Title: An Emerging Concern: Weight Loss Medications and Vasovagal reaction during Peripheral Nerve Block

Authors: Aminat Haruna, MD, MPH1; Austin Puchany DO, Mario Montoya MD1

Organization: 1Department of Anesthesiology & Perioperative Medicine, University of Pittsburgh & University of Pittsburgh Medical Center, Pittsburgh, PA

 

Introduction:

The rising use of sympathomimetic weight loss medication introduces new perioperative considerations

These agents can alter autonomic tone, increase vagal sensitivity and delay gastric emptying1

Physiological changes can impact hemodynamic stability and aspiration risk during anaesthesia.

Case highlights potential peri block safety concern in patients on phentermine or similar agents

 

Case Summary:

51-year-old male with morbid obesity, presents for ventral hernia repair.

Bilateral paravtebral blocks for post operative pain management

After needle insertion patient had Vasovagal event

Symptoms: bradycardia, hypotension, syncope, nausea and vomiting

Response: Ephedrine, glycopyrrolate, famotidine, ondansetron

Imaging: EKG showed NSR, no ST changes

The regional procedure was aborted.

Induced uneventfully with RSI and video laryngoscopy

Surgery proceeded uneventfully, without need for vasopressors

Successful extubation at end of case

 

Main Diagnosis/Interventions:

Rapid growth in Anti-obesity medications has been observed in recent years

Phentermine: A sympathomimetic amine historically used for short-term weight loss; can increase catecholaminergic activity and may affect autonomic tone1.

Emesis secondary to vagal event or Delayed gastric emptying, or combination of both?

Point-of care gastric ultrasound can noninvasively assess gastric contents to stratify gastric content and volume to stratify aspiration risk preoperatively. Recent reviews report sensitivity (~53%-100%) and specificity (~48-99%), depending on operator experience and protocols.

 

Figures/Images:

Procedure3:

Position Patient supine

Place probe at epigastrium (under Xiphoid)

Dot of probe aimed cephalad

Liver on left of screen, Aorta/IVC at bottom

Scan to observe stomach contents

Place pt in RLD position

This pushes stomach contents to antrum

- Empty stomach: "Bulls-eye" appearance w/ small collapsed antrum

- Clear Liquids: hypoechoic and homogenous

- Thick Liquids: hyperechoic and homogenous

- Solids: heterogenous, "frosted glass" appearance, may have trouble seeing structures bellow.

For clear liquids calculate CSA

Free-tracing function -trace the entire circumference of the antrum,

Gastric Volume = 27 + (14.6 * CSA) – (1.28 * age)

 

Discussion:

Discussion

Obesity, DM, abdominal pathology, pain and prior abdominal surgeries can increase risk

Delayed gastric emptying augments the risk of emesis and aspiration, even in non-general anesthesia settings

Sympathomimetic weight loss agents may potentiate autonomic dysregulation increasing susceptibility to vasovagal episode during block placement4

GLP-1 agonists known for delayed gastric emptying and aspiration risk

Compounded risk with these agents plus underlying pathology

 

Anesthetic Considerations

Review of medication use and appropriate discontinuation

Evaluation of gastric mobility and aspiration risk

Use of gastric ultrasound to assess stomach contents

Contents > 1.5ml/kg puts pt at increased risk

If Elective, consider delay/cancelation

If Emergent -> full aspiration precautions: minimize/avoid sedation, RSI, decompress stomach with gastric tube

Emergency medications & equipment readily available

Be prepared for delayed extubation

 

References:

Jeffers, L. Anesthetic Considerations for the New Anti-Obesity Medications. The Internet Journal of Anesthesiology. 1996; 1(4).

Gastric UltraSound. Image Acquisition. Accessed November 13, 2025. [https://www.gastricultrasound.org/en/acquisition/](https://www.gastricultrasound.org/en/acquisition/)

Flynn DN, Doyal A, Schoenherr JW. Gastric Ultrasound. [Updated 2023 Feb 20]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2025 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK580524/

Stephens LC, Katz SG. Phentermine and Anaesthesia. Anaesthesia and Intensive Care. 2005;33(4):525-527. doi:10.1177/0310057X0503300418