Question 7

Created on Tue, 05/12/2015 - 19:11
Last updated on Tue, 08/11/2015 - 18:40
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Discuss the role of nor-adrenaline in the management of hypotension post cardiac surgery.

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College Answer

Introduction

Hypotension following cardiac surgery is a common and important problem. Appropriate management includes correct diagnosis of the underlying problem and definitive treatment of the cause as well as supportive care.

Rationale

Primarily alpha agonist (vasoconstriction) with increasing beta actions (ino/chronotrophy) as dose increases. 
Has a short half- life and so given as continuous intravenous infusion and easily titratable. Increases blood pressure mainly by increase in diastolic BP and so increasing MAP and also increasing coronary artery perfusion pressure

Reflex bradycardia with lower doses may also allow increased time for diastole and so increased ventricular filling and coronary artery perfusion

Pros

Appropriate for post- pump vasodilation / SIRS response to CBP – a common cause of post cardiac surgery hypotension

There is less risk of the Beta adrenergic side effects of adrenaline such as tachyarrhythmias, hyperlactataemia and hyperglycaemia.

It has the potential advantage of increasing DBP and myocardial perfusion and subsequently contractility in context of ischaemia.

Familiar agent in ICU setting

Cheap and widely available (not all countries e.g. South Africa)

Cons

Must be used with caution as a single agent in scenarios where preload or contractility is not optimal.

I.e. exclude / correct hypovolaemia, tamponade and treat poor myocardial function appropriately

Excessive use can result in end-organ hypoperfusion.

Own practice.

Any reasonable practice and justification acceptable.

Summary

Nor-adrenaline is useful drug in this situation when hypotension due to vasodilation or reduced coronary perfusion pressure but important to ascertain and treat the underlying cause.

Discussion

The above answer does not call for a superior level of pharmacological insight. "Any reasonable practice and justification acceptable" they say.

Noradrenaline in general is well discussed elsewhere.

A brief discussion of the role of noradrenaline in the post-cardiotomy setting can be found in the  "Required Reading" section concerned with cardiothoracic intensive care.  Highlights include the following:

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

References

Maas, Jacinta J., et al. "Cardiac Output Response to Norepinephrine in Postoperative Cardiac Surgery Patients: Interpretation With Venous Return and Cardiac Function Curves*." Critical care medicine 41.1 (2013): 143-150.

Hajjar, L., et al. "Vasopressin Versus Norepinephrine for the Management of Shock After Cardiac Surgery (VaNCS study): a randomized controlled trial." Critical Care17.Suppl 2 (2013): P222.

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