On the neonatal unit in Derby, two types of probes are in routine use: Mindray 520 N and Mindray 521 N. Feedback from parents and staff show that there are concerns that the two probes given very different oxygen saturation readings and, often, do not agree with each other. This has raised concerns that infants' clinical care may be affected by the choice of probe. It is important to know if the two probes give similar results or not to ensure that infants get the appropriate monitoring and respiratory support as needed for good neonatal care. In this study, we will compare the reading made by the two probes and determine whether the readings of the two probes agree with each other and if any disagreement is such that clinical decision making is affected by the difference.

Continuous monitoring of oxygen saturation level is a key component of neonatal intensive care and NICE recommends that all neonatal services "ensure that systems are in place for preterm babies to have a target saturation level of 91% to 95%" and that this is monitored using "continuous pulse oximetry" (NICE Quality statement 4 in Quality Standard QS193: https://www.nice.org.uk/guidance/qs193/chapter/Quality-statement-4-Oxygen-saturation). Oxygen saturation monitoring is used to provide optimal respiratory support to preterm infants to ensure adequate oxygenation of tissues while preventing risks of conditions such as retinopathy of prematurity and bronchopulmonary dysplasia [1]. It is equally important in term born infants who require intensive care such as for determining adequate oxygenation for respiratory support and screening for congenital heart disease [2]. For these reasons, most infants in neonatal units are continuously monitored using pulse oximetry, a simple and painless test that measures blood oxygen levels by passing a small beam of light through the infant's hand or foot. This measures the changes in light absorption to calculate the levels of oxygenated and deoxygenated blood. To do this the light (or probe) has to be attached to the infant's hand or foot using a tie or a sticker. The probe must be attached firmly for the saturation monitor to pick up the correct readings. As neonatal skin is delicate and it is often difficult to stick objects to it, neonatal oxygen saturation probes are carefully designed. Many different types of saturation probes are in routine use in neonatal units. It is important to ensure that they give accurate and comparable readings. In the neonatal unit in Derby, two types of probes are in routine use: Mindray 520 N and Mindray 521 N. Feedback from parents and staff show that there are concerns that the two probes given very different oxygen saturation readings and, often, do not agree with each other. This has raised concerns that infants' clinical care may be affected by the choice of probe. It is important to know if the two probes give similar results or not to ensure that infants get the appropriate monitoring and respiratory support as needed for good neonatal care. In this study, we will compare the reading made by the two probes and determine whether the readings of the two probes agree with each other and if any disagreement is such that clinical decision making is affected by the difference.

Inclusion Criteria:

• Infants who need oxygen saturation monitoring for clinical care
• Infants born preterm (<37 weeks' gestation) who are < 7 days of age and need respiratory support including supplemental oxygen
• Infants born preterm (<37 weeks' gestation) who are in supplemental oxygen at >34 weeks' gestation
• Infants born at term gestation (< 37 weeks' gestation) who require respiratory support including supplemental oxygen
• Infants with suspected cardiac disease

Exclusion Criteria:

• Infants who have intravenous or arterial lines attached to either foot.
• Infants who have any condition that may cause differential oxygen saturation or blood flow to the lower limbs such as venous thrombosis.
• Infants who have local infections or skin lesions on either foot.
• Infants older than 5 months of age

A computer-generated random number sequence will be obtained to determine which probe is attached to which foot. The sequence will be kept in opaque, sequentially numbered envelopes that will be opened just before the probes are attached to the feet of the participant. The clinical team nurse who will record the oxygen saturation readings will be blinded to which probe is attached to which foot by covering the feet securely after the probes have been attached. The probes will be designated as A and B. The study statistician will be blind to which probe is A and which is B until all data analyses are completed.