Intraoperative metabolic monitoring of the heart: II. Online measurement of myocardial tissue pH

Under conditions of ischemia, the hydrogen ion [H+] accumulates in the myoc ardial tissue in proportion to the magnitude of the ischemic insult. The ac cumulation of [H+] is the result of both increased anaerobic production of [H+] secondary to decreased substrate and decreased washout of [H+] seconda ry to decreased coronary perfusion. The Khuri tissue pH electrode/monitorin g system has been developed and validated over the past two decades. Its sc ientific basis and correlates have been established, and it is the only sys tem that has been approved for use in humans. Myocardial tissue pH has been monitored in the anterior and posterior walls of the left ventricle in mor e than 700 patients undergoing major cardiac surgery. An understanding of t he relationship between pH and temperature and between the pH and [H+] in t issues is important for the proper interpretation of the myocardial pH data generated in the course of an operation. Intraoperative monitoring of myoc ardial pH is the only modality available to the cardiac surgeon for online assessment and improvement of the adequacy of myocardial protection. By def ining myocardial protection in terms of protection from myocardial tissue a cidosis, this technology provides a new tool with which the comparative eff icacy of the various myocardial protection techniques can be assessed. It a lso provides an online tool for assessing the adequacy of coronary revascul arization, and has the potential of improving procedures and outcomes for o ff-pump coronary artery bypass grafting. (C) 2001 by The Society of Thoraci c Surgeons.