Pulse oximetry

Abstract

Pulse oximetry is one of the most commonly employed monitoring modalities in the critical care setting. This review describes the latest technological advances in the field of pulse oximetry. Accuracy of pulse oximeters and their limitations are critically examined. Finally, the existing data regarding the clinical applications and cost-effectiveness of pulse oximeters are discussed.

Figure 1

Sequential distribution plots of oxygen saturation at intervals of2 min over a 3-h period in a stable patient (A) and unstable patient (B). Theunstable patient shows episodic desaturations. Published with permission [3].

Figure 2

Red (R) and infrared (IR) scaled alternating current (AC) signals at arterial oxygen saturation (S_aO₂) of 0%, 85% and 100%. The numeric value of the red-to-infrared (R/IR) ratio can be easily converted to S_aO₂. Published with permission [10].

Figure 3

Common pulsatile signals on a pulse oximeter. (Top panel) Normal signal showing the sharp waveform with a clear dicrotic notch. (Second panel) Pulsatile signal during low perfusion showing a typical sine wave. (Third panel) Pulsatile signal with superimposed noise artifact giving a jagged appearance. (Lowest panel) Pulsatile signal during motion artifact showing an erratic waveform. Published with permission [8].

Figure 4

Pulse oximeter probes placed on the finger, ear, nose or foreheadranked for accuracy in terms of bias under conditions of poor perfusion. Biasof pulse oximeters ranged from 0.2 to 1.7 for finger probes and 0.1 to 8.1 forother probes. Adapted with permission [20].

Figure 5

Number of false alarms for devices used to monitor respiratoryrate, mean systemic blood pressure from an arterial catheter, heart rate froman electrocardiogram (EKG), heart rate measured by pulse oximetry (POx) andO₂ saturation measured by a pulse oximetry(S_pO₂). Forty-five per cent of all false alarms were dueto the S_pO₂ signal. Data from [39].

Figure 6

Artifactual pulse oximetry signals during nonrhythmic motion(i.e., gross arm motion; top panel) and during Parkinsonian tremor (lowerpanel). Solid line denotes Masimo signal extraction technology(SET^™), aimedat minimizing spurious pulse oximetry readingsdue to motion artifact; dashed line denotes conventional pulse oximetry.Spurious changes in S_pO₂ were less with MasimoSET^™ than with conventional pulse oximetry. Published withpermission [46].

Figure 7

Arterial oxygen tension (P_aO₂) values atpulse oximetry O₂ saturation (S_pO₂) value of90, 92, 94, and 95%. The inspired O₂ concentration(F_iO₂) was adjusted until the desired steady-stateS_pO₂ value was achieved. The solid horizontal linerepresents the mean P_aO₂ value obtained for eachS_pO₂ target. The closed and open circles represent valuesobtained in black and white patients, respectively. In whitepatients, anS_pO₂ target of 92% resulted in a satisfactory level ofoxygenation, whereas a higher S_pO₂ target, 95%, wasrequired in black patients. Published with permission [19].