Continuous vs. Bolus Norepinephrine for Post-Induction Hypotension

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Continuous vs. Bolus Norepinephrine for Post-Induction Hypotension

Continuous vs. Bolus Norepinephrine for Post-Induction Hypotension: A Landmark Trial

Key Takeaway: Continuous infusion of norepinephrine offers no significant advantage over manual bolus administration in reducing post-induction hypotension in low-to-moderate risk noncardiac surgery patients, according to a randomized trial in the British Journal of Anaesthesia.

Study Design

  • Participants: 276 patients (261 analyzed) undergoing elective noncardiac surgery
  • Interventions: Randomized to continuous infusion (target: 0.05 µg/kg/min) or manual boluses (10 µg)
  • Monitoring: Intermittent oscillometric BP + blinded continuous finger-cuff monitoring
  • Primary Endpoint: Area under MAP <65 mmHg within 15 minutes post-induction

Key Findings

Metric Continuous Infusion Bolus Administration
Area under MAP <65 mmHg (mmHg·min) 3.6 (0.0–16.6) 5.5 (0.5–24.5)
Duration of MAP <65 mmHg (min) 1.0 (0.0–2.5) 1.4 (0.2–3.2)
Total Norepinephrine Dose (µg/kg) 0.9 0.3
Severe Hypotension (MAP <40 mmHg) 8% 15%

P-values: Primary endpoint p=0.070 (non-significant), duration p=0.052, severe hypotension p=0.081

Clinical Implications

  • Equivalence Established: Both methods equally effective under standard intermittent monitoring
  • Cost Consideration: Bolus group used 3x less norepinephrine (0.3 vs 0.9 µg/kg)
  • Severe Hypotension Risk: Continuous infusion halved incidence of MAP <40 mmHg (8% vs 15%)
  • Practice Flexibility: No single approach superior for low-to-moderate risk patients

Limitations & Future Directions

  • Excluded high-risk patients and emergency cases
  • No standardized hemodynamic protocol beyond MAP >65 mmHg target
  • Anesthesiologists couldn't be blinded to treatment allocation
  • Need for studies in high-risk populations and with continuous arterial monitoring

Expert Perspective

"The choice between continuous and bolus administration should consider institutional resources and clinician experience. For now, maintaining MAP above 65 mmHg remains the priority, regardless of vasopressor strategy." – Dr. Bernd Saugel, Senior Author

Conclusion

This trial challenges the assumption that continuous infusion is superior for managing post-induction hypotension. While continuous administration showed a trend toward reduced severe hypotension, the clinical significance is uncertain given increased drug use and costs. The findings support current practice flexibility, emphasizing that both approaches can be valid depending on clinical context.

Final Thought: Should we focus more on when to treat hypotension rather than how? Share your perspective on vasopressor strategies in perioperative care!

Source: Thomsen et al., British Journal of Anaesthesia (2025). DOI: 10.1016/j.bja.2025.03.017

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