The method of administering anesthetic and vasopressor agents affects perioperative physiology and clinical outcomes. Bolus delivery can rapidly correct hypotension, but it also abruptly changes intravascular pressure and organ perfusion. In contrast, continuous infusion achieves more gradual hemodynamic adjustment. It is important to understand the impact of bolus pressure on anesthesia outcomes, as short-term hemodynamic fluctuations may have clinically significant consequences for immediate stability and long-term outcomes.

In obstetric anesthesia, maternal hypotension after spinal anesthesia is common and is typically treated with vasopressors, such as phenylephrine. While pushing a bolus is effective for acute episodes of low blood pressure, it can produce overshoot hypertension, with its own impacts on anesthesia and surgical outcomes. In a systematic review and meta-analysis, Yalla et al. reported that bolus regimens were associated with greater hemodynamic variability and lower neonatal umbilical cord pH values compared with infusion regimens (1). Low cord pH reflects fetal acidosis and indicates impaired oxygen delivery to the fetus. Transient acidemia can also increase the risk of neonatal morbidity and adverse neurodevelopmental outcomes.

The effects of bolus pressure extend beyond obstetrics. For example, Zhang et al. evaluated the use of vasopressors in patients undergoing major abdominal surgery. They found that bolus dosing of phenylephrine and ephedrine produced sharp fluctuations in cerebral oxygenation. In contrast, infusion regimens maintained greater stability (2). Although cerebral autoregulation buffers against changes in systemic blood pressure, rapid pressure surges can exceed these mechanisms and result in uneven cerebral perfusion. These fluctuations may contribute to postoperative cognitive dysfunction or neurological complications in susceptible patients.

Similar concerns have been identified in resuscitation research. Putzer et al. compared bolus and continuous administration of adrenaline during experimental cardiopulmonary resuscitation (3). Bolus dosing transiently improved cerebral oxygenation, but it also produced large oscillations that may increase the risk of reperfusion injury. These findings imply that, while bolus delivery can achieve short-term hemodynamic targets, it may compromise tissue-level stability.

Bolus pressure administration in cardiac anesthesia has also been questioned. Song et al. investigated the administration of remimazolam during catheter ablation procedures under general anesthesia (4). Compared with agents that are more commonly administered as intermittent boluses, continuous remimazolam infusion resulted in fewer hypotensive episodes and reduced vasopressor requirements. Since abrupt hemodynamic shifts increase procedural risk in cardiac patients, these findings support infusion strategies as a means of promoting cardiovascular stability in high-risk settings.

Broader perioperative data reinforce these observations. Saugel et al. conducted a randomized trial comparing continuous and bolus norepinephrine administration for post-induction hypotension in noncardiac surgery (5). Continuous infusion reduced arterial blood pressure variability and minimized hypotensive episodes compared with bolus therapy. Since intraoperative hypotension is associated with myocardial and kidney injury and increased postoperative morbidity, these findings support infusion regimens to enhance perioperative organ protection.

Overall, the current evidence suggests that, while bolus administration is effective in rapidly correcting hypotension, it carries risks of hemodynamic variability and associated downstream effects, including fetal acidosis, unstable cerebral oxygenation, and organ hypoperfusion. Continuous infusion provides steadier pressure control and may improve maternal-fetal and surgical outcomes. Therefore, clinical practice should consider infusion the preferred method for preventing and maintaining blood pressure while reserving bolus therapy for acute correction when a rapid response is required.

References

1. Garg H, Narayanan M R V, Khanna P, Yalla B. Comparison of Phenylephrine Bolus and Infusion Regimens on Maternal and Fetal Outcomes During Cesarean Delivery: A Systematic Review and Meta-Analysis. Anesth Analg. 2024;139(6):1144-1155. doi:10.1213/ANE.0000000000007156
2. Li X, Zheng Y, Zhang J. Cerebral oxygenation and hemodynamic changes during ephedrine and phenylephrine administration for transient intraoperative hypotension in patients undergoing major abdominal surgery: a randomized controlled trial. BMC Anesthesiol. 2025;25(1):87. Published 2025 Feb 20. doi:10.1186/s12871-025-02944-z
3. Wagner J, Mathis S, Spraider P, et al. The effects of bolus compared to continuous administration of adrenaline on cerebral oxygenation during experimental cardiopulmonary resuscitation. Resusc Plus. 2024;19:100738. Published 2024 Aug 5. doi:10.1016/j.resplu.2024.100738
4. Yim S, Choi CI, Park I, Koo BW, Oh AY, Song IA. Remimazolam to prevent hemodynamic instability during catheter ablation under general anesthesia: a randomized controlled trial. Can J Anaesth. 2024;71(8):1067-1077. doi:10.1007/s12630-024-02735-z
5. Thomsen KK, Külls F, Vokuhl C, et al. Continuous versus bolus norepinephrine administration to treat hypotension after induction of general anaesthesia in low-to-moderate risk noncardiac surgery patients: a randomised trial. Br J Anaesth. Published online May 2, 2025. doi:10.1016/j.bja.2025.03.017