Prevention of Post Herpetic Neuralgia by Ultrasound Guided Single Nerve Block in the Emergency Department

Study Objectives The goal of this study is to evaluate the rate of PHN development in emergency department patients who receive ultrasound guided nerve blocks using bupivacaine and dexamethasone for acute herpes zoster. The investigators will also study the effectiveness of the block in managing acute herpes zoster pain. The primary outcome is the percentage of patients who have significant herpetic pain at 1 month and 3 months after receiving the nerve block. Secondary outcomes measured are pain scores at 1 hour, 1 month, and 3 months post-nerve block. The amount of opioids used after discharge as well as the number of return visits for herpetic pain will also be recorded.

Hypothesis The hypothesis is that patients who receive nerve blocks will decrease the occurrence of PHN development at 1 month and 3 months post-treatment. The secondary hypothesis is that nerve blocks will decrease pain scores at 1 hour, 1 month, 3 months, as well as reduce the amount of opioids used and number of return visits for herpetic pain.

IStudy Design This study will be a single center prospective observational study that will be conducted in the emergency department of an urban hospital center. A trained emergency medicine physician will screen and assess the patient for eligibility. Once the patient is determined to be eligible, informed consent will be obtained. A trained EM physician will then administer a nerve block using bupivacaine and dexamethasone to a patient with acute herpes zoster. The patient will be started on Acyclovir 800 mg five times daily for seven days. For mild to moderate breakthrough pain, the patient will be prescribed a 5-day course of Tylenol 650 mg and Ibuprofen 400 mg taken up to every 8 hours together. For severe breakthrough pain, the patients will be prescribed a two-day course of 7.5 mg morphine sulfate immediate release to be taken up to every 6 hours. The location of the nerve block and dosage of injected medications will depend on the distribution of the affected dermatome. The dermatomal distributions with their associated nerve blocks and medication dosages are shown the table below.

Herpes Zoster Distribution Nerve Block Type Medication T2-T9 Serratus Plane 30 mL 0.25% bupivacaine and 8 mg Dexamethasone C2-C3 Greater Occipital Nerve 2 mL 0.25% bupivacaine and 4 mg dexamethasone C3-C4 Superficial Cervical Plexus 10 mL 0.25% bupivacaine and 4 mg dexamethasone Anterior Abdominal Wall T6 - L1 Transversus Abdominis Plane 30 mL 0.25% bupivacaine and 8 mg dexamethasone

A numerical verbal rating scale will be used to assess the patient's pain pre-injection and at 1-hour post nerve block. We will then call the patient at the 1 week, 1 month, and 3-month post-nerve block time intervals to assess the patients' pain. The investigators will also record the number of follow-up visits for herpetic pain and the amount of additional pain medications used.