Data Interpretation 1 Flashcards
Name the borders of the mediastinum
Superior - thoracic inlet Inferior - diaphragm Anterior - sternum Posterior - vertebral column Lateral - Pleura and pleural space
What are the three compartments of the mediastinum
ON LATERAL CXR
Anterior = Prevascular compartment (includes superior)
Middle = Visceral compartment
Posterior = Paravertebral compartment
What lesions occur in the anterior (including superior) compartment of the mediastinum
The terrible t’s
Thymoma
Teratoma/germ cell tumour
Terrible lymphoma
Thyroid tissue
Aortic aneurysm (superior only)
What causes mass lesions in the middle compartment
1. Lymphadenopathy Lymphoma Metastatic Ca TB Sarcoid 2. Aortic aneurysm 3. Pericardial cysts 4. Dilated oesophagus 5. Hiatal hernia
What causes masses in the posterior mediastinal compartment?
Neurogenic tumours
Spinal masses
If it is not stated, how can one tell the difference between AP and PA CXR
PA view
- Scapula on periphery of thorax
- Clavicles project over lung fields
- Posterior ribs distinct
- Position of markers
AP view
- Scapula encroach on lung fields
- Clavicles above apex of lung fields
- Anterior ribs distinct
- Position of markers
What are the differences between small and large bowel obstruction on AXR
Small bowel
- Central
- Valvulae coniventae
- 3 cm max diameter
Large bowel
- Peripheral
- Houstration
- 6 cm max diameter
What is Bazettes formula
Formula used to correct the QT interval for heart rate: QTc
QTc = QT / ⎷RR
quick way to screen the QT interval is to look if the t-wave is beyond the middle of the RR interval - if it is - likely prolonged
What is significant reversibility during the bronchodilator test with regard to lung function tests
Increase in FEV1 by more than 12% and 200 mls
How is the Anion Gap corrected for decreased albumin
For every 1g/dl decrease in albumin there will be a 2.5 mmol/L decrease in the anion gap
What are the causes of a low anion gap metabolic acidosis
Multiple myeloma
Lithium or bromide toxicity
What are the causes of normal anion gap acidosis
DURHAM
Diarrhoea (loss HCO3)
Ureteral diversion into GIT (Gain of excreted H)
RTA (Loss HCO3 or inadequate excretion H+)
Hyperalimentation (Loss HCO3 like diarrhoea)
Acetazolamide (Loss HCO3)
Miscellaneous
- Pancreatic fistula (Loss HCO3)
- Cholestyramine (Loss HCO3)
- Calcium Chloride Ingestion (Gain Strong anion - decreased SID)
When should an osmolar gap be calculated and why is this useful
It is used in the context of suspicion of toxic ingestion. If an element other than ethanol is to be excluded then the osmolar gap can be used.
Osmolar gap = Measured osmolarity - Calculated osmolarity
Calculated osmolarity = 2Na + urea + glucose
The amount of ethanol can be added to this and if there is still a high osmolar gap then an additional intoxicant can be considered.
How is the delta gap calculated, what does it mean and when should it be used
Delta gap = Anion gap - normal anion gap (10)
This basically subtracts the albumin and gives you the amount of extra acid in the plasma that has combined and removed HCO3.
Therefore if the delta gap is added to the measured HCO3 then this should give you the HCO3 in the absence of a HAGMA.
- –> if this is < 22 then concomitant NAGMA
- –> if this is > 26 then concomitant metabolic alkalosis
How can expected renal compensation for respiratory acid base disorders be remembered
RESPIRATORY A-B DISTURBANCE - expected HCO3 compensation
ACUTE
Acidosis:
⇧ 10 mmHg CO2 –> ⇧ HCO3 1 mEq/L
Alkalosis:
↓ 10 mmHg CO2 –> ↓ HCO3 2 mEq/L
CHRONIC
Acidosis:
⇧ 10 mmHg CO2 –> ⇧ HCO3 3 mEq/L
Alkalosis:
↓ 10mmHg CO2 –> ↓ HCO3 4 mEq/L
