21st February 2025

A 34-year-old woman with metastatic breast cancer presents to A&E with a 1-week history of worsening breathlessness.

A 34-year-old woman with metastatic breast cancer presents to A&E with a 1-week history of worsening breathlessness. A chest X-ray on admission reveals a large right-sided pleural effusion. A chest drain is inserted and 3L of fluid is drained immediately, following which the drain is clamped. Her breathing feels immediately improved, and her oxygen saturations improve from 95% on 3L oxygen to 96% on 1L.

Two hours after the chest drain is inserted, she reports feeling unwell and a set of observations reveal a new tachypnoea, with oxygen saturations of 91% on 1L.

What is the most likely cause of her deterioration?

Select the SINGLE most appropriate option from the list below. Select ONE option only.