Interventional Agents

Anaesthetic agents have a number of side effects and it is often necessary to treat these issues using some of the following drugs -

Dobutamine

Dobutamine is used in patients with heart failure. It can be used as emergency treatment in patients with cardiogenic shock. It can be used in anaesthesia when there is hypotension or bradycardia due to poor myocardial contractility.

Dobutamine is a synthetic catecholamine which acts as a β1 selective adrenoceptor agonist. Dobutamine is a sympathomimetic and postive inotrope. It exerts this effect by stimulating β1 adrenergic receptors. This causes a rise in cAMP though the activation of adenylate cyclase. This increase causes an increase in slow inward calcium currents. It also increases calcium storage in the sarcoplasmic reticulum making more calcium available to contractile muscle fibres, thereby increasing myocardial contractility. It also acts at β1 and β2 receptors in the peripheral vasculature.

Dobutamine has a low half life and so is given via a continuous rate intravenous infusion. Due to its potential side effects however, it can only be administered for a maximum of 48 hours.

Side Effects

• Reflex hypertension may develop
• Cardiac arrhythmias

Dopamine

Dopamine is used in the short term for patients with systolic dysfunction as well as in the management of oliguric renal failure. It can be used as a pressor agent to help treat hypotension in concious and anaesthetised patients.

Dopamine is a noradrenaline precursor which acts on both α and β cardiac receptors, as well as dopaminergic receptors found peripherally. It is a positive inotrope that is very similar to dobutamine in action. It should be administered via a continuous rate infusion.

Ephedrine

Ephedrine can be used as a bronchoconstrictor as well as a pressor agent for shock patients. In non emergency situations it is used to increase the tone of the bladder spincter in cases of urinary incontinance.

Ephedrine has the same action as epinephrine but has slightly different properties. It is similar to amphetamines in that ephedrine causes noradrenaline release leading to catecholaminergic receptor stimulation. Ephedrine has a lower potency but longer duration of action when compared with epinephrine. It also has more pronounced CNS effects.

Contraindications

• Severe cardiovascular disease
• Use with caution in patients with diabetes mellitus, hyperthyroidism, prostatic hypertrophy and glaucoma.
• Irritability
• Tachycardia
• Hypertension
• Anorexia

Use of ephedrine can induce tachycardia and hypertension and animals should be monitored carefully with this in mind.

Ephedrine has been used in Chinese tradition medicine for thousands of years and is a natural product essentially having the same action as epinephrine but different properties.

Phenylephrine

Phenylephrine is used to treat hypotension caused by a number of factors including barbituate anaesthesia. In non emergency situations, it has diagnostic properties when used opthlamically.

Phenylephrine is an α adrenergic sympathomimetic used to treat hypotension without cardiac stimulation. Due to metabolism in the gastrointestinal tract, it is presented in an injectable form. It acts by causing peripheral vasoconstriction leading to an increase in blood pressure, both systolic and diastolic. However, a reflex bradycardia may be seen. There is a increase in coronary blood flow. If administered intravenously onset is almost immediate, and duration of action is approximately 20 minutes; if administered intramuscularly onset of action is approximately 10-15 minutes with a duration of action of approximately 1 hour.

Contraindications

• Hypertension
• Ventricular Tachycardia
• Geratric patients
• Pregnant patients - causes uterine contraction.

Vasopressin

Vasporessin is indicated in patients with vasodilatory shock or ventricular fibrillation.

Vasopressin is a non-catecholamine vasopressor. It is a hypothalamic hormone found in the posterior pituitary which promotes renal reabsorption of water as well as smooth muscle contraction particularly of capillaries and small arterioles. This smooth muscle contraction may lead to decreased blood flow to internal body systems but increased hepatic blood flow.

Contraindications

• Vascular disease
• A history of seizures
• Heart failure
• Pregnancy

Possible side effects include vasconstriction and arrhythmias.