Hyperoxia for management of acid-base status during deep hypothermia with circulatory arrest.

BACKGROUND: Which blood gas strategy to use during deep hypothermic circulatory arrest has not been resolved because of conflicting data regarding the advantage of pH-stat versus alpha-stat. Oxygen pressure field theory suggests that hyperoxia just before deep hypothermic circulatory arrest takes advantage of increased oxygen solubility and reduced oxygen consumption to load tissues with excess oxygen. The objective of this study was to determine whether prevention of tissue hypoxia with this strategy could attenuate ischemic and reperfusion injury. METHODS: Infants who had deep hypothermic circulatory arrest (n = 37) were compared retrospectively. Treatments were alpha-stat and normoxia (group I), alpha-stat and hyperoxia (group II), pH-stat and normoxia (group III), and pH-stat and hyperoxia (group IV). RESULTS: Both hyperoxia groups had less acidosis after deep hypothermic circulatory arrest than normoxia groups. Group IV had less acid generation during circulatory arrest and less base excess after arrest than groups I, II, or III (p < 0.05). Group IV produced only 25% as much acid during deep hypothermic circulatory arrest as the next closest group (group II). CONCLUSIONS: Hyperoxia before deep hypothermic circulatory arrest with alpha-stat or pH-stat strategy demonstrated advantages over normoxia. Furthermore, pH-stat strategy using hyperoxia provided superior venous blood gas values over any of the other groups after circulatory arrest.

Blood anion gaps and venoarterial carbon dioxide gradients as risk factors in long-term extracorporeal support.

Increases in the blood anion gap (AG) and venoarterial carbon dioxide gradients [p(V-A)CO2] may indicate changes in intracellular acid concentration not demonstrated by blood gas measurements. This prospective study examines these two physiologic markers to determine their relationship to extracorporeal membrane oxygenation (ECMO) survival and duration in 100 patients. Serum electrolytes were drawn every 6 hours and the AG calculated. Simultaneous arterial blood gases and venous blood gases were drawn every 4 hours and the p(V-A)CO2 calculated. Cumulative averages were then calculated from all the AG and p(V-A)CO2 values during each ECMO treatment. The average AG was 11 mEq/L. The average p(V-A)CO2 was 9 mm of mercury (mmHg). Patients with an AG of 11 mEq/L or less had a 12% mortality and those with a higher AG had a 43% mortality (p = 0.0005). Patients with a p(V-A)CO2 of less than 9 mmHg had a 13% mortality and those with a 9 mmHg or higher gradient had a 35% mortality (p = 0.0126). Patients with both a low AG and a low p(V-A)CO2 had a 7% mortality and survivors were on ECMO 100 (+/-37) hours. Patients with both a high AG and a high p(V-A)CO2 had a 56% mortality and survivors were on ECMO 190 (+/-105) hours. Both mortality and survivors' ECMO time increase as one or both risk factors increase. Patients with increases in both risk factors have a mortality rate 8 times greater and survivors remain on ECMO almost twice as long as those without increased risk factors. Patients may benefit from a perfusion strategy that seeks to minimize the AG and p(V-A)CO2.

Decreased incidence of intracranial hemorrhage using cephalic jugular venous drainage during neonatal extracorporeal membrane oxygenation.

Intracranial hemorrhage (ICH) remains one of the more common serious complications of extracorporeal membrane oxygenation (ECMO) in neonates. In 1990 this center began routine use of cephalic jugular venous drainage during neonatal ECMO to augment blood return to the ECMO pump and potentially decrease the incidence of ICH by decreasing cerebral venous pressure. Thirty-four ECMO cases utilizing cephalic jugular venous drainage were compared with the previous 34 ECMO cases. The incidence of ICH decreased from 35% (12/34) to 6% (2/34) when neonates without cephalic jugular venous drainage are compared with those being subject to this technique (P < .01). No differences were found between the two groups in gestational age, birth weight, duration of ECMO, survival, platelet counts, activated clotting times, or incidence of other bleeding complications. Cephalic jugular venous drainage during neonatal ECMO appears to be safe and may decrease the incidence of ICH.

Cephalic jugular venous blood gas measurement during neonatal venoarterial extracorporeal membrane oxygenation.

Cannulation of the cephalic portion of the right internal jugular vein during extracorporeal membrane oxygenation (ECMO) allows for increased venous return flow to the circuit. This procedure also allows access to venous drainage from the brain. We reviewed data from simultaneous blood gases obtained from the cephalic jugular vein and the mixed venous return in 5 neonates during venoarterial ECMO. Cephalic venous pO 2 values were significantly lower than mixed venous pO 2 values (P less than .001). The values for pH and pCO 2 did not vary between the sites. Our experience with 34 infants using cephalic jugular drainage is reviewed. Since the institution of right jugular venous drainage, the intracranial hemorrhage rate in neonates undergoing ECMO at our center has decreased from 34% to 6% (p less than .01).

Assessment of alveolar function in neonates on ECMO using the measurement of net CO2 transfer by the artificial lung.

The measurement of the net transfer of the CO2 by the artificial lung (Delta Cap) during ECMO indicates the rate at which the alveoli are becoming functional and allows the prediction of when weaning can best begin. Usually, an infant with lung disease placed on ECMO will need to excrete most of his CO2 production via the artificial lung. But as the alveoli heal, CO2 will be removed in increasing amounts by the infant's own lungs. When the Delta Cap reaches zero, all of the infant's CO2 production is being removed by his own lungs, an indication that he has adequate alveolar function to exchange O2. A capnagraph is used to measure the CO2 concentration of affluent and effluent sweep gas and the Delta Cap is determined by their difference.