By Terrence Shenfield, MS, RRT-ACCS, RPFT, NPS, AE-C
Efficient airway clearance is critical for maintaining respiratory health, particularly in patients with weakened respiratory muscles due to conditions like neuromuscular disorders or mechanical ventilation. Among the arsenal of airway clearance techniques available to respiratory therapists, Mechanical Insufflation-Exsufflation (MI-E) stands out as a vital tool.
This guide will provide an in-depth exploration of MI-E, theories behind its use, practical applications, and its optimization as a part of airway clearance techniques for respiratory therapists.
What is Mechanical Insufflation-Exsufflation?
Mechanical Insufflation-Exsufflation (MI-E) is a cough augmentation technique used to assist individuals unable to generate an effective cough. MI-E involves two primary phases:
Insufflation delivers positive pressure to inflate the lungs.
Exsufflation applies rapid negative pressure to simulate a strong cough effort.
MI-E devices are especially beneficial for airway clearance with MIE devices in patients with neuromuscular disorders, impaired respiratory muscle function, or secretion retention secondary to weak cough mechanisms.
Why Airway Clearance is Crucial
Respiratory secretions are typically cleared through natural airway expansion and contraction during breathing, assisted by the mucociliary escalator. However, patients with weakened cough mechanisms, whether due to lung disease or neuromuscular impairment, often face secretion retention that can lead to severe complications, including infection, hypoxia, or respiratory failure.
Airway clearance techniques for respiratory therapists, especially using devices like MI-E, can bridge the gap for patients struggling with secretion mobilization.
Who Benefits from MI-E?
Neuromuscular Disorders
Patients with ALS, Duchenne muscular dystrophy, or spinal muscular atrophy often lack the muscular strength required for effective coughing. MI-E enables these patients to clear secretions effectively, reducing the risk of infections.
Mechanical Ventilation
Patients who are intubated or on mechanical ventilation face challenges in clearing secretions due to limited natural airflow and coughing capabilities. MI-E offers a non-invasive means of airway clearance in these contexts.
Other Conditions
MI-E usage has extended beyond neuromuscular disorders to patients suffering from weak cough mechanisms caused by other chronic or acute diseases, demonstrating its versatility.
Steps to Perform a Cough Assessment
Before initiating MI-E therapy, assessing the patient’s cough function is vital. A normal cough consists of four phases:
Deep Inspiration
Glottic Closure
Building of Intrathoracic Pressure
Forceful Expulsion
A visual and auditory assessment can provide preliminary insights. Measuring unassisted Cough Peak Flow (CPF) further quantifies cough strength. A pediatric peak flow meter attached to a mask works effectively for this purpose.
CPF < 160 L/min indicates impaired natural clearance.
CPF > 270 L/min is indicative of a stronger, effective cough.
The Process of MI-E Application
Setting Up MI-E for Clinical Use
MI-E devices are non-invasive and connect to the patient via a face mask, tracheostomy, or endotracheal tube. Newer devices offer customizable pressure and time settings, as well as oscillatory vibrations to optimize secretion clearance.
Pressure Settings aim to generate sufficient peak expiratory flow. These typically range from +/- 30 cmH2O to +/- 50 cmH2O, but tailoring to patient-specific needs improves efficacy.
Interface Matters as the integrity of the face mask or tubing impacts therapy outcomes.
Potential Limitations
Laryngeal dysfunction (often seen in patients with bulbar involvement) may result in glottic closure during exsufflation. For such cases, transnasal fiberoptic laryngoscopy can evaluate laryngeal response, guiding pressure adjustments to prevent airway collapse.
Electrical impedance tomography can additionally offer monitoring to assess MI-E efficacy during therapy for enhanced customization.
Benefits of MI-E in Airway Clearance
Enhanced Cough Strength
MI-E amplifies the force of air expelled during cough, effectively loosening and ejecting deep-seated secretions.
Reduced Mortality and Morbidity
Expelling retained secretions prevents infection and hypoxia, major contributors to patient morbidity.
Non-Invasive Approach
Compared to invasive suction techniques, MI-E comfortably augments cough without causing undue discomfort.
Improved Patient Quality of Life
Routine MI-E sessions decrease hospitalizations and respiratory complications, allowing patients to live more independently.
Evolving Device Features
Recent advancements in MI-E devices include oscillatory vibrations, aimed at mobilizing thick, adherent secretions. However, studies suggest limited evidence to support the routine use of oscillation. Hence, respiratory therapists should use discretion when applying these additional features.
Optimizing Airway Clearance with MI-E Devices
Therapists play a pivotal role in optimizing MI-E therapy. Key considerations include:
Selecting the right interface for minimal air leakage.
Evaluating patient tolerance to ensure overall comfort during therapy.
Tailoring pressure settings to achieve a balance between effective clearance and patient safety.
Challenges and Areas for Future Research
While MI-E has demonstrated efficacy in managing secretion retention, much of the supporting evidence stems from small, single-center studies. Broad, multicenter trials are necessary to establish universally accepted pressure and timing protocols.
Additionally, investigating the role of technologies like electrical impedance tomography during MI-E could further refine its application. Such innovations may allow therapists to monitor therapy success more effectively.
Learning Resources
Expand your expertise in adult critical care and airway clearance techniques for respiratory therapists by exploring valuable resources available at A&T Respiratory Lectures.
Practical Demonstration of MI-E
For a detailed demonstration of how to employ MI-E devices clinically, watch this practical video tutorial by Terrence Shenfield on YouTube.
Integrating MI-E into Your Practice
Respiratory therapists have a growing arsenal of tools to combat secretion retention. Incorporating MI-E into airway clearance techniques allows therapists to provide comprehensive care to patients with diverse respiratory needs.
By understanding the nuances of its application, tailoring therapy to individual patient needs, and staying updated through continuous education, respiratory therapists can maximize therapy outcomes and improve overall patient well-being.
References to Expand Your Knowledge
Explore more critical care insights at A&T Respiratory Lectures.
Watch clinical best practices in action on YouTube.
Empower yourself with knowledge and refine your skills as a respiratory therapist today!