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J Thorac Cardiovasc Surg 2001;121:0204-0205
© 2001 The American Association for Thoracic Surgery

Editorials

Optimal pH strategy for hypothermic circulatory arrest

Richard A. Jonas, MD

From Children's Hospital (Cardiovascular Surgeon-in-Chief) and Harvard Medical School (William E. Ladd Professor of Surgery), Boston, Mass.

Received for publication Aug 11, 2000. Accepted for publication Aug 22, 2000. Address for reprints: Richard Jonas, MD, Department of Cardiac Surgery, Children's Hospital, 300 Longwood Ave, Boston, MA 02115.

For related article, see p. 336.

It was several years after the beginning of open heart surgery before hypothermia was introduced as a component of cardiopulmonary bypass (CPB). At about this time in the late 1950s, blood gas analysis became more readily available and revealed a surprising fact: when blood is cooled by the heat exchanger in the circuit, pH changes in an alkaline direction. The usual response in the 1960s and 1970s was to compensate for this alkaline shift by adding carbon dioxide, a technique that has come to be known as the pH-stat strategy. This also had what was perceived to be an important advantage in that carbon dioxide is a potent cerebral vasodilator. It was believed that adding carbon dioxide would increase the safety margin for cerebral oxygen supply and reduce the risk of major neurologic injury, which was all too common in the early years of CPB.

In the late 1970s and early 1980s, a number of reports appeared that questioned whether the pH-stat strategy was indeed the correct response to the alkaline shift with hypothermia. It was found that cold-blooded vertebrates simply allow their blood pH to drift in an alkaline direction. It appeared that this alpha-stat strategy optimized intracellular enzyme function. Studies in dogs showed that the threshold for ventricular fibrillation was lower with the more acidotic pH-stat strategy. It also became increasingly apparent that the most common cause of neurologic injury in adults . . . [Full Text of this Article]


Related Article

Comparison of neurologic outcome after deep hypothermic circulatory arrest with alpha-stat and pH-stat cardiopulmonary bypass in newborn pigs
Margaret A. Priestley, Jeffrey A. Golden, Irene B. O'Hara, John McCann, and C. Dean Kurth
J. Thorac. Cardiovasc. Surg. 2001 121: 336-343. [Abstract] [Full Text] [PDF]





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