Is spinach really good for you?

A case of

Methaemoglobinaemia

Jonathan Mervis

Case Study

• M.M. is a 3 month old female infant

• diarrhoea and vomiting for 3 days

• herbal medications given (oral and enema)

• increasing irritability, dyspnoea, poor feeding, depressed level of consciousness

• Family have running water, electricity, sewage

M.M., SHOWING CYANOSIS OF LIPS

What are possible causes of M.M.’s cyanosis?

Causes of cyanosis in children

1. Inadequate O2 of haemoglobin (common)• Pulmonary disorders

• R-L shunts

• Congestive heart failure

• Cardiovascular collapse

Causes of cyanosis in children, continued

2. Methaemoglobinaemia (rare)• Congenital:

– Cytochrome B5 reductase deficiency

– cytochrome B5 deficiency

– haemoglobin M

• Acquired:– Toxins

– Drugs

Normal Physiology

PaO2

% SaO2

50

100

2 6 12( Kpa)

Ph CO2

Temp2,3 DPG

Methaemoglobin

• Oxidation= Loosing an electron

• Reduction=gaining an electron

Fe(2+) Ferrous ion = good

Fe(3+) Ferric ion = bad

Methaemoglobin

Fe(3+) Fe(2+)

Cytochrome B5 Reductase

Cytochrome B5

Methaemoglobinaemia

• 20% acute increase = fatigue

• 30% acute increase = raised heart rate

• 50% acute increase = weak/ dyspnoeic/ confused

• 70%-80% acute increase= coma and death

Toxin induced MetHb

• Dependant on toxin, dose and duration of exposure

• Neonates and infants are more susceptible

Common toxins producing MetH

• Water from wells

• Drugs (over-the-counter meds, metoclopramide, nitrites, anti-malarials)

• Vegetables (SPINACH!)

• Diarrhoea

Case Study, continued

• M.M. was profoundly acidotic, shocked

• initial blood gas – Ph= 6.75/ CO2 =1.53/ O2 =26.4 unrecordable

• Poor perfusion, cyanosed, but good air entry and easy to ventilate

• Blood gas in ICU– Ph=6.78/ CO2=2.41/O2=57.2/ -27/ 3.4

Case Study, continued

• Central venous access yielded chocolate brown blood

• Lactate 17.6• throughout this time his O2 saturation

remained 80%-83%• Hb= 7.8

Blood on swab – note chocolate colour

What is the management of methaemoglobinaemia?

Management

• Ascorbic acid (vitamin C)– reduces methaemoglobin directly

• Methylene blue– acute levels >40%– IV 1-2mg/kg– repeat dose– G6PD deficiency– Dramatic response

Blood samples, showing improvement after methylene blue therapy

Treatment - note rapid improvement

09h00

10h00

1500VBG

Ph 6.89 6.99 7.28 CO2 2.51 2.58 6.06 O2

57.5 44.2 5.6 HCO3

3.4 4.4 20.9 BE -27 -25 -4.8 Met Hb %

84% 50% 0.1%

Treatment

Conclusion

Consider methaemoglobinaemia when there is

• Cyanosis with high PaO2 ,

• Child is easy to ventilate and well-perfused

Further reading

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