Inotropes and vasopressors have excitatory and inhibitory actions on the heart and vascular smooth muscle. They also effect the metabolic, central nervous system and presynaptic autonomic nervous system.
They are powerful drugs used in intensive care to regulate a patient’s heart rate, blood pressure and the force of the heart’s contraction. They do this by working on specific receptors throughout the body. Small changes in the rate of infusions of these agents may produce a rapid response in the patient’s heart rate and blood pressure. In some intensive care unit patients, the maintenance of blood pressure is extremely dependent on the inotrope and vasopressor infusions and hence careful titration and continuous monitoring is essential.
UseInotropes: Agents that increase myocardial contractility.
Vasopressors: Agents that cause vasoconstriction by stimulating vascular smooth muscle contraction.
Vasodilators: Agents that relax the smooth muscle in blood vessels, causing:
• Dilation of arterial (resistance) vessels which reduces systemic vascular resistance, and leads to a fall in arterial blood pressure
• Dilation of venous vessels which decreases venous blood pressure.
Inotropes are indicated if you think the patient will benefit from increased cardiac output. For example, a patient with cardiogenic shock with acute decompensated heart failure. Vasopressors are indicated if you think the patient will benefit from vasoconstriction and elevated mean arterial pressure. For example, a patient who is hypotensive due to septic shock and its associated vasodilatation.
A tachycardia produced by the Β1 effects of inotropes will increase the workload and myocardial oxygen requirement of the heart.
• In patients who have cardiac disease, the myocardial oxygen demands may exceed the myocardial oxygen supply and myocardial ischemia may result. α1 effects cause vasoconstriction and the systemic vascular resistance or afterload increases.
• This will improve blood pressure, but it also means the heart will have to work a lot harder in order to eject the blood from the ventricle.
• Increased heart workload means increased myocardial oxygen demands.
• If this exceeds myocardial oxygen supply, then ischaemia may occur.
• This could have a significant impact on patients with a cardiac history. As dobutamine exhibits minimal α properties, blood pressure is only supported by increased myocardial contractility; therefore if hypotension persists an α agonist may be required.
Modes of action
1. Most drugs produce their effects by acting on specific protein molecules known as receptors.
2. These receptors are activated by neurotransmitters or hormones. Neurotransmitters are substances that activate a receptor and produce a response.
3. Drugs that bind to receptors and produce a response are called agonists. Drugs that bind to receptors but do not activate them are called antagonists.
4. By binding to receptors, antagonists reduce the probability of transmitter substances or hormones binding to the receptor and therefore are often used to block the action of other endogenous transmitters or hormones.
Safe administration of inotropes and vasopressors
Small changes in the rate of infusions of these agents may produce a rapid response in patients’ heart rate and blood pressure. In some ICU patients, the maintenance of blood pressure is extremely dependant on the inotrope and vasopressor infusions and hence careful titration and continuous monitoring is essential.
Inotropes and vasopressors need to be regulated by continuous infusion to maintain a consistent dose delivery and haemodynamic control.
Continuous monitoring of blood pressure with arterial lines is necessary to help close monitoring and titration of therapy. ICU patients commonly require multiple drug infusions together with intermittent drug administration. These infusions and drugs need to be distributed amongst the available lumens according to safe administration, drug compatibilities and the number of lumens available.
Issues to consider in safe administration
• How ‘secure’ the lumen is, with the more distal lumens being the most secure (i.e. drug delivery is less likely to be affected if the line migrates outwards). In general, the most distal lumen should be reserved for emergency drug access and the second most distal lumen reserved for vasoactive drugs.
• The use of double/multiple concentrations with inotropes and vasopressors is not considered best practice. For patients on fluid restrictions, aim to optimise their fluid management in other ways.
• The rate of administration of drugs on the same lumen (co-administration of a fast-running drug can increase the delivery of a slow running drug through the venturi effect. This can result in unexpected cardiovascular changes if a drug is bolused through a lumen through which a vasoactive drug is also being delivered).
Drug administration is also limited by drug compatibilities. All lines should be monitored for the formation of precipitates when more than one drug is delivered to a lumen. The ongoing need for a central venous catheter should be reviewed daily and the central venous catheter removed if it is no longer necessary.