This document discusses arterial blood gas (ABG) analysis, including how to interpret ABG results, indications for ABG testing in the emergency room, and examples of ABG readings in different clinical scenarios. ABG analysis determines the concentration of hydrogen ions (pH) and helps identify respiratory and metabolic acid-base disturbances. The primary pathologies can be metabolic, respiratory, or mixed. Compensatory mechanisms aim to return the pH to normal range. Anion gap should be considered in metabolic insults.

1. BY DR.
MOATAZ AHMED SALAMA

2. Aim of the work
What is ABG?
How to interpret ABG
Indications of ABG in ER
examples

3. ABG
Is Determination Of H+ Concentration By
The Balance Between Pco2 And Hco3
H+(neq)=24 * ( Pco2 / HCO3 )
H+ CONCENTRATION IS heigh , EXPRESSED
BY NANOGRAM,
pH = - Log 10( H+ )

4. ACIDOSIS Normal values ALKALOSIS
Metabolic Acidosis pH = 7.35-7.45 Metabolic Alkalosis
HCO3 < & PCO2 =/- Pco2= 4.5- 6 kPA HCO3 >& PCO2 =/+
Respiratory
Acidosis
HCO3= 24- 26
mmgh
Respiratory Alkalosis
HCO3 +/= & PCO2> PO2= > 10.5 kPa HCO3 =/- & PCO2 <

6. base excess
indicates the amount of excess or insufficient level of
bicarbonate in the system
Nomal range -2 : +2
Metabolic acidosis: < -2 mmol/L
Mild-4 to -6
Moderate-6 to -9
Marked-9 to -13
Severe < -13
Metabolic alkalosis: > +2 mmol/L
Mild4 to 6
Moderate6 to 9
Marked9 to 13
Severe> +13

7. Degree Of Compensation
In respiratory causes:
oIf acute acidosis: pH falls by 0.08 and HCO3 rises by
1 mmol/L for each 1.5 kPa above 5.5.
oIf chronic acidosis: pH falls by 0.03 and HCO3 rises
by 2-4 mmol/L for each each 1.5 kPa above 5.5 kPa.
oFor respiratory alkalosis, the opposite directions are
present for all changes.
In metabolic causes
oIf metabolic acidosis: Expected PaCO2 = (1.5 x
[HCO3] + 8) +/- 2.
oIn metabolic alkalosis: Expected PaCO2 = (0.9 x
[HCO3] + 9) +/- 2.

8. Aninon gap:
(Na + K ) – (Cl + HCO3) = 12+/-4
Normal (hyperchloremic) AG metabolic acidosis
•Hyperaldosteronism
•Acatazolamid
•Renal tubular acidosis
•Diarrhea
•Uretrosegmoidostomy
•Pangreatic fistula
High AG Metabolic Acidosis ( MUDPILES)
•Methanol
•Uraemia
•DKA
•Paraldehyde
•Iron
•Lactic Acidosis
•Ethanole & Ethelyne Glycol
•Salisylate Toxicity

9. Differrence between ABG and VBG
ITEMS ABG VBG
PH 7.35-7.45 7.35-7.45
PCO2 4.5-6 5.8-6.4
PO2 >10.5 5.3
HCO3 24-28 21-22

10. Mixed Acid Base Disorder
When to suspect?
The expected compensatory response doesn’t occur
Compensatory response occur but insufficient or too
extreme
When PCO2 and HCO3 becomes in opposite directions
pH is normal and PCO2 or HCO3 are abnormal
In AG metabolic acidosis, if the change of HCO3 is not
proportional to the change of AG( IF delta ratio >2or <1)
In simple acid base disorders, the compensatory response
should never return pH to normal. If happened, suspect
mixed disorder

11. Mixed Acid Base Disorder
Delta ratio = (Increase in Anion Gap / Decrease in
bicarbonate)
Delta ratio = AG – 12 / 24 – HCO3
NORMAL 1- 2
Mixed metabolic disorders
oAnion Gap and Normal Anion Gap Acidosis.
Delta ratio <1 , that means HCO3 lower than expected
Ex. Lactic acidosis + sever diarrhea
oAnion Gap Acidosis and Metabolic Alkalosis
Delta ratio > 1 , that means HCO3 higher than
expected
Ex. Lactic acidosis in a patient who is actively
vomiting or who requires nasogastric suction

12. Mixed Acid Base Disorder
Mixed metabolic respiratory disorder
When the PCO2 is elevated and the [HCO3-] reduced,
respiratory acidosis and metabolic acidosis coexist. And vice
vecra
oChronic Respiratory Acidosis and Anion Gap Metabolic
Acidosis
Example:
COPD patient who develops shock and lactic acidosis
oChronic Respiratory Acidosis and Metabolic Alkalosis
Example:
Pulmonary insufficiency and diuretic therapy
oRespiratory Alkalosis and Metabolic Acidosis
Example:
Salicylate intoxication

13. INDICATIONS OF ABG:
Respiratory failure - in acute and chronic states.
Any severe illness which may lead to a metabolic
acidosis - for example:
Cardiac failure.
Liver failure.
Renal failure.
Hyperglycaemic states
Multiorgan failure.
sepsis
Burns.
Poisons/toxins.
Acute confusion state

14. Poisons and ABG
Metabolic acidosis
Direct: Salicylate, ethanole, methanol, ethylene
glychol, paraldehyde, iron
Indirect:
•Convulsions: asTCA and theophyllin ( respiratory
alkalosis followed by MA)
•Hypotension: as narcotics, digitalis toxicity
•Hypoxaemia as CO and Cyanid poisoning

15. Acute respiratory failure:
Mr B, a 22 year old male, was admitted to A&E by
ambulance with a GCS of 5/15. Passers-by reported
he was stabbed in the left chest with a knife.
Inspection reveals an incised wound in the left
thorax which makes a sucking noise on inspiration.
The patient is breathing at 30 breaths per min, has a
heart rate of 150 bpm and a BP of 150/100mmHg.
Analysis of an ABG showed the following:
pH 6.9
pCO2: 12.4 kPa
pO2: 8.7 kPa
HCO3-: 23 nmol/l

16. Acute respiratory failure:
A distressed 33 year old male patient was brought
to A&E by her parents. The man was "unable to
catch her breath" and was hyperventilating.
ABG analysis revealed:
pH: 7.6
p02: 11 kPa
pCO2: 3.7 kPa
HCO3: 27 nmol/l

17. METABOLIC ACIDOSIS
A 21 year-old female is found outside a pub
unconscious and smelling of alcohol. On admission to
hospital, doctors identified the smell as being ketone
bodies rather than alcohol. The patient had a
respiratory rate of 8 breaths/min, heart rate of 60 bpm,
BP 80/60 mmHg and a core temperature of 35 degrees.
ABG revealed:
pH6.9
pO2: 9.3 kPa
pC02 6.2 kPa
HCO3: 9 nmol/l

18. METABOLIC ALKALOSIS
Mr A is brought into A&E with a severe bout of
vomiting. His vomiting persists despite administration
of antiemetic therapy. As his vomiting continues he
begins to drop in consciousness, his breathing becomes
shallow and his respiratory rate falls. You take an ABG
sample and the results are as follows (the results were
taken on room air):
pH: 7.55
p02: 8 kpa
pC02: 10 kpa
HCO3: 40 mmol/l

19. 33 years old male patient, heavy smoker, presented to
ER with 3 days of exaggerated symptoms of SOB,
dyspnea and productive cough. On examination his
temp was 38.5, RR 20/min, pulse 120/min, sat 85%
on room air and BP 160/88. His skin is hot and damp
and his lips and nails are bluish (cyanotic). Listening
to his chest, you hear scattered wheezes and very
decreased breath sounds in both lungs.

20. J.B. is a 52-year-old man admitted to the hospital
after a sudden onset of severe chest pain and
shortness of breath. Within 5 min after presentation,
he suffered a cardiopulmonary arrest. CPR was
initiated and was successful after approximately 10
minutes. The initial examination after CPR revealed
that pt had hypotension with a spontaneous
respiratory rate of 40 breaths/min and a heart rate
of 120 beats/min. He was comatose, with central
cyanosis, cool extremities, inspiratory and expiratory
coarse crackles, and weak pulses. The initial blood
gas measurements after resuscitation were as
follows:

21. 76 years old female patient, known with IHD, HTN and
DM presented with acute attack of SOB, dyspnea, orthpnea
and excessive sweating. On examination, BP230/120.
pulse 25/min, temp 37.1, RPG 17mmol, O2sat 84%, chest
showed crackles up to upper lung zone and her ABG
showed

22. 16 years old female patient with no past medical hx,
presented with acute confusional state following 2
days of mild abd. Pain and vomiting twice. On
examination patient was afebrile, BP130/90, RR
10/min, RPG 6.5, pupils RRR and neck lax and her
ABG was as follow:
pH: 70.8
PCO2: 8.5 kPa
PO2: 9.5 kPa
HCO3: 15

23. SUMMARY
ABG IS ONE OF THE MOST USEFULL DIAGNOSTIC
TOOLS IN EMERGENCY MEDICINE
PH IS THE –LOG (H+)
THE PRIMARY PATHOLOGY MAY BE METABOLIC OR
RESPIRATORY OR MIXED
COMPENSATORY MECHANISMS ARE RESPONSIBLE
FOR RETURN PH TO NORMAL RANGE
ANION GAP SHOULD BE CONCERNED IN METABOLIC
INSULTS