[Effects of selective head cooling on cerebral blood flow and cerebral metabolic rate in newborn piglets].

OBJECTIVE

To study the change in regulation of cerebral blood flow (CBF) and cerebral metabolism rate (CMR) during selective head cooling (SHC) in newborn piglets.

METHODS

Sixteen newborn piglets, aged 5 approximately 7 days, were randomly assigned to one of the following three groups: SHC in normal piglets (n = 4), SHC after hypoxia-ischemia HI (n = 6) and normal temperature after HI (n = 6). Nasopharyngeal temperature was respectively reduced to 35 degrees C and then 32 degrees C in SHC group. HI was induced by using temporary occlusion of the bilateral carotid arteries and mechanical ventilation with low concentration of oxygen (6%) for 30 minutes. CBF was measured with color microspheres method. Mixed venous blood and arterial sample were collected at the same time from superior sagittal sinus and forelimb artery respectively for blood gas analysis, blood glucose and lactate measurement. Cerebral oxygenation metabolism rate (CMRO(2)), cerebral glucose metabolism rate (CMR(Glu)) and cerebral lactate production (CLP) were calculated.

RESULTS

In normal piglets, CBF, CMRO(2) and CMR(Glu) were significantly decreased at 35 degrees C and 32 degrees C respectively, while CLP did not change. When nasopharyngeal temperature decreased to 35 degrees C, The ratios of CBF/CMRO(2), CBF/CMR(Glu) and CBF/CLP did not significantly change, coupling of CBF and CMR was maintained. While nasopharyngeal temperature decreased to 32 degrees C, the ratios of CBF/CMR(Glu) and CBF/CLP significantly decreased. Maintained newborn piglets normal temperature after HI, the CBF and CMRO(2) were significantly reduced, while CMR(Glu) and CLP were markedly increased. The ratio of CBF/CMRO(2) increased, CBF/CMR(Glu) and CBF/CLP decreased. Uncoupling of CBF and CMR was observed. During SHC after HI, the same decrease was observed in CBF and CMR(Glu) and CLP was markedly reduced. The ratio of CBF/CMRO(2), CBF/CMR(Glu) and CBF/CLP were restored at 35 degrees C and 32 degrees C as compared to the same time point in normal temperature, respectively.

CONCLUSION

CBF and CMR decreased in normal piglets during SHC and coupling of CBF and CMR was maintained. After HI, CBF was reduced and the disturbance of cerebral oxygenation metabolism occurred. CBF and CMR was uncoupled. SHC after HI can improve CMR and correct uncoupling of CBF and CMR.