Cerebral Oxygen Monitoring during Cardiopulmonary Bypass and Deep Hypothermia Circulatory Arrest
by H. Abdul-Khalig et al.

I read with great interest the study by Abdul Khaliq et al. [1] describing cerebral oxygen measurements by a near-infrared spectrophotometry (NIRS) device (Critikon RedOx Monitor 2020) in a neonatal piglet model. The authors aimed to “investigate the physiological effects of cardiopulmonary bypass (CPB) and deep hypothermic circulatory arrest (DHCA) on cerebral oxygen metabolism estimated by near infrared spectroscopy”. This has been done several times, both clinically and experimentally, and was pioneered by Dr. Richard Jonas' group from Children's Hospital Boston [2] [3]. The results were similar, and NIRS measurements correlated well with high-energy phosphates in brain tissue [4], brain histology, hematocrit, acid-base management, and other physiological parameters. Disappointingly, none of the previous experimental work is cited or discussed in the paper. However, measurements with the Critikon RedOx monitor 2020 are rare since the device is not commercially available (as incorrectly stated in the paper). The manufacturer Johnson and Johnson withdrew the device from the market due to technical difficulties and sold Critikon in 1998.

The authors conclude that NIRS measurements of the redox status of cytochrome a,a3 “represent related effects on intracellular oxidative metabolism”. We would all be more than happy to find such an eagerly desired parameter. Unfortunately, a recent study demonstrated that NIRS cytochrome measurements during CPB depend far more on the hematocrit level than on the redox-status of cytochrome [5] since the hemoglobin signal overwhelms the cytochrome signal. The drop in CytOx with the onset of DHCA therefore most likely only reflects the exsanguination of the animal. Differences due to temperature are to be expected, as vasoconstriction and hemoglobin content depend on body temperature.

References

• 1 Abdul-Khaliq H, Troitzsch D, Schubert S, Wehsack A, Böttcher W, Gutsch E, Hübler M, Hetzer R, Lange P E. Cerebral Oxygen monitoring during neonatal cardiopulmonary bypass and deep hypothermic circulatory arrest.  Thorac Cardiovasc Surg. 2002;  50 77-81
• 2 Nollert G, Shin'oka T, Jonas R A. Near infrared spectrophotometry in cardiac surgery.  Thorac Cardiovasc Surg. 1998;  46 167-175
• 3 Nollert G, Jonas R A, Reichart B. Optimizing cerebral oxygenation during cardiac surgery: A review of experimental and clinical invetigators with near infrared spectrophotometry.  Thorac Cardiovasc Surg. 2000;  48 247-253
• 4 Shin'oka T, Nollert G, Shum-Tim D, du Plessis A, Jonas R A. Utility of near-infrared spectroscopic measurements during deep hypothermic circulatory arrest.  Ann Thorac Surg. 2000;  69 578-583
• 5 Sakamoto T, Jonas R A, Stock U A, Hatsuoka S, Cope M, Springett R J, Nollert G. Utility and Limitations of Near-Infrared Spectroscopy during Cardiopulmonary Bypass in a Piglet Model.  Ped Pesearch. 2001;  49 770-776