Age-related differences in the response to myocardial ischemic stress.

Clinical experience indicates that the risk of reparative cardiac operations is increased in the neonatal period relative to that in older infants and children. Age-related differences in the susceptibility to myocardial ischemic dysfunction were evaluated by comparison of left ventricular function and metabolism in neonatal (mean age = 7 days) and weanling (mean age = 96 days) piglets. Six animals in each group supported on cardiopulmonary bypass were subjected to (1) 120 minutes of hypothermic crystalloid cardioplegic arrest (CP-120) and (2) 15 minutes of normothermic ischemic arrest (NA-15) after a 60 minute interval of reperfusion. Left ventricular systolic and diastolic function was measured after each intervention via endocardially implanted ultrasonic dimension crystals in a septolateral minor-axis position. In both groups, systolic dysfunction was evidenced by an increase in the dimension-axis intercept (p = 0.001), but not the slope of the end-systolic pressure-dimension relation. Left ventricular end-diastolic stiffness, expressed as left ventricular end-diastolic pressure versus Lagrangian strain, increased to a similar degree in both groups (p = 0.001). Adenosine triphosphate levels declined significantly (p = 0.001) in both groups in response to the ischemic interventions with no evident intergroup differences. Lactate levels increased significantly during the course of the experiment (p = 0.04); however, the increases were greater (p = 0.009) at all intervals in the neonatal group. This study demonstrates age-related metabolic differences in response to ischemia consistent with a greater dependence on glycolysis in neonatal myocardia. However, the fact that discriminating age-related differences in left ventricular function were not evident suggests that factors other than young age per se account for the increased surgical mortality in the neonatal period.

Intraoperative autotransfusion in blunt abdominal trauma.

We have used intraoperative autotransfusion in three cases of massive intraabdominal hemorrhage following blunt trauma. Based on this experience we recommend that: (1) To prevent sudden collapse the abdomen should be decompressed slowly through a small incision while blood is collected into the autotransfusion reservoir; (2) A skilled person is required to operate the autotransfusor; and (3) To prevent consumption coagulopathy, autotransfusion must be supplemented by the use of blood components, especially fresh frozen plasma.

Sequestration of fentanyl by the cardiopulmonary bypass (CPBP).

Immediately following the connection of pediatric patients to cardiopulmonary bypass we have consistently observed a steep decrease in fentanyl plasma concentration (74 +/- 8.7%) (mean +/- SD), much greater than would have been expected from hemodilution alone (50.6% +/- 12.0%) (p less than 0.0001). Priming of the pump with 20 ng/ml of fentanyl before connection to the patients did not prevent this phenomenon. In order to study the possibility that fentanyl is sequestered by the bypass, levels of the primed drug in the bypass were assessed before connecting the pump to the children and a steep fall from 20 ng/ml to zero was shown before initiation of bypass. Pharmacokinetic assessment of fentanyl in a closed pump circuit showed that levels of 120 ng/ml fall to 2 ng/ml within 3 min and remain stable at the lower concentration for at least 30 min. Further studies have identified the membrane oxygenator as the major site of fentanyl sequestration. Concentrations across the membrane fall from 120 ng/ml to 10 ng/ml. The attached siliconized tubing is associated with a minor binding effect sufficient to reduce concentrations from 110 to 84 ng/ml. The pvc tubing, aluminium heat exchanger and plastic reservoir had no binding effect on fentanyl. The possibility that a decrease in fentanyl protein binding caused the fall in serum concentration was checked in 5 patients undergoing open heart surgery. After initiation of the cardiopulmonary bypass, there was a significant decrease in albumin serum concentrations from 32.0 +/- 2.3 mM to 15.0 +/- 1.6 mM (p less than 0.0001).(ABSTRACT TRUNCATED AT 250 WORDS)

Changes in pericardial surface pressure during pulmonary hypertensive crises after cardiac surgery.

Reactive pulmonary hypertension in children after surgical repair of large left-to-right shunts is an important cause of postoperative low cardiac output. Low output may be caused by impaired left ventricular filling from right ventricular dilatation. We studied 12 children during the first 72 hr after surgery by measuring right ventricular pericardial surface pressure with a flat balloon and compared the results with acute changes in pulmonary arterial pressure (PAP). All 12 children (ages 4 to 14 months) had preexisting large left-to-right shunts with systemic PAPs. We found a highly significant linear correlation between acute rises in PAP and rises in the pericardial pressure (PP). The regression equation was PAP = 1.48(PP) + 5.7, R2 = .61, p less than .001. There was an average of 15.6 pulmonary hypertensive episodes per patient during the 72 hr study period, but only 9% of these episodes were associated with either no change or a fall in systemic pressure. We conclude that changes in right ventricular pericardial pressure reflect acute changes in PAP.

Neonatal autoperfused working heart-lung preparation: assessment of factors determining survival.

The function and survival of the autoperfused working heart-lung preparation in the newborn period was studied in six newborn pigs (3 to 5 days old). Normothermic autoperfusion was maintained by a closed blood-primed circuit. Left ventricular afterload was determined by positioning the blood reservoir, and the venous return was adjusted to maintain a right atrial pressure of 6 to 8 mm Hg. Left ventricular function was assessed by a conductance catheter in the left ventricle and was determined by the slope of the end-systolic pressure-volume relationship. Left ventricular diastolic compliance was measured from the end-diastolic pressure-volume relationship. Serial measurements at 60, 120, 180, and 240 minutes showed no change in the end-systolic pressure-volume relationship, whereas there was a significant leftward shift of the end-diastolic pressure-volume relationship after 240 minutes (0.42 +/- 0.02 ml-1 to 0.66 +/- 0.04 ml-1, p less than 0.05). Cessation of effective cardiac function occurred at 268 +/- 10 minutes (+/- SEM). This followed progressive deterioration in pulmonary function based on measurement of arterial blood gases and peak airway resistance. This study shows the feasibility of maintaining systolic cardiac function in a newborn autoperfused working heart-lung preparation. Extended survival beyond 4 hours will require improved methods to preserve left ventricular diastolic function and especially pulmonary function.