Misconceptions in the assessment of cough peak flow measurements for extubation or decanulation protocols
M.. Chioua,, , J.R.. Bacha, M.R.. Gonçalvesb, L.. Vudayagiria
a Department of Physical Medicine and Rehabilitation, Rutgers New Jersey Medical School, Newark, NJ, USA
b Department of Pulmonology, University Hospital of S. Jo��o, Faculty of Medicine, University of Porto, Portugal

Dear Editor,

Winck et al. proposed routine use of cough peak flow (CPF) measurements in the assessment of extubation and decanulation readiness.1 However, intubated patients cannot cough because they cannot close their glottis to hold pressure, and the paper the authors cited suggesting that 90 L/m predicts successful extubation2 is irrelevant for patients with neuromuscular respiratory muscle weakness since they can almost always be successfully extubated even when their unassisted CPF and vital capacities are unmeasurable.3, 4 The paper that the authors referred to that used 160 L/m as a reference reported the need for maximum unassisted or assisted CPF to reach 160 L/m after extubation.5 Assisted CPFs are attained by patients air stacking to the maximum lung volumes that can be held by the glottis and then an abdominal thrust is applied to generate CPF.6 It is the maximum flow that can be generated through the upper airways that is important and not whether the patient can generate that flow him/herself because the greater the flow, the greater the patency of the airways, and the more effective mechanical insufflation–exsufflation (MIE) will be in eliminating airway secretions via an oronasal interface once the tube is out.4 Thus, the distinction between unassisted and assisted CPF is important. The fact is that in a recent report, many patients (e.g. babies with spinal muscular atrophy type 1) could generate no measurable flows via the upper airway, but were almost invariably successfully extubated anyway because following extubation, MIE generated effective flows to clear the airways.4

Decanulation protocols begin by transitioning from cuffed to cuffless fenestrated tracheostomy tubes or tracheostomy buttons so that the patient can practice CNVS and MIE and speak without the tube obstructing the upper airways. Failure to permit verbal communication almost invariably results in severe reactive depression.7 The first step in the process of decannulation to noninvasive management is cuff deflation. We have seen numerous other tragic examples of failure to deflate the cuff, and this has been reported.7 Switching patients to cuffless fenestrated tubes does not always clear the upper airway sufficiently to use NVS comfortably because the fenestration can abut against the back wall of the trachea rather than be in the airway. When there is obstruction to the tube, the NVS backs up into the patient's cheeks. Tracheostomy buttons can eliminate this problem by clearing the airway of the tube so that air can leak up through the vocal cords for speech, and the leak is compensated by increasing ventilator settings to maintain normal alveolar ventilation.

Conflicts of interest

The authors have no conflicts of interest to declare.

Corresponding author. chioumi@njms.rutgers.edu

Bibliography
1
The value of cough peak flow measurements in the assessment of extubation or decannulation readiness. Rev Port Pneumol. 2015; 21:94-8.
2
Cough peak flows and extubation outcomes. Chest. 2003; 124(1):262-8.
3
Extubation of unweanable patients with neuromuscular weakness: a new management paradigm. Chest. 2010; 137(5):1033-9.
4
Efficacy of mechanical insufflation–exsufflation in extubating unweanable subjects with restrictive pulmonary disorders. Respir Care. 2015; 60(4):477-483.5.
5
Criteria for extubation and tracheostomy tube removal for patients with ventilatory failure. A different approach to weaning. Chest. 1996; 110:1566-71.
6
Maximum insufflation capacity: vital capacity and cough flows in neuromuscular disease. Am J Phys Med Rehabil. 2000; 79(3):222-7.
7
Cuff deflation: rehabilitation in critical care. Am J Phys Med Rehabil. 2014; 93(8):719-23.

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