Ian M. Mitchell

Energy expenditure in children with congenital heart disease, before and after cardiac surgery

Failure to thrive is a common feature of children with congenital heart disease. Whether this is the result of poor nutrition or an abnormally high basal metabolic rate is unknown, yet the state of nutrition has a profound effect on the metabolic response to injury and strongly influences the outcome of surgical treatment. The aim of this study was therefore to measure the preoperative and postoperative energy requirements of children with congenital heart disease. Eighteen children (aged 4 to 33 months) were given two oral doses of doubly labeled water (H2(18)O and 2H2O), the first 1 week before operation and the second 6 hours after the end of cardiac surgery. By measuring the relative loss of each isotope from the body water pool, we were able to calculate the rate of carbon dioxide production and therefore total energy expenditure. In five patients, energy expenditure was clearly elevated, suggesting that a raised basal metabolic rate is an important factor in the observed failure to thrive in at least a proportion of such children. Postoperatively, energy expenditure fell to values below normal for healthy children (not having an operation), which suggests that the stress of surgery leads to smaller energy requirements than have previously been thought.

Bovine internal mammary artery as a conduit for coronary revascularization: Long-term results

Graft patency after coronary artery bypass grafting depends largely on the choice of conduit. Because an increasing number of patients have insufficient or poor-quality autologous material, there is a need for a suitable synthetic graft that is readily available and easy to handle and that has good long-term patency. Early results suggest that the bovine internal mammary artery graft may meet these criteria. We have used a total of 26 such grafts in 18 patients. Postoperative angiography has been performed in 19 grafts in 14 patients, 3 to 23 months after operation; of these grafts, 3 are currently patent (15.8%, compared with 85.7% and 75.0% patency for native internal mammary artery and saphenous vein grafts in the same patients). We report the results of clotting studies and an analysis of lipid status. These patients do not, however, appear to represent any atypical group, either in terms of coagulopathy, native coronary artery size, or the type of vessel disease. Nevertheless, our poor results contrast markedly with the early enthusiasm reported from other centers.

Transcutaneous iodine absorption in infants undergoing cardiac operation

Povidone-iodine is an effective antiseptic, but its topical use has been associated with a number of adverse reactions in burn patients and in neonates as a result of transcutaneous absorption. In particular, high plasma iodine concentrations are known to cause renal failure, metabolic acidosis, and thyroid suppression. Because of the permeable nature of the skin in small infants and the large areas cleaned before cardiac operations, it is possible that significant transcutaneous iodine absorption might occur in this situation. We have studied 17 infants, less than 3 months of age, who were undergoing closed cardiac or thoracic procedures. After povidone-iodine skin preparation in 15 (covering 20% to 30% of body surface area), plasma total iodine concentrations rose fourfold (range, 160% to 1,440%). This increase was significantly different from the preoperative level at 6, 12, 18, and 24 hours. There was no increase in plasma iodine concentration in 2 patients who were not exposed to povidone-iodine or any other iodine-containing compound. We discuss the implications for a topical antisepsis policy in infants.

Patent ductus venosus

SummaryA patent ductus venosus has been reported on only two previous occasions. Both involved adults who presented with recurrent bouts of encephalopathy. We present the case of an infant with complex congenital heart disease and multiple other abnormalities, in whom a patent ductus venosus was an incidental finding at necropsy. The etiology of this condition and the options for management are discussed.

The effects of congenital heart disease and cardiac surgery on I iver blood flow in children

Children with congenital heart disease may have some degree of hepatic impairment, with further impairment developing shortly after surgical correction of the cardiac defect. The redistribution of organ blood flow that occurs during cardiopulmonary bypass implicates ischaemia as one of the principal causes of injury. The aim of this study was to measure liver blood flow in children with congenital heart disease and to determine both the effects of cardiopulmonary bypass and the consequences of corrective surgery. Indocyanine green clearance and auricular densitometry, were used in 31 children. In 83% we demonstrated a reduced liver blood flow, with a mean percentage disappearance rate (PDR) of 12.9% (SEM ± 1.2). This finding was unrelated to the patients age, the type of congenital heart defect or the presence or absence of cyanosis. During cardiopulmonary bypass, hepatic perfusion was further reduced in 77% of children, by an average of 67%, out of proportion with the iatrogenic reduction in total body flow. Six hours after surgery, liver blood flow had increased significantly above preoperative levels (p< 0.001; t-test) to approximately normal values with a mean PDR of 20.4% (SEM ± 1.5).

The validation of auricular densitometry for indocyanine green clearance measurement of hepatic blood flow during and after cardiopulmonary bypass in children

The clinical measurement of hepatic perfusion is complicated by a dual blood supply and the invasive nature of the majority of techniques available. The aim of this study was to validate indocyanine green clearance and noninvasive auricular densitometry as a measure of hepatic perfusion in the context of paediatric cardiac surgery. The effects of different dye concentrations on densitometer recording were assessed in vitro and found to have a linear relationship. Similarly, variations in haematocrit, within the range 21-47%, also had little effect on accuracy. Comparison of densitometry and direct blood sampling with plasma spectrophotometry in six postoperative, normothermic children showed no significant difference between the noninvasive and invasive techniques (r = 0.968; p > 0.05, t-test). Comparison in 10 hypothermic children during cardiopulmonary bypass also showed no significant difference between the two methods, provided that no further cooling or rewarming took place (r = 0.83; p > 0.05, Wilcoxon test). Noninvasive auricular densitometry can, therefore, provide a reliable assessment of hepatic perfusion in children undergoing cardiac surgery.

Effects of dopamine on liver blood flow in children with congenital heart disease

BACKGROUND A reduction in liver function is common after cardiac operations, particularly in children with preexisting cardiac failure. The etiology is multifactorial, but the redistribution of organ blood flow that occurs during cardiopulmonary bypass implicates ischemia as one of the principal causes of injury. Dopamine hydrochloride is known to have specific effects on the renal circulation, and the aim of this study was to investigate its effects on hepatic perfusion. METHODS Eight children with congenital heart disease were studied 6 hours after the end of cardiopulmonary bypass when they were fully rewarmed and hemodynamically stable. Using noninvasive auricular densitometry, we determined the percent disappearance rate of indocyanine green as an index of liver blood flow both before and 1 hour after commencing an infusion of dopamine at 4 micrograms.kg-1.min-1. RESULTS Results showed an increase of approximately 31% in the percent disappearance rate of indocyanine green with the addition of low-dose dopamine (4 micrograms.kg-1.min-1) (p < 0.01). CONCLUSIONS Dopamine may have a therapeutic role in increasing hepatic perfusion and minimizing any loss in liver function.

Effect of increased pump flow on hepatic blood flow and systemic inflammatory response following on-pump coronary artery bypass grafting

Reduced organ perfusion during cardiopulmonary bypass (CPB) is responsible for morbidity associated with cardiac surgery. Non-pulsatile flow and hypothermia during CPB have been shown to cause reduced perfusion. During CPB, cardiac output is directly proportional to the pump flow rate. Therefore, we hypothesised that increasing pump flow during hypothermic CPB would improve organ perfusion and reduce the inflammatory response in the post-operative period. Methods: Ethics committee approval was obtained. Twelve consecutive patients with good or moderate left ventricular function undergoing elective or inpatient coronary artery bypass grafting were included in the study after obtaining informed consent. Patients were randomised to receive either normal flow or higher pump flow (20% more than the usual flow during hypothermia). Hepatic blood flow, cytokines such as interleukins 1β, 6, 8, 10 and 12, tumour necrosis factor-α and complements C3a, C4a and C5a were measured during the peri-operative period. Data were analysed using SPSS (ver.15). Categorical data were compared using the chi-square test and trends in cytokines were compared using a repeated measures ANOVA test. Results: Both the groups were similar in pre- and peri-operative variables. Hepatic blood flow almost doubled in the high-pump-flow group following an increase in the flow rate during hypothermia(p=0.026). The release of serum complement IL-6 and 8 appeared to be reduced in the high-flow group; however, the difference did not reach statistical significance. Conclusions: Higher pump flows during hypothermic CPB increase hepatic blood flow. There was a trend towards attenuation of post-operative inflammatory response; however, larger studies will be needed to confirm these findings.

The effect of fenoldopam and dopexamine on cytokine and endotoxin release following on-pump coronary artery bypass grafting: a prospective randomized double-blind trial.

BACKGROUND Surgical trauma, exposure to an external circuit, and reduced organ perfusion contribute to the systemic inflammatory response following cardiopulmonary bypass (CPB). Reduced splanchnic perfusion causes disruption of the gastrointestinal mucosal barrier and the release of endotoxins. Fenoldopam (a new dopamine 1 receptor agonist) has been shown to be a specific renosplanchnic vasodilator in animal and human studies. We studied the effects of fenoldopam on the systemic inflammatory response and the release of endotoxins after CPB and compared the results with those for dopexamine. METHODS Our prospective randomized study included 42 consecutive patients with good to moderate left ventricular function who were to undergo elective or inpatient coronary artery bypass grafting. We used closed envelope method to randomize patients to receive 0.2 μg/kg per minute of fenoldopam (n = 14), 2 μg/kg per minute of dopexamine (n = 14), or normal saline (n = 14). Patients received their respective treatments continuously from anesthesia induction until the end of the first 24 postoperative hours. Interleukin 1β (IL-1β), IL-6, IL-8, IL-10, IL-12, tumor necrosis factor α, complement 3a (C3a), C4a, C5a, and endotoxins were measured during the perioperative period. Repeated-measures analysis of variance was used to evaluate the results for the timed samples. RESULTS There were no statistical differences between the groups with respect to pre- and intraoperative variables. Release of C3a was attenuated in the fenoldopam group (P = .002), and release of IL-6 and IL-8 was attenuated in the postoperative period in the fenoldopam group (P = .012 and .015, respectively). The other interleukins showed no uniform release in any of the 3 groups. There were no statistically significant differences in serum endotoxin elevation between the 3 groups. CONCLUSION A partial attenuation in the inflammatory response is possible with fenoldopam infusion. The elevation in serum endotoxin levels was not affected by dopexamine or fenoldopam infusion.

Total body water in children with congenital heart disease, before and after cardiac surgery

The aim of this study was to measure total body water in children with congenital heart disease before and after cardiac surgery and to compare the results of deuterium and 18oxygen dilution methods. Seventeen children (aged 4 to 33 months) were given aliquots of isotopically labeled water 1 week before and 6 hours after cardiac surgery. Isotope equilibration and analysis of the declining enrichment of daily urine samples allowed calculation of the total body water content. Before operation, total body water was significantly elevated (p < 0.001, Wilcoxon test); after operation it fell to approximately normal values. This finding is in contrast to those of previous reports, but may be explained in that the method used for calculation depended on measurements taken over a 7-day period rather than on a single measurement of isotope dilution as used elsewhere. Nevertheless, these results do suggest that surgery can correct the preoperative fluid overload. Comparison of deuterium and 18oxygen dilution methods showed a 2% to 2.5% overestimation of the total body water content with deuterium sampling.