Changes in heart rate variability after sitting following interscalene block

Area of Science:

• Anesthesiology
• Autonomic Nervous System Research
• Cardiac Electrophysiology

Background:

• Hypotensive bradycardic events (HBEs) are a common complication, occurring in 5-28% of patients undergoing arthroscopic shoulder surgery in the sitting position after an interscalene brachial plexus block (ISBPB).
• Understanding the physiological mechanisms behind HBEs is crucial for developing preventative strategies.

Purpose of the Study:

• To investigate the impact of the sitting position following ISBPB on heart rate variability (HRV).
• To identify potential predictors of HBEs in patients undergoing ISBPB for shoulder surgery.

Main Methods:

• A prospective case-control study involving 64 patients undergoing arthroscopic shoulder surgery under ISBPB and 49 non-surgical controls.
• HRV power spectral analysis was performed before ISBPB and after assuming the sitting position.
• Patients were categorized into HBE and non-HBE groups based on the occurrence of HBEs.

Main Results:

• HBEs occurred in 28.1% of patients.
• The transition to the sitting position after ISBPB did not significantly alter the low-frequency to high-frequency power ratio (lnLF/HF).
• A significant decrease in high-frequency power (lnHF) was observed in the patient group compared to controls, with higher lnHF in the HBE group.

Conclusions:

• Sustained vagal activity, indicated by higher lnHF, is associated with HBE development.
• A failure to shift sympathovagal balance towards sympathetic predominance in response to sitting after ISBPB is linked to HBEs.
• HRV analysis may offer insights into the pathophysiology of HBEs following ISBPB.