SIMULTANEOUS IN-VIVO COMPARISON OF 2-VERSUS 3-WAVELENGTH MIXED VENOUS(SVO2) OXIMETRY CATHETERS

Objective, Venous oximetry catheters provide useful realtime informati on about mixed venous hemoglobin saturation (Svo(2)). Currently availa ble systems utilize either two or three wavelengths of light to obtain these measurements. Previous animal and clinical studies have attempt ed to compare the accuracy of these two devices under similar circumst ances. However, the relative accuracy of the two-wavelength versus thr ee-wavelength systems has never been assessed under identical conditio ns. For this purpose, we designed an animal model for simultaneous mea surement of Svo(2) over a wide range of physiologic and pathologic sta tes. Methods. Seven anesthetized swine underwent simultaneous placemen t of two- and three-wavelength catheters. Paired data points consisted of values obtained from a reference oximeter and from each of the cat heters. Observations were obtained every 15 min during the following m anipulations: (1) eucarbic hypoxia induced by reducing Fio(2) to 0.18, 0.15, and 0.12 for 15 min each; (2) simulated surgical manipulation; and (3) hypovolemic shock produced by hemorrhage to a mean arterial pr essure of 50 torr for 1 hr. Data were analyzed by calculation of mean error (bias) and precision for each system in comparison with the oxim eter. Results. The overall error of the two-wavelength system was +0.1 5%, with a precision of +/- 2.54%. The three-wavelength system had an overall error of +3.71%, with a precision of +/- 2.30%. Overall correl ation between catheter Svo, and oximeter values was the same for both devices (r = 0.99). Conclusions. Both currently available in vivo spec trophotometric systems are capable of producing satisfactory results o ver wide ranges of Svo(2). In contradistinction to older reports, we f ound that the two-wavelength Svo(2) system produced results equivalent to those obtained from the three-wavelength device. In this regard, t here is no detectable advantage in accuracy to measuring in vivo Svo(2 ) With three rather than with two wavelengths.