Is deep anesthesia dangerous?

Regarding the question of an adequate depth of anesthesia, over the past decade anesthesiologists have focused on the prevention of intraoperative consciousness in combination with explicit memory. Recent studies approached the topic from a different way postulating that deep anesthesia, quantified as time with a bispectral index (BIS)< 45, is associated with increased postoperative mortality and four out of the five published studies revealed such a correlation. However, the finding is limited by a suboptimal study design, e.g. none of the studies presented randomized data. Furthermore, it is ambiguous whether the correlation is causal as the administration of deep anesthesia determines higher postoperative mortality or the study results reveal an epiphenomenon. An epiphenomenon implies e.g. that patients with cancer respond to general anesthesia with deeper cortical depression. In summary, as long as there is a lack of adequately performed randomized trials, there is no reason why anesthesiologists should change the current practice.