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• Response
  M J Reed
  Published on: 29 April 2016
• Administering a glyceryl trinitrate infusion: faster is better than slower
  Alistair Steel
  Published on: 29 April 2016
• Effective treatment of ACPO
  Dominic Williamson
  Published on: 29 April 2016

• Published on: 29 April 2016

  Response

  • M J Reed

  Dear Editor,

  I would like to thank Alistair Steel and James Varley for their interest in my paper and for their extremely useful comments. I would agree with them that infusions should be purged prior to connection, something which I suspect is commonly done, and that higher doses of GTN should be used, a point which I make in my paper. I also agree with them that a bolus should be given in critically unwell p...

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  Dear Editor,

  I would like to thank Alistair Steel and James Varley for their interest in my paper and for their extremely useful comments. I would agree with them that infusions should be purged prior to connection, something which I suspect is commonly done, and that higher doses of GTN should be used, a point which I make in my paper. I also agree with them that a bolus should be given in critically unwell patients while the infusion is being set up, however I suspect this is not done routinely. For this reason I still believe that it is very useful to make practioners aware of the extreme differences in dead space depending on the cannula size and initial infusion rate used. I hope after the considerable interest the article has generated, an initial bolus, a higher initial infusion rate and a move away from large diameter cannulae will become common practice.

  Yours faithfully.

  Matthew Reed

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  Conflict of Interest:
  None declared.

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• Published on: 29 April 2016

  Administering a glyceryl trinitrate infusion: faster is better than slower

  • Alistair Steel, Anaesthetics & Critical Care Specialist Registrar
  • Other Contributors:
    • James Varley

  Dear Editor,

  Matthew Reed highlights the importance of practical issues in his article promoting the use of small-diameter cannulae for glyceryl trinitrate infusions.(1) However, there are several other issues that should be considered when administering drugs at low infusion rates.

  Firstly, mechanical slack within an infusion device may mean an infusion set at 1ml/hr will take many minutes for the dri...

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  Dear Editor,

  Matthew Reed highlights the importance of practical issues in his article promoting the use of small-diameter cannulae for glyceryl trinitrate infusions.(1) However, there are several other issues that should be considered when administering drugs at low infusion rates.

  Firstly, mechanical slack within an infusion device may mean an infusion set at 1ml/hr will take many minutes for the driver to contact and advance the syringe plunger. For this reason infusions should be purged prior to patient connection.(2)

  Secondly, the pharmacokinetics of the drug should be considered. At low infusion rates it will take significant time for a steady state to be achieved (a drug such as GTN, with a half like of two minutes, would require 10 minutes to achieve steady state) For clinical effects to be seen quickly, a bolus should be given prior to commencing infusions.(3)

  Thirdly, the use of 1ml/hr infusions (8mcg/min of a 0.5% solution) may be excessively cautious – the British National Formulary recommends a therapeutic dose range from 10 to 200mcg/min.(4) Furthermore, there is emerging evidence that when used for decompensated heart failure, higher doses of GTN are associated with more favourable outcomes.(5)

  Finally, at low infusion rates any obstruction in the IV system will take a proportionally longer time to become apparent, as it will take longer for the pressure to build up and trigger the syringe pump’s pressure alarm.

  When bearing these aspects in mind, the diameter of the cannula becomes less important.

  Yours faithfully,

  Alistair Steel MRCP FRCA

  James Varley MRCS FRCA

  1) Reed MJ. Administering a glyceryl trinitrate infusion: big is not always best. Emerg Med J. 2007; 24(6):423-4.

  2) Stephen Keay and Chris Callander The safe use of infusion devices CEACCP, 2004; 4: 81 - 85.

  3) SA Hill Pharmacokinetics of drug infusions CEACCP, 2004; 4: 76 - 80.

  4) http://www.bnf.org/ Accessed on 8th August 2007

  5) Levy P, Compton S, Welch R, Delgado G, Jennett A, Penugonda N, Dunne R, Zalenski R. Treatment of severe decompensated heart failure with high-dose intravenous nitroglycerin: a feasibility and outcome analysis. Ann Emerg Med. 2007;50(2):144-52.

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  Conflict of Interest:
  None declared.

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• Published on: 29 April 2016

  Effective treatment of ACPO

  • Dominic Williamson, Consultant in Emergency Medicine

  Dear Editor,

  I welcome Matthew Reed's article emphasising the role of nitrates in the emergency management of severe acute cardiogenic pulmonary oedema (ACPO). I also welcome his appreciation of the dead space involved in the use of any cannula, which so often seems to be ignored.

  ACPO occurs as a result of decompensation of the left ventricle initiating a circle of increasing preload, often with incr...

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  Dear Editor,

  I welcome Matthew Reed's article emphasising the role of nitrates in the emergency management of severe acute cardiogenic pulmonary oedema (ACPO). I also welcome his appreciation of the dead space involved in the use of any cannula, which so often seems to be ignored.

  ACPO occurs as a result of decompensation of the left ventricle initiating a circle of increasing preload, often with increasing afterload, in the presence of worsening oxgenation. Any intervention that acutely improves oxygenation and/or reduces preload (and afterload) will often initiate a recovery. The quicker this occurs the more likely the patient will make a prompt recovery.

  The use of intravenous nitrates is a very effective means of reducing preload and subsequently improving cardiac output but there is inevitably a delay in initiating this therapy. This delay, as Matthew Reed points out, will be exacerbated by using a slow infusion rate through a wide bore cannula.

  I would therefore advocate the use of sublingual or buccal nitrates as soon as the condition is recognised (and this is often in the pre- hospital phase) which 'buys time' to set up a nitrate infusion. I would also advocate initiating any nitrate infusion at the higher end of the recommended dose schedule (12mg/hour for glyceryl trinitrate, 10mg/hour for isosorbide dinitrate). This not only overcomes the potential dead space issue but more importantly ensures the patient will receive an effective dose in an appropriate timescale. These patients are usually critically unwell and will be managed in a high dependency area of any hospital. They will therefore be closely observed. Any adverse effect of high dose nitrates on perfusion pressure, which is uncommon in ACPO in my experience, can be easily managed by titrating back on the infusion rate. We must overcome many practitioners, in Emergency as well as other specialities, use of less effective treatments in what is an extremely distressing and potentially life threatening condition.

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  Conflict of Interest:
  None declared.

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