Inferior Vena Cava (IVC) Diameters Before & After Interscalene Block

Evaluating the Mechanism of Changes to Inferior Vena Cava Diameter Using Point of Care Ultrasound in Patients Undergoing Interscalene Brachial Plexus Block

The purpose of this study is to understand how changes to breathing patterns in the chest affect blood flow to the heart from the inferior vena cava in the abdomen. Ultrasound of the upper abdomen will be used to visualize changes in breathing patterns in the chest and blood flow in the abdomen.

In recent practice, point-of-care ultrasound has been used to assess the size and respiratory variation of the inferior vena cava as a marker for volume status and fluid responsiveness. Little investigation has occurred regarding the mechanism of observed respiratory variation. Anesthetic plans for surgery (e.g. shoulder replacement) frequently employ interscalene injections to target and block the brachial plexus, which (on the same side) results in phrenic nerve palsy and paralysis of the diaphragm. The goal of this study is to examine the relationship between diaphragmatic function and variation in IVC diameter. Specifically, the investigators will evaluate and compare the size and variability of the inferior vena cava by point-of-care ultrasound before and after brachial plexus block.

Inclusion Criteria:

• Adult (age > 18 years)
• Scheduled to receive an interscalene block

Exclusion Criteria:

• Any person with known, pre-existing phrenic nerve, diaphragmatic, or inferior vena cava anomaly.
• Patients who cannot be successfully imaged by ultrasound or who cannot participate in spirometry will additionally be excluded.
• Non-English speaking patients will be excluded as well as there is no research funding to translate consent forms. Given that there is no potential benefit to participation in the study, this does not exclude these individuals from any potentially beneficial therapy.