What is the Bezold‑Jarisch reflex during spinal anesthesia and how should it be managed?

Bezold-Jarisch Reflex During Spinal Anesthesia

The Bezold-Jarisch reflex (BJR) during spinal anesthesia is a cardioinhibitory reflex triggered by ventricular mechanoreceptors that produces the triad of profound bradycardia, hypotension, and apnea/bradypnea, requiring immediate recognition and aggressive treatment with epinephrine, intravenous fluids, and left-lateral positioning. 1, 2

Pathophysiology

The BJR originates from sensory receptors in the inferoposterior wall of the left ventricle, with unmyelinated vagal C fibers transmitting the reflex through cranial medullary centers that control respiration, heart rate, and vasomotor tone. 3, 2 During spinal anesthesia, the reflex is triggered when:

• Sympathetic blockade causes peripheral vasodilation and venous pooling, reducing venous return and left ventricular filling 1, 4
• The relatively empty, vigorously contracting left ventricle activates mechanoreceptors, paradoxically triggering vagal-mediated cardioinhibition 2, 5
• This produces uncoupled cardioinhibition with the classic triad: severe bradycardia (heart rate can drop to <20 bpm), profound hypotension (systolic BP to 30s mmHg), and respiratory depression or apnea 1, 4

Clinical Presentation

BJR presents differently from typical anaphylaxis and must be distinguished rapidly:

• Bradycardia is the hallmark (versus tachycardia in anaphylaxis, which occurs in 90% of cases) 3, 1
• Absence of cutaneous manifestations (urticaria, flushing, angioedema present in 72% of anaphylaxis) 6
• No bronchospasm or respiratory distress (present in 40% of anaphylaxis) 6
• Onset within minutes of spinal injection, not hours later 1, 4
• Profound hypotension with bradypnea (respiratory rate may drop to 6/min) 1

High-Risk Clinical Scenarios

BJR is more likely when multiple factors converge:

• High spinal block combined with acute hemorrhage creates profound relative hypovolemia 4
• Sitting position during upper extremity blocks increases risk 7
• Autonomic disturbances (e.g., gestational diabetes mellitus) may exaggerate the reflex 4
• Cesarean section under spinal anesthesia represents a particularly vulnerable scenario due to aortocaval compression and blood loss 1, 4

Immediate Management Algorithm

When BJR is suspected (bradycardia + hypotension + apnea/bradypnea within minutes of spinal injection):

1. Stop any ongoing anesthetic administration immediately 1

2. Position the patient in left-lateral tilt to relieve aortocaval compression 1

3. Administer epinephrine 50 µg IV bolus as first-line vasopressor (not atropine alone, which addresses only the bradycardia component) 6, 1

   • If inadequate response, give epinephrine 100 µg IV 6
   • Epinephrine addresses both the bradycardia and hypotension simultaneously 1

4. Rapid crystalloid bolus 1 L IV, repeat as needed to restore preload 6, 1

5. Provide supplemental oxygen and support ventilation if bradypnea or apnea present 8, 1

6. If hypotension persists after 10 minutes, add norepinephrine infusion (0.05–0.5 µg·kg⁻¹·min⁻¹) 6

7. In obstetric cases, initiate continuous fetal monitoring and prepare for emergent cesarean delivery if fetal bradycardia develops 1

Critical Pitfalls to Avoid

• Do not treat with atropine alone—this addresses only bradycardia while ignoring the vasodilation and hypotension that are equally life-threatening components 1, 5

• Do not assume anaphylaxis based solely on hypotension; the presence of bradycardia (not tachycardia) and absence of cutaneous/respiratory signs points to BJR 3, 6

• Do not delay epinephrine while attempting fluid resuscitation alone; the reflex requires both chronotropic and vasopressor support 1

• Do not overlook fetal compromise in obstetric cases; maternal bradycardia and hypotension rapidly translate to fetal bradycardia requiring emergent delivery 1

Monitoring and Prevention

Standard monitoring during spinal anesthesia must include:

• Continuous pulse oximetry, electrocardiography, and non-invasive blood pressure measurement 8
• Reassess sensory block height every 5 minutes until stabilized to detect unintended cephalad spread that increases BJR risk 9, 8
• Supplemental oxygen throughout the procedure 8

Prophylactic measures in high-risk patients:

• Aggressive preloading with crystalloid before spinal injection 4
• Avoid sitting position when feasible 7
• Have epinephrine drawn up and immediately available 1
• Maintain left-lateral tilt in obstetric cases 1

Post-Event Considerations

After successful resuscitation from BJR:

• Monitor for ventricular arrhythmias (ventricular tachycardia has been reported following epinephrine administration) 1
• Continue cardiac monitoring and hemodynamic support until fully stable 1, 7
• Document the event thoroughly, including time course, interventions, and response 7
• Both maternal and neonatal outcomes are typically excellent with prompt recognition and treatment 1, 4