Thread by @Loki_bandana

Hye gais

masa round, u saw an ABG & u were like "ni respiratory acidosis ni"

then MO come "eh this is Chronic respiratory acidosis"

Then your specialist come "walao, ni acute on chronic respiratory acidosis"

then consultant come "eh got concurrent metabolic acidosis sumore"

then you were like "eh where got lah ??"

i know some of you already know how to interprete ABG so well ady. BUt ill just put it out there for those yg still find ABG a tad difficult to read. ill try to simplify it for you

WARNING: Long post

step by step ABG interpretation macam ni:
step 1: is it acidosis or alkalosis (tgk pH)
step 2: is it respiratory or metabolic (tgk CO2, HCO3)

okay upto this point semua org tahu kan. even the normal value all? so aku x mention

kalau respiratory biasa CO2 yg akan too high (acidosis) or low (alkalosis)

Metabolic pulak HCO3 high (alkalosis), low (acidosis)

semua ni konfem semua org tahu kan

step 3: kalau korg dapat respiratory, korg kena tahu, is it acute, chronic, or acute on chronic?

step 4: kalau dpt metabolic pulak, x payah bother pasal acute chronic semua tu, tapi KENA kira Anion Gap (AG)

Step 5: kalau metabolic acidosis, ada respi compensation tak?

so ramai yg start jammed dekat step 3 ke atas. dia senang je sbnanya..

step 3 tu mcm ni.

kalau Respiratory acidosis (PCO2 naik) :
- acute; setiap 10mmHG PCO2 yang naik, HCO3 akan naik 1 meq/L
- chronic; setiap 10mmHG PCO2 yang naik, HCO3 akan naik 3.5 meq/L

acute : 1
chronic: 3.5

Kalau respiratory alkalosis (PCO2 turun) pulak :
- acute; setiap 10mmHG PCO2 yang turun, HCO3 akan turun 2 meq/L
- chronic; setiap 10 mmHG PCO2 yang turun, HCO3 akan turun 5 meq/L

acute : 2
chronic : 5

ok aku kasi contoh

pH 7.2 (normal 7.35 - 7.45) - acidotic

PCO2 60 (normal 40) -> raised 20

PO2 65 (normal 80-100)

HCO3 26 (normal 24) -> raised 2

primary disorder dia ialah respiratory acidosis. but acute ke chronic?

so kita kira EXPECTED raised HCO3 in
-acute: (20/10) x 1= 2
-Chronic: (20/10) x 3.5 = 7

so ABG kat atas, HCO3 raised by 2 meq/L from normal value (24) n match the expected HCO3 in acute.

so this is acute respiratory acidosis

kalau HCO3 tu raised by around 7, jadila dia chronic

kalau raised HCO3 tu fall between 2-7, jadilah dia acute on chronic

Macam tu je... huhi

so nnti korg WAJIB kira expected raised HCO3 dulu, pastu tgk yg measured HCO3 tu, dia raised masuk teritory acute ke chronic ke or acute on chronic

mesti korg confuse sebb HCO3 normal value is 22-26 kan. kenapa aku letak 24 je? pastu PCO2 normal value 35-45, tapi aku letak 40..

adik2 kakak2, kita letak single value je utk pemudah cara untuk kira for the sake of interpretation sahaja. this is the way XD.

tips: bila dapat ABG, keluarkan kertas conteng, tulis balik mcm kat atas, letak single normal value mcm aku buat kat atas, n kira siap2 berapa dia naik, berapa dia turun

moving on, lets talk about step 4: macam mana kalau dapat metabolic disorder pulak? yang ni korg xyah bother pasal acute chronic semua tu.

kena ingat, once korg interprete ABG tu primary disorder dia as Metabolic acidosis, kena kira Anion Gap (AG)

AG = Na - (HCO3+ CL)
Normal value = 3-11

x payah include K, tak payak kira corrected NA

kalau high AG, kita diagnose as HAGMA ( High AG metabolic acidosis)

cause for HAGMA ni ialah CAT-MUDPILES. so dia narrow down our diagnosis

next step, once dapat metabolic acidosis, kita nak tahu dia ada Respiratory compensation ke tak. Haa yg ini penting gais. mcm mana nak tahu? guna Winters formula

(1.5 x HCO3) + 8

winters formula for expected PCO2: (1.5 x HCO3) + 8

kalau ABG result keluar PCO2 lagi tggi dari yg expected, so diagnosis now is Metabolic acidosis with concurrent respiratory acidosis.

kalau result lebih kurang je dgn yg kita kira , so dia appropriate respiratory compensation

contoh macam ni.. katakan:

pH 7.34 - acidotic

PO2 90 - comey

PCO2 36 (normal 40) -turun 4
HCO3 18 (normal 24) -turun 6
Na 136
Cl 100

primary disorder is Metabolic acidosis

pastu kira lah anion gap AG : 136-(100+18) = 18

so this is High AG metabolic acidosis (HAGMA)

next, ada respiratory compensation ke x? so kiralah guna winters formula (expected PCO2)
= (1.5 x HCO3) + 8
= (1.5 x 18) + 8
= 35

tapi kat result PCO2 36 kan? so dekat2 dah dgn 35 tu.

so final diagnosis is HAGMA with appropriate respiratory compensation...
gituhh tepukk

let say result PCO2 is 45 which is higher than the expected PCO2 from formula tu, so diagnosis now is HAGMA with concurrent respiratory acidosis..

if lower, concurrent respiratory alkalosis

kalau metabolic alkalosis, formula lain pula

expected PCO2 = [ (0.6 x (HCO3-24) ] + 40

konsep sama, kalau pco2 higher than expected, ada concurrent respi acidosis, if lower ada concurrent respi alkalosis.. kalau sama or lebih kurang, then appropriate compensation.. nice kan?

i know this is overwhelming. so aku nak ambik inisiatif untuk post 1 contoh per day for next 1 week. so that by the end of the day, your ABG interpretation is not just "metabolic acidosis" but "high AG metabolic acidosis with concurrent respiratory acidosis"

If pH is NORMAL, PaCO2 & HCO3 are both ABNORMAL =
Compensated

If pH is ABNORMAL, PaCO2 and HCO3 are both ABNORMAL =Partially Compensated

If pH is ABNORMAL, PaCO2 or HCO3 is ABNORMAL =
Uncompensated