KEY INVESTIGATIONS

Question 1

List at least 3 contraindications to performing an ABG

Answer 1

• Sampling from an arm with an IV infusion in progress -
• Abnormal or infectious skin processes at the puncture site -
• Arterial graft, surgical shunt, or AV fistula in the arm -
• History of arterial spasm following previous ABG -
• History of clotting disorders or anticoagulant use -
• Known, or suspected, aneurysm at the puncture site

Question 2

List at least two potential complications of performing an ABG

Answer 2

• Vascular thrombosis or spasm -
• Distal and proximal embolus -
• Bleeding or haematoma formation -
• Pain, infection, and local damage

Question 3

What test should always be performed prior to performing an ABG?

Answer 3

Allen’s test to assess for ulnar arterial supply to the hand

Question 4

Within how many seconds should blood supply return to the hand following release of the ulnar artery in Allen’s test?

Answer 4

7

Question 5

Give two potential causes of a metabolic alkalosis

Answer 5

vomiting and hyperaldosteronism (Loss of hydrogen ions in the urine occurs when excess aldosterone (Conn’s syndrome) increases the activity of a sodium-hydrogen exchange protein in the kidney)

Question 6

Causes of respiratory acidosis can be divided into 3 main categories. What are the categories? Give an example for each

Answer 6

Decreased respiratory drive

• CNS: CVA, tumour, infection (encephalitis), haemorrhage
• Drugs: Narcotics and sedatives

Decreased chest wall movement

• Neurological: NM disorders, Guillain-Barre, Myasthenia gravis, demyelinating disorders
• Tetanus
• Toxicity: Muscle relaxants, organophosphates, fentanyl
• Respiratory (Acute)
• Trauma, surgery, chest wall deformity
• Tension pneumothorax, pleural effusion
• Upper airway obstruction
• Increased dead space, improper connection

Obstructive pulmonary disease (chronic)

• COPD, asthma, pneumonia

Question 7

Give 2 causes of a respiratory alkalosis?

Answer 7

• Anxiety -
• Hypoxia -
• Acute pulmonary insult (T1RF) (pulmonary oedema, pneumonia, COPD, asthma, acute respiratory distress syndrome, chronic pulmonary fibrosis, pneumothorax, pulmonary embolism, pulmonary hypertension.)

Question 8

The interpretation of metabolic acidosis uses anion gap to aid diagnosis. What is the anion gap and how should it be interpreted?

Answer 8

• the balance between cations (+ve) and anions (-ve) is typically measured as a balance between sodium vs bicarb and chloride. however this leaves out other anions which are difficult to emasure. hence there is an anion gap which is used to determine the amount of unmeasured anions.
• the important consideration is whether or not the anion gap is high or normal.
  
  • high: develops due to decreased bicarb as it is mopping up excess H+ ions, examples include lactic acidosis, CKD and DKA
• if the reduction in bicarb is offset by an increase in chloride ions then anion agp will be normal, examples include renal tubular acidosis and diarrhoea

Question 9

What are the score ranges for NEWS and what action do they correlate to?

Answer 9

• 0- low clinical risk, 12 hourly monitoring
• 1-4- low clinical risk, 4-6 hourly monitoring, review by rgeistered nurse
• 4-6- moderate clinical risk, hourly monitoring, review by Dr
• 7+- high clincial risk, continuous monitoring, medical team immediately informed, urgent review, transfer to HDU/ITU

Question 10

if there is st elevation in leads 2 ,3 and avf, what territory of the heart is ischaemic and what blood vessel supplies it?

Answer 10

Inferior surface

Right coronary (80%), circumflex artery (20%)

Question 11

if there is st elevation in leads V1 v2 v3 v4, what territory of the heart is iichaemic and what blood vessel supplies it?

Answer 11

• anteroseptal
• LAD (anterior interventricular artery which is a septal branch of the left anterior descending artery)

Question 12

if there is st elevation in leads I avl v5 v6, what territory of the heart is iichaemic and what blood vessel supplies it?

Answer 12

• lateral
• left circumflex

Question 13

if there is st depression in v1 v2 v3 and a dominant r wave in v2 what is this indicative of and what vessel is likely involved?

Answer 13

• posterior MI
• RCA

Question 14

What are the 6 classic signs on CXR of pulmonary oedema?

Answer 14

• Bat-wing appearance, in which the oedema (shadowing) extends out from the hilum -
• Kerley B lines, which indicate fluid trapped in the space between lobules -
• Fluid in the horizontal fissure -
• Upper lobe diversion, where there is shadowing at the apices due to increased blood flow -
• Bilateral pleural effusion -
• Cardiomegaly

Question 15

Give 3 causes of bilateral hilar lymphadenopathy

Answer 15

• malignancy
• infection
• lymphoma
• sarcoidosis

Question 16

Other than location and size how can you tell you’re looking at small bowel on an AXR?

Answer 16

presence of plicae circularis/valvulae connieventes which extend across the whole of the small bowel

Question 17

Other than location and size how can you tell you’re looking at large bowel on an AXR?

Answer 17

presence of haustra whic do not extend across the whole of the large bowel.

also the large bowel will contain faeces

Question 18

What is the importance of the ileocaecal valve in bowel obstruction?

Answer 18

• a competent ileocaecal valve increases the likelihood of bowel perforation secondary to obstruction as the pressure is maintained within the large bowel as opposed to spreading to the small bowel via an incompetent valve

Question 19

give 3 causes of large bowel obstruction

Answer 19

• colon cancer
• diverticular disease
• hernia (rare)
• volvulus
  *

Question 20

give 3 causes of small bowel obstruction

Answer 20

• adhesions
• hernia
• foreign body
• tumours
• gallstone ileus

Question 21

what pharse are you going to use when remembering how to interpret AXRs

Answer 21

• details
• gases
• masses
• bones
• stones
• artefacts