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Year : 2018  |  Volume : 12  |  Issue : 4  |  Page : 843-847  

The study of intraoperative consciousness after tracheal intubation

Department of Anaesthesia, M.S. Ramaiah Medical College, Bengaluru, Karnataka, India

Date of Web Publication18-Dec-2018

Correspondence Address:
Dr. Sandyarani D Channaiah
Department of Anaesthesia, M.S. Ramaiah Medical College, MSRIT Post, Bengaluru - 560 054, Karnataka
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/aer.AER_139_18

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Introduction: Awareness following noxious stimuli like intubation could be as high as 25% compared to postoperative recall. The isolated forearm technique (IFT) allows us to assess consciousness by verbal command to move isolated hand. Hence we conducted study to establish IFT responses following intubation under standard general anaesthesia. Methods: We enrolled 132 adult patients undergoing general anaesthesia. A tourniquet was applied on other arm. Following intravenous induction of anaesthesia, torniquet was inflated 100mmhg above systolic BP. After giving muscle relaxant, three minutes patients were ventilated with oxygen and inhalational agent. Before laryngoscopy first verbal command (Squeeze my hand) was given to the patient. Once intubation and tube confirmation done, second verbal command was given. Lack of paralysis in isolated hand was confirmed with TOF stimuli and tourniquet was deflated. Surgery was carried in routine manner. Postoperatively all patients were evaluated for any explicit recall using Modified Brice questionnaire. The primary outcome is number of patients who responded to verbal command postintubation. Secondary outcome is number of patients responded prelaryngoscopy and number of patients reporting explicit recall in the Modified Brice interview. Results: None of the patients had positive IFT response. On postoperative interview none reported awareness. 10.7% of patients had dreams which were pleasant. Worst thing about surgery was pain.(43%). Conclusion: Our study suggests that intraoperative consciousness after intubation and postoperative recall is an uncommon occurrence.

Keywords: Anaesthesia, awareness, intraoperative consciousness

How to cite this article:
Parate LH, Channaiah SD, Rajappa GC, Singh R, Madhav A, Mahdiyyah M. The study of intraoperative consciousness after tracheal intubation. Anesth Essays Res 2018;12:843-7

How to cite this URL:
Parate LH, Channaiah SD, Rajappa GC, Singh R, Madhav A, Mahdiyyah M. The study of intraoperative consciousness after tracheal intubation. Anesth Essays Res [serial online] 2018 [cited 2019 Jun 25];12:843-7. Available from:

   Introduction Top

Awareness under anesthesia is a potential problem which is gaining widespread attention globally. Awareness may lead to postoperative sequelae such as sleep disturbances, fear of future anesthetics, and posttraumatic stress disorder.

Awareness under anesthesia is defined as postoperative recall of events occurring during general anesthesia. Recall is the patients' ability to retrieve stored memories. The awareness is an uncommon phenomenon accounting for 0.1%–0.2% of general anesthesia.[1],[2] The incidence calculated based on the postoperative interview may miss the events of intraoperative consciousness. Anesthetic agents are effective amnestic agents, and the incidence of intraoperative awareness is underestimated. Intraoperative awareness is defined as a state of connectedness to the environment and consciousness.[3] Sanders et al. found that awareness following noxious stimuli-like intubation could be as high as 25% compared to postoperative recall.[3] They found the incidence of connected consciousness posttracheal intubation to be around 4.6%. Tracheal intubation and laryngoscopy are associated with more profound stimulation than surgical incision.[3],[4]

Isolated forearm technique (IFT) is not dependent on explicit recollection of events as an evidence of consciousness. Hence, it is the best available tool for real-time monitoring of intraoperative consciousness. It is based on the isolation of forearm from the effect of muscle relaxants by occluding the circulation with tourniquet. The unparalyzed hand is free to respond the verbal command.

The incidence of intraoperative consciousness in India has not yet been studied. Hence, we conducted a prospective observational study on intraoperative consciousness following endotracheal intubation in adult patients under general anesthesia.

   Methods Top

The study protocol was approved by the hospital's Ethical Committee (MSRMC/EC/2017). The study was registered on (CTRI/2017/08/009408).

We enrolled 132 American Society of Anesthesiologists physical status classes I or II adult patients undergoing general anesthesia with endotracheal intubation. Informed consent to participate in the study was taken. We excluded pregnant patients, patients not able to follow verbal commands (psychiatric disorder), and if any contraindication for tourniquet is present. We aimed to conduct a pragmatic study without changing standard anesthesia practice. Patients were explained the study protocol. The verbal command to squeeze hand was told and practiced with the patients.

Minimum mandatory monitoring was done with electrocardiography, pulse oximetry, noninvasive blood pressure, and capnography. We did not use bispectral index (BIS) monitor, but end-tidal inhalational agent monitoring was done in most of the cases. A Tunstall's IFT was used to test intraoperative consciousness.[5] A tourniquet was applied on the arm (preferably right arm). Following standard intravenous induction with midazolam (0.02 mg/kg), fentanyl (2ug/kg), and propofol (2–2.5 mg/kg), the tourniquet was inflated 100 mmHg above baseline systolic blood pressure. This isolates the hand from systemic circulation and action of muscle relaxants. Injection atracurium (0.5 mg/kg) was given and patients were ventilated with oxygen and isoflurane for 3 min.

The first command was given immediately before laryngoscopy. The command given was “Name” squeeze my hand. The response was noted by an anesthesiologist. Laryngoscopy and intubation were performed. Any difficulty and multiple attempts were noted. After intubation and confirmation of tube, a second command was given (approximately within 1 min of intubation). The response was noted. The integrity of neuromuscular transmission in the isolated hand was checked with the train of four stimuli and the tourniquet was deflated. Postintubation, heart rate and blood pressure were noted. None of the patients had BIS monitoring, but agent gas monitoring was done in most of the cases. Postoperatively (within 12–24 h), the patients were evaluated for any explicit recall using the Modified Brice Questionnaire[6],[7] [Appendix 1]. The anesthesiologist not involved in the study conducted the postoperative interview and filled the questionnaire.

Statistical considerations

The study by Sanders et al. had observed an incidence of IFT responsiveness after intubation to be 4.6%. In the present study, expecting similar results with 95% confidence interval and 20% relative precision, the study requires a minimum of 113 participants. We selected 132 patients to make up for possible dropout. Data were entered into statistical software Statistical Package for the Social Sciences (SPSS) (version 18.0, SPSS Inc., Chicago, IL, USA) for analysis. Data were expressed as mean (standard deviation) for continuous variables and count (%) for categorical variables. Paired t-test was used for analysis and P < 0.05 was considered statistically significant.

The primary outcome is the number of patients who responded to verbal command postintubation. The secondary outcome is the number of patients who responded to prelaryngoscopy and the number of patients reporting explicit recall in the Modified Brice interview.

   Results Top

A total of 132 patients were enrolled in the study. Out of that, 9 patients had spontaneous movements postintubation. Hence, IFT could not be applied and they were excluded from the study. Two patients required unplanned ventilation postoperatively and thus excluded. The remaining 121 patients were analyzed.

Demographic parameters of patients studied are shown in [Table 1]. Other intraoperative parameters are shown in [Table 2].
Table 1: Patients' baseline characteristics

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Table 2: Intraoperative characteristics

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None of the patients had IFT response either prelaryngoscopy or postintubation. In postoperative interview, no patient had explicit recall. About 10.7% of patients had dreams which were pleasant. The worst thing about surgery was pain (43%) followed by anxiety (36.4%). Feeling mask on the face (25.6%) was the most common thing patients remembered postoperatively.

Postintubation, heart rate and diastolic blood pressure increased significantly [Table 3].
Table 3: Hemodynamic parameters

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   Discussion Top

In this prospective, pragmatic study, none of the patients had IFT responses or postoperative recall.

Previous studies have reported the incidence of IFT responsiveness after intubation to be around 0%–46%.[3],[8],[9],[10],[11],[12] The incidence of awareness based on the questionnaire varies from 0.1% to 0.2%. Sanders et al. found postintubation IFT responsiveness to be around 4.6%.[3] St Pierre et al. tested three different doses of etomidate and found that IFT responsiveness is a dose-dependent reaction.[12] In another small study of ketamine and succinylcholine anesthesia, Baraka et al. noticed that none of the patients responded to IFT.[8] Schneider et al. reported that 40% (8 out of 20) of patients showed IFT responsiveness after intubation when BIS-guided propofol-alfentanil anesthesia was given.[10]

The difference between our results and previous results could be multifactorial. The variation in anesthetic techniques could be one of the factors. Single bolus dose of intravenous induction agent is inadequate for preventing awareness reaction.[12] After intravenous induction, commencing inhalational agent before laryngoscopy could be a potential solution to reduce awareness reaction. Total intravenous anesthesia (TIVA)-based technique carries more risk of awareness than end-tidal anesthetic concentration (ETAC)-based potent inhalational agent technique.[13],[14],[15] Propofol has wider interpatient variability in adequate dose requirement and at present lacks modality for monitoring target-site concentration. Compared to TIVA, ETAC-based inhalational agent technique may reduce the interpatient variability with propofol. The propofol dose required to make the patient unresponsive may not be adequate to attain unconsciousness. In our study, all patients received inhalational-based balanced anesthesia. In most of the cases, it was guided by ETAC monitor which acts as a surrogate measure for depth of anesthesia.

Another factor which could be responsible is the genetic and ethnic impact on anesthetic requirements.[16],[17] In this respect, our results are similar to the study done by Ambulkar et al.[18] They found that awareness is an uncommon phenomenon in Indian cancer patients who are at high risk for awareness. In our study, we had patients who are at risk of awareness such as female gender, young age (<40 years), patients with signs of sympathetic activation, and positional changes during surgery. However, we did not encounter any episode of awareness.

The B-Aware trial showed that BIS-guided anesthesia technique reduces the incidence of awareness compared with standard anesthesia technique.[19] In contrast to their finding, the B-Unaware trial and BAG-RECALL trial failed to establish the superiority of BIS over ETAC monitoring for the prevention of awareness in patients at high risk for this complication.[20],[21] They concluded that a target level of ETAC at 0.7–1.3 minimum alveolar concentration should be aimed to prevent the awareness reaction.

Postoperative recall is a subjective outcome. To overcome this bias, we used a structured questionnaire. Modified Brice Questionnaire is more valid tool than unstructured postoperative questionnaires to detect explicit recall.[22] Sanders et al. noted that IFT responsiveness was not associated with postoperative recall.[3] This suggests that even subhypnotic doses of anesthetic drugs are clinically efficient in suppressing the memory formation. In our study, none of the patients had postoperative explicit recall. The incidence of dreaming under anesthesia is around 1.1%–27%.[2],[23] Our findings also fall within this range. None of the dreams reported in our study were disturbing to the patients. All dreams experienced were pleasant.

There are few limitations in our study. The tourniquet was not always applied on the dominant arm. Hence, patients would have got confused as to which hand to move. Interpretation of a negative IFT response is more complex as objective confirmation of unconsciousness is not possible with the available technology. Anesthetic agents can result in lack of motivation or impaired motor response.[3],[14] Hence, it is possible that despite hearing verbal command, patients may not choose to respond it. Finally, we conducted the postoperative interview only once and not at three time points as recommended. Delayed recall of events can occur 1 week after surgery.[1]

In order to get the real estimate of intraoperative consciousness, we neither change our standard anesthesia technique nor we used any depth of anesthesia monitor. This ensures us that the finding of the study could be applied on a day-to-day basis.

Depth of anesthesia monitors poorly correlate with the actual consciousness of the patient.[10],[24],[25] Clinical signs of inadequate depth of anesthesia such as increased blood pressure and heart rate can be affected by multiple factors such as beta-blockers, hypovolemia, hypercarbia, and inadequate analgesia. Further studies are required on larger sample size, in patients at risk for awareness and to search the objective markers of intraoperative consciousness. Wider range in the IFT responses in the literature highlights the need for brain function monitor to study anesthetic-induced unconsciousness.

   Conclusion Top

Under standard anesthesia protocol, we did not find any event of intraoperative consciousness and postoperative recall.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

   Appendix Top

Appendix 1:

Modified Brice Questionnaire

1. What is the last thing you remember before going to sleep (please tick one box)?

-Being in the preoperative area □ -Seeing the operating room □

-Being with family □ -Hearing voices □

-Feeling mask on the face □ -Smell of gas □

-Burning or stinging in the intravenous line □ -Other [Please write below]:


2. What is the first thing you remember after waking up (please tick one box)?

-Hearing voices □ -Feeling breathing tube □

-Feeling mask on the face □ -Feeling pain □

-Seeing the operating room □ -Being in the recovery room □

-Being with family □ -Being in intensive care unit □

-Nothing □ -Other [Please write below]:


3. Do you remember anything between going to sleep and waking up (please tick box)?

-No □

-Yes: -Hearing voices □ -Hearing events of the surgery □

-Unable to move or breathe □ -Anxiety/stress □

-Feeling pain □ -Sensation of breathing tube □

-Feeling surgery without pain □ -Other [Please write below]


4. Did you dream during your procedure (please tick box)?

-No □ -Yes □

-What about [Please write below]: [Pleasant/unpleasant/unidentified]


5. Were your dreams disturbing to you (please tick box)?

-No □ -Yes □

6. What was the worst thing about your operation (please tick box)?

-Anxiety □ -Pain □

-Recovery process □ -Unable to carry out usual activities □

-Awareness □ -Other [Please write below]:


Details of recall/awareness

(any conversation heard, feeling of paralysis, pain, surgical manipulation, Operation theater light, procedure like intubation, catheterization, and change in the position during surgery).

   References Top

Sandin RH, Enlund G, Samuelsson P, Lennmarken C. Awareness during anaesthesia: A prospective case study. Lancet 2000;355:707-11.  Back to cited text no. 1
Sebel PS, Bowdle TA, Ghoneim MM, Rampil IJ, Padilla RE, Gan TJ, et al. The incidence of awareness during anesthesia: A multicenter united states study. Anesth Analg 2004;99:833-9.  Back to cited text no. 2
Sanders RD, Gaskell A, Raz A, Winders J, Stevanovic A, Rossaint R, et al. Incidence of connected consciousness after tracheal intubation: A prospective, international, multicenter cohort study of the isolated forearm technique. Anesthesiology 2017;126:214-22.  Back to cited text no. 3
Vuyk J, Lim T, Engbers FH, Burm AG, Vletter AA, Bovill JG. The pharmacodynamic interaction of propofol and alfentanil during lower abdominal surgery in women. Anesthesiology 1995;83:8-22.  Back to cited text no. 4
Tunstall ME. Detecting wakefulness during general anaesthesia for caesarean section. Br Med J 1977;1:1321.  Back to cited text no. 5
Brice DD, Hetherington RR, Utting JE. A simple study of awareness and dreaming during anaesthesia. Br J Anaesth 1970;42:535-42.  Back to cited text no. 6
Avidan MS, Palanca BJ, Glick D, Jacobsohn E, Villafranca A, O'Connor M, et al. Protocol for the BAG-RECALL clinical trial: A prospective, multi-center, randomized, controlled trial to determine whether a bispectral index-guided protocol is superior to an anesthesia gas-guided protocol in reducing intraoperative awareness with explicit recall in high risk surgical patients. BMC Anesthesiol 2009;9:8.  Back to cited text no. 7
Baraka A, Louis F, Dalleh R. Maternal awareness and neonatal outcome after ketamine induction of anaesthesia for caesarean section. Can J Anaesth 1990;37:641-4.  Back to cited text no. 8
Russell IF, Wang M. Absence of memory for intraoperative information during surgery under adequate general anaesthesia. Br J Anaesth 1997;78:3-9.  Back to cited text no. 9
Schneider G, Wagner K, Reeker W, Hänel F, Werner C, Kochs E. Bispectral index (BIS) may not predict awareness reaction to intubation in surgical patients. J Neurosurg Anesthesiol 2002;14:7-11.  Back to cited text no. 10
Zand F, Hadavi SM, Chohedri A, Sabetian P. Survey on the adequacy of depth of anaesthesia with bispectral index and isolated forearm technique in elective caesarean section under general anaesthesia with sevoflurane. Br J Anaesth 2014;112:871-8.  Back to cited text no. 11
St Pierre M, Landsleitner B, Schwilden H, Schuettler J. Awareness during laryngoscopy and intubation: Quantitating incidence following induction of balanced anesthesia with etomidate and cisatracurium as detected with the isolated forearm technique. J Clin Anesth 2000;12:104-8.  Back to cited text no. 12
Avidan MS, Mashour GA. Prevention of intraoperative awareness with explicit recall: Making sense of the evidence. Anesthesiology 2013;118:449-56.  Back to cited text no. 13
Sanders RD, Tononi G, Laureys S, Sleigh JW. Unresponsiveness ≠ unconsciousness. Anesthesiology 2012;116:946-59.  Back to cited text no. 14
Morimoto Y, Nogami Y, Harada K, Tsubokawa T, Masui K. Awareness during anesthesia: The results of a questionnaire survey in Japan. J Anesth 2011;25:72-7.  Back to cited text no. 15
Sonner JM. Ethnicity can affect anesthetic requirement. Anesthesiology 2007;107:4-5.  Back to cited text no. 16
Ezri T, Sessler D, Weisenberg M, Muzikant G, Protianov M, Mascha E, et al. Association of ethnicity with the minimum alveolar concentration of sevoflurane. Anesthesiology 2007;107:9-14.  Back to cited text no. 17
Ambulkar RP, Agarwal V, Ranganathan P, Divatia JV. Awareness during general anesthesia: An Indian viewpoint. J Anaesthesiol Clin Pharmacol 2016;32:453-7.  Back to cited text no. 18
[PUBMED]  [Full text]  
Myles PS, Leslie K, McNeil J, Forbes A, Chan MT. Bispectral index monitoring to prevent awareness during anaesthesia: The B-aware randomised controlled trial. Lancet 2004;363:1757-63.  Back to cited text no. 19
Avidan MS, Zhang L, Burnside BA, Finkel KJ, Searleman AC, Selvidge JA, et al. Anesthesia awareness and the bispectral index. N Engl J Med 2008;358:1097-108.  Back to cited text no. 20
Avidan MS, Jacobsohn E, Glick D, Burnside BA, Zhang L, Villafranca A, et al. Prevention of intraoperative awareness in a high-risk surgical population. N Engl J Med 2011;365:591-600.  Back to cited text no. 21
Mashour GA, Kent C, Picton P, Ramachandran SK, Tremper KK, Turner CR, et al. Assessment of intraoperative awareness with explicit recall: A comparison of 2 methods. Anesth Analg 2013;116:889-91.  Back to cited text no. 22
Leslie K, Sleigh J, Paech MJ, Voss L, Lim CW, Sleigh C. Dreaming and electroencephalographic changes during anesthesia maintained with propofol or desflurane. Anesthesiology 2009;111:547-55.  Back to cited text no. 23
Russell IF. The narcotrend 'depth of anaesthesia' monitor cannot reliably detect consciousness during general anaesthesia: An investigation using the isolated forearm technique. Br J Anaesth 2006;96:346-52.  Back to cited text no. 24
Russell IF. The ability of bispectral index to detect intra-operative wakefulness during isoflurane/air anaesthesia, compared with the isolated forearm technique. Anaesthesia 2013;68:1010-20.  Back to cited text no. 25


  [Table 1], [Table 2], [Table 3]


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