Effect of penehyclidine hydrochloride on the incidence of intra-operative awareness in Chinese patients undergoing breast cancer surgery during general anaesthesia

Authors


Correspondence to: Z. M. Tan

Email: zmtan166@163.com

Summary

Intra-operative awareness can lead to serious adverse psychological consequences. We conducted a prospective, randomised, double-blinded trial in 920 patients undergoing breast cancer surgery under bispectral index-guided total intravenous anaesthesia to evaluate the effect of penehyclidine hydrochloride on intra-operative awareness. Patients were randomly divided to receive 0.01 mg.kg−1 penehyclidine hydrochloride or saline intravenously 30 min before surgery. The pre-administration, pre-operative anxiety levels were assessed using a 100-mm visual analogue scale. Intra-operative awareness was defined as recall of intra-operative events using a modified Brice interview administered 2–6 h postoperatively, and in the next 24–48 h. A committee of three experts, blinded to the study conditions, independently scrutinised all reported recollections. We found no differences in depth of anaesthesia and patients' pre-operative anxiety levels between the two groups. The incidence of awareness with penehyclidine hydrochloride (0/456 patients; 0%) was significantly lower than with saline (5/452; 1.1%), p = 0.030. We conclude that penehyclidine hydrochloride reduced the incidence of intra-operative awareness in patients undergoing breast cancer surgery during general anaesthesia.

Intra-operative awareness is defined as recall of intra-operative events (explicit recall) [1, 2].The incidence of intra-operative awareness reported in China is reported as up to 6%, higher than reported in western countries [3, 4]. Previous studies have suggested that patients undergoing obstetric [5], cardiac [6] or trauma surgery [7], and especially female patients receiving total intravenous anaesthesia [8-11] are more prone to complain about intra-operative awareness. Intra-operative awareness could cause serious adverse consequences such as post-traumatic stress disorder [12, 13] and often leads to legal proceedings [11]. The Joint Commission on Accreditation of Healthcare Organizations (JCAHO) has recommended best efforts to prevent intra-operative awareness [14], which include measures like education of clinical staff about anaesthesia awareness, identification of patients at high risk of awareness using dedicated monitoring and appropriate postoperative follow up [15].

Neurologically, the basal forebrain cholinergic system appears to play an extremely important role in explicit memory [16-18]. It has a two-way link with the limbic system, and connects to many areas of the cortex, thus forming ‘memory neural circuits’. Penehyclidine hydrochloride (PHC; 2-hydroxyl-2-cyclopentyl- 2-phenyl- ethoxy quinuclidine) is a new anticholinergic drug with both antimuscarinic and antinicotinic activity [19]. It can easily pass through the brain barrier and maintain high-level concentration of drug in the brain. Penehyclidine hydrochloride selectively acts on M1 and M3 muscarinic acetylcholine receptors and N1 and N2 nicotinic acetylcholine receptors. It blocks M1 muscarinic acetylcholine receptors and inhibits arousal, resulting in a central sedative effect [20], whereas it has little effect on heart rate and myocardial oxygen consumption.

Previous literature [21] has indicated that scopolamine (hyoscine) can prevent dreams in patients undergoing general anaesthesia. Dreams imply that the brain has retained some ability to formulate thoughts and ideas, but additional studies are needed to determine whether scopolamine could also be effective in preventing awareness. Given the similarity of pharmacological profile, we hypothesised that PHC might reduce the incidence of intra-operative awareness. A secondary aim was to assess whether pre-operative stress levels are related to awareness. In this study, bispectral index (BIS) was used to monitor the depth of anaesthesia.

Methods

After approval of the study protocol by the Cancer Hospital, Fudan University Institutional Human Ethics Committee, and obtaining written informed consent, 920 female patients, of ASA physical status 1-3 and aged 15–75 years, undergoing breast cancer surgery including modified radical mastectomy, total mastectomy, lumpectomy, breast-conserving surgery and breast reconstruction, were included in this prospective randomised, double-blinded, placebo-controlled trial. The study was conducted from January 2010 to October 2011. During the pre-operative period, exclusion criteria were pregnancy, breast cancer, hyperthyroidism, psychosis or memory impairment, history of intra-operative awareness or brain injury, history of electroencephalographic abnormality, habitual use of benzodiazepines, opioids, alcohol, barbiturates, carbamazepine, glucocorticoids, phenytoin and rifampicin, and surgical procedure or positioning of the patient preventing BIS monitoring.

Before surgery, a peripheral intravenous catheter was placed in the leg. Standard monitors (including heart rate, mean arterial pressure, BIS) were applied (GE Datex-Ohmeda S/5, Anaesthesia Monitor, Helsinki, Finland). A BIS sensor was applied to every patient's forehead and connected to an Aspect A-2000 XP BIS monitor (Aspect Medical Systems, Newton, MA, USA). General anaesthesia was induced by propofol plasma target-controlled infusion (a target plasma concentration of 3.5–4.5 μg.ml−1) using a Graseby target-controlled infusion pump (Sims Graseby Limited, Warterford, Herts, UK) and an intravenous bolus injection of midazolam (0.03 mg.kg−1) and bolus sufentanil (0.3 μg.kg−1). Tracheal intubation was facilitated with 0.2 mg.kg−1 cisatracurium when the BIS value was reduced to < 45. The target plasma propofol concentration was adjusted maintain the values of BIS 40–60 during surgery. Neuromuscular blockade was guided by train-of-four monitoring. Cisatracurium was added in 4-mg aliquots when needed. Interventions for cardiovascular instability were made if the blood pressure deviated by > 30% of its pre-operative baseline value for > 5 min.

Random assignment of patients was established by computer-generated codes. Allocation concealment was established by placing the randomisation sequence in consecutively numbered, opaque envelopes. The PHC group received 0.01 mg.kg−1 PHC intravenously, whereas the saline group patients received saline intravenously as placebo. Penehyclidine hydrochloride or saline solutions were prepared in a syringe by the first anaesthesiologist, who was also responsible for subject grouping. The PHC was diluted (1 mg in 1 ml) to 10 ml, to be delivered at 0.01 mg.kg−1.

The second anaesthesiologist, blinded to the test solution, used a 100-mm visual analogue scale (VAS) [22, 23] for quantitative assessment of pre-operative anxiety level 30 min before surgery (where 0 mm indicated no anxiety and 100 mm indicated the ‘most anxious I can imagine’). This second anaesthesiologist was also responsible for the anaesthetic management and recording the variables (BIS values every 5 min).

The third anaesthesiologist served as the postoperative interviewer. Awareness was defined as recall of intra-operative events. The modified Brice interview [1, 24, 25] was used to assess awareness in the study (by the following questions: (i) What was the last thing you remember before going to sleep? (ii) What is the first thing you remember after waking up? (iii) Do you remember anything between going to sleep and waking up? (iv) Did you dream during your procedure? (v) What was the worst thing about your operation?). The time and frequency of conducting the interview are important. Previous studies have shown that anaesthesia awareness is not reliably detected with only a single interview [2, 26, 27]. Therefore, in this study, patients were contacted between 2 h and 6 h postoperatively and in the next 24–48 h after surgery. If there was any report of dreaming or suggestion of recall, a narrative report was collected from the patient at the time of the interview and recorded in the patient's own words. A committee of three experts, blinded to the study conditions and knowledgeable about awareness, independently scrutinised all reported recollections and classified the reports as ‘awareness’, ‘possible awareness’ or ‘no awareness’. Confirmed awareness was defined as two or three experts coding ‘awareness’. ‘Possible awareness’ was defined as only one member coding ‘awareness’ or at least two members coding ‘possible awareness’. Others were regarded as ‘no awareness’.

All statistical analyses were performed using the SPSS version 16.0 software package (SPSS Inc., Chicago, IL, USA). The primary outcome was to evaluate the effect of PHC on intra-operative awareness. The sample size was based on previously published studies [3, 4, 28, 29] and with an α level of 0.05 and a power of 0.8, a minimum of 385 patients per group was required to detect a difference in incidence of intra-operative awareness.

Student's t-test was used to compare patients' basal haemodynamic data. The Mann–Whitney U-test was used to compare VAS values, BIS values, consumption of midazolam and propofol and duration of operation. Fisher's exact test was used to compare the difference in incidence of intra-operative awareness. A value of p < 0.05 was considered statistically significant.

Results

Patients' data were not included if: two consecutive recorded BIS values were outside the target range 40–60; the time of surgery was longer than 10 h or shorter than 30 min; and patients required ephedrine or atropine because of circulatory instability.

In all, data from 12 patients were not analysed (four in the PHC group, eight in the saline group), which left 908 patients' data (456 in the PHC group and 452 in the saline group) available for analysis (Fig. 1).

Figure 1.

Flow diagram of subjects. PHC, penehyclidine hydrochloride.

The two groups were similar for patients' characteristics (age, year; weight, kilogram; ASA status); Table 1). There were no differences in consumption of propofol and midazolam, duration of operation or baseline haemodynamic data.

Table 1. patients' characteristics and clinical data. Values are mean (SD), number (proportion) or median (IQR [range])
 PHC group (n 456)Saline group (n 452)p value
  1. PHC, penehyclidine hydrochloride; VAS, visual analogue scale; for pre-operative anxiety level HR, baseline heart rate; MAP, baseline mean artery pressure; BIS, bispectral index over course of study; Interview 1, interviewed between 2 h and 6 h postoperatively; Interview 2, interviewed between 24 h and 48 h postoperatively.

Age; years52.9 (9.8)53.3 (9.6) 
Weight; kg59.0 (7.5)59.2 (7.3) 
ASA status
1214 (47%)236 (52%) 
2237 (52%)210 (47%) 
35 (1%)6 (1%) 
HR; beats.min−172.4 (7.6)72.9 (7.6) 
MAP; mmHg82.7 (7.4)82.3 (7.9) 
VAS50 (40–50 [10–90])50 (40–60 [10–80])0.304
BIS52 (50–53 [40–59])52 (49–53 [40–59])0.234
Total midazolam; mg2 (2–2 [2–5])2 (2–2 [2–5])0.360
Total propofol; mg1045 (900–1200 [400–3000])1000 (864–1260 [450–2400])0.225
Duration of operation; min120 (105–150 [60–330])120 (105–165 [60–285])0.452
Interview 1 awareness05 (1.1%)0.030
Interview 2 awareness05 (1.1%)0.030

There were no differences in depth of anaesthesia (BIS values). However, in the PHC group, none of the patients had recall of intra-operative events (0%), whereas in the saline group, five of 452 patients reported intra-operative awareness (1.1%); p = 0.030 (one-sided Fisher's exact test). The descriptions of awareness are presented in Table 2.

Table 2. Descriptions of awareness
Serial numberAgePrevious anaesthesiaVAS valueDescriptions
  1. VAS, visual analogue scale for pre-operative anxiety level.

140No65No pain, something in mouth, heard someone talking
232No80A little pain, heard the doctor was talking about something
338Yes70Felt doctor suturing the skin but no pain, tried to open eyes, but failed
457Yes60No pain, heard music and somebody was speaking
553No70No pain, heard sounds of instruments intermittently

There were no differences in patients' pre-operative anxiety levels between the groups. The median (IQR [range]) VAS values in the PHC and saline groups were a 50 (40–50 [10–90]) and 50 (40–60 [10–80]), respectively; p = 0.304. The VAS values of one patient in the five patients complaining recall of intra-operative events were within the range 40–60, whereas the other four were in the range 60–80.

Discussion

We found that PHC reduced the incidence of intra-operative awareness in patients undergoing breast cancer surgery during general anaesthesia.

We were surprised by the very high incidence in a group of patients monitored by BIS titrated to a range 40–60. There are several possible reasons for this. Awareness may be more common in women than men [10, 11] and they are also more likely to be less satisfied overall with their surgery and anaesthesia [30]. An increased risk of awareness with total intravenous anaesthesia (TIVA) has also been suggested [31, 32]. The breast cancer surgery we focused on in our study may have heighted anxiety and therefore increased the possibility of awareness. It is still not established whether BIS in fact can reduce effectively the incidence of intra-operative awareness [27, 33]. Avidan et al. [33] found that intra-operative awareness occurred even when BIS values were within the target range 40–60. Myles et al. [27] reported the incidence of awareness (i.e. both definite and possible awareness) to be 1.8% even when using the BIS monitor. Vassiliadis et al. reported that awareness occurs despite low electroencephalography device values [34].

In line with previous studies, we included patients younger than 18 years of age [26, 32, 35] and were reassured that the performance of BIS and other processed electroencephalography devices is probably as good in older children as it is in adults [36].

Previous studies have demonstrated that basal forebrain cholinergic system is an important anatomical structure involved in the formation of explicit memory [16-18, 21]. Power et al. [17] found that activation of muscarinic cholinergic receptors in the basolateral amygdala play an essential role in enabling other neuromodulatory influences on memory consolidation. Toscano et al. [21] reported that scopolamine could prevent dreaming during general anaesthesia, but whether scopolamine could also be effective in preventing awareness was unknown. In animals studies, Boccia et al. [18] found that atropine could block memory formation in mice. Penehyclidine hydrochloride selectively blocks M1, M3 and N1, N2 subtype receptors. With its ether-based structure containing a non-quaternary ammonium cation, PHC readily passes across the blood–brain barrier to achieve a central sedative effect [20]. Furthermore, cholinergic neurotransmission is a potential mediator of general anaesthetic drug effects [37, 38]. We therefore speculate that these neuropharmacological effects underlie the efficacy of PHC in our study [39].

We were unable to assess whether pre-operative stress levels were related to awareness as only five patients experienced recall of intra-operative events (although four of these did exhibit high anxiety).

There are several limitations of this study. First, although we suggest a benefit of PHC over a saline group, other anticholinergic drugs may have a similar effect and we did not compare PHC with a more commonly used anticholinergic. Second, our results are confined to female patients suffering from breast cancer. Whether the same or similar conclusions could be drawn from male patients or patients undergoing other types of surgeries is unknown. We chose this group to maximise the possible incidence of awareness, as previous studies have demonstrated a propensity for women to recover more rapidly from anaesthesia than do men [10, 30], and also perhaps to claim awareness more often [10, 11]. Third, we only administered the Brice questionnaire on two occasions, whereas many authors recommend that three administrations are undertaken, up to a month after surgery. This may have detected some awareness in our PHC group and altered our conclusions [27].

For the test of our main hypothesis, we used a one-sided test for data with a zero numerator. The problem of zero numerators has been previously discussed in the anaesthetic literature [40, 41]. If we apply either a correction for the zero numerator as previously suggested, or use the upper limit of the 95% confidence intervals, then our primary comparison is not statistically significant [42].

We feel, however, that in this trial, a one-sided test was justified and in conclusion, PHC warrants further investigation as a means of reducing the incidence of intra-operative awareness.

Acknowledgements

This study was supported by a grant from Fudan University, Shanghai Cancer Centre, grant No. YJ200906.

Competing interests

No competing interests declared.

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