The Study of Intraoperative Consciousness after Tracheal Intubation.

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.

INTRODUCTION

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.[12] 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.[34]

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

The study protocol was approved by the hospital's Ethical Committee (MSRMC/EC/2017). The study was registered on ctri.nic.in (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[67] [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

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

Table 2

Intraoperative characteristics

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

DISCUSSION

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%.[389101112] 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.[131415] 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.[1617] 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.[2021] 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%.[223] 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.[314] 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.[102425] 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

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

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.