WEANING FROM VENTILATORY SUPPORT

doi:10.1016/S0272-5231(05)70328-2

Clinics in Chest Medicine

Volume 17, Issue 3, 1 September 1996, Pages 475-489

https://doi.org/10.1016/S0272-5231(05)70328-2 Get rights and content

Weaning from mechanical ventilation is the process of abruptly or gradually withdrawing ventilatory support when the cause of the acute respiratory failure is under resolution. For many patients, resuming spontaneous unassisted breathing is accomplished easily. In others, the weaning process induces important changes in respiratory and nonrespiratory parameters and may be associated with complications and failure.²⁸ Such patients require more gradual withdrawal of their ventilatory support, especially those who are recovering from a prolonged episode of respiratory failure or patients with chronic obstructive pulmonary disease (COPD), severe heart failure, or severe central neurologic disorders. For those patients, the weaning period may account for more than 40% of the time spent on mechanical ventilation (Fig. 1).²⁸ In addition, adaptation of several physiologic systems to the new breathing conditions is necessary for the success of this process.

This article reviews the criteria used to determine whether the patient is ready for weaning from ventilatory support, the causes of difficult weaning, the methods of weaning, and the management of the difficult-to-wean patient.

Section snippets

General Conditions

As a general rule, weaning should begin as soon as the patient's condition has improved and allows spontaneous breathing. Many complications are associated with endotracheal intubation and with mechanical ventilation per se,⁷⁸ and a shorter duration of mechanical ventilation should be associated with a reduced incidence of complications. Premature weaning trials, however, also should be avoided. Although an experienced physician often can determine accurately the time a patient is ready to

CAUSES OF DIFFICULT WEANING

Causes of weaning failure

1
Inadequate respiratory center output
- Residual effect of sedative drugs
- CNS damage
- Severe metabolic alkalosis
2
Increase in respiratory workload
- Increased minute ventilation
- Hyperventilation (pain, anxiety, restlessness)
- Increased metabolic rate (excessive feeding, sepsis)
- Increased physiologic dead space
- Increased elastic workload
- Low thoracic or lung compliance
- Intrinsic PEEP
- Increased resistive workload
- Lower airway obstruction
- Thick or copious airway

T-piece Trials

The abrupt discontinuation of mechanical ventilation and resumption of spontaneous breathing through a T-tube system is the simplest method of weaning. It can be used successfully in many patients, mainly when no problem with the resumption of unassisted breathing is expected. Moreover, it also has been found an effective method in difficult-to-wean patients.²⁹ Patients are observed for a short period (usually up to 2 hours) to assess tolerance of spontaneous breathing.³⁵ If the weaning trial

Incidence of Difficult Weaning

Many different definitions have been used for an unsuccessful weaning from mechanical ventilation—inability to maintain spontaneous unassisted breathing for a period of 24,74, 94 48,13, 29, 84 or 72 hours,15, 27 or even 7 days,²⁰ after discontinuation of mechanical ventilation. Likewise, a definition of difficult weaning can be a failure of a previous weaning trial13, 29 or a prolonged weaning period (>48–72 hours).⁴⁵ According to the criteria used and the study population, incidences of

Noninvasive Mechanical Ventilation

In the past few years, noninvasive face mask ventilation has emerged as an effective modality of ventilatory assistance, mainly in patients with neuromuscular weakness, pulmonary edema, nocturnal sleep apnea, and acute exacerbations of COPD.11, 12, 63 Noninvasive ventilation might have a few indications in the process of weaning from mechanical ventilation as well. First, some patients require ventilatory assistance shortly after extubation because of excessive airway secretions, laryngeal

SUMMARY

Resumption of spontaneous unassisted breathing after an episode of acute respiratory failure often is achieved without major difficulty. In a significant number of patients however, weaning from mechanical ventilation is a long and difficult process that markedly increases the duration of mechanical ventilation and consumes a significant fraction of critical care resources. Some criteria have been suggested to predict early and more accurately the moment the patient is ready to be separated

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Citation Excerpt :
Premature removal may increase the rate of reintubation, the length of ICU stay or result in patient's death.2 Many different weaning predictors have been proposed.3 These indices have different specificities and sensitivities.4
Cardiovascular dysfunction has been reported as an important mechanism of weaning failure. Brain natriuretic peptide (BNP) is a sensitive and specific marker for cardiovascular dysfunction.
To determine the value of BNP levels measured at initiation and end of a 2 h spontaneous breathing trial (SBT) as a predictor of successful weaning of mechanical ventilation in patients with respiratory illness.
Thirty consecutive patients ready for weaning were prospectively enrolled in this cross-sectional analytic study over a 6-month period. All patients had been on spontaneous mode of weaning for at least 2 h. Tidal volume, respiratory rate, rapid shallow breathing index (RSBI), minute ventilation and PaO₂/FiO₂ were observed at initiation of SBT. BNP was measured at the initiation (BNP1) and at the end of SBT (BNP2). Weaning failure is defined as either the failure of SBT or the need for reintubation within 48 h following extubation.
Out of the 30 included patients, 14 (46.6%) patients had failed weaning. PaCO₂ and BNP2 were significantly higher in the patients with failed weaning as compared to those with successful weaning (P = 0.025, P = 0.031 respectively). However, BNP1 levels were not statistically significant between the 2 groups (P = 0.722). On multiple regression analysis, BNP% (percent change in the BNP level during the 2-h SBT) was the only predictor of weaning success. As compared to other weaning parameters, BNP% ≤ 14.9 had the best sensitivity, specificity, positive and negative predictive value.
Measuring the percentage change in the BNP level during a SBT may be a good predictor of weaning success from mechanical ventilation in respiratory patients.
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Emphysema is caused by exposure to cigarette smoking as well as alpha¹-antitrypsin deficiency. It has been estimated to cost the National Health Service (NHS) in excess of £800 million per year in related health care costs. The challenges for Critical Care nurses are those associated with dynamic hyperinflation, Auto-PEEP, malnutrition and the weaning from invasive and non-invasive mechanical ventilation. In this paper we consider the impact of the pathophysiology of emphysema, its effects on other body systems as well as the impact acute exacerbations have when patients are admitted to the Intensive Care Unit.
Weaning newborns from mechanical ventilation
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While there is a relative consensus as to whether mechanical ventilation should be initiated, the management of babies during recovery from respiratory failure remains largely subjective and is predominantly determined by institutional or individual practices or preferences. This can lead to babies either being left on the ventilator too long, or extubated too hastily, thus requiring repeated re-intubation. The current scientific literature fails to provide a uniform view of the most appropriate way to wean babies from mechanical ventilation. This might stem from a lack of understanding of the relative merits of the different techniques of discontinuing mechanical ventilation, given the availability of a variety of primary ventilatory modes which were not available to a neonatal population before, and limited research into the pathophysiological mechanisms responsible for an unsuccessful extubation. The purpose of this paper is to review the physiological, mechanical, and clinical principles of weaning, and to highlight areas still in need of investigation.
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: Address reprint requests to Martin R. Lessard, MD, De´partement d'Anesthe´sie-Re´animation, Hoˆpital de l'Enfant-Je´sus, 1401 18e Rue, Que´bec, Canada G1J 1Z4

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WEANING FROM VENTILATORY SUPPORT

Section snippets

General Conditions

CAUSES OF DIFFICULT WEANING

T-piece Trials

Incidence of Difficult Weaning

Noninvasive Mechanical Ventilation

SUMMARY

Chest

Chest

Chest

J Thorac Cardiovasc Surg

Chest

Chest

Chest

Chest

Chest

Chest

Chest

Chest

Chest

J Crit Care

Chest

Chest

Chest

Am J Med

Chest

Chest

Chest

Chest

Chest

Diaphragmatic dysfunction after open-heart surgery: Treatment with a rocking bed

Ann Intern Med

Hypophosphatemia as a cause of failed weaning: The importance of metabolic factors

Crit Care Med

Weaning from mechanical ventilation: Adjunctive use of inspiratory muscle resistive training

Crit Care Med

Physiologic effects of positive end-expiratory pressure and mask pressure support during exacerbation of chronic obstructive pulmonary disease

Am J Respir Crit Care Med

Effects of hypophosphatemia on diaphragmatic contractility in patients with acute respiratory failure

N Engl J Med

Polyneuropathy in critically ill patients

J Neurol Neurosurg Psychiatry

Improved efficacy of spontaneous breathing with inspiratory pressure support

Am Rev Respir Dis

Inspiratory pressure support prevents diaphragmatic fatigue during weaning from mechanical ventilation

Am Rev Respir Dis

Reversal of acute exacerbations of chronic obstructive lung disease by inspiratory assistance with a face mask

N Engl J Med

Noninvasive ventilation for acute exacerbation of chronic obstructive pulmonary disease

N Engl J Med

Comparison of three methods of gradual withdrawal from ventilatory support during weaning from mechanical ventilation

Am J Respir Crit Care Med

Inspiratory pressure support compensates for the additional work of breathing caused by the endotracheal tube

Anesthesiology

Reduction of duration and cost of mechanical ventilation in an intensive care unit by use of a ventilatory management team

Crit Care Med

Early prediction of successful weaning during pressure support ventilation in chronic obstructive pulmonary disease patients

Crit Care Med

Evaluation of risk factors for laryngeal edema after tracheal extubation in adults and its prevention by dexamethasone: A placebo-controlled, double-blind, multicenter study

Anesthesiology

Alteration in swallowing reflex after extubation in intensive care unit patients

Crit Care Med

Incidence and morbidity of extubation failure in surgical intensive care patients

Crit Care Med

Modification of the work of breathing induced by tracheotomy during weaning from mechanical ventilation [abstract]

Am J Respir Crit Care Med

A knowledge-based system for assisted ventilation of patients in intensive care units

Int J Clin Monit Comput

Evaluation of a knowledge-based system providing ventilatory management and decision for extubation

Am J Respir Crit Care Med

Diaphragmatic contractility after upper abdominal surgery

J Appl Physiol

Etiology of extubation failure and the predictive value of the rapid shallow breathing index

Am J Respir Crit Care Med

A comparison of four methods of weaning patients from mechanical ventilation

N Engl J Med

The “cuff-leak” test for extubation

Anaesthesia

Inhibition of breathing associated with gallbladder stimulation in dogs