The Science Journal of the American Association for Respiratory Care

2007 OPEN FORUM Abstracts

COMPARISON OF APNEA DETECTION BY PULSE OXIMETRY VERSUS CAPNOGRAPHY

J. B. Waugh1, S. A. Stanley2, C. Beckett3, K. H. Niebel4, E. L. Wright1, W. M. Granger1


Background: Pulse oximetry has become a common indicator of cardiopulmonary status in clinical settings. Although it has limited utility for monitoring ventilatory status, clinicians often rely on it for such because of its availability and ease of use. As patient-controlled analgesia becomes more widely used, a simple, accurate means to monitor the ventilatory status of these patients is needed. Continuous monitoring of CO2 has long been used to measure and understand intrapulmonary gas mixing and ventilation/ perfusion relationships.

Methods:
Fifty-nine adult volunteers were tested (30 at high altitude [2134 m/7000 ft] and 29 near sea level [2 m/9 ft]) using an IRB-approved protocol. Normal FEV1, FVC, and FEV1% were verified using NHANES III predicted normal equations. Ventilation data (PETCO2, respiratory frequency), oxygen hemoglobin saturation by pulse oximeter (SpO2), and heart rate were recorded using an Alaris® monitoring system (Alaris Medical Systems Inc., San Diego, CA) while participants were coached to breathe at a normal resting pattern for ten minutes (resting baseline measurement), a 45-second breath hold, followed by a one-minute recovery period. Changes in SpO2 and PETCO2 before, during and after the breath hold were analyzed using multiple paired t-test comparisons.

Results: A summary of variable means with standard deviations are given in table (45 sec BH = 45 seconds into breath hold, Post BH = immediately after breath hold, 1 min recovery = 1 min after end of breath hold). P-values represent a comparison of column measurement to baseline.

Conclusions: Results indicated that SpO2 remains mostly unchanged after a considerable period of apnea in this group of normal participants. In contrast, PETCO2 measurements exhibit significant change during the same periods. These findings are similar at high and low altitudes and have important clinical implications for patient monitoring, especially for the increasing number of monitored but unattended individuals on patient-controlled analgesia in clinical settings. [Sponsored by Oridion Capnography Inc.]

Breath Hold and Recovery PetCO2 and SpO2 Data

Group Baseline45 sec Breath Hold Post Breath Hold One Minute Post Breath Hold
Altitude PETCO2 32.5±3.6 7.9 (p<0.001) 35.9 (p=0.021) 33.7 (p=0.064)
Altitude SpO2 96.2±1.8 96.6 (p=0.190) 96.7 (p=0.214) 96.4 (p=0.459)
Sea Level PETCO2 37.1±4.3 6.0 (p<0.001) 43.6 (p<0.001) 38.0 (p=0.024)
Sea Level SpO2 98.9±1.2 98.7 (p=0.483) 97.1 (p=0.010) 99.2 (p=0.059)
Combined PETCO2 34.7±4.6 7.0 (p<0.001) 39.7 (p<0.001) 35.8 (p=0.005)
Combined SpO2 97.5±2.0 97.6 (p=0.631) 97.3 (p=0.289) 97.7 (p=0.068)
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