Mechanically assisted coughing

Chest physiotherapy MH Percusssion/vibration Manually or mechanically assisted cough suctioning... 

When the VC is <50% predicted or MIP is <30% predicted, daytime ABG should be checked (46). Since accurate devices for measuring Pa02 and Paco2 noninvasively are now available, this is the recommended standard practice. Daytime Sa02 <95% may be associated with inspiratory or expiratory muscles, or bulbar dysfunction (10). In ALS, when the Sa02 cannot be normalized by NIV and mechanically assisted cough, a tracheostomy should be performed, if the bulbar dysfunction is severe (10). 

Bulbar muscle dysfunction should he evaluated in all patients with ALS. Apart from rating scales like the ALSFRS (101), one of the best ways to measure muscle dysfunction objectively is by comparing the MIC with the VC and the PEF with the PCF. The wider the gradient, the better the hulhar function (33,35). Bach has shown that in ALS, the ahdity to generate assisted PCF > 180 L/min and to have a high MIC to VC difference is associated with the capacity to use continuous NIV (36). However, when strictly tailored NIV and mechanically assisted cough do not prevent oxygen desaturation below 95%, aspiration is likely and tracheostomy should be offered (10). 

The issue of secretion management is addressed elsewhere in this text. However, mechanically assisted cough is an essential complement of NIV and a key to successful fulltime NIV (97). 

Because of their young age, intact mental status, and bulbar musculature, high-level tetraplegic patients are perfect candidates for NIV (136). Patients with lesions below Cl can be managed with NIV, respiratory aids, and manual plus mechanically assisted coughing, provided their assisted PCF > 160 L/min (98). 

Gomez-Merino E, Bach JR. Duchenne muscular dystrophy prolongation of life by noninvasive ventilation and mechanically assisted coughing. Am J Phys Med Rehabil 2002 81(6) 411-415. 

Airway secretions must be manageable, with suctioning or mechanically assisted coughing (7). The ability to clear secretions will influence the choice of tracheostomy or the decision to use NIV. 

Except after a meal, an abdominal thrust is applied in conjunction with the insufflation-exsufflation mechanically assisted coughing (MAC) (66). MI-E can be provided via an oronasal mask (Eig. 11), a simple mouthpiece, or via a translaryngeal or tracheostomy tube. When delivered via the latter, the cuff, when present, should be inflated (73). 

Mechanically assisted coughing used via the invasive tube up to every few minutes as needed to fully expand and quickly empty the lungs to reverse oxyhemoglobin desaturation due to airway mucus accumulation when baseline Spc>2 decreases, when there is auscultatory evidence of secretion accumulation, and on patient demand. Tube and upper airway are suctioned following use of expiratory aids. 

Abbreviations-. Sp02, saturation of oxygen in arterial blood NIPPV, noninvasive intermittent positive pressure ventilation MAC, mechanically assisted cough CO2, carbon dioxide IPAP, inspiratory positive airway pressure BiPAP, bi-level positive airway pressure. 

Secretion clearance is addressed in detail elsewhere in the text. However, physical therapy and careful hydration are the cornerstones of management. Mucupurulent secretions are often noted in acute respiratory failure. Administration of acetylcysteine 600 mg/day will decrease sputum viscosity hut its value in NIV patients has been less well studied. In patients with NMD, manually assisted coughing, air stacking, and mechanical devices can all be used in patients with a facial mask. On rare occasions, bronchial lavage under local anesthesia can be carried out during NIV. Secretion clearance reduces the ventilation pressures required to overcome the impedance to airflow. 

In this chapter we will discuss recommendations from the hterature regarding dec-aruiulation as well as our personal clinical experience. We will comment on the pathophysiology of ventilator dependence, the determination of candidates for weaning from ventilation and tracheostomy, and a stepwise approach to decannulation. Lastly, we will discuss the choices of noninvasive ventilatory supports and techniques that clinicians may utilize, such as lung volume recruitment (LVR), assisted coughing and mechanical airway clearance. 

Sivasothy P, Brown L, Smith IE, et al. 2001. Effects of manually assisted cough and mechanical insufflation on cough flow of normal subjects, patients with chronic obstructive pulmonary disease (COPD), and patients with respiratory muscle weakness. Thorax 56 438 44. 

Whereas the mucociliary elevator is the primary mechanism for clearing the peripheral 21 divisions of the airway, coughing clears the most central 6 divisions. Chest percussion and vibration can help mobilize peripheral airway secretions but they are not substitutes for coughing and, unlike for assisted coughing, have never been shown to decrease pulmonary morbidity and mortality. Cough can be assisted by manual and mechanical means. 

It is useful to define the disease category in order to predict the natural history and specific intervention. It is well known that patients with primarily restrictive disorders can have both inspiratory and expiratory muscle weakness, and apart from noninvasive ventilation (NIV), they also need cough assistance (4,5). On the other hand, patients with obstructive disorders rarely need mechanical expiratory aids except when they have a severe infectious exacerbation at which time difficulties in clearing copious secretions can occur (4,6,7). 

Bach JR. Mechanical insufflation-exsufflation. Comparison of peak expiratory flows with manually assisted and unassisted coughing techniques. Chest 1993 104(5) 1553-1562. 

Techniques for controlling and assisting the mobilization of secretions from the airways have long been advocated for use in the patient with impairment in mucociliary clearance or an ineffective cough mechanism. The goals of this therapy are to reduee airway obstruction, improve mucociliary clearance and ventilation, and optimize gas exehange. 

Mechanical insufflator-exsufflators (Cough-Assist, J. H. Emerson Co., Cambridge, Massachusettes, U.S.A.) deliver deep insufflations (at positive pressures of 30 to 50 cmH20) followed immediately by deep exsufflations (at negative pressures of -30 to -50 cmH20). The insufflation and exsufflation pressures and delivery times are independently adjustable (71). With an inspiratory time of two seconds and an expiratory time of three seconds, there exists a very good correlation between the pressures used and the flows obtained (72). 

Respiratory muscle assistance involves the manual or mechanical application of forces to the body or pressure changes to the airway to assist inspiratory or expiratory muscle function. Negative pressure applied to the airway during expiration assists the expiratory muscles for coughing, just as positive pressure applied to the airway during inhalation (noninvasive IPPV) assists inspiratory function. 

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