ABG analysis measures levels of oxygen, carbon dioxide, pH and bicarbonate in arterial blood to diagnose acid-base imbalances and respiratory issues. Normal values include a pH of 7.35-7.45, PaCO2 of 35-45 mm Hg, PaO2 of 75-100 mm Hg, and HCO3 of 22-26 meq/L. Respiratory failure occurs when blood gas levels fall outside normal ranges, and is classified as type I (low PaO2) or type II (low PaO2 and high PaCO2). Causes include lung diseases, infections, injuries or disorders that impact breathing. Treatment focuses on addressing underlying causes, improving oxygen levels and managing complications through

1. Arterial Blood Gas Analysis
&
Respiratory Failure
Dr. Shilpasree Saha (PT)
MPT- Cardio-Thoracic Disorders)
Assistant Professor, JVWU

2. What do it mean by ABG analysis?
• Arterial blood gas (ABG) analysis is an essential part of
diagnosing and managing a patient’s oxygenation status and acid–
base balance.
• Blood gas analysis is a commonly used diagnostic tool to evaluate
the partial pressures of gas in blood as well as acid-base content.
• Disorders of acid–base balance can create complications in many
disease states, and occasionally the abnormality may be so severe
so as to become a life-threatening risk factor.
•

3. Terminologies
• pH: pH is a scale used to specify the acidity or alkality of an aqueous solution.
• paO2: Partial pressure of oxygen measures the pressure of O2 dissolved in the
blood and how well O2 is able to move from airspace of the lungs into the blood.
• paCO2: Partial pressure of carbondioxide is the measure of CO2 within arterial or
venous blood. It often serves as a marker of sufficient alveolar ventilation within
the lungs.
• HCO3ˉ: It measures the bi carbonate in arterial blood.

4. Normal Blood Gas Value
• pH: 7.35-7.45
• PaCO2: 35-45 mm Hg
• PaO2: 75-100 mm Hg
• HCO3: 22-26 meq/L

5. Sample For ABG Analysis
• Site of choice:
The first choice is the radial artery.
Alternative sites for access are:
Brachial and Femoral artery.

6. Assessing acid-base disorders
• A low pH, ˂7.35 indicates a tendency towards acidosis, a high pH˃7.45
indicates a tendency towards alkalosis.
• Increase in paCO2 indicates acidosis, decrease in paCO2 indicates alkalosis.
• Increase HCO3ˉ leads to alkalosis, decrease HCO3ˉ leads to acidosis.

7. Assessment
• Establish whether the patient’s pH is acidotic, alkalotic or normal.
• If the pH is acidotic & PaCO2 increased, then it is RESPIRATORY ACIDOSIS.
• If the pH is acidotic & HCO3ˉ decreased, then it is METABOLIC ACIDOSIS.
• If the pH is alkalotic & PaCO2 decreased, then it is RESPIRATORY ALKALOSIS.
• If the pH is alkalotic & HCO3ˉ increased, then it is METABOLIC ALKALOSIS.

9. Respiratory Failure
• It is defined as an inability of the respiratory system to maintain blood gas
values within normal ranges. They are two types:
Type-I Respiratory Failure
Type-II Respiratory Failure

10. Type-I Respiratory Failure
• Type-I Respiratory Failure is defined as a condition with decreased PaO2
(hypoxemia) and a normal or slightly reduced PaCO2 due to inadequate gas
exchange. It is also called hypoxemic respiratory failure.
• PaO2˂60 mm Hg or, ˂8 kPa

11. Type-II Respiratory Failure
• Type-II Respiratory Failure is defined as a condition with decreased PaO2
(hypoxemia) and an increased PaCO2 (hypercapnea). It is also called
ventilatory failure.
• PaO2˂60 mm Hg or, ˂8 kPa, and PaCO2 ˃50 mm Hg or ˃6.7 kPa.

12. Causes
• Respiratory failure can be caused by:
Conditions that make it difficult to breathe in and get air into your
lungs: Examples include weakness following a stroke, collapsed airways, and
food getting stuck in and blocking your windpipe.
Conditions that make it difficult for you to breathe out: e.g- Asthma,
COPD.
 Lung collapse. When no air is able to enter your lungs, one or both lobes
may collapse and cause a condition called atelectasis.

13. Fluid in lungs , e.g.- Pneumonia.
Respiratory muscle dysfunction, e.g.- muscular dystrophy, spinal cord injury.

14. Risk factors
• Age: Premature babies who have neonatal respiratory distress have a higher
risk of respiratory failure. Older adults have more risk factors for respiratory
failure.
• Environment: Breathing in lung irritants, include air pollution, chemical
fumes, asbestos, dust, and smoke can lead to lung damage over the long
term.
• Nerve and muscle disorders such as amyotrophic lateral sclerosis.

15. • Lung and airways diseases, such as asthma, cystic fibrosis, COPD,
and interstitial lung diseases.
• Infections such as pneumonia.
• Airway blockages.
• Chest or back injuries that damage your ribs or lungs.
• Severe scoliosis.

16. Clinical features
• Symptoms of respiratory failure depend on its cause, the levels of oxygen and
carbon dioxide in your blood.
Low oxygen levels in blood can cause:
• Difficulty or extreme tiredness with routine activities such as dressing, taking a
shower, and climbing stairs
• Shortness of breath, also called air hunger.
• Drowsiness
• A bluish color on your fingers, toes, and lips

17. High carbon dioxide levels in blood can cause:
• Blurred vision
• Confusion
• Headaches
• Rapid breathing
Symptoms of respiratory failure in newborns include rapid breathing, grunting,
widening of the nostrils with each breath, a bluish tone to baby's skin and lips, and a
pulling inward of the muscles between the ribs between the ribs while breathing.

18. Complications
Respiratory failure can cause serious or life-threatening problems such as:
• Arrhythmias (irregular heartbeats)
• Brain injury
• Kidney failure
• Lung damage

19. Diagnosis
1. Medical history: Look for the risk factors & the symptoms of respiratory
failure such as shortness of breath, rapid breathing, and confusion.
2. Physical examination:
• Check for cyanosis.
• Auscultation to check heart beat & lung sound.
• Blood oxygen level with pulse oximetry.
• Blood pressure measurement.

20. • Arterial blood gas tests to measure levels of oxygen, carbon dioxide, pH, and bicarbonate.
• Blood tests to find the cause of respiratory failure. Blood tests can also help to see how well
other organs are working.
• Bronchoscopy to check for blockages, tumors or other possible causes of respiratory failure.
• Chest X-ray to identify any lung or heart conditions that may be causing respiratory failure.
• Chest computed tomography (CT) scan to image the lungs and look for inflammation or
damage.
• Electrocardiogram (EKG or ECG) to check heart rhythm..
• Pulmonary function tests.

21. Management
• Antibiotics to treat bacterial lung infections such as pneumonia.
• Bronchodilators to open your airways or treat an asthma attack.
• Corticosteroids to shrink swollen airways and treat any inflammation.

22. • Fluids may be given to improve blood flow throughout body. Fluids are usually given
through an intravenous (IV) line.
• Nutritional support.
• Physical therapy :
• Helps to maintain & improve muscle strength and prevent sores from forming. Movement
may also help shorten the time of ventilatory support and improve recovery.
• Positioning your body. For severe respiratory failure, prone position is preferred which
helps the lungs to get more oxygen.
• Pulmonary rehabilitation program to educate and teach exercises & breathing techniques
that can improve your oxygen levels.

24. References
• Physiotherapist’s Pocketbook
• Respiratory Failure | NHLBI, NIH