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TECHNOLOGY, COMPUTING, AND SIMULATION

Measurements of Optical Pathlength Using Phase-Resolved Spectroscopy in Patients Undergoing Cardiopulmonary Bypass

Kenji Yoshitani, MD^*, Masahiko Kawaguchi, MD, Takashi Okuno, MD^*, Tomoko Kanoda, MD^*, Yoshihiko Ohnishi, MD^*, Masakazu Kuro, MD^*, and Mitsunori Nishizawa, BS

From the *Department of Anesthesiology, National Cardiovascular Center, Suita, Osaka; Department of Anesthesiology, Nara Medical University, Kashihara, Nara; and System Engineering, Systems Division, Hamamatsu Photonics K.K. Hamamatus, Shizuoka, Japan.

Address correspondence and reprint requests to Kenji Yoshitani, MD, Department of Anesthesiology, Duke University Medical Center, Box 3094, Durham, NC 27710. Address e-mail to kenji.yoshitani{at}duke.edu.

BACKGROUND: Near infrared spectroscopy (NIRS) has been used during cardiac surgery to monitor cerebral oxygenation although the validity of this technique has yet to be established. Although optical pathlength included in the algorithm for calculating NIRS values is supposed to be constant, recent evidence has suggested that optical pathlength could be affected by acute hemodilution in animals. We conducted the present study to investigate whether optical pathlength changes during cardiopulmonary bypass (CPB), and whether these changes affect NIRS values in adult patients.

METHODS: Nine patients undergoing elective cardiac surgery with CPB were enrolled in this study. Optical pathlength and cerebral NIRS values (oxyhemoglobin [O₂Hb] and tissue oxygen index) were measured by phase-resolved spectroscopy and NIRO 100, respectively. Optical pathlength, hemoglobin concentration, and NIRS values were measured at the following points: 1) after the induction of anesthesia, 2) 10 min after the start of CPB, 3) 60 min after the start of CPB, and 4) 1 h after CPB. The associations between optical pathlength and other variables were analyzed by Pearson correlation coefficients and multiple regression analysis.

RESULTS: Optical pathlength significantly increased starting at 27.7–30.8 cm at 10 min, and 31.3 cm at 60 min after the start of CPB (P < 0.0001). Hemoglobin concentrations significantly decreased (from 11.2 to 7.1 g/dL at 10 min and 7.7 g/dL at 60 min P < 0.0001). There was a significant correlation (r = 0.55, P < 0.001) between percentage changes in pathlength and hemoglobin concentration. Multiple regression analysis showed that optical pathlength was a significant determinant of O₂Hb.

CONCLUSION: The results indicate that optical pathlength can change during CPB and its changes may affect O₂Hb.

Anesthesia & Analgesia® is published for the International Anesthesia Research Society® by Lippincott Williams & Wilkins with the assistance of Stanford University Libraries' HighWire Press®. Copyright 2006 by the International Anesthesia Research Society. Online ISSN: 1526-7598   Print ISSN: 0003-2999