Comparison of neurologic outcome after deep hypothermic circulatory arrest with alpha-stat and pH-stat cardiopulmonary bypass in newborn pigs.

OBJECTIVE: Deep hypothermic circulatory arrest for neonatal heart surgery poses the risk of brain damage. Several studies suggest that pH-stat management during cardiopulmonary bypass improves neurologic outcome compared with alpha-stat management. This study compared neurologic outcome in a survival piglet model of deep hypothermic circulatory arrest between alpha-stat and pH-stat cardiopulmonary bypass. METHODS: Piglets were randomly assigned to alpha-stat (n = 7) or pH-stat (n = 7) cardiopulmonary bypass, cooled to 19 degrees C brain temperature, and subjected to 90 minutes of deep hypothermic circulatory arrest. After bypass rewarming/reperfusion, they survived 2 days. Neurologic outcome was assessed by neurologic performance (0-95, 0 = no deficit and 95 = brain death) and functional disability scores, as well as histopathology. Arterial pressure, blood gas, glucose, and brain temperature were recorded before, during, and after bypass. RESULTS: All physiologic data during cardiopulmonary bypass were similar between groups (pH-stat vs alpha-stat) except arterial pH (7.06 +/- 0.03 vs 7.43 +/- 0.09, P <.001) and arterial PCO (2) (98 +/- 8 vs 36 +/- 8 mm Hg, P <.001). No differences existed in duration of cardiopulmonary bypass or time to extubation. Performance was better in pH-stat versus alpha-stat management at 24 hours (2 +/- 3 vs 29 +/- 17, P = 0.004) and 48 hours (1 +/- 2 vs 8 +/- 9, P =.1). Also, functional disability was less severe with pH-stat management at 24 hours (P =.002) and 48 hours (P =.053). Neuronal cell damage was less severe with pH-stat versus alpha-stat in the neocortex (4% +/- 2% vs 15% +/- 7%, P <.001) and hippocampal CA1 region (11% +/- 5% vs 33% +/- 25%, P =.04), but not in the hippocampal CA3 region (3% +/- 5% vs 16% +/- 23%, P =.18) or dentate gyrus (1% +/- 1% vs 3% +/- 6%, P =.63). CONCLUSIONS: pH-stat cardiopulmonary bypass management improves neurologic outcome with deep hypothermic circulatory arrest compared with alpha-stat bypass. The mechanism of protection is not related to hemodynamics, hematocrit, glucose, or brain temperature.

Anesthesia for the micropremie.

Providing anesthesia for the micropremie involves many considerations beyond what is needed for the full-term neonate. Immaturity of the airway, lungs, cardiovascular system, liver, kidneys, and central nervous system makes the micropremie susceptible to anesthestic complications. Immature respiratory mechanisms and respiratory control increase the risk of apnea, hypoxemia, and hypercapnia intraoperatively as well as postoperatively. Anesthetic drugs depress myocardial contractility and impair baroreflexes in the micropremie to increase the risk of hypotension during anesthesia. Drug metabolism in the micropremie is slow because of the immature liver and kidneys. The micropremie brain requires less drug to achieve the anesthetized state. As a result, administration of the dose and timing of anesthetic drugs differs in the micropremie compared with the full-term neonate. This article describes anesthetic considerations for a few surgical prodedures common in the micropremie.

Comparison of pH-stat and alpha-stat cardiopulmonary bypass on cerebral oxygenation and blood flow in relation to hypothermic circulatory arrest in piglets.

BACKGROUND: Deep hypothermic circulatory arrest is used in neonatal cardiac surgery. Recent work has suggested improved neurologic recovery after deep hypothermic arrest with pH-stat cardiopulmonary bypass (CPB) compared with alpha-stat CPB. This study examined cortical oxygen saturation (ScO2), cortical blood flow (CBF), and cortical physiologic recovery in relation to deep hypothermic arrest with alpha-stat or pH-stat CPB. METHODS: Sixteen piglets were cooled with pH-stat or alpha-stat CPB to 19 degrees C (cortex) and subjected to 60 min of circulatory arrest, followed by CPB reperfusion and rewarming and separation from CPB. Near infrared spectroscopy and laser Doppler flowmetry were used to monitor ScO2 and CBF. Cortical physiologic recovery was assessed 2 h after the piglets were separated from CPB by cortical adenosine triphosphate concentrations, cortical water content, CBF, and ScO2. RESULTS: During CPB cooling, ScO2 increased more with pH-stat than with alpha-stat bypass (123 +/- 33% vs. 80 +/- 25%); superficial and deep CBF were also greater with pH-stat than with alpha-stat bypass (22 +/- 25% vs. -56 +/- 22%, 3 +/- 19% vs. -29 +/- 28%). During arrest, ScO2 half-life was greater with pH-stat than with alpha-stat bypass (10 +/- 2 min vs. 7 +/- 2 min), and cortical oxygen consumption lasted longer with pH-stat than with alpha-stat bypass (36 +/- 8 min vs. 25 +/- 8 min). During CPB reperfusion, superficial and deep CBF were less with alpha-stat than with pH-stat bypass (-40 +/- 22% vs. 10 +/- 39%, -38 +/- 28% vs. 5 +/- 28%). After CPB, deep cortical adenosine triphosphate and CBF were less with alpha-stat than with pH-stat bypass (11 +/- 6 pmole/mg vs. 17 +/- 8 pmole/mg, -24 +/- 16% vs. 16 +/- 32%); cortical water content was greater with alpha-stat than with pH-stat bypass (superficial: 82.4 +/- 0.3% vs. 81.8 +/- 1%, deep: 79.1 +/- 2% vs. 78 +/- 1.6%). CONCLUSIONS: Cortical deoxygenation during hypothermic arrest was slower after pH-stat CPB. pH-stat bypass increased the prearrest ScO2 and arrest ScO2 half-life, to increase the cortical oxygen supply and slow cortical oxygen consumption. Improved cortical physiologic recovery after hypothermic arrest was suggested with pH-stat management.

Brain cooling efficiency with pH-stat and alpha-stat cardiopulmonary bypass in newborn pigs.

BACKGROUND: For infant cardiac surgery, recent studies suggest improved neurological outcome after deep hypothermic circulatory arrest when pH-stat cardiopulmonary bypass is used compared with alpha-stat cardiopulmonary bypass. The pH-stat method is hypothesized to protect the brain through improved cooling and/or rewarming. We examined brain cooling and rewarming during pH-stat and alpha-stat cardiopulmonary bypass in 12 newborn pigs. METHODS AND RESULTS: Microthermistors were inserted into the caudate and cortical gray and white matter, and a cranial window was created to map neocortical temperature gradients by using infrared imaging. Piglets were cooled with pH-stat or alpha-stat cardiopulmonary bypass until all brain regions were less than 20 degrees C; then they were subjected to 60 minutes of circulatory arrest, and afterward, rewarmed with cardiopulmonary bypass. During cardiopulmonary bypass cooling, cortical gray and white matter and caudate temperatures were up to 5 degrees C less in pH-stat than in alpha-stat (P<.05), although after 10 minutes of cooling, only cortical white matter temperature remained significantly less in pH-stat. Neocortical thermal gradients during cardiopulmonary bypass cooling were greater in pH-stat versus alpha-stat during the initial 8 minutes (4 degrees C to 5 degrees C versus 2 degrees C to 3 degrees C, P<.01) but were less by 18 to 20 minutes (0.9 degrees C versus 1.7 degrees C, P<.01). Cardiopulmonary bypass cooling time to less than 20 degrees C was shorter for pH-stat than for alpha-stat in cortical gray matter (14 versus 17 minutes, P<.05) and cortical white matter (17 versus 23 minutes, P<.001) but not in caudate (13 versus 16 minutes, P=NS). Cooling time to less than 1 degrees C neocortical thermal gradient was shorter in pH-stat than in alpha-stat (15 versus 23 minutes, P<.001). During rewarming, regional brain temperatures and neocortical thermal gradients were not different between groups. CONCLUSIONS: pH-stat improves brain cooling efficiency during cardiopulmonary bypass because all regions cooled more rapidly, especially cortical white matter, and less time was required to achieve uniform cerebral deep hypothermia. pH-stat and alpha-stat cardiopulmonary bypass rewarm the brain similarly after deep hypothermic arrest.