Developing slow wave activity saturation as a marker of depth of anaesthesia

全身麻醉是在手术过程中给病人实施的，目的是让他们无法意识到周围发生了什么，防止任何疼痛，并使身体固定，这样手术就可以安全进行。不幸的是，麻醉师是负责麻醉的专业医生，目前还没有可靠的方法来测量手术中个体大脑失去知觉的确切时间点。他们倾向于根据普通人失去意识的时间来判断麻醉剂的剂量。然后他们根据病人的心脏或肺在手术中的反应增加或减少剂量。我们相信，我们已经发现了大脑电活动中一个有趣的变化，这个变化表明，当一个接受手术的人失去对外界发生的事情的感知时。这可能意味着麻醉师可以为特定的人提供适量的药物。这一点很重要，因为虽然麻醉是非常安全的，但一些年龄较大或病情特别严重的患者如果麻醉过多，可能会产生长期副作用。它还将防止在手术过程中有人意识到的非常罕见的事件。我们有趣的观察是，当麻醉剂量增加时，大脑中的慢波达到最大水平，然后即使给更多的麻醉药物也不会再增加。这些慢波是大脑中的低频振荡（大约每秒1赫兹或1个周期），也是深度睡眠的一个重要特征。我们把这种观察称为慢波活动饱和度（或SWAS），它可以通过在头皮上应用电子传感器来测量——一种称为脑电图（或简称EEG）的技术。当我们发现SWAS时，我们同时用一种叫做功能性磁共振成像（FMRI）的技术对大脑进行了成像，发现当个体的脑电活动达到SWAS水平时，大脑对疼痛和语言的反应发生了巨大的变化。在SWAS时，这些刺激激活的大脑网络与他们清醒时激活的大脑网络非常不同，甚至与在较低麻醉浓度下激活的大脑网络也非常不同。正是这种大脑处理刺激方式的变化，让我们相信这个人不再意识到外部世界。我们最近开发了一个数学模型，当应用于脑电图系统时，可以实时动态跟踪慢波活动的变化。该模型将允许我们预测个体何时进入SWAS状态。我们希望，通过麻醉来达到这种状态，我们可以确保每个接受手术的人都不知道发生了什么，但也不会接受太多的药物治疗，这样他们就需要更长的时间来恢复。为了验证这一点，我们计划在200名接受手术的病人身上使用我们的系统，并给予足够的麻醉，使他们的大脑活动达到饱和状态。然后，我们将通过两种方式检查SWAS是否是评估某人麻醉程度的好方法。首先，我们将在手术前使用一种称为孤立前臂测试的技术来确认患者对周围发生的事情没有意识。其次，我们将通过测量他们术后的不适程度和疼痛程度来检查他们从手术中恢复的情况。我们希望我们可以证明，接受麻醉的患者在手术后恢复到SWAS状态比以常规方式麻醉的患者有更好的恢复。如果我们能证明这项研究是成功的，我们希望从长远来看，我们能创造出一种深度麻醉监测器，使全世界的病人都能在手术中获得适量的麻醉剂。

General anaesthesia is delivered to individuals during an operation to stop them being aware of what is going around them, prevent any pain and immobilise the body so surgery can be carried out safely. Unfortunately the anaesthetists, who are the specialist doctors responsible for delivering the anaesthesia, do not currently have a reliable way of measuring the exact point when an individual's brain becomes unconscious during the surgery. They tend to judge the amount of anaesthetic they give depending on when the average person would lose consciousness. They then increase or decrease the dose for that person depending on how their heart or the lungs react during the operation. We believe that we have discovered an interesting change in the brain's electrical activity that indicates the point when an individual person having surgery loses perception of what is happening in the outside world. This potentially means that anaesthetists could give just the right amount of drug for that particular person. This is important because, whilst anaesthesia is very safe, some patients who are older or particularly sick may suffer from long-term side effects if they are given too much anaesthesia. It will also prevent the very rare event that someone is aware during the operation. Our interesting observation is that when the anaesthetic dose is increased, slow waves in the brain reach a maximum level, and then do not increase any further even though much more anaesthetic drug is given. These slow waves are low frequency oscillations in the brain (at around 1 Hz or 1 cycle per second) and are also an important feature of deep sleep. We have called this observation slow wave activity saturation (or SWAS) and it can be measured by applying electrical sensors to the scalp - a technique called electroencephalography (or EEG for short). When we discovered SWAS, we also performed simultaneous brain imaging with a technique called functional magnetic resonance imaging (FMRI), and found that brain's response to pain and words altered dramatically when the individual's electrical activity reached this SWAS level. The brain network activated in response to these stimuli at SWAS was very different to the one that was activated when they were awake, or even the brain network that was activated at lower anaesthetic concentrations. It was this change in how stimuli are processed in the brain that makes us believe that the person is no longer aware of the outside world.We have recently developed a mathematical model that, when applied to an EEG system, can dynamically track the changes in slow wave activity in real-time. The model will allow us to predict when an individual has entered this SWAS state. We hope that, by delivering the anaesthesia to achieve this state, we can make sure everyone who has surgery is unaware of what is going but also doesn't receive too much medication so that it takes them longer to recover. To test this, we plan to use our system in 200 patients having surgery and deliver just enough anaesthesia so that their brain's activity reaches the saturation state. We will then check whether SWAS is a good measure to assess how deeply someone is anaesthetised in two ways. Firstly, we will use a technique called the isolated forearm test before the surgery to confirm that the patient is not aware of what is going on around them. Secondly, we will check how they recover from the operation by measuring how sick they feel afterwards and how much pain they are in. We hope that we can show that patients who receive anaesthesia delivered to the SWAS state have an improved recovery after surgery than patients who have anaesthesia delivered in the usual way. If we can show that this study is a success, we hope that in the long-term we can create a depth of anaesthesia monitor that will enable patients all over the world to be given just the right amount of anaesthetic for their operations.