To the Editor:
Tailoring depth of anesthesia to the needs of each individual patient, while mastering the inevitable cardiovascular side effects represents a core anesthesiologist’s skill. Novel inspiration to this daily challenge has recently been brought by Sessler et al. ,1identifying the combination of low blood pressure, low bispectral index (BIS), and low minimum alveolar concentration of volatile anesthesia as a troika of death. Looking at the cutoff parameters of this “triple low” may cause a wave of reflection, if not immediate malaise in each anesthesiologist, as values below the mortality threshold are routinely tolerated. The question arises: Are we harming all these patients, if not worse?
All three phenomena are inextricably entwined and intraoperative management is largely dictated by patient characteristics and intraoperative course. Low blood pressure was shown to determine adverse outcome in relation to age and duration of surgery,2and the establishment of a causal relationship between low BIS values and intermediate-term outcome previously failed when malignancy and physical status were considered.3Moreover, left ventricular dysfunction, systemic illness, or a complicated intraoperative course was shown to account for accumulated low BIS values, with no relation to end-tidal anesthetic gas concentrations.4The abovementioned results emphasize that anesthetic management is influenced not only by anesthesia-related, but also a plethora of surgery-related, and patient-specific factors. It seems difficult to control all these interfering factors to achieve clear-cut scientific conclusions; however, discrimination of at least American Society of Anesthesiologists physical status and cause of death seems mandatory. It is hard to believe that a triple low in a 20-yr-old American Society of Anesthesiologists class I patient has the same prognostic value, if any at all, as that of a 70-yr-old American Society of Anesthesiologists class III patient. Although Sessler et al . certainly would agree with these considerations, their current study misses the opportunity to provide conclusive new insights in conjunction with clinically applicable concepts as the predictive role of important variables such as comorbidities, American Society of Anesthesiologists physical status, duration and difficulty of surgery (e.g. , transfusion requirements), and cause of death were neglected. Moreover, no single low was associated with increased mortality, further impeding the identification of distinct manipulations of either mean arterial pressure, BIS, or minimum alveolar concentration as causal or pure epiphenomena. Hence, observation of a “double low,” and triple low should not be misinterpreted as differences in anesthetic sensitivity or outcome determinants per se . As before, attention is required not to injudiciously confound low BIS values as a pure reflection of anesthetic depth in the critically ill, just as the sufficient supply of minimum alveolar concentration values and provision of adequate perfusion pressures should be self-evident hallmarks of anesthesia.
However, despite its limitations, the study shines with its conceptual approach of desperately needed outcome research in anesthesiology. Many aspects of narcosis remain unexplored and things working as a matter of course on a daily basis are likely to impact patient morbidity and mortality. Prospective studies regarding the prognostic value of anesthetic characteristics are desirable, in particular, those targeting outcome improvement. Data supporting clinical decision making will help to manage the core anesthesiologist’s task of tailoring anesthetic depth to each individual needs and answer the question: How can we make a difference for the better?