pH-stat cooling improves cerebral metabolic recovery after circulatory arrest in a piglet model of aortopulmonary collaterals.

Cardiopulmonary bypass with deep hypothermic circulatory arrest increases the risk of neurologic injury in patients with aortopulmonary collaterals. Experimental studies have demonstrated that such collaterals decrease the rate of cerebral cooling before arrest and cerebral metabolic recovery after circulatory arrest. Use of pH-stat blood gas management has been shown to increase cerebral blood flow during cooling. The current study was designed to test whether cooling with pH-stat blood gas management can decrease the cerebral metabolic impact of aortopulmonary collaterals. Twenty 4- to 6-week-old piglets underwent placement of a shunt between the left subclavian artery and main pulmonary artery. In control animals (n = 10) the shunts were immediately ligated, whereas in the shunt animals (n = 10) the shunts were left patent. All animals were supported with cardiopulmonary bypass, cooled to 18 degrees C by means of either alpha-stat (five control and five shunt animals) or pH-stat (five control and five shunt animals) blood gas management, subjected to circulatory arrest for 90 minutes, and rewarmed to 37 degrees C. The cerebral metabolic rate of oxygen consumption (a marker for neurologic function) was significantly lower after circulatory arrest in the shunt animals cooled with alpha-stat blood gas management than in the control animals subjected to alpha-stat management (1.2 +/- 0.2 vs 2.3 +/- 0.2 ml oxygen per 100 gm/min, p < 0.05). By contrast, there was no difference between the pH-stat shunt animals and either control group (2.1 +/- 0.2 vs 2.3 +/- 0.2 [alpha-stat] and 2.0 +/- 0.3 [pH-stat] ml oxygen per 100 gm/min, p = not significant). pH-Stat cooling protected the brain from shunt-related injury. When circulatory arrest is used in the presence of aortopulmonary collaterals, the use of pH-stat blood gas management during cooling results in better cerebral protection than alpha-stat blood gas management.