Characterisation of manual chest physiotherapy and respiratory response in mechanically ventilated children

Abstract

Chest physiotherapy is integral to the management of mechanically ventilated children and previous research has confirmed that chest wall vibrations are the manual techniques used most frequently by physiotherapists in this population. Chest wall vibrations involve the application of a compressive force to the chest during expiration, with the aim of removing accumulated secretions and improving lung aeration. However, these techniques are largely unquantified and may vary greatly between practitioners and clinical units, with any significance of such variability remaining unknown.
In order to evaluate the effectiveness of any therapy it is important to have a means of quantifying the treatment. It is challenging to measure techniques which involve manual contact between the therapist and patient, and at the inception of this project no means existed of directly measuring the force applied through the hand during treatments. The effectiveness of chest physiotherapy in mechanically ventilated patients is likely to be influenced by the interactions between different treatment components, such as the magnitude and pattern of the chest wall vibrations and the accompanying lung inflations. It is therefore essential to assess both the forces applied during the vibrations with the simultaneous changes in air flow, recording the ventilatory pattern throughout the treatment.
The study hypotheses were:
1. It is possible to create a technique to measure chest wall vibration forces during clinical treatments, and to relate such forces to simultaneous changes in respiratory flows, volumes and pressures
2. Maximum and mean force applied during chest wall vibrations increase with the size and age of the child
3. Manual lung hyperinflations with chest wall vibrations result in an increase in peak expiratory flow above that observed during baseline mechanical ventilation
4. After adjusting for inflation volume, application of chest wall vibrations result in an increase in peak expiratory flow above that obtained during manual lung inflations alone
The primary objectives of this research were to:
1. Develop a method of quantifying chest wall vibration forces and a means of evaluating simultaneous changes in force with those of respiratory flow and pressure in ventilated infants and children of all ages
2. Estimate the variability over time, within and between individual physiotherapists when treating the same and different subjects with chest wall vibrations
3. Conduct a study to:
i) Assess the feasibility of measuring force and respiration in a population of critically ill, mechanically ventilated children
ii) Characterise the magnitude and pattern of forces applied during chest wall vibrations and evaluate the direct effects of these manoeuvres on flow and pressure changes in the lungs
iii) Determine the relative contribution of manual lung inflations and chest wall vibrations to any observed increase in expiratory airflow A secondary objective was to explore the short term effects of chest physiotherapy, by recording changes in ventilation, respiratory system mechanics and blood gases following treatment.
The thesis comprises four chapters:
Chapter 1 contains a comprehensive literature review of published studies demonstrating the current knowledge base of the respiratory problems of mechanical ventilation in children, chest physiotherapy in intensive care and the relationship of chest physiotherapy to normal mechanisms of airway clearance.
Chapter 2 describes the process of creating a dynamic force-sensing technique to characterise manual chest physiotherapy, detailing protocol and analysis refinement during pilot force and respiratory data collection. Assessment of the variability within and between physiotherapists is also assessed.
Chapter 3 details a clinical study undertaken in intensive care units at Great Ormond Street Hospital for Children NHS Trust, London. The results are presented and interpreted.
Chapter 4 discusses the findings of the thesis in relation to earlier research, highlights the strengths and limitations of the current study, interprets the clinical implications of the research and suggests future work.

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