Introduction to vasopressors

What are vasopressors (and why do we use them)?

• Vasopressors are drugs that raise arterial blood pressure, mainly by tightening blood vessels (increasing vascular tone).
• They are used when blood pressure is too low and this risks poor blood flow to vital organs (brain, heart, kidneys).
• Blood pressure depends on: cardiac output (pump) × systemic vascular resistance (vessel tone). Vasopressors mostly increase vessel tone; some also increase heart contractility and heart rate.
• They treat the symptom (hypotension) while you identify and treat the cause (e.g., bleeding, sepsis, anaesthetic depth).
• They are not a substitute for fluids when the patient is volume-depleted.

First principles: assess before you press

• Confirm the reading: check cuff size/position, repeat BP, look at waveform if arterial line present.
• Look at the patient and the context: recent induction? neuraxial block? bleeding? sepsis? anaphylaxis? arrhythmia?
• Check basics quickly: airway/ventilation/oxygenation, anaesthetic depth, ECG rhythm, capnography, temperature.
• Think in patterns: vasodilation (warm, low SVR) vs low preload (bleeding/relative hypovolaemia) vs pump failure (poor contractility/arrhythmia).
• Aim for organ perfusion, not a single number: mental state (if awake), urine output trend, lactate trend, capillary refill, skin temperature, ECG ischaemia.

Common vasopressors you will meet (UK practice)

• Metaraminol: commonly used in theatre for anaesthesia-related hypotension; mainly vasoconstriction (alpha-1). Often given as small IV boluses; can be infused if ongoing need.
• Phenylephrine: pure vasoconstrictor (alpha-1). Useful when hypotension is due to vasodilation and heart rate is adequate/high; can slow the heart rate (reflex bradycardia).
• Ephedrine: increases heart rate and contractility and also causes some vasoconstriction (mixed action). Useful when hypotension is associated with bradycardia (e.g., after induction).
• Noradrenaline (norepinephrine): first-line vasopressor for septic/vasodilatory shock and often used for persistent hypotension requiring infusion; strong vasoconstrictor with some beta effect.
• Adrenaline (epinephrine): strong beta and alpha effects; used in anaphylaxis, cardiac arrest, and severe shock with poor cardiac output; higher risk of tachyarrhythmias and lactate rise.
• Vasopressin/terlipressin: non-adrenergic vasoconstrictors; specialist use (e.g., catecholamine-resistant vasodilatory shock) under senior guidance.

Choosing a vasopressor: simple approach for new starters

• If hypotension soon after induction with vasodilation: consider metaraminol or phenylephrine; reduce anaesthetic depth if appropriate; give fluid if indicated.
• If hypotension with bradycardia: consider ephedrine (and treat causes of bradycardia).
• If ongoing vasodilatory shock (e.g., sepsis) needing repeated boluses: escalate early to an infusion (often noradrenaline) and call for senior help/critical care support.
• If anaphylaxis suspected: adrenaline is the key drug (plus airway/oxygen, fluids, and follow anaphylaxis guidance).
• If cardiogenic picture (poor contractility, pulmonary oedema, ischaemia): avoid reflex bradycardia and excessive afterload; seek senior help early—may need inotrope rather than pure vasoconstrictor.

Bolus vs infusion: when to switch

• Boluses are useful for short, predictable drops in BP (e.g., after induction, position change).
• Repeated boluses suggest an ongoing problem: consider starting an infusion and treating the underlying cause.
• Infusions provide steadier control and reduce peaks/troughs in BP, but require close monitoring and clear prescribing.
• Escalate early if you are giving frequent boluses, the patient is unstable, or there is suspected major pathology (bleeding, sepsis, anaphylaxis, cardiogenic shock).

Practical safety: administration and monitoring

• Use the lowest effective dose and reassess frequently; avoid chasing the cuff without addressing cause.
• Monitoring: frequent non-invasive BP cycling (e.g., every 1–2 min during instability) and consider arterial line for ongoing vasopressor requirement or high-risk patients.
• IV access: ensure a reliable cannula; check for patency before giving boluses. Vasopressors can cause tissue injury if they leak into tissues (extravasation).
• Peripheral vs central: short-term dilute infusions may be acceptable per local policy with a good cannula in a large vein and close checks; central access is preferred for ongoing/high-dose infusions.
• Label syringes/lines clearly; use infusion pumps; document drug, concentration, rate, and target BP.

Extravasation: what to look for and what to do

• Watch for pain, swelling, blanching, cool skin, or poor flow around the cannula site during/after vasopressor administration.
• Stop the infusion/bolus immediately but leave the cannula in place initially (so it can be used to aspirate if appropriate).
• Call for senior help and follow local extravasation policy promptly.
• Elevate the limb and mark/photograph the area if required by local policy; consider surgical/plastics input if severe.

Common first-time scenarios in theatre

• Post-induction hypotension: check depth, give oxygen, confirm BP, consider fluid bolus if appropriate; treat with metaraminol/phenylephrine (or ephedrine if bradycardic).
• Spinal anaesthesia hypotension: left uterine displacement in pregnancy, fluid as appropriate, vasopressor early (often phenylephrine; ephedrine if bradycardic) and treat nausea as a sign of hypotension.
• Positioning-related hypotension (head-up, prone): reassess venous return, ventilation pressures, and surgical factors; treat with vasopressor while correcting cause.
• Bleeding: vasopressors may temporise but do not replace volume/blood; activate haemorrhage pathway early and communicate with surgeons.
• Sepsis/vasoplegia: early antibiotics/fluids, consider noradrenaline infusion, arterial line, and critical care involvement.