MRCP2-3622
A 67-year-old woman with a history of metastatic breast cancer to her liver and bones presents to the medical admissions unit with confusion five days after starting her first course of palliative capecitabine chemotherapy. She appears dehydrated and disoriented in place and time during the mental state examination. Her vital signs are stable, with a temperature of 36.5°C, pulse of 90 BPM regular, BP of 130/80 mmHg, oxygen saturations of 99% on air, and respiratory rate of 18. There are no other notable findings on examination.
What would be the most appropriate initial investigation to perform?