What is a fingertip pulse oximeter, and who needs them?

Pulse oximeters seek to quantify the level of oxygenated haemoglobin in the blood, and are used extensively in the emergency, perioperative and intensive care settings (in both human and veterinary medicine), and - particularly given the greater accessibility and affordability of oximetry equipment - increasingly in general practice. They are also making their way into the home care setting for patients with pulmonary hypertension, asthma, COPD, sleep apnoea, emphysema, pulmonary fibrosis and even anxiety, as well as into the hands of sports people in gyms, mountaineering, cycling etc.