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

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

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

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

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

Components of an ABG pH paCO2 PaO2 HCO3- Base excess

Alkalosis vs acidosis Acidosis pH <7.35 Alkalosis pH >7.45

Hypoxia <11.0 kPa

Respiratory or metabolic pH CO2 HCO3- ↓ ↑ Respiratory acidosis Respiratory alkalosis Metabolic acidosis Metabolic alkalosis

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

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

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 (7.35-7.45) PaCO2 5.2 (5.0-5.5) PO2 12.0 (>11.0) HCO3 18 (22-28) ABG result: Metabolic acidosis Diagnosis DKA

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 (7.35-7.45) PaCO2 5.2 (5.0-5.5) PO2 14.0 (>11.0) HCO3 32 (22-28) ABG result: Metabolic alkalosis Cause Vomiting

A 52 year old lifelong smoker presents to the emergency department feeling generally unwell with some breathing difficulties. ABG: pH 7.30 (7.35-7.45) PaCO2 8.90 (5.0-5.5) PO2 8.0 (>11.0) HCO3 25 (22-28) ABG result: Respiratory acidosis Hypoxia Type 2 respiratory failure Diagnosis Acute exacerbation of COPD

Chest X Rays

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

Anatomy

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

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

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

Inspiration At least 5-6 anterior ribs visible above diaphragm

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

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

Airway Trachea deviated? Airway patent Any foreign body?

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?

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

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’

Everything else Bones Soft tissue Any foreign objects

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

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.

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

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

Tom Stevens aged 25 presents after a stabbing.

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