Diaphragmatic Motion Using Linear Ultrasound

Background:

Multiple pathologies cause diaphragmatic dysfunction, including: respiratory, abdominal and neurological disease. Established clinical tests of diaphragmatic function, include: the transdiaphragmatic pressure, the maximal static inspiratory pressure, the sniff inspiratory pressure, pulmonary function tests, electromyography, a chest radiograph or fluoroscopy.

However ultrasound assessment of diaphragmatic function is a non-invasive, radiation-free technique that has gained traction in clinical practice in recent years. Several different methods have been described, that examine motion in two different areas of the diaphragm, either the zone of apposition, or the dome of the diaphragm, however no one method has emerged as the standard of care.

The current conventional technique (using B-mode or M-mode ultrasound via a phased array or curvilinear probe) in the subcostal region, has several limitations:

• It can be difficult to measure right hemi-diaphragm excursion with deep breathing, with a failure rate of up to 28% described for quantitative assessment.
• It is even more difficult to quantitatively assess left hemi-diaphragmatic excursion with deep breathing, as the spleen provides a smaller window compared to the liver window. Failure rates of 79% and 65% have been reported.
• When using M-mode, the ultrasound beam must image the diaphragmatic excursion line at a perpendicular angle, otherwise reproducibility and accuracy are adversely effected.

The investigators propose a novel method, using linear ultrasound to examine the zone of apposition, and determine diaphragmatic excursion at end inspiration and expiration. In theory this technique may have a number of advantages over the conventional method. It is likely easier to learn, quicker to perform, and has a lower failure rate for imaging the diaphragm on both sides during deep breathing. The investigators will compare this method to the conventional method, i.e. a curvilinear probe as described above.

Hypothesis:

Diaphragmatic motion can be assessed more rapidly, and more reliably via a linear high frequency ultrasound probe, than a curved low frequency probe.

Primary Objective:

• To evaluate the ease and success of using a novel technique of point-of-care ultrasound diaphragm assessment with a linear probe in the mid-axillary line to measure diaphragmatic motion. The ease of procedure will be determined by the time and the number of attempts required to perform the ultrasound assessment.

Secondary Objectives:

• To determine the normal range of diaphragmatic excursion values from full expiration to full inspiration in men and women;
• To quantify the reduction in diaphragmatic motion following phrenic nerve palsy - due to an interscalene, upper trunk or supraclavicular brachial plexus block;
• To compare the finding of diminished diaphragmatic excursion with the conventional method of measurement; i.e. compare the sensitivity and specificity of the tests.
• To analyze the success rate of measuring the left and right hemi-diaphragmatic movement as compared with the conventional method of measurement.

This prospective observational study, will involve patients undergoing elective surgery, and will consist of two phases:

Phase 1:

The first phase will be to evaluate a new lung ultrasound technique to measure diaphragmatic excursion using a linear probe in the mid-axillary line. This will involve scanning 75 healthy patients undergoing elective surgery to determine normal reference values for this technique in men and women.

Phase 2:

The second phase will involve 100 patients who are undergoing an inter-scalene, upper trunk of cervical plexus, or supraclavicular brachial plexus block as part of their perioperative analgesic management for shoulder or arm surgery. This cohort of patient is likely to develop phrenic nerve palsy as a side effect of the brachial plexus block. The resultant phrenic nerve palsy, will result in reduced diaphragmatic motion, and the aim will be to evaluate the ability of using a linear probe technique to measure this reduction as compared to the conventional method of measurement.

Inclusion criteria

Phase 1 Any healthy adult patient undergoing elective surgery

Phase 2 Any adult patient, undergoing elective upper limb surgery that involves an interscalene or supraclavicular brachial plexus block.

Exclusion criteria

(i) Inability to obtain an informed consent (e.g. language barrier) (ii) BMI > 35 (iii) Known pre-existing diaphragmatic dysfunction (iv) Existing lung pathology

• Smoker
• Known abnormal pulmonary function tests
• Severe pulmonary disease e.g., COPD, asthma, pulmonary fibrosis, or any other significant respiratory disease that would adversely affect diaphragm function or pulmonary function tests

Additional Criteria for Phase 2 Any contraindication to an interscalene or supraclavicular brachial plexus block