Objective. To review the technical principles of transcutaneous Po2 (tcPo2) monitors and pulse oximeters and to discuss methodological and practical issues related to the use of these devices in infants and children.
Design. Literature review and summary of personal experience.
Results. tcPo2 measurements are influenced by skin thickness, sensor temperature, amount of contact gel used, and state of peripheral perfusion. The average in vivo response time to a rapid decrease in Pao2 is approximately 16 seconds. Sensitivity to both hypoxemia (Pao2 < 50 mm Hg) and hyperoxemia (Pao2 > 80 to 100 mm Hg) is approximately 85%. Pulse oximeters require careful sensor placement (to avoid optical shunts) and adequate pulse pressures (> 20 mm Hg). They are prone to movement artifact. There are considerable differences in bias and precision between different brands, resulting, for example, in quite different upper alarm limits required to detect hyperoxemia reliably. The normal range of oxygen saturation measured by pulse oximetry, measured with one brand of pulse oximeter (Nellcor) during regular breathing, is 95% to 100% in preterm infants and 97% to 100% in full-term infants and children.
Conclusions. Because both devices have their specific shortfalls, they should ideally be used in combination, particularly in critically ill preterm neonates. Where this is not feasible or necessary, clinicians must be aware of the limitations of the device they are using.
