Experimental Intracerebral pO2 and pCO2 Monitoring by Mass Spectrography

Abstract

'HAT therapy is indicated for cerebrovascular occlusion? How effective is it when employed? Will the same therapeutic measure be effective in each patient? Since some stroke patients improve without therapy, how is it possible to claim benefits from treatment? These are questions which to date have no clear objective answers. A technique for following localized cerebral circulatory responses before, during, and after therapy is needed. Woldring, et al., in 19666 reported that intravascular gases could be measured instantaneously, simultaneously, and continuously by inserting into a blood vessel a cannula tipped by a gas-permeable rubber membrane, which in turn was connected to a mass spectrometer. This instrument operated at a near vacuum so that minute quantities of any gas to which the membrane was exposed would enter the vacuum environment in quantities determined by partial gas pressures and by the diffusion properties of the membrane, including its thickness and surface area. Molecules entering the analyzing section of the mass spectrometer were ionized, accelerated in a variable electric field, deflected in a constant magnetic field, and projected to a target point (collector), upon which they confered their charge. Different molecular masses were brought into focus by manipulation of the electrical parameters of the analyzer. It was suggested that this technique might also measure gases in tissues. Our initial efforts in direct measurement of intracerebral gases were unsuccessful. When a cannula tipped by rubber was inserted into brain tissue, pO2 levels dropped