Published in 2011 by Schmidt et al (free full-text in Stroke), this article looks at CPP thresholds for cerebral hypoxia in SAH patients. They went through multimodal monitoring data for 30 patients with poor-grade SAH. Using microdialysis and brain tissue oxygenation as their main determinants of hypoxia, they found that patients with a CPP <70 mmHg were more prone to develop findings deemed consistent with cerebral ischemia.
“There was a threshold effect of CPP on the likelihood of metabolic crisis, occurring 10% of the time when mean hourly CPP was >70 mm Hg compared to 24% when CPP was ≤70 mm Hg (P<0.001). “
Although a small-scale study, the findings seem to indicate an interesting association that may warrant further study in a larger cohort. The value of modalities such as microdialysis and PbtO2 as adequate surrogates of brain oxygenation and metabolism in patients with complex brain pathophysiology is also a matter of some debate.