The Geniohyoid Muscle in Critical Illness

Assessing the Feasibility and Reliability of an Ultrasound-based Method of Measuring the Geniohyoid Muscle in Mechanically Ventilated Patients - an Observational Study

Many patients lose muscle due to being unwell in an intensive care unit. This muscle loss can lead to weakness of the arms and legs when they leave the unit, and when they go home. For many years investigators have measured the size of these arm and leg muscles using an ultrasound machine, to take a picture of the muscles.

It is also known that patients who are on a ventilator (or "breathing machine") often have problems swallowing when the breathing tube is removed from their mouth. This may be because the muscles of swallowing may also shrink. One of these muscles sits under the jaw and can be measured with ultrasound - the method has been shown to be accurate and reliable in awake volunteers, but these volunteers are usually sat upright in a chair with their mouth closed.

Before it can be assed whether these muscles get smaller, it is needed to assess whether the chosen method is suitable in patients on a ventilator; these patients are lying in bed, and their mouths are open slightly due to the breathing tube.

Proposed Method

This investigation will measure the size of a muscle under the jaw (called the geniohyoid muscle) in patients who are sedated and have a breathing tube in their mouth connected to a ventilator.

Using a normal hospital ultrasound machine, one researcher will place the ultrasound probe under the patient's jaw. When the researcher is happy the probe is in the right place, they will take a picture of the muscle and measure its size and thickness. After a short break, the researcher will repeat this process. After a second short break, another researcher who did not watch the first researcher will also place the probe under the jaw and take a picture of the muscle.

These measurements can be used to to answer the following questions:

1. How many patients scanned produced images that could be measured?
2. How consistent are the measurements if one person measures the same muscle twice?
3. If two people measure the same muscle, do their measurements agree with each other?

The patients will be under sedation when they take part in the study. Because of this, they cannot consent to take part in the study. The patient's next of kin or carer would advise on whether the patient would want to take part. When the patient is awake and has the breathing tube removed, the research team would ask them to sign a consent form to use their data.

Introduction

Many patients who are mechanically ventilated due to critical illness have difficulty in swallowing after the endotracheal tube is removed, a phenomenon known as Post Extubation Dsyphagia (PED). Although multifactorial, atrophy of the swallowing muscles is a potential cause.

Ultrasound is a commonly used investigative modality for the measurement of muscles in critically unwell patients. Measurements can be performed repeatedly over time to track changes in muscle size during the course of a patient's admission. In critically unwell patients, much of the research is focussed on muscles of the limbs and trunk. The muscles of swallowing have been measured using ultrasound, but in awake patients adopting an optimal seated position. Critically unwell patients are bedbound, and the endotracheal tube leaves their mouth in an open position. Before embarking on a study using ultrasound to attempt to track changes in muscle size in the muscles of swallowing, the investigators first wish to assess if such a method is both feasible and reliable.

Methods

Critically unwell patients who are sedated and mechanically ventilated will be recruited into the study after discussion with a patient's personal consultee. The geniohyoid (GH) muscle will be scanned in both the coronal and sagittal planes. The patient will be scanned three times. Twice by one assessor, and once by a second assessor. Cross sectional areas (CSA) of GH will be measured at a later time using image processing software (ImageJ, NIH, USA). Echogenicity, a measurement of the brightness of muscle on ultrasound, will also be assessed.

Results

The primary outcome is to obtain the proportion of patients whose images from ultrasound can provide satisfactory measurement data, in each plane. Furthermore, we will assess the repeatability of each measurement by calculating the intra-rater agreement, and the inter-rater agreement to assess agreement between assessors. An estimate of the mean CSA in each plane will be calculated.

Conclusions

This preliminary data will give us an estimate of the proportion of patients who can provide satisfactory images of GH, in preparation for a larger study assessing longitudinal changes in CSA. Further, the study will give data on both the inter- and intra-rather agreement of the method.

Inclusion Criteria:

• · Mechanically ventilated patient on the intensive care unit

  • Endotracheal tube via the mouth in-situ (size 7.0 and above)
  • Can be recruited at any time during their admission

Exclusion Criteria:

• · Ventilated via a nasal endotracheal tube

  • Ventilated via a tracheostomy
  • Ventilated via a micro-endotracheal tube
  • Any previous or active history of head and neck cancer
  • Any previous head and neck surgery (excluding tonsillectomy and adenoidectomy)
  • Any cranio-facial deformity that would render access to the jaw difficult, including but not limited to short thymo-mental distance
  • Any neuromuscular disorder, including previous stroke
  • Any previous history of dysphagia or swallowing disorder
  • Pregnant patients
  • Patients under 18 years of age
  • Agitation or movement that would make measurement difficult or inaccurate