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Hospital Clínico Universitario Universidad de Valencia Valencia, Spain
Correspondence to: Emilio Servera, MD, FCCP, Blasco Ibañez 84, 46021 Valencia, Spain; e-mail: Emilio.Servera{at}uv.es
To the Editor:
We read with interest a recent article in CHEST (July 2002)1 reporting that life could be prolonged for a year or more by providing continuous noninvasive ventilatory support (NIV) for many patients with amyotrophic lateral sclerosis (ALS). It is clear that for NIV to be successful in the long term, airway secretion management must be addressed. In particular, patients too weak to cough out secretions can require and obtain assistance, and thereby avoid the need for tracheotomy. What is surprising is how rarely this point is appreciated in the medical literature. We would like to point out just two examples of this. The Cedarbaum score is an internationally accepted instrument that estimates the functional limitations of patients with ALS.2 However, this functional rating scale did not consider lung hypoventilation until recently and it now mentions only the use of nasal bilevel positive pressure.3 This is clearly grossly inadequate for long-term success in using noninvasive alternatives to tracheostomy, the success of which can depend on the daytime use of mouthpiece ventilation or the intermittent abdominal pressure ventilator driven by portable volume-cycled ventilators.1 4 This classification also completely ignores the patient’s ability to cough, perhaps the most important measure of the success of using NIV. We propose adding a new item, that of staging the cough to the Cedarbaum index (Table 1 ), and are currently studying the relevance of this. Secondly, the British Thoracic Society (BTS)5 has published guidelines for using NIV in managing acute respiratory failure. The BTS has proposed an "audit record" to monitor physiologic and clinical parameters during use of NIV; however, we found that while the audit record noted "excessive secretions" as a reason for the failure of NIV, there was no mention of methods directed to expulsing the secretions. We consider noninvasive airway secretion management as important as noninvasively maintaining alveolar ventilation.1 Failing to maintain clear airways results in increased airway resistance to NIV, patient fatigue, and worsening of the arterial-alveolar oxygen gradient, and can precipitate respiratory failure. We agree with Dr. Bach that the most important cause of failure of NIV for patients with neuromuscular disease is failure to properly assist patients in expulsing airway secretions, and not in failure of the NIV methods themselves. Factors such as secretion quantity, consistency, the extent of any glottic or expiratory muscle impairment, or fixed airway obstruction need to be taken into account. Thus, while the audit record of the BTS guidelines5 might be valid for patients with COPD, it is inappropriate when considering NIV failure for patients with neuromuscular weakness.
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References
* New Jersey Medical School Newark, NJ
Correspondence to: John R. Bach, MD, FCCP, Physical Medicine and Rehabilitation, University Hospital, B-403, 150 Bergen St, Newark, NJ 07103-2406; e-mail: bachjr{at}umdnj.edu
To the Editor:
The letter by Servera and colleagues concerning the inappropriateness of "lumping" patients with neuromuscular weakness in with lung disease patients when assessing success or failure of noninvasive mechanical ventilation (NIV) is absolutely correct. The problem is that cough should be objectively rather than subjectively assessed, and Serveras’ "cough capacity staging" will not do this. It is important to understand that patients with neuromuscular weakness have some combination of weakness of inspiratory, expiratory, and bulbar musculature. Inspiratory and expiratory dysfunction, no matter how severe, can be entirely compensated by using noninvasive inspiratory1 and expiratory2 muscle aids, essentially NIV and mechanically assisted coughing (Cough-Assist; J. H. Emerson; Cambridge, MA); however, when bulbar dysfunction is so severe that continuous aspiration of airway secretions results in persistent oxyhemoglobin desaturation, patients need tracheostomy tubes to survive. Bulbar dysfunction is best assessed by measuring the maximum insufflation capacity/vital capacity difference3 and by measuring assisted cough peak flows (CPFs) via peak flow meters.4 We have found that once assisted CPFs decrease to <300 L/min, that failure to train and equip patients with Duchenne muscular dystrophy in mechanically assisted coughing will usually result in hospitalization for acute respiratory failure within a year.4 Further, patients with completely intact bulbar musculature, such as patients with traumatic tetraplegic, can have assisted CPFs exceed 500 L/m and will not require mechanically assisted coughing despite having little or no vital capacity or autonomous ability to breathe without continuous use of NIV. Thus, objective assessment of CPF is probably the most important parameter in monitoring patients with neuromuscular weakness.
References
This article has been cited by other articles:
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  E. Servera and J. Sancho Appropriate Management of Respiratory Problems Is of Utmost Importance in the Treatment of Patients With Amyotrophic Lateral Sclerosis Chest, June 1, 2005; 127(6): 1879 - 1882. [Full Text] [PDF]
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