The Physiological Responses to Stellate Ganglion Blockade under Ultrasound-Guidance in the Rat
Authors: Tran Robert M. N. , Malik Shaista , Reist Christopher , Oh Chad K , Abdul-Musawir Najeebah , Tjen-A-Looi Stephanie , Fu Liang-Wu 
Published: May 2024

The stellate ganglion (SG) is an essential component of the sympathetic nervous system, where inhibition via local anesthetics is used as a practical approach to manage many clinical disorders, including regional pain syndrome and cardiovascular diseases. However, this procedure is often technically challenging, with side effects including pneumothorax and vascular injection. Ultrasound-guided SG blockade (SGB) is currently adopted as a more effective method than blind injection techniques as it allows for visualizing SG’s location. However, there is not yet enough information on the physiological responses of this procedure. The present study examined physiological changes following ultrasound-guided SGB in normal rats. We hypothesized that ultrasound-guided SGB is a safe and effective method to inhibit sympathetic nerves in the rat. Male Sprague-Dawley rats (310-350 g) were anesthetized with 2-4% isoflurane and placed on the animal monitor platform (VisualSonics Vevo, SR200) that allowed for monitoring and recording the electrocardiogram, respiratory rate, and body temperature. Normal saline (0.9%) or 1.0-1.5% lidocaine mixed with Chicago blue dye was loaded in a 1 ml insulin syringe with a 26 G needle. Each tested solution in 40-60 μl was injected into the right or left SG region once under ultrasound guidance (VisualSonics Vevo 3100 LT). Ten minutes after the injection, rats were allowed to recover from the anesthesia, and the status of the eyelid and the general condition were examined. Ptosis was observed on the ipsilateral side as the lidocaine was administered to the right (n=9) or left (n=7) sides of SG, indicating the successful execution of SGB. No ptosis was noted in any controls as normal saline was injected into the right (n=6) or left (n=6) SG. Respiratory rate and body temperature were unchanged following the injection in either the right or left side in any control or treatment groups. Heart rate (HR) was significantly decreased after administering lidocaine (354 ± 14 vs. 292 ± 16 bpm, P = 0.008; pre- vs. after-injection) but not normal saline into right SG. Reduced HR lasted for about 7-10 minutes. HR was unaltered after injecting lidocaine or normal saline into the left SG. These data imply that sympathetic nerves controlling HR are likely predominantly associated with right SG. Besides, no abnormal behaviors were noted in any rat. Chicago blue dye was confirmed to be distributed in the SG region. No bleeding and tissue damage were evident in the injected SG area. The results suggest that non-invasive ultrasound-guided SGB is likely a safe and effective approach with a small injection volume to block sympathetic nerves in the rat, which sheds light on its employment in experimental research and clinical practice. Research fund from AEON Biopharma, Inc. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.