A more detailed review of noradrenaline is available, where its many virtues are gleefully explored. The generic approach to the haemodynamically unstable cardiac surgical patient is also discussed elsewhere; noradrenaline forms a small part of the overall approach.
However, in Question 7 from the first paper of 2013, , the candidate was expected to reason throughtfully about the advantages and disadvantages of using a α-1 agonist specifically in the management of a post-bypass patient.
The summary below, therefore, relates only to this specific use of noradrenaline.
- Hypotension in the post-cardiothoracic surgery patient can be due to a multitude of factors.
- Noradrenaline theoretically addresses at least some of them, namely:
- Improves preload (by venoconstriction)
- Improves vasoplegia (by arterioconstriction)
- Improves cardiac contractility (β-1receptor effect increases with increasing dose)
- Improves diastolic filling of coronary arteries (by increasing diastolic pressure)
- Improves diastolic filling of the ventricles (by producing a reflex bradycardia)
Advantages of noradrenaline
- Cheap, by the standards of a developed country
- Short half life: easily titrated
- Relatively pure α-1 agonist effect; thus, no lactic acidosis due to its use
- Relatively linear dose-response relationship; predictable effects.
Disadvantages of noradrenaline
- Expensive, by the standards of a developing country (dopamine is still in use in many places owing to its gentle effect on the ICU budget)
- Increased afterload increases LV workload and decreases subendocardial perfusion, potentially worsening ischaemia
- In hypotension due to cardiogenic shock, noradrenaline will do little to improve blood pressure
- Temporary improvement in hemodynamic variables may obscure another cause of hemodynamic instability, eg. haemorrhage, infarction or cardiac tamponade.
Evidence for its use
- Guidelines support the use of noradrenaline.The AHA still recommends it as the pharmacological agent of choice (though not by name) in cardiogenic shock with poor fluid response (level C recommendation).
- However, in shocked post-cardiac-surgery patients, at least one trial has suggested that vasopressin is better.