Innovations in Mechanical In-Exsufflation: Past, Present & Future
As part of our ongoing commitment to education, Breas Medical were proud to sponsor two symposia at the 2018 JIVD conference in Lyon. It is our belief that innovation stems from understanding the real-world problems in treating re-spiratory disorders. Through our continued support to pro-vide free education to respiratory clinicians, Breas aim to improve outcomes for patients from hospital to home.Mechanical insufflation-exsufflation (MI-E), or cough assist devices have been around for many years. Today, not only has the environment in which these devices are used changed, but the patient groups are also changing as there is a greater clinical understanding of optimal settings.This symposium looked back at the history of MI-E, its cur-rent use and innovations in use and technology through the eyes of world leading experts.Delegates’ ideas concerning the application of MI-E are chal-lenged with a disregard for convention and focus on scien-tific techniques in order to resolve the challenges of using these devices with both conventional and complex patient groups to ultimately optimise patient outcomes.
Introduction to History of MI-E and its future – John Bach
In his summary of the history of cough aug-mentation and airway clearance over the last 70 years, Dr Bach referred to the first polio out-break where airway secretions were managed which reduced mortality rates and the need for tracheostomy. He discussed the practice of tilting an iron lung to create positive pressure, an early form of MI-E, and led on to the development of MI-E devices across the decades.
He reported a key misunderstanding between mmHg and cmH₂O when measuring airway pressures. Early studies reported 40mmHg was an appropriate level of inspiratory pressure; this was conse-quently applied in clinical practice, despite many modern devices measuring pressure in cmH₂O. 40mmHg equates to 54cmH₂O, therefore many MI-E devices were being used ineffectively until this was recently understood.
Dr Bach provides evidence for using Non-invasive Positive Pres-sure Ventilatory support or Mouthpiece ventilation in conjunction with MI-E for dependent patients as an alternative to tracheostomy (Bach, Alba and Saporito, 1993). He also describes the role of this method of ventilation following a period of intubation (Bach, Za-niewski and Lee, 1990) and referred to a case series of patients who had no spontaneous breathing ability but were successfully extu-bated using an oximetry /CNVS / MI-E protocol (Bach, Gonçalves et al, Chest 2010).
What have we learnt from the bench tests of MI-E devices with regards to MI-E settings? – Michelle Chatwin
Dr Chatwin reports on the wide variation of MI-E settings used by clinicians and describes some bench test studies that may help inform practice. However, we are reminded that each patient is different and there is no “one size fits all”. Furthermore, the dynamics are different across the range of MI-E devices, there-fore an individual approach and clinical assessment are required.
Dr Chatwin recommended that to achieve alveolar insufflation, it is necessary to set the Ti > 1 second and to set the exsufflation pressure greater than the insufflation pressure, even in children, in order to produce a greater change in expiratory flow (Striegl etal 2011). It is also important to note that when MI-E is used with endotracheal tubes or tracheostomy interfaces, higher insufflation and exsufflation pressures are required to produce effective peak expiratory flow.
Implication of High Pressure Mechanical In-Exsufflation – Dr Patrick Murphy
Dr Murphy began with a reminder that MI-E aims to mimic natural cough, which can gener-ate pressures of > 200cmH₂O and flows of >12L/sec. Generating high pressure itself is not the aim; the ultimate aim is to increase expiratory flow to clear the airways. If high pressures do not increase expirato-ry flow, then it is not an appropriate strategy.
He referred to some of the negative effects caused by use of high pressures including altered cough mechanics, abnormal laryngeal movement and poor patient tolerance. However, Dr Murphy also added that if high pressures are required, some of the negative effects can be countered with post treatment re-insufflation breaths.
To provide further evidence on this topic, Dr Murphy presented data from a study of 10 patients with Duchenne Muscular Dystro-phy (Shah et al 2017) where EIT (Electrical Impedance Tomogra-phy) was used to measure quantification of lung recruitment and regional ventilation following MI-E. Both high and low pressures were shown to produce clinically relevant expiratory flows with sig-nificant off-loading of respiratory muscles.
When to use low pressures? – Tiina Andersen
Tiina began by reviewing the anatomy of the upper airways and led on to show the differ-ence in response to MI-E between a healthy cough and that of a bulbar MND/ALS pa-tient. In bulbar MND, supraglottic closure occurs during insufflation, resulting in inadequate insufflation delivery. However, it was found that aryepiglottic fold adduc-tion during insufflation managed to keep these structures more open with positive pressures of 20-30cmH₂O. In the study, asymmetric treatment pressures with lower insufflation pres-sures and flows, provided less adduction in the larynx; both at supra-glottic and glottic level (Andersen et al, 2018). Tiina presented the need to fine-tune insufflation settings: ensure the patient triggers each insufflation, decrease insufflation flow and insufflation pressure, and increase insufflation time.
Is there a role for MI-E in intubated patients for weaning and extubation? – Miguel Gonçalves
Dr Gonçalves noted that patients in the inten-sive care setting often have impaired airway clearance and referred to studies showing the importance of cough strength and the amount of secretions for a successful extubation. Conventional manage-ment of respiratory secretions in patients with an artificial airway, endotracheal tube or tracheostomy tube is transtracheal suctioning with a catheter. This fails to enter the left main stem bronchus more than 90% of the time and secretions in peripheral airways are not directly removed. In contrast, when MI-E is used through an inva-sive interface, it mobilises secretions from the medium and small bronchi in addition to clearing the central airways and both left and the right main stem bronchus.
Secretion management with MI-E may work as a useful comple-mentary technique to prevent reintubation in patients in whom acute respiratory failure develops in the first 48 hours after ex-tubation. This suggests MI-E is safe and efficient in critical care patients. It has been proven in an RCT that the re-intubation rates related to NIV failure were significantly lower in the group using MI-E when compared with controls not using MI-E (Goncalves et al. Crit Care 2012).
To successfully wean patients, Miguel suggests extubating directly to NIV with frequent use of MI-E. Mouthpiece ventilation can also be added to enable the patient to control weaning.
Innovation in acute care – Rachael Moses
Rachael’s presentation raised several discussion points: patients who are difficult to wean, the use of innovative approaches to support decan-nulation and the use of laryngoscopy during NIV and MI-E as an indicator of airway stability. Rachael gave direct visualisation as to why there is resistance to weaning from a clinician’s perspective: the impression that people don’t know how to wean, because it’s easier not to wean and be-cause tracheostomy patients generate more money.
To demonstrate the success of weaning techniques, Rachael pro-vided three case studies. The first saw the use of MI-E for wean-ing / decannulation whereby MI-E was used > 8 times a day for 25 days. In the second case, subglottic oxygen entrainment was used to increase vocalisation which also helped to promote laryngeal flow gradually and also reduced hyper sensitivity in the larynx. In the final case study, High Flow Nasal Oxygen (HFNO) was used for weaning in the critical care setting which was shown to splint the upper airway and reduce dead space.
Overall, the key points from this symposium focused on the impor-tance of patient-centred care, a tailored approach and consider-ation of these new, innovative techniques to achieve the best result for your patient.
