Iowa Neonatology Handbook: Pulmonary

Pulse Oximetry

Jonathan M. Klein, MD
Peer Review Status: Internally Peer Reviewed

 I. Pulse oximeters determine oxygen saturation noninvasively through absorption spectrophotometry. Oxygen delivery to the tissues is a direct function of cardiac output, oxygen capacity (hemoglobin concentration) and the oxygen affinity of the patient's hemoglobin (see Figure 1). In the presence of both normal cardiac output and normal Hgb, measurement of oxygen saturation can be a guide to both oxygen exchange and delivery. 

We tend to keep the oxygen saturation in premature infants between 88% - 95% (higher in term infants). Pulse oximeters are accurate within ±4%, thus a reading of 95% could represent a saturation of 99% with a concomitant PO2 of 160 (see Figure 2). Thus, to avoid hyperoxia, we would decrease the oxygen concentration for saturations greater than or equal to 95%.

II. Causes for Inaccurate Readings: 

A. Jaundice - causes falsely decreased values. 

B. Direct high intensity light - i.e. phototherapy lights - increases inaccuracy, so cover sensor site from lights, or use a phototherapy blanket. 

C. Impaired perfusion - need good pulsatile blood flow for accurate readings, manage by treating shock. 

D. Severe hypoxemia - at saturations less than 70% accuracy begins to fall off with the pulse oximeters overestimating the measured value. Manage by directly checking an arterial PaO2, or by using a transcutaneous oxygen monitor 

References: 

Oski FA, and Delivoria-Papadopoulos M. The red cell, 2, 3-diphosphoglycerate, and tissue oxygen release. J Pediatr, 1970;77:941-956. 

Tobin MJ. Respiratory monitoring in the intensive care unit. Am Rev Respir Dis 1988;138:1625-1642. 

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