types of system, e.g. adaptive support ventilation (ASV) found to perform as well as physician-led ‘usual’ care
• ASV combines PRVC/VS ventilation with an automated Vt/f inspiratory/expiratory ratio setup based on respiratory system mechanics and a V̇e target set by the clinician
• ASV is the most studied closed loop system
• need to be compared with protocol-driven weaning
• multiple strategies possible
• little evidence
• It is likely that changes in the demand for mechanical ventilation, severity of patient illness, and staffing issues will make automated weaning more attractive.

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.

Grant et al, 2013

• SC RCT from 2000 – 2010
• Inclusion: patients required mechanical ventilation for > 21 days and failed a 5 day screening procedure of spontaneous breathing were included in the study.
• PSV versus tracheostomy collar arm
• 316 patients (from 500 screened)
• Primary outcome: duration of ventilator weaning.
• Secondary outcomes: 6 and 12 month mortality.
• 160 (32%) were weaned on the initial screening procedure
•  tracheostomy collar arm had 4 fewer days on the ventilator (15 days vs. 19 days)
• no difference in mortality
• Conclusion: SBT leads to more rapid liberation from ventilator than PSV; clinicians were slow to wean/ extubate

References and Links

LITFL

• CCC — Weaning from mechanical ventilation (Hot Case)
• CCC — Extubation assessment (Hot Case)

Review articles

• Branson RD. Modes to facilitate ventilator weaning. Respir Care. 2012 Oct;57(10):1635-48. Review. PubMed PMID: 23013901. [Free Fulltext]
• El-Khatib MF, Bou-Khalil P. Clinical review: liberation from mechanical ventilation. Crit Care. 2008;12(4):221. doi: 10.1186/cc6959. Epub 2008 Aug 6. Review. PubMed PMID: 18710593; PubMed Central PMCID: PMC2575571.
• Haas CF, Loik PS. Ventilator discontinuation protocols. Respir Care. 2012 Oct;57(10):1649-62. Review. PubMed PMID: 23013902. [Free Fulltext]
• Heunks LM, van der Hoeven JG. Clinical review: the ABC of weaning failure–a structured approach. Crit Care. 2010;14(6):245. doi: 10.1186/cc9296. Epub 2010 Dec 8. Review. PubMed PMID: 21143773; PubMed Central PMCID: PMC3220047.
• Jackson M, Strang T, Rajalingam Y. A practical approach to the difficult-to-wean patient. JICS 2012(13)4:327-331. [Free Fulltext]
• Macintyre NR. Evidence-based assessments in the ventilator discontinuation process. Respir Care. 2012 Oct;57(10):1611-8. Review. PubMed PMID: 23013898. [Free Fulltext]
• MacIntyre N. Discontinuing mechanical ventilatory support. Chest. 2007 Sep;132(3):1049-56. Review. PubMed PMID: 17873200. [Free Fulltext]
• Sellarés J, Ferrer M, Torres A. Predictors of weaning after acute respiratory failure. Minerva Anestesiol. 2012 Sep;78(9):1046-53. Epub 2012 Jun 28. Review. PubMed PMID: 22743787. [Free Fulltext]

Trials and Systematic Reviews

• Blackwood B, Alderdice F, Burns KE, Cardwell CR, Lavery G, O’Halloran P. Protocolized versus non-protocolized weaning for reducing the duration of mechanical ventilation in critically ill adult patients. Cochrane Database Syst Rev. 2010 May 12;(5):CD006904. doi: 10.1002/14651858.CD006904.pub2. Review. PubMed PMID: 20464747. [Free Fulltext]
• Burns KE, Adhikari NK, Keenan SP, Meade MO. Noninvasive positive pressure ventilation as a weaning strategy for intubated adults with respiratory failure. Cochrane Database Syst Rev. 2010 Aug 4;(8):CD004127. doi: 10.1002/14651858.CD004127.pub2. Review. PubMed PMID: 20687075.[Free Fulltext]
• Esteban A, Frutos F, Tobin MJ, Alía I, Solsona JF, Valverdú I, Fernández R, de la Cal MA, Benito S, Tomás R, et al. A comparison of four methods of weaning patients from mechanical ventilation. Spanish Lung Failure Collaborative Group. N Engl J Med. 1995 Feb 9;332(6):345-50. PubMed PMID: 7823995. [Free Fulltext]
• Jubran A, Grant BJ, Duffner LA, Collins EG, Lanuza DM, Hoffman LA, Tobin MJ. Effect of pressure support vs unassisted breathing through a tracheostomy collar on weaning duration in patients requiring prolonged mechanical ventilation: a randomized trial. JAMA. 2013 Feb 20;309(7):671-7. doi: 10.1001/jama.2013.159. PubMed PMID: 23340588.
• Yang KL, Tobin MJ. A prospective study of indexes predicting the outcome of trials of weaning from mechanical ventilation. N Engl J Med. 1991 May 23;324(21):1445-50. PubMed PMID: 2023603. [Free Fulltext]

FOAM and web resources

• ICU Rounds — Weaning (liberating) from the mechanical ventilator
• PulmCCM.org — Tobin: “Minimal” PEEP and pressure support during SBT kills some patients (AJRCCM)