To the Editor:-We read with interest the study by Kurth and associates [1]relating to the comparison of pH-stat and alpha-stat strategies for cardiopulmonary bypass on cerebral blood flow and oxygenation using near-infrared spectroscopy and laser Doppler flowmetry in piglets. Kurth et al. [1]concluded that the use of pH-stat acid-base management compared to alpha-stat improved cortical physiologic recovery after deep hypothermic circulatory arrest.

There are significant differences between their experimental design and clinical protocols for pediatric cardiopulmonary bypass. Mean arterial pressures immediately before deep hypothermic circulatory arrest were 74 +/− 11 mmHg and 72 +/− 8 mmHg in the alpha-stat and pH-stat groups, respectively. These pressures are extremely high for 2- to 3-kg piglets at pre- deep hypothermic circulatory arrest. In the clinical setting, mean arterial pressures are typically kept below 40 mmHg.

A bubble oxygenator was used in their study. According to the 1994 pediatric survey, 93.5% of all pediatric centers use membrane oxygenators exclusively in the United States. [2]Only 6.5% of all centers use membrane and bubble oxygenators. Bubble oxygenators are used only for short, uncomplicated cases, not with deep hypothermic circulatory arrest. It has been clearly documented that the use of membrane oxygenators significantly reduces gaseous and particulate microemboli. [3,4] 

Despite these concerns, it is interesting that pH-stat management significantly improved cortical recovery with high mean arterial pressures in their experimental setup.

Akif Undar, Ph.D.

Congenital Heart Surgery Service; Texas Children's Hospital; Houston, Texas; Cullen Cardiovascular Surgery Research Laboratories; Texas Heart Institute; Houston, Texas; Department of Surgery; Baylor College of Medicine; Houston, Texas;

Dean B. Andropoulos, M.D.

Departments of Pediatrics and Anesthesiology; Baylor College of Medicine; Houston, Texas

Charles D. Fraser, Jr., M.D.

Congenital Heart Surgery Service; Texas Children's Hospital; Houston, Texas; Departments of Surgery and Pediatrics; Baylor College of Medicine; Houston, Texas

(Accepted for publication November 17, 1998.)

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Groom RC, Akl BF, Albus R, Lefrak EA: Pediatric cardiopulmonary bypass: A review of current practice. Int Anesthesiol Clin 1996; 34:141-63
Blauth CI, Smith PL, Arnold JV, Jagoe JR, Wooten R, Taylor KM: Influence of exygenator type on the prevalence and extent of micro-embolic retinal ischemia during cardiopulmonary bypass. J Thorac Cardiovasc Surg 1990; 99:61-9
Padayachee TS, Parsons S, Theobold R, Linley J, Gosling RG, Deverall PB: The detection of microemboli in the middle cerebral artery during cardiopulmonary bypass: A transcranial Doppler ultrasound investigation using membrane and bubble oxygenators. Ann Thorac Surg 1987; 44:298-302