Mr Johnson is a 52 year old man with a past medical history of colorectal cancer, for which he underwent a left hemicolectomy 3 weeks ago. He presents to the GP with a 1 day history of increasing dyspnoea and left-sided pleuritic chest pain. On examination, heart sounds are normal and there is a pleural rub audible. He also has unilateral right calf swelling.
On examination, blood pressure is 102/64 mmHg, his heart rate is 114 beats per minute and his respiratory rate is 30 breaths per minute.
Based on the likely diagnosis, what is the most appropriate initial management option?