Vasopressors -

Vasopressors are a class of medications that induce vasoconstriction, thereby increasing blood pressure. They are critical in managing various forms of shock and severe hypotension. Here is a detailed overview of different types of vasopressors, their mechanisms, uses, doses, preferred routes, maximum doses, side effects, and monitoring requirements according to UK standards.

Types of Vasopressors

Norepinephrine (Noradrenaline)
Epinephrine (Adrenaline)
Dopamine
Phenylephrine
Vasopressin
Dobutamine (also has inotropic effects)

Detailed Overview

1. Norepinephrine (Noradrenaline)

Mechanism:

Primarily stimulates alpha-1 adrenergic receptors causing vasoconstriction.
Also stimulates beta-1 adrenergic receptors, increasing myocardial contractility and heart rate to a lesser extent.

Uses:

First-line agent for septic shock.
Acute hypotension.

Preferred Route:

Intravenous infusion (central venous access preferred).

Dose:

Initial: 0.05–0.1 micrograms/kg/min IV infusion.
Maintenance: Titrate to effect, usually 0.05–.5 micrograms/kg/min.
Maximum: Up to 1 micrograms/kg/min, though higher doses may be used in refractory cases under close monitoring.

Side Effects:

Arrhythmias
Hypertension
Peripheral and visceral ischemia
Reflex bradycardia

Monitoring:

Continuous blood pressure monitoring.
Heart rate and rhythm.
Peripheral perfusion (e.g., capillary refill, limb temperature).

2. Epinephrine (Adrenaline)

Mechanism:

Stimulates alpha and beta-adrenergic receptors.
Increases heart rate (beta-1), myocardial contractility (beta-1), and causes vasoconstriction (alpha-1).

Uses:

Anaphylactic shock.
Cardiac arrest.
Severe asthma exacerbations.
Septic shock (second-line agent).

Preferred Route:

Intramuscular (IM) for anaphylaxis.
Intravenous (IV) bolus and infusion for cardiac arrest and shock.

Dose:

Anaphylaxis: 0.5 mg (0.5 mL of 1:1,000 solution) IM, repeated every 5 minutes if necessary.
Cardiac Arrest: 1 mg (10 mL of 1:10,000 solution) IV every 3-5 minutes during resuscitation.
Infusion: 0.05–0.5 micrograms/kg/min IV, titrated to response.
Maximum: Typically up to 1 microgram/kg/min, though higher doses may be considered in refractory cases.

Side Effects:

Tachycardia
Arrhythmias
Hypertension
Hyperglycemia
Lactic acidosis

Monitoring:

Blood pressure and heart rate.
ECG for arrhythmias.
Blood glucose levels.
Lactate levels.

3. Dopamine

Mechanism:

Dose-dependent effects:
Low dose: Stimulates dopamine receptors causing vasodilation.
Moderate dose: Stimulates beta-1 receptors increasing heart rate and contractility.
High dose: Stimulates alpha-1 receptors causing vasoconstriction.

Uses:

Shock (cardiogenic, septic).
Acute heart failure.

Preferred Route:

Intravenous infusion.

Dose:

Low dose: 2–5 micrograms/kg/min IV (renal dose).
Moderate dose: 5–10 micrograms/kg/min IV (cardiac dose).
High dose: >10 micrograms/kg/min IV (vasopressor dose).
Maximum: Typically up to 20 micrograms/kg/min.

Side Effects:

Tachycardia
Arrhythmias
Vasoconstriction at high doses
Nausea and vomiting

Monitoring:

Blood pressure and heart rate.
ECG for arrhythmias.
Renal function (urine output).

4. Phenylephrine

Mechanism:

Pure alpha-1 adrenergic agonist.
Causes vasoconstriction without significant effect on heart rate or contractility.

Uses:

Neurogenic shock.
Hypotension during anesthesia.
Septic shock (alternative agent).

Preferred Route:

Intravenous bolus and infusion.

Dose:

Bolus: 50–100 micrograms IV, repeated as necessary.
Infusion: 0.1–1.0 micrograms/kg/min IV, titrated to effect.
Maximum: Up to 5 micrograms/kg/min in refractory cases.

Side Effects:

Reflex bradycardia
Hypertension
Peripheral ischemia

Monitoring:

Blood pressure.
Heart rate.
Peripheral perfusion.

5. Vasopressin

Mechanism:

Non-adrenergic vasoconstrictor.
Acts on V1 receptors in the vascular smooth muscle to induce vasoconstriction.
Also retains water by acting on V2 receptors in the kidneys.

Uses:

Septic shock (added to norepinephrine).
Vasodilatory shock.

Preferred Route:

Intravenous infusion.

Dose:

Infusion: 0.01–0.04 units/min IV.
Maximum: Typically not exceeding 0.04 units/min.

Side Effects:

Hyponatremia
Ischemia (cardiac, mesenteric, peripheral)
Increased blood pressure

Monitoring:

Blood pressure.
Serum sodium levels.
Signs of ischemia.

6. Dobutamine (also a Positive Inotrope)

Mechanism:

Primarily stimulates beta-1 adrenergic receptors increasing heart contractility and stroke volume.
Mild beta-2 and alpha-1 effects leading to vasodilation and slight vasoconstriction.

Uses:

Cardiogenic shock.
Acute heart failure.

Preferred Route:

Intravenous infusion.

Dose:

Initial: 2.5–5 micrograms/kg/min IV infusion.
Maintenance: Up to 20 micrograms/kg/min, titrated to response.
Maximum: Generally up to 20 micrograms/kg/min.

Side Effects:

Tachycardia
Arrhythmias
Hypotension (due to beta-2 effects)

Monitoring:

Blood pressure and heart rate.
ECG for arrhythmias.
Cardiac output and perfusion parameters.

Clinical Use of Vasopressors

Indications

Septic Shock: Vasopressors are essential to maintain blood pressure and perfusion.
Cardiogenic Shock: To support cardiac output and systemic perfusion.
Neurogenic Shock: To counteract loss of vascular tone.
Hypotension: Severe hypotension unresponsive to fluid resuscitation.

Administration

Intravenous Infusion: Administered through central venous access to ensure rapid and controlled delivery.
Titration: Dosage is carefully titrated to achieve the desired hemodynamic response while minimizing side effects.

Side Effects and Risks

Ischemia: Excessive vasoconstriction can lead to tissue ischemia, particularly in extremities, kidneys, and gastrointestinal tract.
Arrhythmias: Increased risk of abnormal heart rhythms, especially with beta-adrenergic stimulation.
Hypertension: Overcorrection of blood pressure can lead to complications like stroke or myocardial infarction.
Reflex Bradycardia: Seen with potent alpha-adrenergic agonists like phenylephrine.

Monitoring

Patients on vasopressors require intensive monitoring, including:

Continuous Blood Pressure Monitoring: Often via arterial line for accurate real-time measurements.
Heart Rate and Rhythm: Continuous ECG monitoring to detect arrhythmias.
Peripheral Perfusion: Regular assessment of capillary refill, limb temperature, and urine output.
Organ Function: Monitoring renal function (creatinine, urine output), liver function (liver enzymes), and metabolic status (lactate levels).

Conclusion

Vasopressors are critical medications in the management of shock and severe hypotension. Their use must be carefully monitored to balance the therapeutic benefits with potential risks. These medications play a vital role in stabilising patients with life-threatening conditions and require careful titration and monitoring in an intensive care setting.