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Communications to the Editor |

Liberation From Mechanical Ventilation Liberation From Mechanical Ventilation: Now for the Rest of the Story FREE TO VIEW

John R. Bach, MD, FCCP
Author and Funding Information

Affiliations: Department of Physical Medicine and Rehabilitation New Jersey Medical School Newark, NJ ,  Yale University School of Medicine Bridgeport, CT University of Chicago Chicago, IL



Chest. 1999;115(4):1217. doi:10.1378/chest.115.4.1217
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Manthous, Schmidt, and Hall in their publication,“ Liberation From Mechanical Ventilation: A Decade of Progress,” (September 1998)1note that a direct method of assessing readiness to wean from ventilator use is simply to initiate a trial of unassisted breathing. However, even 24 h of unassisted breathing can fail to signal ability for ventilator liberation, unless airway secretions can be effectively eliminated following extubation. No conventionally monitored weaning parameter can accurately predict a patient’s ability to wean, in large part, because these parameters assess inspiratory muscle function when some combination of expiratory dysfunction and bulbar muscle dysfunction often result in extubation failure. Indeed, the ability to breathe is not a requirement for extubation. We reported successful extubation for patients with predominant neuromuscular ventilatory failure, many of whom had no ability to breathe, provided that 160 L/min of unassisted or assisted peak cough flows (PCF) could be generated.2 All patients with lower PCF failed extubation even when they comfortably tolerated unassisted breathing for 24 h. This was because postextubation patients who cannot generate PCF over 160 L/min cannot effectively clear airway secretions. On the other hand, patients with no autonomous ability to breathe, but who had adequate assisted PCF, used continuous intermittent positive pressure ventilation via mouthpieces or nasal interfaces upon extubation. Those who could then “weaned” themselves by taking fewer and fewer assisted breaths as tolerated.

Further, these authors’ recommendation of extubation following demonstration of unassisted breathing ability for 1 h receiving continuous positive airway pressure or T piece with a Fio2 of 40% to 50% may be appropriate for the general population of ventilator users primarily with lung disease, but it should not be applied to patients with purely neuromuscular ventilatory failure. Prior to extubation of these patients, oxyhemoglobin desaturation below 95% signals hypercapnia, considerable airway encomberment, or persistent lung disease, such as pneumonia. The need for supplemental O2 administration before and following extubation is very likely to be a harbinger of extubation failure.2 Patients with neuromuscular weakness have essentially normal lung tissue and should not be extubated until their oxyhemoglobin saturation level is normal on room air.2,,3 Discussions on mechanical ventilation and ventilator weaning should not lump patients with neuromuscular weakness with patients primarily with oxygenation impairment.

Correspondence to: John R. Bach, MD, FCCP, Department of Physical Medicine and Rehabilitation, University Hospital, 150 Bergen Street, Room B-239, University Heights, Newark, NJ 07103-2406

Manthous, EA, Schmidt, GA, Hall, JB (1998) Liberation from mechanical ventilation: a decade of progress.Chest114,886-901. [PubMed] [CrossRef]
 
Bach, JR, Saporito, LR Criteria for extubation and tracheostomy tube removal for patients with ventilatory failure: a different approach to weaning.Chest1996;110,1566-1571. [PubMed]
 
Niranjan, V, Bach, JR Noninvasive management of pediatric neuromuscular ventilatory failure.Crit Care Med1998;26,2061-2065. [PubMed]
 

Liberation From Mechanical Ventilation

To the Editor:

Dr. Bach’s concerns reflect the important point that assessment of the ability to breathe free of a mechanical ventilator—a state we have termed “liberation”—requires a judgment separate from the assessment of the need for an artificial airway. We have made this distinction in our review and feel it is an important one.1-1 Unfortunately, his letter suggests confusion over these two different aspects of extubation by referring to a prior publication by Dr. Bach and Dr. Saporito1-2 regarding the correlation of cough flows with extubation success. In that study, peak cough flow rate predicted successful removal of the artificial airway but not liberation. Indeed, the majority of patients reported in that study were ventilated (noninvasively) for an average of 20 months after the airway was removed. Our paper addressed the ability to remove the patient from the ventilator, an issue not rigorously studied in the Bach paper.

We reiterate that assessment of the respiratory rate:tidal volume ratio (RVR) measured during 1 to 2 min of unassisted breathing is the best validated, objective measure of the ability to sustain spontaneous breathing.1-3,,1-4 We know of no data supporting the speculation that patients with neuromuscular disease represent an unusual group for whom the RVR is inaccurate. In our own practice, we routinely use the RVR in patients with Guillain-Barré, myasthenia gravis, amyotrophic lateral sclerosis, and other neuromuscular conditions. Of course, it is possible that different patient groups will exhibit differences in response to assessment for spontaneous breathing, and we would be interested in future studies of these patient subsets. At present, however, the literature does not support a different approach to patients with neuromuscular disease.

Once a patient has demonstrated the ability to breathe free of a ventilator, coma, weakness, excessive secretions, and several other, comorbid conditions may mandate the continued use of an artificial airway. As a separate but contemporaneous assessment, we examine our patients’ gag and cough reflexes (subjectively) and the character of secretions. If the patient can tolerate both liberation and removal of the artificial airway, we proceed swiftly to extubation.

Correspondence to: Constantine A. Manthous, MD, FCCP, Director, Medical Intensive Care Unit, Bridgeport Hospital, 267 Grant Street, PO Box 5000, Bridgeport, CT 06610-0120; e-mail: pcmant@bpthosp.chime.org

References
Manthous, CA, Schmidt, GA, Hall, JB Liberation from mechanical ventilation: a decade of progress.Chest1998;114,886-901. [PubMed] [CrossRef]
 
Bach, JR, Saporito, LR Criteria for extubation and tracheostomy tube removal for patients with ventilatory failure: a different approach to weaning.Chest1996;110,1566-1571. [PubMed]
 
Yang, KL, Tobin, MJ A prospective study of indexes predicting the outcome of trials of weaning from mechanical ventilation.N Engl J Med1991;324,1445-1450. [PubMed]
 
Ely, EW, Baker, AM, Dunagan, DP, et al Effect on the duration of mechanical ventilation of identifying patients capable of breathing spontaneously.N Engl J Med1996;335,1864-1869. [PubMed]
 

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References

Manthous, EA, Schmidt, GA, Hall, JB (1998) Liberation from mechanical ventilation: a decade of progress.Chest114,886-901. [PubMed] [CrossRef]
 
Bach, JR, Saporito, LR Criteria for extubation and tracheostomy tube removal for patients with ventilatory failure: a different approach to weaning.Chest1996;110,1566-1571. [PubMed]
 
Niranjan, V, Bach, JR Noninvasive management of pediatric neuromuscular ventilatory failure.Crit Care Med1998;26,2061-2065. [PubMed]
 
Manthous, CA, Schmidt, GA, Hall, JB Liberation from mechanical ventilation: a decade of progress.Chest1998;114,886-901. [PubMed] [CrossRef]
 
Bach, JR, Saporito, LR Criteria for extubation and tracheostomy tube removal for patients with ventilatory failure: a different approach to weaning.Chest1996;110,1566-1571. [PubMed]
 
Yang, KL, Tobin, MJ A prospective study of indexes predicting the outcome of trials of weaning from mechanical ventilation.N Engl J Med1991;324,1445-1450. [PubMed]
 
Ely, EW, Baker, AM, Dunagan, DP, et al Effect on the duration of mechanical ventilation of identifying patients capable of breathing spontaneously.N Engl J Med1996;335,1864-1869. [PubMed]
 
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