Proceedings of The Physiological Society
Puerto de la Cruz, Tenerife (2003) J Physiol 548P, P57
The use of cerebral NIRS monitoring during hypoperfusion events in cardiopulmonary bypass
J. Alder, J.A. Pickett, S.E. Stacey, I. McGovern, H. Bishop, M. Ward, R.R.D. Marks and M.S. Thorniley
Department of Instrumentation and Analytical Science, UMIST, Manchester, M609 1QD and Barts and The London NHS Trust, Bonner Road, Whitechapel, London E1 2BL, UK
Cardiopulmonary bypass is frequently carried out under mild hypothermia since cooling is used to reduce metabolic rate and hence can offer protection from cerebral and myocardial ischaemia. However, there is increasing concern that rewarming following hypothermia may adversely affect the neurological outcome (Grigore et al. 2002). We have studied the cerebral effects of hypoperfusion events during cardiopulmonary bypass under mild hypothermia, and following rewarming using near infrared spectroscopy (NIRS). NIRS has been used to assess cerebral oxygen delivery, utilisation and perfusion.
We studied 10 patients who underwent coronary artery bypass grafting by the same surgeon. Ethical approval was granted and patient consent obtained. A standardised anaesthetic technique was used. Total body oxygen consumption was measured by continuous arteriovenous oximetry (Crerar-Gilbert et al. 2001). Cerebral oxygenation was measured simultaneously using a CRITIKON (Johnson & Johnson Medical) near infrared instrument (Thorniley et al. 1997). Statistical analysis was carried out using the independent samples t test (SPSS 10.0). Data are given as means ± S.D.
A total of 51 hypoperfusion episodes were recorded during hypothermia (32°C) and 20 episodes following rewarming to 37.5°C. The basal oxygen consumption at 32°C was 38.3 ± 17.0 ml min-1 m-2 increasing significantly to 71.5 ± 23.0 ml min-1 m-2 (mean ± S.D.) at 37.5°C (P < 0.002). Episodes of hypoperfusion resulted in a significant reduction in total body oxygen consumption, associated with significant reductions in the concentration of cerebral oxyhaemoglobin and total haemoglobin (P < 0.05, 95% CI). Figure 1 shows a typical example of desaturation of oxyhaemoglobin during a hypoperfusion event. Oxyhaemoglobin concentrations decreased by -30.8 ± 17.6
Where applicable, experiments conform with Society ethical requirements