Noradrenaline in the post-cardiotomy setting

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.

Rationale

• 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.