Carbon dioxide (CO(2)) is the gas most commonly used to inflate the body cavities during 'keyhole' surgery (e.g. laparoscopy and thoracoscopy). However, CO(2) can be absorbed, leading to increased arterial CO(2) and increased CO(2) elimination from the lungs. These increases in CO(2) are observed following a wide variety of procedures both in adults and in infants and children. Although it is usually assumed that increases in arterial or end-tidal CO(2) directly reflect absorption of CO(2) from body cavities, this is not necessarily true, as either increases in metabolically produced CO(2) or respiratory compromise making it more difficult to eliminate CO(2) could also be responsible for these changes. Recently, a new technique has been introduced which enables absorbed CO(2) to be distinguished from metabolic CO(2).