“Incidence of Connected Consciousness After Tracheal Intubation: A Prospective, International, Multicenter Cohort Study of the Isolated Forearm Technique”, 2017-02 (; backlinks):
In a prospective, multicenter study of the incidence of connected consciousness in response to tracheal intubation in 260 anesthetized surgical patients, 4.6% had connected consciousness detected by the isolated forearm technique, none of whom had explicit recall.
Background: The isolated forearm technique allows assessment of consciousness of the external world (connected consciousness) through a verbal command to move the hand (of a tourniquet-isolated arm) during intended general anesthesia. Previous isolated forearm technique data suggest that the incidence of connected consciousness may approach 37% after a noxious stimulus. The authors conducted an international, multicenter, pragmatic study to establish the incidence of isolated forearm technique responsiveness after intubation in routine practice.
Method: 260 adult patients were recruited at 6 sites into a prospective cohort study of the isolated forearm technique after intubation. Demographic, anesthetic, and intubation data, plus postoperative questionnaires, were collected. Univariate statistics, followed by bivariate logistic regression models for age plus variable, were conducted.
Results: The incidence of isolated forearm technique responsiveness after intubation was 4.6% (12⁄260); 5⁄12 responders reported pain through a second hand squeeze.
Responders were younger than non-responders (39 ± 17 vs. 51 ± 16 yr old; p = 0.01) with more frequent signs of sympathetic activation (50% vs. 2.4%; p = 0.03). No participant had explicit recall of intraoperative events when questioned after surgery (n = 253). Across groups, depth of anesthesia monitoring values showed a wide range; however, values were higher for responders before (54 ± 20 vs. 42 ± 14; p = 0.02) and after (52 ± 16 vs. 43 ± 16; p = 0.02) intubation. In patients not receiving total intravenous anesthesia, exposure to volatile anesthetics before intubation reduced the odds of responding (odds ratio, 0.2 [0.1–0.8]; p = 0.02) after adjustment for age.
Conclusion: Intraoperative connected consciousness occurred frequently, although the rate is up to 10× lower than anticipated. This should be considered a conservative estimate of intraoperative connected consciousness.
[Keywords: consciousness related finding, endotracheal intubation, forearm, intubation, mental recall, anesthesia depth]