Study objectives: To determine if there were any differences in the time to detect hypoxemia related to the site of peripheral pulse oximetry (ear, hand, and foot) during the rapid induction of hypoxemia in healthy volunteers.
Design: Repeated-measures, longitudinal, observational study.
Setting: Anesthesia clinical research area of the Department of Anesthesiology.
Patients: 13 healthy volunteers, aged 18 to 44 years.
Interventions: Nellcor N-200 (Nellcor, Inc., Pleasanton, CA) oximeter probes were placed at the ear, hand, and foot. All units were turned on simultaneously with averaging times set for 5 seconds and signals sampled at 2 Hz. A computer-controlled anesthesia circuit was employed to induce mild hypercapnia and hyperoxia (end-tidal gas partial pressures: PETCO2 = 42 +/- 2 mmHg and PETO2 = 130 mmHg) for 5 minutes. PETO2 was then decreased to 45 +/- 2 mmHg over 60 seconds and held at that value for 5 minutes.
Measurements and main results: The mean differences in time (sec) for pulse oximeters to detect hypoxemia (read less than 90%) between probe sites were determined and compared. The following mean differences in time (sec) for pulse oximeters to detect hypoxemia (read less than 90%) between probe sites were found: ear-hand = 6; hand-foot = 57; ear-foot = 63. Paired t-tests revealed statistically significant mean time delay differences of 51 seconds (p < 0.005) and 57 seconds (p < 0.005) for ear-hand versus hand-foot and for ear-hand versus ear-foot, respectively.
Conclusions: In healthy volunteers, significant delays in the detection of acute hypoxemia by pulse oximetry occur when pulse oximeters are placed at the toe as compared with probes at either the ear or hand.