[Changes in canine conjunctival and cerebral oxygen tension during hemorrhagic hypotension]

On-line conjunctival oxygen tension (PcjO2) and cerebral cortical oxygen tension (PcxO2) were measured simultaneously using polarographic oxygen sensors during hemorrhagic hypotension in dogs. Mean arterial pressure (MAP) decreased from a control value of 119 +/- 7 to 52 +/- 1 (SEM) mmHg during initial bleeding of 30 minutes, and then this level of MAP was maintained for another 150min by adjusting the height of the reservoir. During the early phase of arterial hypotension, PcjO2 fell sharply, and this was accompanied by a parallel decrease of carotid artery blood flow and cardiac output, whereas PcxO2 remained unaffected with this level of hypovolemic hypotension which was possibly due to the cerebral tissue autoregulatory mechanism. Thus, it was demonstrated that despite the anatomical similarity and proximity of their blood supply, the conjunctival tissue responded differently to the intracranial cerebral tissues when compared during hemorrhagic hypotension. The study also suggests that monitoring the PcjO2 during surgery may be a useful monitoring tool in detecting early signs of tissue ischemia and hypoxia during hypovolemic shock.