Why is timing important when performing CTPAs?
Like all contrast scans, timing is especially important. With CTPA we are looking in a very specific area (the pulmonary arteries) which will likely only enhance for a few seconds at most, before contrast passes through and enhances other structures. Most centres will use a ROI (region of interest) over the pulmonary trunk, which will trigger the scan when it reaches a certain Hounsfield unit indicating contrast.
How does cannula size affect this?
As there is a short time window to get this scan, we rely on a decent flow of contrast in the vessels and this can only be achieved if the cannula delivering the contrast allows this flow. Position also plays a factor as a little cannula in a foot will not work as well as a 18G in the right antecubital fossa.
What other investigation and management should this patient receive?
A source for these emboli could be investigated by examination and ultrasound of the limbs if a deep vein thrombosis is suspected or abdomen/pelvis if other causes are indicated. The patient should receive appropriate anti-coagulation therapy and be covered by heparin in the first instance.
Multiple bilateral pulmonary emboli, largest focus in right lower lobe. Evidence of right heart strain with dilatation of right ventricle and atrium.
Right basal consolidation is a possible site of infarction given distribution of emboli. Small right pleural effusion. Linear atelectasis in both lower lobes.
No airway compromise. No significant lymphadenopathy. Visualised abdomen unremarkable. No bony lesion.