[Experimental animal study of cerebral oxygen metabolism changes during the process of brain death].

Objective: To reproduce a stable animal model of brain death in pigs, observe the change regularity of cerebral oxygen metabolism during the process of brain death, and to evaluate the significance and value of cerebral oxygen metabolism parameters for the diagnosis of brain death.

Methods: Twelve landrace pigs were used to create the brain death models using modified method of increasing epidural intracranial pressure (ICP). The mean arterial pressure (MAP) and ICP were monitored continuously during the process. The pigs were divided into four groups according to cerebral perfusion pressure (CPP) decreasing degree during brain death, namely CPP normal group and CPP decreasing 0%-30%, 30%-70%, and 70%-100% groups. Blood gas analysis of the external carotid artery and internal jugular vein were monitored discontinuously. The changes in cerebral oxygen metabolism parameters, including external carotid artery-internal jugular vein bulb oxygen content difference (AJDO), internal jugular bulb-external carotid artery carbon dioxide partial pressure difference (DPCO) and DPCO/AJDO ratio, were observed.

Results: Brain death model were successfully reproduced in 12 experimental pigs. With MAP and ICP monitoring, the models at different stages of CPP could be repeatedly induced. The levels of AJDO and DPCO were increased gradually and then decreased, while the ratio of DPCO/AJDO was constantly increased with the decrease of CPP. The level of AJDO in CPP decreasing 0%-30% group was significantly higher than that in CPP normal group [(5.86±1.21)% vs. (3.92±0.64)%], the levels of DPCO in CPP decreasing 0%-30% and CPP decreasing 30%-70% groups were significantly higher than those in CPP normal group [mmHg (1 mmHg = 0.133 kPa): 10.33±1.83, 11.48±2.32 vs. 6.11±1.43], and the ratios of DPCO/AJDO in CPP decreasing 30%-70% and CPP decreasing 70%-100% groups were significantly higher than those in CPP normal group and CPP decreasing 0%-30% group (2.81±0.53, 4.12±1.07 vs. 1.57±0.64, 1.62±0.81). All the differences above were statistically significant (all P < 0.05).

Conclusions: With the decrease of CPP, cerebral oxygen metabolism showed a regular change during brain death. DPCO combined with DPCO/AJDO is a reliable blood gas analysis index indicating intracranial hypoperfusion, which has certain reference value for the determination of brain death.