Clinical or technological evaluation of depth of anesthesia at induction time: A simple study for an easy message.

At the time where technology applied to anesthesia is securing more and more our daily practice with an evolution to less death and complications, Veena Asthana et al. have performed an original study about clinical appreciation of induction depth of anesthesia: “Clinical vs. bispectral index-guided propofol induction of anesthesia.[12]

Many studies have demonstrated the superiority of technology over clinical appreciation in many fields of our practice. Acceleromyographic monitoring of residual neuromuscular block antagonisation is better than clinical evaluation, target-controlled is better than manually-controlled infusions of propofol for intubation under spontaneous breathing anesthesia; the use of a hand-held manometer is better than digital palpation of the pilot balloon to assess the intra-cuff pressure of tracheal tubes, etc.[3-5]

The originality of the study of Veena Asthana et al. is to demonstrate that the dosing of propofol for anesthesia induction is similar whether they use loss of verbal control or Bispectral Index of electroencephalogram (BIS) monitoring as reference.[1] BIS level was comparable in both groups at intubation time.

The need to optimize drug administration during anesthesia is now well recognized and tracheal intubation time is a critical while. Thefirst concern is for hemodynamic stability: In the example, the results of a recent study confirm that the duration of a 30% reductions in mean blood pressure from baseline, was associated with postoperative stroke in patients undergoing non-cardiac, non-neurosurgical surgery.[6] In Veena Asthana et al. study, no difference was recorded in heart rate and non-invasive arterial pressure value between clinical and BIS groups. The variations between pre-induction and post intubation time where clinically insignificant.

The second concern is the risk of memorization. In the Veena Asthana et al. study the BIS value at intubation time was 52.91±11.04 in clinical group and 53.43±7.60 in BIS group.[1] With or without BIS monitoring the values are in a good range to limit this complication.

The third concern is to coordinate drugs effect site peak concentration at intubation time (hypnotic, curare and morphinomimetic): This is the key for a successful and less traumatic tracheal access. At least, I want to precise that continuous target controlled administration of propofol is a good alternative to manual infusion, especially when intubation is difficult. This is the best option to maintain a sufficient anesthesia depth during airway management.[7] But, here is exactly one of the methodological limitation of the Veena Asthana et al. study: The authors don′t include the monitoring of curarization in the study. The other limitation is the young ASA 1-2 population of patients (34.17±10.54 years in clinical group and 32.69±12.70 in BIS group): Indeed, the message of is this study is limited to this range of patients.

In conclusion, the authors demonstrate with a simple study that BIS monitoring is not necessary for induction in a young population of patients. It is important to know the limitation of technology applied to anesthesia. Of course, it remains now impossible to circumvent this helps to clinical appreciation in anesthesia daily practice.