Inotrope Initiation and Titration

Inotropes raise cardiac output when low output persists despite adequate preload and perfusion pressure, such as cardiogenic shock, septic cardiomyopathy with low output, and right heart failure. They increase myocardial oxygen demand and arrhythmia risk, so they are used at the lowest dose for the shortest time.

Indication. Evidence of low output: cold peripheries, raised lactate, low central venous oxygen saturation, reduced urine output, or poor function on echocardiography, despite filling and a mean arterial pressure of 65 mm Hg.

Mechanisms. Dobutamine acts on beta receptors. Adrenaline acts on alpha and beta receptors. Milrinone inhibits phosphodiesterase 3 and gives vasodilation. Levosimendan sensitises calcium and opens potassium channels.

First line. Dobutamine, with noradrenaline to maintain pressure. Adrenaline when both inotropy and pressure are needed.

Alternatives. Milrinone or levosimendan when the patient takes a beta blocker, or when pulmonary vascular resistance is raised.

Avoid. Inotropes in outflow tract obstruction (hypertrophic cardiomyopathy), and take care in severe aortic stenosis and hypovolaemia.

Special groups.

• Children: weight-based doses with adrenaline or milrinone.

• Pregnancy and the postpartum period: peripartum cardiomyopathy is a recognised cause of shock, so involve cardiology early.

• Beta blocker users: dobutamine may be less effective, so use milrinone or levosimendan.

• East Africa: rheumatic heart disease and cardiomyopathy are recognised causes of cardiogenic shock, so check valve lesions before inotropes.

• Dobutamine: start 2.5 micrograms/kg/min, titrate every 10 to 15 minutes, usual range 2.5 to 20 micrograms/kg/min.

• Adrenaline: 0.01 to 0.1 micrograms/kg/min for inotropy, higher for pressure.

• Milrinone: loading 50 micrograms/kg over 10 minutes (often omitted in hypotension), then 0.375 to 0.75 micrograms/kg/min. Reduce for kidney function: 0.43 micrograms/kg/min at creatinine clearance 50, 0.33 at 30, 0.23 at 10 mL/min.

• Levosimendan: 12 micrograms/kg loading over 10 minutes (omit if hypotensive), then 0.1 micrograms/kg/min for 24 hours, range 0.05 to 0.2.

Monitoring. Check the ECG continuously, potassium and magnesium, lactate and venous oxygen saturation every 2 to 4 hours, and repeat echocardiography after a change.

Stop rules. Reduce or stop the infusion for sustained tachycardia over 140 beats each minute, new ventricular arrhythmia, hypotension from vasodilation, or myocardial ischaemia. Wean over hours once output is restored.

Referral and escalation. Seek cardiology and mechanical circulatory support review early for cardiogenic shock that does not improve in a few hours, for rising lactate, or for the need for a second inotrope.

Common errors. Using inotropes in an underfilled patient, giving milrinone without kidney adjustment, and missing outflow tract obstruction.