You are a young #medicine resident!
You are working in a heavy emergency when:
23,โ๏ธ,p/w acute breathlessness
You check his SpO2, it's๐๐ป
You are worried and start him on supplemental 02, but he remains hypoxic๐ญ
Read on for the diagnosis and a brief review!
1/20
#MedTwitter
You are working in a heavy emergency when:
23,โ๏ธ,p/w acute breathlessness
You check his SpO2, it's๐๐ป
You are worried and start him on supplemental 02, but he remains hypoxic๐ญ
Read on for the diagnosis and a brief review!
1/20
#MedTwitter
Let's start with the causes of hypoxic that don't respond to supplemental oxygen !
๐ธRโก๏ธL cardiac shunts
๐ธMethemoglobinemia
๐ธSulfmethemoglobinemia
The ABG that you sent is back!!
It shows a normal Pa02 but your pulse oximeter is still reading 85% ๐คทโโ๏ธ
2/20
#MedTwitter
๐ธRโก๏ธL cardiac shunts
๐ธMethemoglobinemia
๐ธSulfmethemoglobinemia
The ABG that you sent is back!!
It shows a normal Pa02 but your pulse oximeter is still reading 85% ๐คทโโ๏ธ
2/20
#MedTwitter
Your registrar is smart and he asks you to send another sample, this time asking the lab for a methemoglobin value.
Voila !!
The lab says: 45% methemoglobin ๐ฎ
3/20
#MedTwitter
Voila !!
The lab says: 45% methemoglobin ๐ฎ
3/20
#MedTwitter
Diagnosis established, registrar is a hero ๐ซก
This is acute methemoglobinemia, most likely acquired, secondary to some drug/toxin ๐ฎ
4/20
#MedTwitter
This is acute methemoglobinemia, most likely acquired, secondary to some drug/toxin ๐ฎ
4/20
#MedTwitter
Let's list out a few drugs/toxins you need to ask about:
1. Primaquine
2. Dapsone
3. Aniline dyes
4. Nitrites
5. Napthalene
6. Rasburicase
7. Topical anesthetic
The list is endless, any oxidant drug can l/t this !
5/20
#MedTwitter
1. Primaquine
2. Dapsone
3. Aniline dyes
4. Nitrites
5. Napthalene
6. Rasburicase
7. Topical anesthetic
The list is endless, any oxidant drug can l/t this !
5/20
#MedTwitter
Our guy was given some medication for fever by his GP, most likely an antimalarial. Maybe that's the trigger !!
It's important to know because it's to be avoided, FOREVER !!
6/20
#MedTwitter
It's important to know because it's to be avoided, FOREVER !!
6/20
#MedTwitter
You start treating him immediately โ
1. Continue oxygen
2. Get an IV in place
3. STOP THAT DRUG
4. Send his G6PD levels !!
Wait, G6PD !! WHYโ
7/20
#MedTwitter
1. Continue oxygen
2. Get an IV in place
3. STOP THAT DRUG
4. Send his G6PD levels !!
Wait, G6PD !! WHYโ
7/20
#MedTwitter
G6PD is important here. To understand this, we need to understand the pathophysiology of metHb'emia
MetHb = Fe++โก๏ธFe+++
i.e. oxidation=loss of electron
This Fe+++ can't deliver 02 to tissues so hypoxia develops, it's like functional anemia
Treatment Aim: reduce it back to Fe++
MetHb = Fe++โก๏ธFe+++
i.e. oxidation=loss of electron
This Fe+++ can't deliver 02 to tissues so hypoxia develops, it's like functional anemia
Treatment Aim: reduce it back to Fe++
How does one convert Fe+++โก๏ธFe++
You add an electron, i.e search for an electron donor !!
In the body, an enzyme called Cytochrome B5 reductase does that.
So if this is โคต๏ธ then one can develop congenital metHb'emia or be predisposed to it at lesser dose of trigger drug!
9/20
You add an electron, i.e search for an electron donor !!
In the body, an enzyme called Cytochrome B5 reductase does that.
So if this is โคต๏ธ then one can develop congenital metHb'emia or be predisposed to it at lesser dose of trigger drug!
9/20
Another way of Fe+++โก๏ธFe++ is to use NADPH from the HMP shunt (uses G6PD)
Normally this is not active in the RBC because RBC has no electron acceptor. This works only if extrinsic electron acceptor like methylene blue is present !!
Phew ๐ด๐ด
10/20
Normally this is not active in the RBC because RBC has no electron acceptor. This works only if extrinsic electron acceptor like methylene blue is present !!
Phew ๐ด๐ด
10/20
Ok, I'll summarise !!
๐ธMetHb is commonly drug induced
๐ธHypoxia despite 02
๐ธNormal Pa02 but โคต๏ธSp02
๐ธCyanosis ++
๐ธTreat:
Stop drug
Give an electron donor to reduce Fe+++
Don't worry, we are ๐๐ป
11/20
#MedTwitter
๐ธMetHb is commonly drug induced
๐ธHypoxia despite 02
๐ธNormal Pa02 but โคต๏ธSp02
๐ธCyanosis ++
๐ธTreat:
Stop drug
Give an electron donor to reduce Fe+++
Don't worry, we are ๐๐ป
11/20
#MedTwitter
Coming back to the patient !
You recieve his G6PD levels and they are within normal limits ๐๐ป
You decide to administer methylene blue ๐ต๐ต๐ต
Dose: 1mg/kg IV
Repeat dose after 1 hr if symptoms persist.
12/20
#MedTwitter
You recieve his G6PD levels and they are within normal limits ๐๐ป
You decide to administer methylene blue ๐ต๐ต๐ต
Dose: 1mg/kg IV
Repeat dose after 1 hr if symptoms persist.
12/20
#MedTwitter
You can't use the ABG now to monitor his methemoglobin levels !!
The methylene blue will cause a false + reading. Can't get into details here, DM for more if interested !
So next dose only if clinically indicated, i.e. dyspnoea still present or worse.
13/20
#MedTwitter
The methylene blue will cause a false + reading. Can't get into details here, DM for more if interested !
So next dose only if clinically indicated, i.e. dyspnoea still present or worse.
13/20
#MedTwitter
What if his G6PD was โคต๏ธ ?
1. The methylene blue wouldn't work
2. The methylene blue could possibly harm him too!
Methylene blue is an oxidant itself and in G6PD deficiency it can paradoxically cause methemoglobinemia๐คทโโ๏ธ
We use high dose Vit C here, upto 10gm
14/20
#MedTwitter
1. The methylene blue wouldn't work
2. The methylene blue could possibly harm him too!
Methylene blue is an oxidant itself and in G6PD deficiency it can paradoxically cause methemoglobinemia๐คทโโ๏ธ
We use high dose Vit C here, upto 10gm
14/20
#MedTwitter
Also don't use methylene blue if a patient is on an SSRI.
There's a risk of serotonin syndrome !!
15/20
#MedTwitter
There's a risk of serotonin syndrome !!
15/20
#MedTwitter
This patient recieved Methylene blue x 1 dose and recovered well ๐๐ป
But did he have some predisposition to develop it in the first place ??
Maybe some enzyme deficiency, like cytochrome B5 reductase as we spoke about earlier !
16/20
#MedTwitter
But did he have some predisposition to develop it in the first place ??
Maybe some enzyme deficiency, like cytochrome B5 reductase as we spoke about earlier !
16/20
#MedTwitter
Maybe !!
Heterozygous state for cytochrome b5 reductase can predispose to developing metHb with minimal exposure d/t borderline enzyme activity.
Any little exposure might push them over the edge ๐๐ป
17/20
#MedTwitter
Heterozygous state for cytochrome b5 reductase can predispose to developing metHb with minimal exposure d/t borderline enzyme activity.
Any little exposure might push them over the edge ๐๐ป
17/20
#MedTwitter
Homozygous state presents in childhood itself w/
1. Chronic cyanosis
2. Minimal hypoxia due to a compensatory โคด๏ธRBC (erythrocytosis)
The acute management won't change so it's not so important to determine this at present. Can order an enzyme activity/NGS after recovery !
18/20
1. Chronic cyanosis
2. Minimal hypoxia due to a compensatory โคด๏ธRBC (erythrocytosis)
The acute management won't change so it's not so important to determine this at present. Can order an enzyme activity/NGS after recovery !
18/20
Summary slide, yeah finally ๐คฃ
๐ธWhen to suspect:
โขHypoxia despite 02
โขUnexplained cyanosis
๐ธEasy to dx on an ABG
๐ธInherited or acquired
๐ธDetailed drug history
๐ธTreat if metHb โฅ10%
๐ธSend G6PD
๐ธStart Vitamin C
๐ธGive methylene blue if normal G6PD
19/20
๐ธWhen to suspect:
โขHypoxia despite 02
โขUnexplained cyanosis
๐ธEasy to dx on an ABG
๐ธInherited or acquired
๐ธDetailed drug history
๐ธTreat if metHb โฅ10%
๐ธSend G6PD
๐ธStart Vitamin C
๐ธGive methylene blue if normal G6PD
19/20
If you've read this far, you are awesome ๐ช๐ผ๐ช๐ผ๐ช๐ผ๐ช๐ผ๐ช๐ผ๐ช๐ผ๐ช๐ผ๐ช๐ผ๐ช๐ผ๐ช๐ผ๐ช๐ผ๐ช๐ผ๐ช๐ผ๐ช๐ผ
Thank you ๐๐ป
#MedTwitter if you like it, share it โ
20/20
#MedEd
Thank you ๐๐ป
#MedTwitter if you like it, share it โ
20/20
#MedEd
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