Non-invasive monitoring of blood gases has become standard procedure in neonatal intensive care units (NICU).1 In particular, continuous monitoring of oxygenation is now considered indispensable to prevent retinopathy of prematurity (ROP) and brain damage that can result from too much or too little oxygen,2^–4 despite randomised trials never having shown continuous monitoring to have an effect on clinically meaningful outcomes.5 6

Two standard techniques are used to monitor oxygenation continuously in the NICU: transcutaneous monitoring of the partial pressure of oxygen (TcPo₂) measures the amount of oxygen dissolved in tissue (which corresponds reasonably well to arterial oxygen tension (Pao₂) when the skin underneath the sensor is heated to 44°C); and pulse oximetry, which measures the proportion of haemoglobin molecules in arterial blood that are loaded with oxygen. TcPo₂ monitoring was introduced in the early 1970s, but was soon replaced by pulse oximetry after that technique became available. Many factors influence the precision and accuracy of TcPo₂ monitoring, including skin thickness, sensor site and temperature, amount of contact gel used and state of peripheral perfusion. It may cause skin burns and requires frequent re-siting and calibration.7 In contrast, pulse oximetry, introduced into the NICU in the 1980, was much easier to do but was prone to motion artefact. There were also considerable differences between brands …