Utility of Cerebral Oxymetry for Assessing Cerebral Arteriolar Carbon Dioxide Reactivity during Cardiopulmonary Bypass
DOI:
https://doi.org/10.1532/HSF98.2014319Abstract
Background: Our study evaluated changes in cerebral arterial oxygen saturation (rSO2) during cardiopulmonary bypass (CPB) that were caused by changes in arterial carbon dioxide tension (PaCO2).
Methods: A group of 126 patients undergoing routine, elective, first-time coronary artery bypass graft surgery (CABG) was entered into a prospective study using bilateral near-infrared spectroscopy (NIRS) before anesthetic induction (T1), after anesthetic induction (T2), and continuing at 5-minute intervals during moderate hypothermic (32°C) CPB. Pump flows were set at 2.5 L/min/m2 and adjusted to maintain mean arterial pressure (MAP) within 10 mmHg of the MAP recorded at the initial fifth minute of CPB (T3). Thirty-two patients were excluded from data collection because MAP could not be stabilized within the target range of 60-90 mmHg. In the remaining 94 patients, after obtaining steady state flow, MAP, and oxygenation, a trial period of hypocarbia (mean PaCO2 of 30 mmHg) was induced by increasing oxygenator fresh gas flow rate (FGFR) to 2.5 L/min/m2 (T4). A reciprocal period was then measured at reduced FGFR (0.75 L/min/m2) (T5).
Results: After 20 minutes of a higher (2.75 L/min/m2) (FGFR), mean PaCO2 decreased from a baseline of 38 ± 4 mmHg to 30 ± 2 mmHg. This was associated with a parallel decrease (-10±9%) in mixed cerebral oxygen saturation without alteration of mean arterial oxygen tension (PaO2), lactate, MAP, CPB flow, or other parameters implying increased cerebral oxygen extraction.
Conclusion: Parallel changes in PaCO2 and rSO2 occur during CPB when other variables remain constant, and are due to the effects of carbon dioxide on cerebral arterioles. Cerebral oxygen saturation measured by NIRS may be a useful indirect measure of PaCO2 when continuous blood gas analysis is not possible during open-heart surgery. Cerebral oximetry values may be useful measurements for setting an optimum gas flow rate through the oxygenator.
References
Austin EH, Edmonds HL, Auden SM. 1997. Benefit of neuromonitoring for pediatric cardiac surgery. J Thorac Cardiovasc Surg 114:707-17.nBoodhwani M, Rubens F, Wozny D, et al. 2007. Effects of sustained mild hypothermia on neurocognitive function after coronary artery bypass surgery: a randomized, double-blind study. J Thorac Cardiovasc Surg 134:1443-52.nBrijen J, Kenneth B, Jennifer L, et al. 2010. Impaired autoregulation of cerebral blood flow during rewarming from hypothermic cardiopulmonary bypass and its potential association with stroke. Anesth Analg 110:321-8.nBrown MM, Wade JPH, Marshall J, et al. 1985. Fundamental importance of arterial oxygen content in the regulation of cerebral blood flow in man. Brain 108:81-93.nDA Moehle. 2001. Neuromonitoring in the cardiopulmonary bypass surgical patient: clinical applications. J Extra Corpor Technol 33:126-34.nEdmonds HL, Pollock SB, Ganzel BL et al. 2000. Neuromonitoring for cardiac and vascular surgery. In: Newman SP, Harrison MJG, eds. The Brain and Cardiac Surgery, Reading, UK: Hardwood Academic Publishers, 143-64.nGiller CA, Bowman G, Dyer H, et al. 1993. Cerebral arterial diameters during changes in blood pressure and carbon dioxide during craniotomy. Neurosurgery 32:737-42.nGottesman R, Sherman P, Grega M, et al. 2006. Watershed strokes after cardiac surgery: diagnosis, etiology, and outcome. Stroke 37:2306-11.nHogue C Jr, Palin C, Arrowsmith J. 2006. Cardiopulmonary bypass management and neurologic outcomes: an evidence-based appraisal of current practices. Anesth Analg 103:21-37.nHyung-sik B, Sang-kwan M, Seong-uk P, et al. 2011. Effects of GV20 acupuncture on cerebral blood flow velocity of middle cerebral artery and anterior cerebral artery territories, and CO2 reactivity during hypocapnia in normal subjects. J Altern Complement Med 17:219-24.nLaffey JG, Kavanagh BP. 2002. Hypocapnia. N Engl J Med 347:43-53.nLaffey JG, Boylan JF, Cheng DC. 2002. The systemic inflammatory response to cardiac surgery. Anesthesiology 97:215-52.nMcCusker K, Anthony C., Gordon de Foe, et al. 2006. Influence of hematocrit and pump prime on cerebral oxygen saturation in on-pump coronary revascularization. Perfusion 21:149.nMinhas PS, Smielewski P, Kirkpatrick PJ, et al. 2004. Pressure autoregulation and positron emission tomography derived cerebral blood flow acetazolamide reactivity in patients with carotid artery stenosis. Neurosurg 55:63-8.nMoraca R, Lin E, Holmes J, et al. 2006. Impaired baseline regional cerebral perfusion in patients referred for coronary artery bypass. J Thorac Cardiovasc Surg 131:540-6.nNewman M, Croughwell N, Blumenthal J, et al. 1994. Effect of aging on cerebral autoregulation during cardiopulmonary bypass. Association with postoperative cognitive dysfunction. Circulation 90:II-243-I-249.nReinhard M, Roth M, Guschlbauer B, et al. 2005. Dynamic cerebral autoregulation in acute ischemic stroke assessed from spontaneous blood pressure fluctuations. Stroke 36:1684-9.nSlater JP, Guarino T, Stack J, et al. 2009. Cerebral oxygen desaturation predicts cognitive decline and longer hospital stay after cardiac surgery. Annals of Thoracic Surgery 87:36-44.nSorteberg W, Lindegaard KF, Rootwelt K, et al. 1989. Blood velocity and regional blood flow in defined cerebral artery systems. Neurochir (Wien) 97:47-52.nSteiner L, Pfister D, Strebel S, et al. 2009. Near-infrared spectroscopy can monitor dynamic cerebral autoregulation in adults. Neurocrit Care 10:122-8.nTan ST. Cerebral oximetry in cardiac surgery. 2008. Hong Kong Med J 14:220-5.nToraman F, Evrenkaya S, Senay S, et al. 2007. Adjusting oxygen fraction to avoid hyperoxemia during cardiopulmonary bypass. Asian Cardiovasc Thorac Ann 15:303-6.nWillie K, Macleod DB, Shaw AD, et al. 2012. Regional brain blood flow in man during acute changes in arterial blood gases. J Physiol 14:3261-75.nZuj KA, Arbeille P, Shoemaker JK, et al. 2012. Impaired cerebrovascular autoregulation and reduced CO reactivity after long duration spaceflight. Am J Physiol Heart Circ Physiol 302:H2592-8.n
