S2E1: Methemoglobinaemia - Inclusion Health

Written By Mohammed Hamza

Welcome back to a new season of TheCase.Report

We're back and we're better than ever!

Special thanks is due to IAEM, the Irish Association for Emergency Medicine for their kind support. Make sure you register for the ASM next month, on October 14th and 15th.

But look, we know it's been a long dry summer for you all without us, so we'll get to the matter at hand.

For our case, Mohammed was joined by his esteemed trainee colleagues, Orla and Karl… (Who let those 3 at it?!)

Thankfully our Adult in the Room Dr Darren McLoughlin was close at hand to check their work!

Mohammed was then Joined by Dr Eamon Keenan for a chat ahead of the release of the report of the Emerging Drug Trends and Drug Checking Working Group.

Right, let's get to it!

Dr Eamon Keenan’s links:

  1. Therapeutic potential of long-acting opioids and opioid antagonists for SARS CoV-2 infection - https://www.sciencedirect.com/science/article/pii/S0007091221005535

  2. Drug-related deaths in Ireland: key patterns and trends 2008-2017. Drug insights report 1. - https://www.drugsandalcohol.ie/34800/

How we present our case matters!

Before we get into the meat of this, let’s touch on good oral case discussion practice. SDMs can’t be everywhere at once in an ED, and much of the time there aren’t enough of them particularly out of hours, so we rely heavily on good quality communication to maintain the function in the department. This is a critical area in terms of CRM and patient safety so we need to be really sharp here. Much of the time the focus is on the incisive probing questions we ask to elicit the important information needed to make a decision or offer advice on a patient/situation, but like with the actual history taking from the patient, we should ideally not have to interject much. An organised structured presentation really helps.

  • Ensures important information isn’t forgotten

  • Ensures important negatives are stated

  • Keeps the discussion concise and pertinent

What’s important/pertinent is a tricky one, something that’s learned with time and experience, but we can help improve our own and each other’s skills with practice and feedback.

This paper from Davenport et al. gives a good overview and gives advice regarding good structure and feedback.

Attitude Awareness


Not just a module in your clinical years. This is real life, and has real consequences to our patients’ lives. 

We know that our attitudes to different patient groups in the absence of active introspection are not what we may think they are, and that these attitudes have real effects on outcomes.

Working somewhere with an inclusion health team or even one specialist can make a great difference in both attitudes and outcomes.

RCEM have published guidance last year on Homelessness and Inclusion Health, and from that we see the importance of having a positive/proactive outlook when dealing with marginalised patient groups or those who are socially isolated. Their ED attendance may be an opportunity to positively intervene.

Specifically in the case of homeless patients, who are 60 times more likely to visit the ED than the general population:
“Chronic homelessness is an associated marker for tri-morbidity, complex health needs and

premature death. Tri-morbidity is the combination of physical ill health needs with mental

health needs and drug and alcohol misuse. This complexity is often associated with

advanced illness at presentation, in the context of a person lacking social support who

often feels ambivalent about accessing care and their own self-worth.

Attending an emergency department represents an opportunity to provide healthcare

advice and offer information regarding accessing social and other support.”

Methaemoglobinaemia

Not an uncommon exam question, but it actually happens in real life too!


What is it?
- Too much methaemoglobin… duh

- Normal level- <1.5%


Breaking it down (how does it work): 

  • Pulse oximetry is inaccurate

  • Normal haemoglobin carries O2 at the iron sites on the globulin chains

  • Methaemoglobin is where the iron sites have been oxidised from ferrous to ferric and lose their oxygen binding capacity

  • In turn this causes the remaining haemoglobin to increase its oxygen binding, resulting in a leftward shift in the oxygen dissociation curve.

  • A higher affinity for oxygen in the normal haemoglobin prevents it from releasing that O2 into tissues, causing tissue ischaemia



Causes:

  • Congenital

    • Cytochrome b5 reductase deficiency (deficiency of methaemoglobin reductase, 2 types)

    • Haemoglobin M disease (rare hereditary disorder where cyanosis is the only symptom, permanently increased methaemoglobin levels between 15-30% but no effect on life expectancy)

  • Acquired

    • Nitrites including “poppers”

    • aniline dyes

    • nitrofurantoin

    • benzene derivatives

    • chloroquine

    • dapsone

    • prilocaine

    • metoclopramide

    • sulphonamides


How do they present?

Vague

  • SOB

  • Chest pain

  • Altered GCS

Specific

  • BLUE

  • Choco-blood

  • Normal PaO2

  • Low SpO2 that does not respond to supplemental oxygen

Symptoms and severity are proportional to the level of methaemoglobin

How do you make the diagnosis:

  • Clinical Hx and Exam

  • Blood gas

    • ABG vs VBG- either will show a high MetHb, but an initial ABG is important as it will confirm a normal/high PaO2

Management:

General:

  • Standard resuscitative measures, ABC

Unblue the patient-

Specific:

  • Remove the cause 

  • Methylene blue (1-2mg/kg over 5 mins)

    • Increases reduction of MetHb through “artificial electron acceptor” and NADPH-dependent pathway

    • Will NOT work in G6PD deficiency

    • Can repeat in 30-60 mins if no improvement 


Indications for Methylene Blue:

  1. Symptomatic methaemoglobinaemia

  2. MetHb >25%, even if asymptomatic (dose dependent on level)


Alternatives:

  • Ascorbic acid

  • Exchange transfusion

  • Hyperbaric oxygen

  • Possibly NAC (in vitro study)

Whichever reducing agent is used, glucose will be required for the generation of NADPH by the hexose monophosphate shunt.





Resources:

Mohammed Hamza
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