Concordance of Methods to Select Tracheostomy Tube Size for Adults in Intensive Care

1. INTRODUCTION This piece of research constitutes one of four workstreams in an NIHR funded PhD programme of work. The overall aims of the PhD project are 1) to create guidance for Health Care Professionals (HCPs) on how to select the right size tracheostomy tube (TT) for patients in an intensive care unit (ICU), and 2) to identify ways to best ensure that HCPs follow the guidance. This protocol is for Workstream 2. In this workstream we will calculate tube size recommendations for each participant using five methods:

• four using sets of criteria that replicate current practice and relate to physical characteristics (sex, shoulder width, height and Body Mass Index)
• a recommended set of criteria based on measurements of tracheal width We will then calculate concordance (%) between tube size recommendations based on tracheal measurements and those based on other physical characteristics. Secondary analysis will determine strength of correlation between tracheal diameter and height, shoulder width, age, sex, Body Mass Index and ethnicity. The findings will provide evidence for clinicians on how the fit of a tracheostomy tube within the trachea may be affected by the size-selection criteria used. This study in isolation is not intended to provide definitive clinical recommendations regarding the selection of tracheostomy tube size, since this also requires knowledge of 1) the impact of tube size on airflow through and around tracheostomy tubes and 2) what is important to patients in terms of functional effects of size of tube. These two issues are the focus of other workstreams within the larger programme of work.

1. BACKGROUND AND RATIONALE Tracheostomy tubes (TT) are breathing tubes that are surgically inserted through the front of the neck. They can:

• allow easier breathing for patients with upper airway obstruction
• provide access to the lungs to clear secretions
• facilitate longer term use of artificial breathing machines (mechanical ventilation, MV) by replacing breathing tubes that go through the mouth
• help patients to be liberated from MV There are an estimated 12,000 tracheostomy insertions a year in England and the majority of these occur in intensive care units (ICUs). There are a number of widely used reference guidelines addressing the general management of patients with a TT. These state that a clinician should consider the size of the TT prior to insertion, but do not fully describe how to select the correct size. In practice, methods of selecting tracheostomy tube vary widely and decisions are often made on the basis of a patient's sex or perceived size. TTs that are the wrong size can cause physical and psychological harm. If the TT is too small there is a risk of a leak around the tracheostomy cuff (a ring-shaped balloon around the tube), leading to difficulty using MV, and aspiration of saliva or stomach contents into the lungs. Over-inflation of TT cuff in an attempt to compensate for the TT being too small can cause long-term damage to the trachea. If the TT is too big there is risk of trauma to the skin around the hole in the neck and to the trachea, and a patient is unlikely to be able to use a speaking valve to talk. In TTs that are too big or small, the tip may abut the anterior or posterior tracheal wall, causing trauma and difficulty breathing around or through it respectively. Any trauma to the tracheal wall or insertion site can lead to narrowing of the airway called tracheal stenosis. The consequences of this range from mild breathing difficulties through to complete blockage of the airway. Treatment for tracheal stenosis ranges from balloon dilatation to major reconstructive surgery and can cause a heavy burden to patients and the health services. Good decision-making regarding size of TT may reduce the incidence of tracheal stenosis and associated financial costs of treatment or increased levels of care. If the TT is too big, a patient is unlikely to be able to talk. Not being able to talk is highly stressful for patients on ICU. It can lead to treatment decisions being delayed or made by others on behalf of the patient, and has been linked with increased levels of anxiety and depression and the development of delirium and post-traumatic stress disorder. There is mixed evidence to support correlation between anthropometrics and tracheal dimensions. A few observational cohort studies have sought to establish normative data for tracheal dimensions, some comparing these with sex, height, or weight. Evidence from a paediatric study supports a correlation between height and tracheal dimensions in children. The literature on adults is inconclusive. No studies to date have investigated a potential correlation between shoulder width and tracheal diameter. Tracheal width in men, like shoulder width, continues to grow beyond the point when full stature is achieved, and has been proposed as a cause for a non-linear relationship between height and tracheal width found in some studies. 'Patient size' is commonly used in tracheostomy tube decisions. Height, shoulder width and BMI are used in this study as surrogates for patient size. Ultrasound is increasingly being used to assess the airway and has shown strong correlation with measurements taken from computed tomography (CT) and magnetic resonance imaging (MRI). Ultrasound has the benefits over other measurement techniques of being non-invasive, not requiring radiation exposure and being relatively inexpensive.

1. OBJECTIVES 3.1 Primary Objective To determine the concordance between a tracheal diameter-based standard for selecting tracheostomy tube size and sets of criteria based on sex, height, shoulder-width and BMI in an adult population. 3.2 Secondary Objectives To estimate the association between tracheal width and standing height, shoulder width, ethnicity, age, sex and other demographic characteristics in an adult population.
2. STUDY DESIGN Type of Study: cross-sectional observational study Population: Adult inpatients, outpatients and hospital staff at the Royal Free London NHS Foundation Trust. Prisoners, patients and staff who are pregnant, those with severe deformity of the spine and patients lacking mental capacity to consent will be excluded. Duration of enrolment: One appointment of 45-60 minutes. No follow-up required. Sample size: a sample of 114 participants will provide 90% power to detect a concordance of 65% (null hypothesis = 50%) between methods of selecting tracheostomy tube size, with a 1-sided significance level of 2.5%. Statistical Analysis: Analysis of concordance will be used to evaluate the level of agreement between methods to select size of tracheal tube using 1. tracheal width as measured using ultrasound 2. other physical characteristics (sex, height, shoulder width, BMI) Concordance will be expressed as proportion (%) of agreement. Univariate and multivariate linear regression analysis will be used to evaluate the association between tracheal width and standing height, shoulder width, ethnicity, age, sex and other demographic characteristics.
3. STUDY SCHEDULE We will advertise the study via flyers, posters, staff communications and word of mouth. Patients will be enrolled following screening and consent procedures outlined below.

The research appointment will last approximately 45 - 60 minutes and include:

• Consent procedures including time for questions
• Brief interview and collection of demographic and clinical data
• Hospital number - (for patients only)
• Sex
• Age
• Ethnicity
• Height
• History of airway disease or surgery (including tracheostomy) or severe kyphosis of the spine
• Major medical or surgical history will be recorded in order to provide context to clinicians reading the findings and enable them to judge applicability to their patient populations
• Measurement of weight
• Measurement of height
• Measurement of shoulder width
• Ultrasound measurement of the width of the trachea (windpipe)
• BMI will be calculated using height and weight

The following process measures will also be taken:

• Time taken to obtain measurements of the trachea
• Inter and intra-rater reliability for measurements of the trachea This information is of interest in the wider PhD programme of work. It will be presented to the Clinical Steering Committee as an indication of 1) how much time measuring the trachea would add to a tracheostomy insertion procedure and 2) accuracy of measurements.

No follow up is required after the initial research appointment. Participants may withdraw at any point up until the end of the data collection appointment. They do not have to give a reason for withdrawing and will be given assurance that their care (patients) or employment (staff) will not be affected by withdrawing. Data already collected will be kept and analysed.

The study will end when data for 114 participants have been recorded and the results described and analysed in the final study report.