1. A basic introduction to ABGs and Chest X Rays
Nick Leaver
5th Year Medical Student

2. Learning outcomes To understand when to order an ABG
To understand the components of an ABG
To understand basic interpretation of ABGs
To understand the basics of a chest x ray
To understand how to present a chest x ray

3. ABG An arterial blood gas is used to: Who needs one?
Assess the oxygenation of a patient
Assess blood pH level
Determine the cause of a deranged pH level
Monitor treatment/disease progression
Who needs one?
Any unexpected deterioration in acutely unwell patient
Anyone with an acute exacerbation of a chest condition
Anyone with impaired consciousness
Signs of CO2 retention (bounding pulse, drowsy, tremor, headache) cyanosis, confusion

4. Physiology
Carbon dioxide cannot dissolve in the bloodstream so carbonic anhydrase coverts CO2 and water into carbonic acid to travel in the bloodstream
Bicarbonate (alkali) is produced by the kidneys
Blood CO2 (acid) is removed in the lungs

5. Bicarbonate production is slow
CO2 can be quickly increased (by hypoventilation) or decreased (by hyperventilation)
So if there is a metabolic problem affecting the pH, the respiratory system can quickly compensate
Bicarbonate production is slow
It takes much longer for renal compensation of a respiratory problem

6. Components of an ABG pH
paCO2
PaO2
HCO3-
Base excess

7. Alkalosis vs acidosis
Acidosis
pH <7.35
Alkalosis
pH >7.45

8. Hypoxia
<11.0 kPa

9. Respiratory or metabolicpH
CO2
HCO3- ↓ ↑
Respiratory acidosis
Respiratory alkalosis
Metabolic acidosis
Metabolic alkalosis

10. Some major causes Respiratory acidosis Respiratory alkalosis
Intrinsic lung disease (COPD), neuromuscular disorders
Respiratory alkalosis
Any cause of hyperventilation
Metabolic acidosis
DKA, lactic acidosis, drugs, diarrhoea
Metabolic alkalosis
Vomiting, burns

11. Type 1 and 2 respiratory failure
Type 1 respiratory failure
Hypoxia with normal or low PaCO2
Type 2 respiratory failure
Hypoxia with raised PaCO2

12. A 15 year old female presents with acute onset of sweating and shivering, she is then found to have a respiratory rate of 30.
ABG:
pH 7.30 ( )
PaCO2 5.2 ( )
PO (>11.0)
HCO3 18 (22-28)
ABG result:
Metabolic acidosis
Diagnosis
DKA

13. A 35 year old male presents with a 4 day history of profuse vomiting
A 35 year old male presents with a 4 day history of profuse vomiting. He is known to have alcohol excess.
ABG:
pH 7.50 ( )
PaCO2 5.2 ( )
PO (>11.0)
HCO3 32 (22-28)
ABG result:
Metabolic alkalosis
Cause
Vomiting

14. A 52 year old lifelong smoker presents to the emergency department feeling generally unwell with some breathing difficulties.
ABG:
pH 7.30 ( )
PaCO ( )
PO2 8.0 (>11.0)
HCO3 25 (22-28)
ABG result:
Respiratory acidosis
Hypoxia
Type 2 respiratory failure
Diagnosis
Acute exacerbation of COPD

15. Chest X Rays

16. Chest X rays Why Any chest disease (lungs or heart) Pre-op for surgery
Septic screen
Unwell patients

17. Anatomy

19. The patient Need 3 identifiers Need to know the history
Name
DoB
Hospital number
Need to know the history
Need to know the indication for the chest x ray

20. Projection Antero-posterior Postero-anterior
Usually for bed bound or unwell patients
Postero-anterior
Most chest xrays
People tend to be more ‘well’

21. Rotation How ‘twisted’ the film is
Measure distance from clavicles to spinous processes
Mainly due to patient position
May hide pathology

22. Inspiration
At least 5-6 anterior ribs visible above diaphragm

23. Picture area
Need to see lung apices, just under the diaphragm, the whole of the lung fields
The scapula should be out of the way

24. Exposure How strong the x ray beam is
Needs to be enough to see all structures clearly
Under or over penetration can cause you to miss something
Should be able to see the vertebrae behind the lower part of the cardiac shadow

25. Airway
Trachea deviated?
Airway patent
Any foreign body?

26. Lungs Are the lung fields clear? Are the lungs fully inflated?
Do the lung markings go all the way to the edge of the lung field?

27. Heart Should be <50% of the CTR in a PA film
A large heart shadow is indicative of heart failure
Look at the aortic knuckle

28. Diaphragm Should be domed on both sides
The right should be higher than the left
Flattened diaphragm is indicative of hyperinflation
Pay attention to the chostophrenic angle ‘blunting’

29. Everything else
Bones
Soft tissue
Any foreign objects

30. Order Patient identifiers Reason for chest x ray Projection Rotation
Inspiration
Picture area
Exposure
Airway
Breathing (Lungs)
Circulation (Heart)
Diaphragm
Everything else (bones, soft tissues)
Summary

31. Presentation - Example
This is Ann Jones a 36 year old female who presented with a 1 week history of productive cough. She has had an AP erect chest x ray. The film is not rotated, the picture is of adequate exposure and she has good inspiratory effort. The airway is central and patent. The left lung field is clear, the right lung field has consolidation in the middle zone. The heart size cannot be accurately measured but appears to be within normal limits. The right heart border is obscured by the consolidation. The left diaphragm is normal, the right side is hard to assess. There is no other pathology.
In conclusion this is a 36 year old female with a 1 week history of productive cough. Her chest x ray shows right middle zone consolidation in keeping with a right middle lobe pneumonia an no other obvious pathology.

32. Maureen Smith aged 75 with a productive cough for 3 days.

33. Tony Jones aged 56 presents with a 5 month history of worsening shortness of breath.

34. Tom Stevens aged 25 presents after a stabbing.

35. Any questions? www.peermedics.com
See Chest Radiograph Interpretation on oscestop.com