Connected consciousness after tracheal intubation in young adults: an international multicentre cohort study.

BACKGROUND: Connected consciousness, assessed by response to command, occurs in at least 5% of general anaesthetic procedures and perhaps more often in young people. Our primary objective was to establish the incidence of connected consciousness after tracheal intubation in young people aged 18-40 yr. The secondary objectives were to assess the nature of these responses, identify relevant risk factors, and determine their relationship to postoperative outcomes. METHODS: This was an international, multicentre prospective cohort study using the isolated forearm technique to assess connected consciousness shortly after tracheal intubation. RESULTS: Of 344 enrolled subjects, 338 completed the study (mean age, 30 [standard deviation, 6.3] yr; 232 [69%] female). Responses after intubation occurred in 37/338 subjects (11%). Females (13%, 31/232) responded more often than males (6%, 6/106). In logistic regression, the risk of responsiveness was increased with female sex (odds ratio [ORadjusted]=2.7; 95% confidence interval [CI], 1.1-7.6; P=0.022) and was decreased with continuous anaesthesia before laryngoscopy (ORadjusted=0.43; 95% CI, 0.20-0.96; P=0.041). Responses were more likely to occur after a command to respond (and not to nonsense, 13 subjects) than after a nonsense statement (and not to command, four subjects, P=0.049). CONCLUSIONS: Connected consciousness occured after intubation in 11% of young adults, with females at increased risk. Continuous exposure to anaesthesia between induction of anaesthesia and tracheal intubation should be considered to reduce the incidence of connected consciousness. Further research is required to understand sex-related differences in the risk of connected consciousness.

Two different methods to assess sympathetic tone during general anesthesia lead to different findings.

Noxious stimulation influences the autonomic nervous system activity. Sympathetic tone monitoring is currently used to assess the adequacy of the balance between nociception and anti-nociception during general anesthesia. The Surgical Plethysmographic Index (SPI) and the EBMi software (Custos©) are commercial devices that use different algorithms to measure it. We aimed at determining whether those devices provide similar information during routine surgical procedures under general anesthesia. Data acquired during a previously published study in patients undergoing surgery under general anesthesia were retrospectively analyzed and passed through the EBMi software. The occurrence of EBMi alarms of increased sympathetic tone was compared to the occurrence of SPI values ≥ 60, a commonly recommended intraoperative SPI threshold. Trends in classical parameters of sympathetic tone during the 5 min preceding a SPI ≥ 60, namely blood pressure, heart rate, and plethysmographic pulse amplitude were assessed. SPI ≥ 60 episodes (n = 307) were more frequent than EBMi alerts (n = 240). Approximately 70% of EBMi alerts occurred during periods where the SPI was below 60. Among all episodes of SPI ≥ 60, absence of any EBMi alerts was much more frequent than the inverse. A majority, but not all SPI ≥ 60 episodes were consistently preceded by an increase in heart rate and/or a decrease in pulse amplitude. Blood pressure did not significantly change before SPI ≥ 60. Longer SPI ≥ 60 episodes were associated with lower anti-nociception anesthetic regimen. Different methods of sympathetic tone assessment during general anesthesia provide conflicting information. Prospective studies should be undertaken to clarify the clinical indications of both techniques.

Standardised noxious stimulation-guided individual adjustment of remifentanil target-controlled infusion to prevent haemodynamic responses to laryngoscopy and surgical incision: A randomised controlled trial.

BACKGROUND: The surgical plethysmographic index (SPI) is one of the available indexes of the nociception-antinociception (NAN) balance. Individually adjusting the NAN balance to prevent somatic responses to noxious stimulation remains a challenge. OBJECTIVES: To assess whether guiding remifentanil administration according to the SPI response to a calibrated noxious stimulus (NANCAL) can blunt the haemodynamic response to tracheal intubation and surgical incision. DESIGN: Randomised multicentre study. SETTING: Two Belgian university hospitals from January 2014 to April 2015. PATIENTS: After ethic review board approval and informed consent, 48 American Society of Anesthesiologists I or II adult patients scheduled for surgery under general anaesthesia were enrolled. INTERVENTIONS: Patients were randomly assigned to a SPI group, where remifentanil effect-site concentration was adjusted according to NANCAL, or a control group, where it was fixed at 4 ng ml. Propofol concentration was always adjusted to maintain the bispectral index close to 40. NANCAL consisted of a 100 Hz, 60 mA electrical tetanic stimulation during 30 s at the wrist before tracheal intubation and before surgical incision. MAIN OUTCOME MEASURES: The primary endpoint was the efficacy of the NANCAL-guided remifentanil administration to prevent the haemodynamic response to tracheal intubation and surgical incision. The secondary aim was to compare the ability of SPI, analgesia nociception index, pupil diameter and mean arterial pressure response to NANCAL to predict the haemodynamic response to tracheal intubation and surgical incision. RESULTS: Our SPI response to NANCAL-based correcting scheme for remifentanil administration was not superior to a fixed remifentanil concentration at blunting the haemodynamic response to tracheal intubation or surgical incision. Among all tested NAN balance indices, only mean arterial pressure had significant predictive ability with regard to the haemodynamic response to surgical incision. CONCLUSION: Further research is needed to define the best NANCAL stimulus and the best remifentanil correcting scheme to help individualised tailoring of antinociception for each specific subpopulation of surgical patients. TRIAL REGISTRATION: Clinicaltrials.gov NCT: 02884310; https://clinicaltrials.gov/ct2/show/NCT02884310.

Incidence of Connected Consciousness after Tracheal Intubation: A Prospective, International, Multicenter Cohort Study of the Isolated Forearm Technique.

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. METHODS: Two hundred sixty adult patients were recruited at six 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 of 12 responders reported pain through a second hand squeeze. Responders were younger than nonresponders (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 to 0.8]; P = 0.02) after adjustment for age. CONCLUSIONS: Intraoperative connected consciousness occurred frequently, although the rate is up to 10-times lower than anticipated. This should be considered a conservative estimate of intraoperative connected consciousness.