Survey on the adequacy of depth of anaesthesia with bispectral index and isolated forearm technique in elective Caesarean section under general anaesthesia with sevoflurane

Hormonal basis of sex differences in anesthetic sensitivity

General anesthesia-a pharmacologically induced reversible state of unconsciousness-enables millions of life-saving procedures. Anesthetics induce unconsciousness in part by impinging upon sexually dimorphic and hormonally sensitive hypothalamic circuits regulating sleep and wakefulness. Thus, we hypothesized that anesthetic sensitivity should be sex-dependent and modulated by sex hormones. Using distinct behavioral measures, we show that at identical brain anesthetic concentrations, female mice are more resistant to volatile anesthetics than males. Anesthetic sensitivity is bidirectionally modulated by testosterone. Castration increases anesthetic resistance. Conversely, testosterone administration acutely increases anesthetic sensitivity. Conversion of testosterone to estradiol by aromatase is partially responsible for this effect. In contrast, oophorectomy has no effect. To identify the neuronal circuits underlying sex differences, we performed whole brain c-Fos activity mapping under anesthesia in male and female mice. Consistent with a key role of the hypothalamus, we found fewer active neurons in the ventral hypothalamic sleep-promoting regions in females than in males. In humans, we demonstrate that females regain consciousness and recover cognition faster than males after identical anesthetic exposures. Remarkably, while behavioral and neurocognitive measures in mice and humans point to increased anesthetic resistance in females, cortical activity fails to show sex differences under anesthesia in either species. Cumulatively, we demonstrate that sex differences in anesthetic sensitivity are evolutionarily conserved and not reflected in conventional electroencephalographic-based measures of anesthetic depth. This covert resistance to anesthesia may explain the higher incidence of unintended awareness under general anesthesia in females.

EEG-Messung in Narkose

Based on the existing literature, the application of designated, processed EEG-monitors to measure anesthetic depth and the associated clinical implications are explained. EEG-monitors quantify the hypnotic portion of anesthesia, but not the nociceptive properties of anesthetics. Depth of anesthesia monitoring is common practice in many German hospitals and helps to visualize the interindividual variability of anesthetics, especially of propofol. Although deep anesthesia is associated with increased long-term mortality, this relation seems not to be causally related. Nevertheless, depth of anesthesia monitors help to identify patients being especially susceptible to anesthetics. Moreover, they have shown to reduce the incidence of intraoperative awareness and postoperative delirium. The application of processed EEG-monitors to reduce the incidence of postoperative delirium is currently recommended by the European Society of Anaesthesiology and Intensive Care.

[Accidental Awareness during General Anaesthesia]

Accidental awareness during general anaesthesia (AAGA) is a rare but severe complication. The reported incidence of AAGA may depend on the assessment of intraoperative awareness with explicit recall and there are substantial variations between subspecialties and groups of patients. The majority of prospective studies using structured interviews reported an incidence of AAGA at 0.1-0.2% during general anaesthesia, however, higher values were observed in paediatric (0.2-1.2%) and obstetric patients (0.47%). Risk factors that predispose to AAGA are patient conditions, ASA status, female gender, patient age, history of AAGA, surgical procedure, anaesthetic drug type, muscle relaxation, dosages of hypnotic or analgesic drugs, monitoring and malfunction of anaesthesia systems. Preventive strategies include careful assessment of risk factors, avoidance of underdosages of hypnotics and analgetics during general anaesthesia and monitoring of depth of anaesthesia in risk patients. The health-related consequences can be serious and psychopharmacological and psychotherapeutic interventions are indicated in patients who have experienced AAGA.

The use of processed electroencephalography (pEEG) in obstetric anaesthesia: a narrative review

Accidental awareness under general anaesthesia (AAGA) remains a major complication of anaesthesia. The incidence of AAGA during obstetric anaesthesia is high relative to other specialities. The use of processed electroencephalography (pEEG) in the form of "depth of anaesthesia" monitoring has been shown to reduce the incidence of AAGA in the non-obstetric population. The evidence for using pEEG to prevent AAGA in the obstetric population is poor and requires further exploration. Furthermore, pregnancy and disease states affecting the central nervous system, such as pre-eclampsia, may alter the interpretation of pEEG waveforms although this has not been fully characterised. National guidelines exist for pEEG monitoring with total intravenous anaesthesia and for "high-risk" cases regardless of technique, including the obstetric population. However, none of the currently available guidelines relates specifically to obstetric anaesthesia. Using pEEG monitoring for obstetric anaesthesia may also provide additional benefits beyond a reduction in risk of AAGA. These potential benefits include reduced postoperative nausea and vomiting, reduced anaesthetic agent use, a shorter post-anaesthetic recovery stay. In addition, pEEG acts as a surrogate marker of cerebral perfusion, and thus as an additional monitor for impending cardiovascular collapse, as seen in amniotic fluid embolism. The subtle physiological and pathological changes in EEG activity that may occur during pregnancy are an unexplored research area in the context of anaesthetic pEEG monitors. We believe that the direction of clinical practice is moving towards greater use of pEEG monitoring and individualisation of anaesthesia.

Comparison of cerebral metabolic rate of oxygen, blood flow, and bispectral index under general anesthesia

Significance

The optical measurement of cerebral oxygen metabolism was evaluated.

Aim

Compare optically derived cerebral signals to the electroencephalographic bispectral index (BIS) sensors to monitor propofol-induced anesthesia during surgery.

Approach

Relative cerebral metabolic rate of oxygen (rCMRO 2 ) and blood flow (rCBF) were measured by time-resolved and diffuse correlation spectroscopies. Changes were tested against the relative BIS (rBIS) ones. The synchronism in the changes was also assessed by the R-Pearson correlation.

Results

In 23 measurements, optically derived signals showed significant changes in agreement with rBIS: during propofol induction, rBIS decreased by 67% [interquartile ranges (IQR) 62% to 71%],rCMRO 2 by 33% (IQR 18% to 46%), and rCBF by 28% (IQR 10% to 37%). During recovery, a significant increase was observed for rBIS (48%, IQR 38% to 55%),rCMRO 2 (29%, IQR 17% to 39%), and rCBF (30%, IQR 10% to 44%). The significance and direction of the changes subject-by-subject were tested: the coupling between the rBIS,rCMRO 2 , and rCBF was witnessed in the majority of the cases (14/18 and 12/18 for rCBF and 19/21 and 13/18 forrCMRO 2 in the initial and final part, respectively). These changes were also correlated in time ( R > 0.69 to R = 1 , p - values < 0.05 ).

Conclusions

Optics can reliably monitorrCMRO 2 in such conditions.

Intraoperative Awareness in Patients Undergoing Cardiac Surgery in an Academic Center in the North of Iran

Background

Coronary artery bypass grafting (CABG) has distinctive characteristics that may increase the risk of awareness during general anesthesia (AGA).

Objectives

This study was conducted to assess the incidence of AGA in cardiac surgery in an academic hospital in Guilan, Iran.

Methods

This descriptive cross-sectional study was performed in Dr. Heshmat Hospital in Rasht, Iran. Eligible patients candidates for CABG were enrolled in the survey in 2022. After surgery, when the patient was cooperative enough, a questionnaire including demographic data and specialized questions related to different stages of anesthesia was completed via face-to-face interviews. The data were analyzed using IBM SPSS Statistics 21 with chi-square, Fisher's exact, and t-test.

Results

The data from 322 patients were analyzed, of whom 14 (4.3%) experienced AGA. Among them, the "feeling of fear and anxiety" reported by 9 (39.1%) cases was the most common awareness state. "Dreaming during surgery and anesthesia" and "feeling unable to move during anesthesia,", each reported by 6 (26.1%) cases, were the other common types of awareness state. None of the demographic data had a significant association with the occurrence of AGA.

Conclusions

The incidence of AGA during CABG was almost acceptable according to the credible evidence.

Adequacy of maternal anesthesia depth with two sodium thiopental doses in elective caesarean section: a randomized clinical trial

Background

Administration of an optimal dose of anesthetic agent to ensure adequate depth of hypnosis with the lowest risk of adverse effects to the fetus is highly important in cesarean section. Sodium thiopental (STP) is still the first choice for induction of anesthesia in some countries for this obstetric surgery. We aimed to compare two doses of STP with regarding the depth of anesthesia and the condition of newborn infants.

Methods

In this clinical trial, parturient undergoing elective Caesarian section were randomized into two groups receiving either low-dose (5 mg/kg) or high-dose (7 mg/kg) STP. Muscle relaxation was provided with succinylcholine 2 mg/kg and anesthesia was maintained with O2/N2O and sevoflurane. The depth of anesthesia was evaluated using isolated forearm technique (IFT) and bispectral index (BIS) in various phases. Additionally, infants were assessed using Apgar score and neurobehavioral test.

Results

Forty parturient were evaluated in each group. BIS was significantly lower in high-dose group at skin incision to delivery and subcutaneous and skin closure. Also, significant differences were noticed in IFT over induction to incision and incision to delivery. Apgar score was significantly lower in high-dose group at 1 min after delivery. Newborn infants in low-dose group had significantly better outcomes in all three domains of the neurobehavioral test.

Conclusion

7 mg/kg STP is superior to 5 mg/kg in creating deeper hypnosis for mothers. However, it negatively impacts Apgar score and neurobehavioral test of neonates. STP seems to has dropped behind as an acceptable anesthetic in Cesarean section.

Trial registration

IRCT No: 2016082819470 N45, 13/03/2019.

Magnesium Sulfate and Clonidine; Effects on Hemodynamic Factors and Depth of General Anesthesia in Cesarean Section

Background

Making stable hemodynamic and also durable unawareness is a daily challenge in the setting of general anesthesia in women who undergo surgical delivery of neonate and have limitations to receive opioids derivatives.

Objectives

We aimed to evaluate the effects of magnesium sulfate and clonidine on hemodynamic changes and depth of anesthesia and in mentioned mothers and also in neonatal APGAR index.

Methods

Current randomized, double-blind controlled trial study was conducted among a total of 360 pregnant females (38 - 41 weeks of gestation) who underwent elective cesarean section. Participants were randomly divided into three drug-receiving groups (equal 120 members): magnesium sulfate (30 mg/kg), clonidine (3 µg/kg), and placebo (0.9% NaCl). Patients’ blood pressure, heart rate, cerebral state index (CSI) in specific time zones, and also late 24-hour recall were recorded. The CSI is an electroencephalographic monitoring method helping to assess the depth of anesthesia. Neonatal parameters, including APGAR score and umbilical venous blood sampling, were measured.

Results

Mean patients’ age was 28 ± 4.5. A significant decreasing and stabilizing effect of magnesium sulfate and clonidine on hemodynamic parameters (blood pressure and heart rate) was revealed (P < 0.001). Evidence implied on deeper anesthesia (lower CSI) among drug receivers comparing to placebo (P < 0.001). None of the participants experienced a late 24-hour recall postoperatively. All neonates were healthy, and no decrease was reported in APGAR score at minutes 1 and 5. Umbilical blood gas analysis showed no signs of acidosis and/or hypoxemia.

Conclusions

Adjuvant administration of either magnesium sulfate or clonidine is associated with hemodynamic stability and favorable unawareness in the setting of elective surgical delivery.

Comparison of electroencephalogram between propofol- and thiopental-induced anesthesia for awareness risk in pregnant women

There have been few comparative studies using electroencephalogram (EEG) spectral characteristics during the induction of general anesthesia for cesarean section. This retrospective study investigated the differences in the depth of anesthesia through EEG analysis between propofol- and thiopental-induced anesthesia. We reviewed data of 42 patients undergoing cesarean section who received either thiopental (5 mg/kg) or propofol (2 mg/kg). EEG data were extracted from the bispectral index (BIS) monitor, and 10-second segments were selected from the following sections: 1) Stage I, BIS below 60 after induction; 2) Stage II, after intubation completion; 3) Stage III, end-tidal sevoflurane above 0 vol%. The risk of awareness was represented by the BIS and entropy measures. In Stage III, the thiopental group (n = 20) showed significantly higher BIS value than the propofol group (n = 22) (67.9 [18.66] vs 44.5 [20.63], respectively, p = 0.002). The thiopental group had decreased slow-delta oscillations and increased beta-oscillations as compared to the propofol group in Stages II and III (p < 0.05). BIS, spectral entropy, and Renyi permutation entropy were also higher in the thiopental group at Stages II and III (p < 0.05). In conclusion, frontal spectral EEG analysis demonstrated that propofol induction maintained a deeper anesthesia than thiopental in pregnant women.

Single-trial classification of awareness state during anesthesia by measuring critical dynamics of global brain activity

In daily life, in the operating room and in the laboratory, the operational way to assess wakefulness and consciousness is through responsiveness. A number of studies suggest that the awake, conscious state is not the default behavior of an assembly of neurons, but rather a very special state of activity that has to be actively maintained and curated to support its functional properties. Thus responsiveness is a feature that requires active maintenance, such as a homeostatic mechanism to balance excitation and inhibition. In this work we developed a method for monitoring such maintenance processes, focusing on a specific signature of their behavior derived from the theory of dynamical systems: stability analysis of dynamical modes. When such mechanisms are at work, their modes of activity are at marginal stability, neither damped (stable) nor exponentially growing (unstable) but rather hovering in between. We have previously shown that, conversely, under induction of anesthesia those modes become more stable and thus less responsive, then reversed upon emergence to wakefulness. We take advantage of this effect to build a single-trial classifier which detects whether a subject is awake or unconscious achieving high performance. We show that our approach can be developed into a means for intra-operative monitoring of the depth of anesthesia, an application of fundamental importance to modern clinical practice.

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.

The fundamental contribution of the electromyogram to a high bispectral index: a postoperative observational study

The electromyogram (EMG) activity has been reported to falsely increase BIS. Conversely, EMG seems necessary to constitute the high BIS indicative of an awake condition, and may play a fundamental role in calculating BIS, rather than distorting the appropriate BIS. However, exactly how EMG is associated with a high BIS remains unclear. We intended to clarify the respective contributions of EMG and various electroencephalogram (EEG) parameters to high BIS. In 79 courses of anaesthesia, BIS monitor-derived EMG parameters (EMGLOW), and other processed EEG parameters [SEF95 (spectral edge frequency 95%), SynchFastSlow (bispectral parameter), BetaRatio (frequency parameter), total power subtypes in five frequency range], were obtained simultaneously with BIS, every 3 s. These EEG parameters were used for receiver operating characteristic (ROC) analysis of detecting three BIS levels (BIS > 80, BIS > 70, and BIS > 60) to assess their diagnosabilities. A total of 218,418 data points derived from 79 cases were used for analysis. Area under the ROC curve (AUC) was calculated and optimal cut-off (threshold) was determined by Youden index. As the results, for detecting BIS > 80, the AUC of EMGLOW was 0.975 [0.974-0.977] (mean [95% confidence interval]), significantly higher than any other processed EEG parameters such as BetaRatio (0.832 [0.828-0.835]), SEF95 (0.821 [0.817-0.826]) and SynchFastSlow (0.769 [0.764-0.774]) (p < 0.05 each). The threshold of EMGLOW for detecting BIS > 80 was 35.7 dB, with high sensitivity (92.5%) and high specificity (96.5%). Our results suggest EMG contributes considerably to the diagnosis of high BIS, and is particularly essential for determining BIS > 80.

Isolated forearm technique: a meta-analysis of connected consciousness during different general anaesthesia regimens

BACKGROUND

General anaesthesia should prevent patients from experiencing surgery, defined as connected consciousness. The isolated forearm technique (IFT) is the current gold standard for connected consciousness monitoring. We evaluated the efficacy of different anaesthesia regimens in preventing IFT responses.

METHODS

We conducted a systematic review with meta-analysis of studies evaluating IFT in adults. Proportions of IFT-positive patients were compared for inhalational versus intravenous anaesthesia and anaesthesia brain monitor (ABM)-guided versus non-ABM-guided.

RESULTS

Of 1131 patients in 22 studies, 393 (34.8%) had an IFT response during induction or maintenance. IFT-positive patients were less frequent during induction (19.7% [95% CI, 17.5-22.1]) than during maintenance (31.2% [95% CI, 27.8-34.8]). Proportions of IFT-positive patients during induction and maintenance were similar for inhalational (0.51 [95% CI, 0.38-0.65]) and intravenous (0.52 [95% CI, 0.26-0.77]) anaesthesia, but during maintenance were lower with inhalational (0.18 [95% CI, 0.08-0.38]) than with intravenous (0.48 [95% CI, 0.24-0.73]) anaesthesia. Proportions of IFT-positive patients during induction and maintenance were not significantly different for ABM-guided (0.64 [95% CI, 0.39-0.83]) and non-ABM-guided (0.48 [95% CI, 0.34-0.62]) anaesthesia but during maintenance were lower with non-ABM-guided (0.19 [95% CI, 0.09-0.37]) than with ABM-guided (0.57 [95% CI, 0.34-0.77]). Proportions of IFT-positive patients decreased significantly with increasing age and premedication use. Of the 34 anaesthesia regimens, 16 were inadequate. Studies had low methodological quality (only seven randomised controlled trials) and significant heterogeneity.

CONCLUSIONS

Standard general anaesthesia regimens might not prevent connected consciousness. More accurate anaesthesia brain monitor methodology to reduce the likelihood of connected consciousness is desirable.

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.

Awareness and Aortocaval Obstruction in Obstetric Anesthesia

Awareness during general anesthesia for cesarean delivery continues to be a major problem. The key to preventing awareness is strict attention to anesthetic technique. The prevalence and implications of aortocaval compression have been firmly established. Compression of the vena cava is a real occurrence when assuming the supine position. Relief of this compression most likely does not occur until the patient is turned 30°, which is not feasible for performing cesarean delivery. Although it is still wise to tilt the patient, the benefit of this tilt may not be as great as once thought.

The 2015 Gerard W. Ostheimer Lecture: What's New in Labor Analgesia and Cesarean Delivery

Every year the Board of Directors of the Society for Obstetric Anesthesia and Perinatology selects an individual to review the literature pertinent to obstetric anesthesiology published the previous calendar year. This individual selects the most notable contributions, creates a syllabus of the articles, and then presents his/her overview in an annual lecture named in honor of the late Gerard W. Ostheimer, a pioneering obstetric anesthesiologist from the Brigham and Women's Hospital. This article reviews the literature published in 2014 focusing on the themes of labor analgesia and cesarean delivery. Its contents were presented as the Gerard W. Ostheimer Lecture at the 47th Annual Meeting of the Society for Obstetric Anesthesia and Perinatology, May 16, 2015, in Colorado Springs, Colorado. The syllabus is available as Supplemental Digital Content (http://links.lww.com/AA/B397).

Feasibility of a 'reversed' isolated forearm technique by regional antagonization of rocuronium-induced neuromuscular block: a pilot study

BACKGROUND

The isolated forearm technique is used to monitor intraoperative awareness. However, this technique cannot be applied to patients who must be kept deeply paralysed for >1h, because the tourniquet preventing the neuromuscular blocking agent from paralysing the forearm must be deflated from time to time. To overcome this problem, we tested the feasibility of a 'reversed' isolated forearm technique.

METHODS

Patients received rocuronium 0.6 mg kg(-1) i.v. to achieve muscle paralysis. A tourniquet was then inflated around one upper arm to prevent further blood supply to the forearm. Sugammadex was injected into a vein of this isolated forearm to antagonize muscle paralysis regionally. A dose titration of sugammadex to antagonize muscle paralysis in the isolated forearm was performed in 10 patients, and the effects of the selected dose were observed in 10 additional patients.

RESULTS

The sugammadex dose required to antagonize muscle paralysis in the isolated forearm was 0.03 mg kg(-1) in 30 ml of 0.9% saline. Muscle paralysis was antagonized in the isolated forearm within 3.2 min in nine of 10 patients; the rest of the patients' bodies remained paralysed. Releasing the tourniquet 15 min later did not affect the train-of-four count in the isolated forearm but significantly increased the train-of-four count in the other arm by 7%.

CONCLUSIONS

Regional antagonization of rocuronium-induced muscle paralysis using a sugammadex dose of 0.03 mg kg(-1) injected into an isolated forearm was feasible and did not have relevant systemic effects.

CLINICAL TRIAL REGISTRATION

The trial was registered at EudraCT (ref. no. 2013-002164-53) before patient enrolment began.

Pre-delivery remifentanil infusion for placenta accreta cesarean delivery under general anesthesia: an observational study

OBJECTIVE

General anesthesia may be required for placenta accreta cesarean delivery. Intrauterine fetal anesthetic exposure should be minimized to avoid neonatal respiratory depression; opioids are often delayed until post-delivery.

METHODS

In this observational study, we compared neonatal outcome using pre-delivery remifentanil versus post-delivery (deferred) opioids for placenta accreta cesarean delivery. Choice of anesthesia was discretionary. The primary outcome was Apgar score at 5 min comparing women who received pre-delivery remifentanil versus deferred opioid administration. We recorded maternal/obstetric characteristics, surgical characteristics, maternal hemodynamic data, neonatal outcomes: Apgar scores, umbilical vein pH and respiratory interventions at birth.

RESULTS

Between February 2007 and April 2014 we identified 40 general anesthesia placenta accreta cesarean deliveries. The remifentanil dose rate ranged from 0.06 to 0.46 mcg kg(-1 )min(-1). Obstetric and maternal characteristics were similar. Neonatal Apgar, umbilical pH and respiratory intervention outcomes were similar in both groups; Apgar scores median (interquartile range IQR [range]) at 5 min were 9 (8-10) for pre-delivery remifentanil versus 9 (9-10) for deferred opioid administration, p = 0.18.

CONCLUSIONS

We did not observe a significant effect on neonatal Apgar scores at 1 and 5 min, or respiratory interventions at birth when remifentanil infusion was administered pre-delivery.

An observational study of the 'isolated forearm technique' in unparalysed, spontaneously breathing patients

The isolated forearm technique enables a patient, otherwise paralysed by neuromuscular blockade, to communicate by movement if wakeful during surgery. The positive response rate to verbal command is high (~32%). The 5th National Audit Project recommended that this monitoring technique should become more widely taught and considered, so this study was designed to assess its utility as a standard of care in unparalysed patients. A positive response rate as high as in the paralysed would justify local adoption. Therefore, 100 consecutive patients undergoing urology surgery were given verbal commands to move at two-minute intervals from induction of anaesthesia (fentanyl and propofol) to full emergence and extubation of the supraglottic airway. Anaesthesia was maintained with isoflurane in oxygen/nitrous oxide. Although 24 patients moved during surgery (and therefore needed additional anaesthetic), none moved to verbal command. Even at extubation, when patients moved to expel the airway, there was no response to command until after wakening. These results suggest that in contrast to its use in paralysed patients, the isolated forearm technique does not yield useful information about the patient's state of wakefulness in the unparalysed. Another interpretation is that unparalysed patients are less prone to wakefulness than the paralysed.