Abstract: Objective Deep hypothermic circulatory arrest(DHCA) has been frequently used during complex congenital heart disease and aortic surgery.DHCA causes brain edema and complications of central nervous system(CNS).Brain injury and altered psychomotor development after DHCA is still a matter of concern.The complications of CNS are not similar in different patients.It is still unclear whether these characteristics are caused by extent of brain edema among different anatomic brain sites.This study determines the variation of water content in different sites of porcine brain after DHCA.The aim to investigate whether brain edema is similar in different sites of brain after DHCA.Methods Six pigs(22～25 kg) were anesthetized,intubated and mechanically ventilated.The animals were connected to CPB by cannulation of the aorta,superior vena cava and inferior vena cava.With CPB,core cooling was initiated and continued until the nasopharyngeal temperature fell to 18 ℃.Once the temperature reached 18 ℃,the animals were treated 90 minutes with DHCA.After DHCA,the body was rewarmed 120 minutes on CPB to 36 ℃.Then the animals were killed,the brain was immediately removed.Left hippocampi,brain cortices,cerebella and medullae were partially harvested and the wet weights measured.After the water dried out(110 ℃ for 24 hours),they were weighed again and the percent of brain water content calculated.Brain edema was determined by measuring brain water content.Results Percent of brain water content was not similar among different anatomic sites.There was no significant difference between brain cortices(81.81%±1.03%) and hippocampi(83.91%±1.80%,P=0.078).But,the water content of them were significantly higher than those of cerebella(77.98%±0.66%,brain cortex versus cerebellum P=0.001,hippocampus versus cerebellum P=0.000) and medullae(74.67%±1.73%,brain cortex versus medulla P=0.000,hippocampus versus medulla P=0.000).The water content of medulla was significantly lower than those in the other sites(cerebellum versus medulla P=0.004).Electron microscopy revealed intracellular and organelle edema.Conclusion Extent of brain edema is not similar among different anatomic sites after DHCA due to different tissue structures.This phenomenon might be related to clinical patterns of CNS complications after DHCA.

Key words: deep hypothermic circulatory arrest, brain edema