Pharmacological Management of Hypotension During Anesthesia

Pharmacological management of hypotension during anesthesia is essential to ensure adequate organ perfusion and reduce perioperative complications. Intraoperative hypotension commonly arises due to vasodilation, myocardial depression, or autonomic suppression, each of which may be triggered or exacerbated by anesthetic agents. A successful pharmacological approach depends on identifying the dominant mechanism and selecting an agent that corrects it effectively and safely.

Peripheral vasodilation is a common cause of intraoperative hypotension, particularly during neuraxial anesthesia, where sympathetic blockade reduces systemic vascular resistance (SVR). In these cases, alpha-1 agonists like phenylephrine and ephedrine are first-line agents. By inducing vasoconstriction, phenylephrine raises SVR and restores arterial pressure, though it may also decrease cardiac output due to reflex bradycardia and increased afterload. Ephedrine, which stimulates both alpha and beta receptors, improves vascular tone while also increasing heart rate and contractility. This dual action makes it especially useful when hypotension is accompanied by bradycardia or reduced cardiac output. In obstetric anesthesia, ephedrine is often the preferred pharmacological intervention for hypotension because of its ability to maintain uteroplacental perfusion without significant fetal compromise (1).

Patients who are chronically treated with angiotensin-converting enzyme (ACE) inhibitors or angiotensin receptor blockers (ARBs) present a unique challenge. These medications are commonly prescribed to manage hypertension, heart failure, and diabetic nephropathy. However, they interfere with the renin-angiotensin-aldosterone system, which impairs the body’s ability to compensate for hypotension via vasoconstriction. During anesthesia, this blunted compensatory mechanism can lead to severe hypotension that does not respond to traditional adrenergic vasopressors, such as phenylephrine or ephedrine. In such cases, vasopressin becomes a critical alternative. Vasopressin acts on V1 receptors through a non-adrenergic pathway, restoring vascular tone independently of the sympathetic nervous system. Its efficacy in patients treated with ACE inhibitors or ARBs has been well documented, and it is now considered a second-line agent for refractory hypotension in this setting (2).

Ketamine is another valuable pharmacological agent for managing hypotension, particularly during anesthesia induction. Unlike most anesthetic agents, which suppress sympathetic tone and lower blood pressure, ketamine stimulates the sympathetic nervous system and inhibits norepinephrine reuptake. This results in increased heart rate, cardiac output, and SVR. These properties make ketamine ideal for patients with hemodynamic instability, including those with hypovolemia, pericardial tamponade, or aortic stenosis. Its potential drawbacks include increased myocardial oxygen consumption and emergence reactions. However, when used appropriately, its ability to provide cardiovascular stability is a major advantage in high-risk populations (3).

Identifying patients at increased risk for hypotension before anesthesia and surgery allows for proactive planning. Reich et al. conducted a large, prospective analysis of more than 4,000 patients undergoing non-cardiac surgery. They found that advanced age, female sex, low baseline systolic blood pressure, and higher (ASA) physical status scores were all associated with post-induction hypotension. They also observed a consistent, dose-dependent hypotensive effect with fentanyl, an opioid often used during induction, highlighting the need for careful agent selection in vulnerable patients.

A mechanism-based approach improves the precision and safety of anesthetic management. Alpha-adrenergic agents, such as phenylephrine, are effective in treating vasodilatory hypotension. When bradycardia or low cardiac output is present, agents with beta activity, such as ephedrine or low-dose epinephrine, provide additional chronotropic and inotropic support. For patients taking ACE inhibitors or ARBs, vasopressin restores vascular tone via non-adrenergic pathways. Ketamine reliably stabilizes hemodynamics during induction in patients with limited cardiovascular reserve. Aligning drug selection with the dominant physiologic disturbance ensures effective, targeted treatment across a range of clinical scenarios.

References

1. Ferré F, Martin C, Bosch L, Kurrek M, Lairez O, Minville V. Control of Spinal Anesthesia-Induced Hypotension in Adults. Local Reg Anesth. 2020;13:39-46. Published 2020 Jun 3. doi:10.2147/LRA.S240753
2. Mets B. Management of hypotension associated with angiotensin-axis blockade and general anesthesia administration. J Cardiothorac Vasc Anesth. 2013;27(1):156-167. doi:10.1053/j.jvca.2012.06.014
3. Morgan P. The role of vasopressors in the management of hypotension induced by spinal and epidural anaesthesia. Can J Anaesth. 1994;41(5 Pt 1):404-413. doi:10.1007/BF03009863
4. Reich DL, Hossain S, Krol M, et al. Predictors of hypotension after induction of general anesthesia. Anesth Analg. 2005;101(3):622-628. doi:10.1213/01.ANE.0000175214.38450.91