Emergency Inotropes

Emergency inotropes increase the force of heart muscle contraction when cardiac output is too low to perfuse organs. They are used in cardiogenic shock, acute severe heart failure with low output, septic shock with myocardial depression, and after cardiac surgery. Many also change vascular tone and heart rate, so the choice depends on blood pressure, rhythm and the cause.

Classification. Beta-1 agonists (dobutamine, adrenaline, dopamine, isoprenaline); phosphodiesterase-3 inhibitors (milrinone, enoximone); calcium sensitisers (levosimendan); glucagon for beta-blocker toxicity.

Mechanism. Beta-1 agonists raise cyclic AMP in heart cells through the receptor. Milrinone raises cyclic AMP by blocking its breakdown, and also dilates vessels. Levosimendan sensitises troponin C to calcium without raising intracellular calcium much.

Pharmacokinetics. Dobutamine, adrenaline and dopamine act within minutes and clear within minutes after stopping. Milrinone has a half-life of 2 to 3 hours and accumulates in kidney failure. Levosimendan has an active metabolite that lasts about a week.

Practical points.

• Aim for adequate perfusion (urine output, lactate clearance, mental state), not a number alone.
• Add a vasopressor when pressure is low, since inotropes with vasodilator action can lower it further.
• Use the lowest dose that achieves the goal and wean early.

• First-line. Dobutamine for low output with adequate blood pressure; adrenaline when pressure is also low.
• Alternative. Milrinone in people on beta-blockers or with pulmonary hypertension; dopamine when other drugs are not available.
• Specialist. Levosimendan, mechanical support (balloon pump, ECMO), inotropes as a bridge to transplant.
• Emergency. Cardiogenic shock, acute heart failure with hypoperfusion, beta-blocker or calcium channel blocker overdose.

Selection. Find and treat the cause (ischaemia, arrhythmia, valve failure, tamponade, sepsis). Choose by blood pressure and heart rate. Do not use inotropes to treat heart failure without hypoperfusion.

Contraindications. Hypertrophic obstructive cardiomyopathy (dobutamine and others), uncorrected hypovolaemia, severe aortic stenosis (relative), ventricular tachycardia, and milrinone in severe hypotension.

Serious adverse effects.

• Tachyarrhythmia, atrial fibrillation, ventricular arrhythmia, myocardial ischaemia.
• Hypotension (milrinone, levosimendan, dobutamine), hypokalaemia, tolerance to dobutamine after 48 hours.
• Lactic acidosis and hyperglycaemia with adrenaline.
• Thrombocytopenia with milrinone (long use); tissue damage at infusion sites.

Major interactions. Beta-blockers blunt dobutamine and adrenaline; monoamine oxidase inhibitors increase pressor effects; digoxin raises arrhythmia risk; milrinone with other vasodilators lowers pressure.

Common prescribing errors.

• Using inotropes in hypovolaemia before fluid.
• Mixing up micrograms/kg/minute and micrograms/minute.
• Forgetting to reduce milrinone in kidney failure.
• Continuing for days without a reassessment.
• Stopping suddenly.

Special groups.

• Pregnancy: use the usual adult drugs when needed to save life; early specialist input.
• Breastfeeding: compatible after the acute episode.
• Children: weight-based; use paediatric tables.
• Older adults: lower starting doses and closer rhythm monitoring.
• Kidney: reduce milrinone dose.
• Liver: titrate to effect.
• East Africa: dobutamine, milrinone and levosimendan may be unavailable, with adrenaline or dopamine as the realistic options; infusion pumps and central lines may be limited; check stock before relying on a plan.

Monitoring. Continuous ECG, blood pressure, lactate, urine output, central venous oxygen saturation if available, echocardiogram, potassium and magnesium.

Referral and escalation. Persistent hypotension, rising lactate, arrhythmia, need for two or more agents, or consideration of mechanical support.

Comparison with alternative classes. Inotropes raise output quickly but increase oxygen demand and arrhythmia. Vasopressors restore pressure. Diuretics and vasodilators help congested patients with adequate perfusion.