Influence of two perfusion strategies on oxygen metabolism in paediatric cardiac surgery. Evaluation of the high-flow, low-resistance technique.

OBJECTIVE

Paediatric cardiac surgery is often performed under hypothermic conditions, that is, with a reduced core body temperature. Certain interventions even require the circulation to be stopped. This can only be done at a body temperature of 18 degrees C, with no risk of neurological damage and harm to the brain and other organs. Vasoconstriction is a natural reaction of the body to cold, causing the blood vessels to contract. Such a reaction would lead to a clear rise in blood pressure on cardiopulmonary bypass (CPB). Since the blood pressure is regulated in the arteriolar loop of the capillary system, there is a marked increase in blood pressure and a suppression of free water into the surrounding tissue, which, in turn, may lead to the intra-operative development of oedemas. This study aimed to investigate whether the high-flow, low-resistance (HFLR) technique offers any benefits over conventional methods.

METHOD: This open, prospective, randomised study was to recruit 48 children scheduled to undergo surgery for congenital heart disease. To investigate the two different perfusion strategies, we have measured intestinal perfusion as well as skin perfusion with laser Doppler spectroscopy. To identify the effects on the immune system, selected immunologic parameters of systemic inflammation were additionally measured. Laser Doppler spectroscopy is a method that uses a glass fibre probe to determine the parameters of oxygen saturation of haemoglobin and relative haemoglobin quantity in an illuminated tissue volume, as well as the perfusion parameters of relative blood flow and blood flow velocity in the sample volume of the probe.

RESULTS

During the study period, the change in oxygen saturation over time was comparable in both groups. At the end of surgery, the patients of the high-flow group had significantly higher saturation levels in the intestinal mucosa (p<0.05). Over the course of intensive care, the groups did not differ in terms of fluid supply, administration of packed red blood cells, platelet concentrates or fresh frozen plasma. Analysis of urinary output revealed significant group differences. It was higher in the patients of the high-flow group than the normal-flow group (p<0.03), without differences in diuretic administration.

CONCLUSION

Laser Doppler spectroscopy is highly suited to the detection even of the slightest changes in flow characteristics and oxygenation of the skin, musculature and intestinal mucosa during surgery with extracorporeal circulation using CPB. At the same time, the technique of HFLR perfusion was found to have benefits over conventional bypass methods.