BLOOD GAS - BLOOD GAS

PromptTHIS IS MY OWN NOTES - NOT PAST EXAM STUFF

ResponseLITFL page is much more consise and better
Do the blood gas book “Own the ABG”

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PromptMETABOLIC ALKALOSIS DDx

ResponseGORE
GIT Acid loss: vomiting, NGT, Diarrhoea, Ileostomy, dehydration
Overdose of Base : Antacids, Laxatives, Milk alkali, Haartmanns’
Renal Acid Loss: Diuretics, Barters syndreme, Guitelan Syndrome
Endocrine: Cushings/Steroid excess, Conn’s (hyperaldosteronism)

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PromptANION GAP

ResponseAG = [Na]-([Cl] + [HCO3])

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PromptHAGMA DDx

ResponseThe big 4:
Ketones
Lactate
Renal failure
Tox

Alternate: CAT MUD PILES
CO, Cyanide
Alcohol
Toluene
Methanol
Uraemia
DKA
Paracetamol
Isonazide
Lactate
Ethanol, Ethylene Glycol
Salycilates

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PromptNAGMA DDx

ResponseUSED CRAP
Uterostomy
Small bowel Fistula
Extra chloride
Diarrhoea
Carbonic anhydrase inhibitor (Acetazolamide)
Renal tubular Acidosis
Adison’s
Pancreaticoduodenal fistula

Alternate: ABCD
Addisons
Bicarb Loss (GI/Renal/RTA), Chloride excess, Drugs (Acetazolamide, Acid)

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PromptRESPIRATORY ACIDOSIS DDx

ResponseDecreased resp drive (CNS, Drugs)
Decreased chest wall movement (Neuro eg: GBS, Tox, Resp disease eg: PTx)
Obstructive pulmonary disease (Chronic - COPD/Asthma/Pneumonia)

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PromptRESPIRATORY ALKALOSIS DDx

ResponseTox - Aspirin, Progesterone
Compensation for metabolic acidosis
Anxiety/pain/drug or alcohol withdrawal
Hypoxia induced - Pneumonia, PE, asthma, Altitude
Head - CVA/ICH
Iatrogenic - Ventilator induced.

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PromptAa GRADIENT CALCULATION

ResponsepAO2 (sea level) = [713*FiO2]-[pCO2*1.25]
Aa Gradient = pAO2 - paO2 … ie: calculated - ABG value
Normal = age/4+4

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PromptCAUSES OF RAISED Aa GRADIENT

ResponseDifusion deficit
VQ mismatch
R→ L Shunt
Increased O2 extraction

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PromptMETABOLIC ACIDOSIS EXPECTED PCO2
(WINTERS FORMULA)

ResponsepCO2 = 1.5 x [Bicarb] + 8

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PromptMETABOLIC ALKALOSIS EXPECTED PCO2

ResponsepCO2 = 0.7 x [Bicarb] + 20

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PromptEXPECTED HCO3 CHANGE FOR EVERY 10 OF CO2

Response

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PromptOSMOLAR GAP

Response= 2x[Na] + Urea + glucose + (EtOH x 1.25)
Normal is <10

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PromptDELTA RATIO + INTERPRETATION

ResponseDelta ratio = (AG – 12) / (24 – HCO3–)
<0.4 Pure NAGMA
0.4 – 0.8 Mixed NAGMA and HAGMA
0.8 – 2.0 Pure HAGMA
>2.0 HAGMA and either metabolic alkalosis or chronic respiratory acidosis

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