Brain Metabolism in Deep Controlled Hypotension in Neurosurgical Patients

Abstract

Changes in the lactate and pyruvate levels and lactic dehydrogenase activity in the cerebrospinal fluid were followed in 56 patients anaesthetised for neurosurgery. Mean arterial blood pressure (MAP) was reduced in these patients from about 90 to about 35 mm Hg. This allowed to safely place a clip at a brain artery aneurysm. In spite of deep hypotension, ischaemia described by other authors in such cases was never observed. Changes in lactate and pyruvate concentrations, lactate/pyruvate ratio and lactic dehydrogenase activity justify the conclusion that we were dealing with an undisturbed metabolism of the brain tissue. The levels of metabolic parameters, even when increased in hypotension, fell well within the range of physiological values. Attention is called to the fact that partial oxygen pressure in arterial blood during controlled hypotension was about 100 mm Hg, a value considered as limiting to oxygen metabolic transformation within the central nervous system in deep hypotension. We also suggest a different mechanism of passage of lactates and pyruvates through the blood-brain barrier.

Is it safe to decrease hemodynamic parameters to achieve bloodless surgical field during transnasal endoscopic procedures? Our experience in fifteen patients

“…Whether moderately decreased cerebral blood flow can harm the brain depends on the duration of ischaemia. In this study, hypotension lasted not longer than 60 min but transient accumulation of adverse metabolites has been reported to occur even during hypotension within this range of time . There are also reports demonstrating a fourfold increase in risk of dementia after only one incident of ischaemia in stroke patients .…”

“…In this study, hypotension lasted not longer than 60 min but transient accumulation of adverse metabolites has been reported to occur even during hypotension within this range of time. 12 There are also reports demonstrating a fourfold increase in risk of dementia after only one incident of ischaemia in stroke patients. 13 Although cerebral autoregulation should be able to maintain constant blood flow when mean arterial blood pressure is higher than 50 mmHg, there is no obvious, sudden cut-off value of blood pressure below which complications occur predictably.…”

Risks and benefits of deliberate hypotension in anaesthesia: a systematic review

“…A prospective clinical trial showed that this protective mechanism works over a range of MAP from 40 to 60 mmHg in humans 199 . In another prospective study, RYBA et al reduced the MAP from 90 to 35 mmHg in normotensive, young and middle-aged adults for not more than 60 min 145 . No ischaemia was observed.…”

Pro-Con Debate: The Clinical (Ir)relevance of the Lower Limit of Cerebral Autoregulation for Anesthesiologists

“…When hypotension was induced in 56 patients for aneurysm clipping (reaching MAPs as low as 35 mm Hg), no neurological complications were reported. 49 Treasure et al 50 found no neurological events in 30 patients who were followed for 1 to 9 years after 1-hour induced deep hypotension for aortic root surgery. In contrast, deep hypotensive episodes resulted in neurological complications in half of the patients after cardiac surgery, ranging from temporary exacerbation of preexisting neurological deficits to coma.…”