Comparing Two Ultrasound-based Methods to Assess Diaphragm Movement

Background and rationale The diaphragm muscle helps to control breathing: upon inhalation, the diaphragm contracts, helping to draw air into the lungs. Air is exhaled when the diaphragm relaxes. Measurement of diaphragmatic movement is an important tool in assessing function of the diaphragm. With the introduction of ultrasound technology to the bedside, the motion of the diaphragm and lungs can be visualized in real time. This affords practitioners the ability to detect when the diaphragm is paralyzed or is not moving properly. For example, the phrenic nerve, which controls diaphragm movement, is often anesthetized during interscalene brachial plexus block. As a result, the diaphragm on the block side is paralyzed, compromising breathing. This can have serious implications for patients who already suffer from respiratory difficulties.

There are several previously described methods for assessing diaphragm movement using ultrasound. The investigators wish to compare two methods to determine which one is more user-friendly and offers the fastest time to measure diaphragm movement. The first method will rely on the ability to identify and image the right and left diaphragms through the acoustic windows of the liver and spleen, respectively, and then record diaphragm movement in M-mode. The second method will rely on the ability to identify the location of the diaphragm by imaging lung sliding, followed by re-orientation of the ultrasound probe to enable measurement of changes in diaphragm thickness with respirations. The investigators hypothesize that, due to the more obvious visibility of the structures involved, the second method will result in more accurate confirmation of diaphragm paralysis.

Study objectives The primary objective is to determine which of two ultrasound-based methods of imaging the diaphragm offers the fastest and easiest way to confirm diaphragm paralysis. A secondary objective is to determine the inter-rater reliability among two individuals using the same scanning method.

Hypothesis The investigators hypothesize that imaging lung sliding with ultrasound followed by diaphragm thickness measurement will be easier and faster for practitioners to detect diaphragm motion/paralysis.

Study procedures Following informed written consent, eligible patients will be recruited in the University of Alberta pre-admission clinic (PAC) or day ward. Once the patient arrives in the block area, a study investigator will scan the patient's diaphragm on both sides using one of the two scanning methods. The scanning method to be used will be determined randomly; the investigator will be given a sealed envelope containing brief instructions on the method of diaphragm imaging to be used. The investigator will scan one side of the patient and then the other side. The order of scanning will be left to the participating investigator. A study team member will record the length of time taken for the investigator to obtain what they deem to be optimal images, which will be saved on the ultrasound machine. Following this, the regional block will be administered.