Myocardial protection

The role of normothermic machine perfusion (NMP) in the preservation of ex-vivo liver before transplantation: A review

The discrepancy between the number of patients awaiting liver transplantation and the number of available donors has become a key issue in the transplant setting. There is a limited access to liver transplantation, as a result, it is increasingly dependent on the use of extended criteria donors (ECD) to increase the organ donor pool and address rising demand. However, there are still many unknown risks associated with the use of ECD, among which preservation before liver transplantation is important in determining whether patients would experience complications survive after liver transplantation. In contrast to traditional static cold preservation of donor livers, normothermic machine perfusion (NMP) may reduce preservation injury, improve graft viability, and potentially ex vivo assessment of graft viability before transplantation. Data seem to suggest that NMP can enhance the preservation of liver transplantation to some extent and improve the early outcome after transplantation. In this review, we provided an overview of NMP and its application in ex vivo liver preservation and pre-transplantation, and we summarized the data from current clinical trials of normothermic liver perfusion.

WITHDRAWN: Surgically induced myocardial ischemia: How best to mitigate the injury

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The effect of intravenous dextrose infusion on postbypass hyperglycemia in pediatric patients undergoing cardiac operations

STUDY OBJECTIVE

To determine whether elimination of intraoperative dextrose-containing infusions affects post-cardiopulmonary bypass hyperglycemia in pediatric patients.

DESIGN

Randomized, unblinded, saline-controlled study of perioperative glucose infusions in children undergoing cardiac surgery.

SETTING

Cardiac surgery suite and pediatric intensive care unit (ICU) of a university medical center.

PATIENTS

33 consecutive, nondiabetic children undergoing cardiac surgery with deep hypothermia over an 8-month period.

INTERVENTIONS

Group A (n = 16) received only normal saline infusions intraoperatively, and Group B (n = 17) received 5% dextrose and lactated Ringer's solution exclusively. Blood glucose was sampled immediately after induction of anesthesia, prior to cardiopulmonary bypass (CPB), after separation from CPB, on arrival in the ICU, and the morning of the first postoperative day. Data were analyzed using Student's t-test for independent samples, paired t-test, and analysis of variance, with p < 0.05 considered significant.

MEASUREMENTS AND MAIN RESULTS

Although moderate elevations in blood glucose (mean less than 165 mg/dl) after CPB were present in Group A, significantly higher levels (mean greater than 250 mg/dl) were noted in Group B. No children were hypoglycemic (glucose less than 40 mg/dl). Glucose levels were normal in both groups on the morning of the first postoperative day despite patients' having received continuous dextrose infusions in the ICU and the presumed stress of emergence from anesthesia.

CONCLUSIONS

Extreme postbypass hyperglycemia can be controlled by eliminating intraoperative dextrose infusions. Hypoglycemia, an unlikely event, can easily be avoided by regular blood sampling, which is facilitated by the routine placement of arterial catheters.

Increased ischemic injury but decreased hypoxic injury in hypertrophied rat hearts

The purpose of this study was to compare the degree of ischemic and hypoxic injury in normal versus hypertrophied rat hearts to investigate basic mechanisms responsible for irreversible myocardial ischemic injury. Hearts from rats with bands placed on the aortic arch at 23 days of age (BAND) and sham-operated rats (SHAM, 8 weeks postoperative) were isolated, perfused with Krebs buffer, and had a left ventricular balloon to measure developed pressure. Hearts were made globally ischemic until they developed peak ischemic contracture and were reperfused for 30 minutes. Additional hearts were perfused for 15 minutes with glucose-free hypoxic buffer followed by 20 minutes of oxygenated perfusion. There was an 87% increase in heart weight of BAND compared with SHAM (p less than 0.01). During ischemia, lactate levels increased faster in BAND compared with SHAM, ischemic contracture occurred earlier in BAND than in SHAM despite no difference in ATP levels, and postischemic recovery of left ventricular pressure was less in BAND (26.8 +/- 5.6% of control left ventricular pressure, mean +/- SEM) compared with SHAM (40 +/- 4.6%, p less than 0.05). During hypoxic perfusion, lactate release was greater in BAND than in SHAM (48.8 +/- 1.2 versus 26.6 +/- 0.97 mumols/g, p less than 0.01), and with reoxygenation, lactate dehydrogenase release was less in BAND than in SHAM (13.2 +/- 0.7 versus 19.5 +/- 0.2 IU/g, p less than 0.01). After hypoxia and reoxygenation, left ventricular pressure recovery was greater in BAND than in SHAM (93 +/- 8.4% versus 66 +/- 5.3%, p less than 0.01). Thus, this study suggests that hypertrophied hearts have a greater potential for glycolytic metabolism, resulting in an increased rate of by-product accumulation during ischemia, which may be responsible for the increased susceptibility of hypertrophied hearts to ischemic injury.

The physiological basis of left ventricular diastolic dysfunction

Overall cardiac pump function requires adequate ventricular diastolic filling as well as normal systolic ejection. Abnormalities of the rate or extent of myocardial relaxation (diastolic dysfunction) have been described in a large variety of clinical conditions, including hypertrophy, ischemia, and after cardiac surgery. Diastolic and systolic dysfunction can be readily distinguished by analysis of pressure volume loops and utilization of echocardiography or nuclear cardiology gated blood pool scans. The mechanisms by which diastolic dysfunction can occur may be structural (hypertrophy, fibrosis) or dynamic (hypoxia, ischemia, alteration of diastolic cytosolic calcium levels). Hypertrophied myocardium is particularly susceptible to diastolic dysfunction by virtue of both structural changes (increased LV mass and interstitial fibrosis) and greater susceptibility to develop impaired myocardial relaxation during hypoxia or ischemia than nonhypertrophied myocardium.