Methaemoglobinaemia: a case study in blue…

Dr CM ShevlinOctober 2013

Presentation of case

• 54 y/o self-employed

gardener/labourer – PmHx:

depression with psychotic

elements

• 12 delayed presentation of

homemade weedkiller ingestion

• Brought up by brother to A&E

after admitting overdose

First contact with ICU

• Asked to see cyanosed

patient “desaturating”

on 15L oxygen 12 hours

post OD of unknown

substance

• ‘Lavender’ hued patient

• Cardiovascularly stable

• GCS 14-15

• Likely diagnosis =

methaemoglobinaem

ia secondary to

probable chloral

hydrate ingestion

• Could not confirm on

blood gas

ICU management

• Transferred to ICU

• Sample methaemoglobin

sent on ice to lab = 60.7!!

• Oxygen therapy, PPI,

fluids, 140mg stat

methylene blue & 10ml/hr

• Serial methaemoglobins

The next day…

• Still cardiovascularly stable…GCS 15…no

seizures/arrhythmias/respiratory symptoms.

MetHb levels 20%

• Methylene blue infusion continued (plan until

metHb levels normal)

• Haptoglobins checked

• Dose of ascorbic acid

• Low threshold CRRT

Methaemoglobinaemia

• Altered state of haemoglobin: irons of

haem oxidised to ferric (Fe3+ state)

• Normal state: 0.5-3% spontaneously

• Overproduction or failure of reduction

• How common is it?

MetHb and methylene blue cause falsely low readingsTends to drive measured saturation towards 85%

• Usually only

one important

pathway for

metHb – Hb

• Methylene

blue activates

underused

alternative

pathway

HeadacheFatigueLethargy

Metabolic acidosisSeizuresComa

Management

• Supportive therapy

• Methyl thioninium chloride aka methylene

blue

• 2mg/kg bolus, if needed infusion

• max 7mg/kg in 24 hr period

• Hyperbaric oxygen

• Blood transfusion/exchange transfusion

Therapeutic methaemoglobinaemia

• Hydrogen sulphide toxicity

• Cyanide toxicity

• Acts as a scavenger:HS greater

affinity for metHB than cytochrome

oxidase

• Methaemoglobinaemia induced with

either amyl nitrate or sodium nitrite

Congenital methaemoglobinaemia

• Cytochrome B5 reductase

deficiency (local or

general)

• Cyanosis - or severe

systemic effects

• Most autosomal recessive

• Haemoglobin M: single

substitution in globin gene

Epidemiology of congenital methaemoglobinaemia

• Two -well-known in the literature -

family enclaves of congenital

methaemoglobinaemia

• The first the Blue Fugates of

Troublesome Creek in the US…

• And the second?

Possible explanation?

• 5 days in ICU – on discharge metHb still 8.8%

• 5 further days in hospital – last measured metHb

still elevated at 8%

• Never experienced the severity of symptoms he

should have had for metHb of 60%...

• From a region with known cases of congenital

metHb…

• Heterozygous genetics risk factor for acquired

methaemoglobinaemia….

Outcome

• Declined admission to Bluestone Unit

• Doing well on psychiatry follow-up

appointments on increased dose of

antidepressants