Objective     To evaluate the influence of positive end-expiratory pressure (PEEP) on intracranial pressure and cerebral perfusion pressure in dogs with or without intracranial hypertension caused by frontal intracerebral hematoma.      Methods     Eighteen dogs were randomly divided into three groups. In Group B and Group C

the intracranial hypertension was respectively higher t

han 25 mmHg but less than 40 mmHg and higher than 40 mmHg induced by autoblood clotting injection into the right frontal lobe

while Group A as control was of normal intracranial pressure. PEEP was applied in increment of 3 cmH

2

O from 0 to 18 cmH

2

O

each level lasting 20 min. The intracranial pressure (ICP) was monitored by an optical fiber transducer implanted into left frontal lobe. Mean arterial pressure (MAP)

heart rate (HR)

and central venous pressure (CVP) were recorded simultaneously. Cerebral perfusion pressure (CPP) was calculated by the equation (CPP=MAP-ICP).      Results     With increasing PEEP level

ICP increased and CPP fell in Group A; ICP fell

MAP and CPP increased in Group B; ICP fell

MAP and CPP increased in Group C. CVP increased in all groups

and the increment was significantly higher in Group C than the other two groups (

P

<

0.01).       Conclusion     During PEEP

the alteration of ICP and CPP results from CVP increase

delayed blood return from brain vein and hemodynamic change. ICP increased when PEEP level rose under normal intracranial pressure

but showed no changes under intracranial hypertension

even decreased under severe intracranial hypertension

indicating MAP should be carefully maintained when under severe intracranial hypertension in order to guarantee the adequate CPP.