ABG case studies & interpretation

It’s not magic understanding ABG’s, it just takes a little practice!

Acid-base imbalances
Metabolic acidosis
Metabolic alkalosis
Respiratory acidosis
Respiratory alkalosis

Metabolic
• METABOLIC ACIDOSIS: Decrease the
HCO3 - --> the pH goes down.
• Compensation: Respiratory Alkalosis (hyperventilation) will bring the pH back near normal.
• Causes: Diarrhea, DKA, LA, renal failure.
• METABOLIC ALKALOSIS: Increase the
HCO3 - --> the pH goes up.
• Compensation: Respiratory Acidosis (hypoventilation) can help to bring the pH+

Respiratory
RESPIRATORY ACIDOSIS: Increase the PCO2---> the pH goes down. Hypoventilation. Compensation: Metabolic Alkalosis can help bring the pH back near normal.
Causes: pneumonia, Bronchitis, Asthma
RESPIRATORY ALKALOSIS:Decrease the PCO2-> the pH goes up. Hyperventilation.
Compensation: Metabolic Acidosis can
help bring the pH back near normal.

METABOLIC ALKALOSIS
CAUSES:
• Vomiting: Lose enough stomach acid to produce alkalosis.
• Diuretics: Loop diuretics and thiazides can lead to hypokalemia ------> secondary metabolic alkalosis.
• Antacids overuse

RESPIRATORY ACIDOSIS:
causes:
CNS DEPRESSION
DRUGS:Opiates,sedatives,anaesthetics
OBESITY HYPOVENTILATION SYNDROME
STROKE
NEUROMUSCULAR DISORDERS:
NEUROLOGIC: POLIO,GBS,TETANUS,BOTULISM
MUSCULAR DYSTROPHY
AIRWAY OBSTRUCTION
ACUTE ASPIRATION, LARYNGOSPASM
CHEST WALL RESTRICTION
PLEURAL: Effusions, empyema,pneumothorax,fibrothorax
CHEST WALL: Kyphoscoliosis, scleroderma,ankylosing spondylitis,obesity
SEVERE PULMONARY RESTRICTIVE DISORDERS
PULMONARY FIBROSIS
PARENCHYMAL INFILTRATION:
Pneumonia, edema

RESPIRATORY ALKALOSIS
Causes:
High altitude.
Neuromuscular disease
Respiratory center depression
Inadequate mechanical ventilation
Sepsis
Burns

Metabolic acidosis
Metabolic acidosis: Is caused by a decrease in HCO3- concentration in blood.
Causes:
Increased production of acids: LA, kA, Salicylate poisoning.
Loss of HCO3-: Diarrhea and kidneys RTA.
Blood profile: pH decreased
[HCO3-] decreased, PCO2 decreased

Compensation of Metabolic acidosis:
Respiratory compensation: decrease in pH stimulates respiratory center causing hyperventilation which produces decrease in PCO2.
Renal Compensation: excess H+ is excreted as titratable acid and NH4+.
Treatment: lactate containing solution which converts HCO3- ion the liver.

Metabolic alkalosis

Metabolic acidosis

Respiratory acidosis

Respiratory Alkalosis

Metabolic Acidosis
pH 7.30
PaCO2 40
HCO3 15

Metabolic Alkalosis
pH 7.50
PCO2 40
HCO3 30

Respiratory Acidosis
pH 7.30
PaCO2 60
HCO3 26

Respiratory Alkalosis
pH 7.50
PaCO2 25
HCO3 23

What are the compensations?
• Respiratory acidosis --metabolic alkalosis
• Respiratory alkalosis --metabolic acidosis
• In respiratory conditions, therefore, the kidneys will attempt to compensate and visa versa.

Buffers kick in within minutes.
Respiratory compensation is rapid and starts within minutes and complete within 24 hours. Kidney compensation takes hours and up to 5 days

Acid base disorder-worksheet

Acid base disorder-worksheet
Practice ABG’s

Answers:
1. Respiratory alkalosis
2. Respiratory acidosis
3. Metabolic acidosis 4.Compensated
Respiratory
acidosis
5. Metabolic alkalosis
6. Compensated Respiratory acidosis
7. Compensated Metabolic
alkalosis
8. Metabolic acidosis
9. Respiratory acidosis
10. Metabolic alkalosis

STEPS OF ASSESSING ABG
STEP 1: Diagnose whether it is acidosis or alkalosis- (pH will help)
STEP2:Diagnose whether compensated or non compensated
STEP 3: Diagnose whether it is metabolic or respiratory(Look at the value of bicarbonate and pCO2)

Work sheet
Diarrhea may lead to----------?
Acid loss due to vomiting and gastric
suction may lead to ______ alkalosis?
Overuse of _________may lead to metabolic alkalosis?

Problem#1
67 year female known diabetic for past 20years presented with sudden onset of severe chest pain and Shortness of breath.
ABG analysis showed:
pH 7.36
PCO2 33 mmHg
HCO3 18 mmol/L
Discuss the probable diagnosis.

Problem #2
A 30-year old man with DM presents with polyuria, polydipsia, fever, cough, and purulent sputum.
His ABG shows the following Na+140 / Cl- 104
K+7.0
pH: 6.95
pCO2 : 33
Hco3 : 7.0
Discuss the probable diagnosis.

Problem#3
45 year old male was admitted to the emergency room with complaints of mild vomiting, associated with disorientation and muscular weakness. His blood investigations showed the following
pH =7.20 Na -137meq/l
HCO3-=16mEq / L Cl-108meq/l
pCO2 = 34mm Hg K -5.8
Glucose=685mg/dl
urea49mg/dl

Problem #4
60 year male presents to the ED from a nursing home. You have no history other than he has been breathing rapidly and is less responsive than usual.
Na+ 123 Cl- 99 HCO3 - 5
pH 7.31pCO2 10
Discuss the probable diagnosis.

Problem # 5
60year old man was admitted with severe abdominal pain, which started some 2 hours back.
Clinically he was in a state of shock with distended abdomen. Femoral pulses could not be palpable
His ABG shows the follows pH : 7.05
pCO2: 26.3 mmHg
HCO3: 7 mmol/L Discuss the probable diagnosis.