Definition and Pathophysiology
In the management of acute heart failure and cardiogenic shock, intravenous vasoactive agents are categorised according to their distinct pharmacodynamic mechanisms. These drugs are broadly utilised to augment myocardial contractility, manipulate systemic and pulmonary vascular resistance, and restore adequate end-organ perfusion.
Dobutamine is a synthetic catecholamine that functions as an agonist of both beta1 and beta2 adrenergic receptors, with variable effects on alpha receptors. Stimulation of beta-receptors increases inotropy and chronotropy by elevating intracellular cyclic adenosine monophosphate (cAMP) and calcium, as well as through the direct activation of voltage-sensitive calcium channels. At lower doses, dobutamine stimulates beta2 and alpha receptors, inducing vasodilation, decreasing aortic impedance and systemic vascular resistance, reducing afterload, and indirectly increasing cardiac output. At higher doses, vasoconstriction may occur, accompanied by decreased venous capacitance and an elevation in right atrial pressure.
Levosimendan represents a distinct class of inodilator. It enhances myocardial contractility and induces peripheral vasodilation through cardiac myofilament calcium sensitisation. This process is achieved via calcium-dependent binding to troponin C during systole. Simultaneously, levosimendan activates vascular smooth muscle potassium channels to produce vasodilation. Although primarily defined by these mechanisms, levosimendan also exhibits some type-3 phosphodiesterase inhibitor (PDEI) activity, which may contribute to its inotropic profile. The drug possesses an active, acetylated metabolite with a half-life exceeding 80 hours, allowing for sustained hemodynamic effects for days after the infusion is discontinued.
Noradrenaline (norepinephrine) acts primarily as a vasopressor. While detailed receptor pharmacology is not specified in the source material, it is utilised alongside inotropes in acute heart failure to support systemic blood pressure through its infusion rate parameters.
Clinical Presentation and Symptoms
Acute heart failure necessitating inotropic or vasopressor support typically manifests in patients with left ventricular systolic dysfunction, low cardiac output, and dyspnea at rest that persists despite administration of diuretics and vasodilators. Clinically, these patients exhibit hypotension—often with a systolic blood pressure less than 90 mmHg—accompanied by signs of poor vital organ perfusion or frank shock states. In the specific context of perioperative care in patients with pulmonary arterial hypertension (PAH), progression of right heart failure may indicate the need for inodilator therapy. Furthermore, acute heart failure and cardiogenic shock can present de novo in pregnant women without pre-existing heart disease, such as in peripartum cardiomyopathy, or secondary to known cardiac conditions; in these patients, symptoms may be challenging to differentiate from normal physiological changes of pregnancy.
Evaluation and Physical Examination
The source material does not provide a detailed description of the physical examination maneuvers specific to the evaluation of patients requiring these infusions. However, it establishes that the clinical evaluation must identify specific hemodynamic profiles: the presence of hypotension, end-organ hypoperfusion, shock states, and pulmonary congestion. In pregnant patients presenting with suspected acute heart failure, urgent hospital admission and referral to an expert centre with advanced heart failure care capabilities, including mechanical circulatory support and transplantation, is warranted.
Diagnostics
Hemodynamic and functional monitoring is central to the safe administration of these agents. Continuous blood pressure and rhythm monitoring are mandatory, particularly when utilising dobutamine, to ensure the lowest effective dose is used. When titrating sodium nitroprusside for afterload reduction in patients with systemic hypertension and severe aortic stenosis, arterial line placement is required for precise blood pressure management and the prevention of hypotension. For patients with severe PAH undergoing non-cardiac surgery, hemodynamic monitoring should continue for at least 24 hours into the postoperative period.
Dobutamine also serves a diagnostic role in the cardiac catheterisation laboratory. In patients with low-flow, low-gradient aortic stenosis, up to one-third may be incorrectly classified as having severe aortic stenosis by the Gorlin formula. Dobutamine infusion can differentiate true from pseudo-severe aortic stenosis. A coronary angiogram is advised before this infusion to exclude ischemia.
Biomarkers and Laboratory Findings
The source material does not detail routine biomarker profiles for the initiation or monitoring of these specific infusions. However, it notes that in clinical trials, levosimendan has demonstrated effects on serial B-type natriuretic peptide (BNP), reflecting its impact on cardiac hemodynamics and wall stress. Additionally, when using high-dose diuretics concomitantly with vasoactive therapies, careful laboratory monitoring is advised due to the risk of severe hypokalemia and renal worsening, such as increases in serum creatinine observed with agents like ularitide.
Treatment and Management
Acute Strategies
Inotropes and vasopressors are reserved for patients with left ventricular systolic dysfunction, low cardiac output, and low systolic blood pressure resulting in poor vital organ perfusion. They must be initiated at low doses and carefully uptitrated with close monitoring. In cardiogenic shock, recommended inotropic agents include levosimendan, dobutamine, and milrinone. Levosimendan is administered as a continuous infusion without an initial loading dose. Dobutamine is a primary option, whereas adrenaline (epinephrine) should be avoided in pregnant patients. Milrinone may be an alternative if benefits outweigh risks, though placental transfer is a consideration. In cases of severe refractory cardiogenic shock, veno-arterial extracorporeal membrane oxygenation (VA-ECMO) should be considered.
In pregnant patients with milder cases of acute heart failure, treatment may consist of oral diuretics, beta1-selective beta-blockers (bisoprolol, metoprolol succinate), hydralazine, and oral nitrates. Diuretics must be used cautiously due to potential reductions in uterine blood flow. In cardiogenic shock complicating pregnancy, urgent delivery by caesarean section with combined spinal/epidural analgesia or general anaesthesia is recommended.
Long-term Strategies and Weaning
Intravenous inotropic agents have not been shown to improve long-term clinical outcomes in heart failure. They may be considered as a palliative strategy in older patients with severe symptoms. Dobutamine should be gradually weaned off, with clinical status reevaluated at each dose adjustment. Temporary adjustments to afterload-reducing agents or diuretics may assist in the weaning process. Tachyphylaxis can occur with dobutamine infusions exceeding 24 to 48 hours due to receptor desensitisation.
For chronic heart failure with reduced ejection fraction (HFrEF), management has evolved from a hemodynamic model to disease-modifying neurohormonal antagonism. Pharmacotherapy pillars include RAAS blockers (including ARNIs), beta-adrenergic receptor blockers, and SGLT-2 inhibitors. In pregnant patients, beta-blockers should be initiated and gradually uptitrated to the maximum tolerated dose. ACE-Is, ARBs, ARNIs, MRAs, ivabradine, SGLT2 inhibitors, and atenolol are contraindicated during pregnancy. Hydralazine and nitrates appear safe. In the post-partum period, ivabradine may be considered for heart rate control. For pregnancy-associated heart failure with a reversible cause, guideline-directed therapy should be maintained for at least 12 months after full left ventricular recovery, followed by gradual tapering.
Drugs, Doses and Practical Considerations
The following table summarises the infusion rates for inotropes and vasopressors used in the treatment of acute heart failure.
| Drug | Infusion Rate |
|---|---|
| Dobutamine | 2-20 µg/kg/min (beta+) |
| Dopamine | 3-5 µg/kg/min: inotropic (beta+); >5 µg/kg/min: inotropic (beta+), vasopressor (alpha+) |
| Milrinone | 0.375-0.75 µg/kg/min |
| Enoximone | 5-20 µg/kg/min |
| Levosimendan | 0.1 µg/kg/min, which can be decreased to 0.05 or increased to 0.2 µg/kg/min |
| Norepinephrine | 0.2-1.0 µg/kg/min |
| Epinephrine | 0.05-0.5 µg/kg/min |
Dobutamine
Dobutamine is the most commonly used positive inotrope despite evidence suggesting it increases mortality. Doses of 1 to 2 µg/kg/min may improve renal perfusion in cardiogenic shock, while higher doses (5 to 10 µg/kg/min) may be necessary for profound hypoperfusion. It is the preferred inotrope in patients with significant hypotension and severe renal dysfunction. Concomitant beta-blocker therapy results in competitive antagonism, necessitating higher doses (10 to 20 µg/kg/min). Adverse effects include tachycardia, increased ventricular response in atrial fibrillation, atrial and ventricular arrhythmias, myocardial ischemia, and potential cardiomyocyte necrosis via direct toxic effects and apoptosis induction. Rare concerns exist for hypersensitivity carditis.
Levosimendan
Levosimendan is utilised in patients with reduced left ventricular systolic function and hypoperfusion in the absence of severe hypotension. Although a bolus of 12 to 24 µg/kg over 10 minutes may be given, many clinicians directly initiate a continuous infusion at 0.05 to 0.10 µg/kg/min, uptitrating to 0.2 µg/kg/min. It significantly increases cardiac output, reduces pulmonary capillary wedge pressure (PCWP) and afterload, and improves dyspnea. Its effectiveness is retained in the presence of beta-blockers. Potent vasodilating effects can cause significant hypotension; this risk may be reduced by maintaining filling pressures. It should not be used in patients with low blood pressure. Initial clinical studies suggested reduced arrhythmias and improved survival compared to placebo and dobutamine, but subsequent trials showed mixed results.
Enoximone
Enoximone is a PDE IIIa inhibitor available in Europe. Its dosing is essentially 10 times that of milrinone, with a bolus dose of 0.25 to 0.75 mg/kg over 10 to 20 minutes, followed by an infusion of 1.25 µg/kg/min. It is extensively metabolised by the liver into renally cleared active metabolites, requiring dose reduction in renal or hepatic insufficiency.
General Practical Considerations
Excessive peripheral vasodilation and hypotension are major limitations of PDE inhibitors and levosimendan, particularly at high doses or when commenced with a bolus. Inotropes with adrenergic mechanisms can cause sinus tachycardia, increase ventricular rate in atrial fibrillation, induce myocardial ischemia and arrhythmias, and increase mortality. Levosimendan or PDE inhibitors may be preferred over dobutamine in patients on beta-blockers.
Guideline Recommendations
Guidelines recommend the use of inodilator drugs (dobutamine, milrinone, levosimendan) to increase cardiac output and lower pulmonary vascular resistance perioperatively according to the hemodynamic status of patients with PAH (Class IIa, Level C). In pregnant patients with cardiogenic shock, levosimendan (administered without an initial loading dose), dobutamine, and milrinone are recommended; adrenaline should be avoided. Mechanical circulatory support, preferably VA-ECMO, should be considered in severe refractory cardiogenic shock.
For pregnant patients, continuation of chronic therapy for PAH in the peri-operative phase of non-cardiac surgery is recommended (Class I, Level C), alongside hemodynamic monitoring for at least 24 hours post-operatively (Class I, Level C). In post-operative right heart failure progression, optimizing diuretic dose and initiating intravenous prostacyclin analogues under experienced guidance is recommended (Class I, Level C).
Prognosis and Follow-up
The prognosis of patients requiring these infusions is guarded, as intravenous inotropic agents have not been shown to improve clinical outcomes in heart failure. In the SURVIVE trial, levosimendan showed an early reduction in mortality compared to dobutamine that was not sustained through 180 days, though it was associated with a lower incidence of worsening heart failure. The REVIVE-II trial demonstrated significant improvements in clinical status, serial BNP, and hospital length of stay with levosimendan, but this came at the cost of more episodes of hypotension, atrial fibrillation, ventricular ectopy, and a nonsignificant increase in early deaths at 14 to 90 days.
Follow-up requires periodic reassessment of patients, documenting pain intensity, level of functioning, progress toward therapeutic goals, presence of adverse events, and adherence to prescribed therapies. Women with pregnancy-associated heart failure should be counselled regarding the risks of recurrence in subsequent pregnancies.
