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美国临床神经生理学会临床脑电图指南:临床脑电图操作的最低技术要求

摘要:尽管我们统一的认为不存在一个适用于所有情况下记录动态脑电图的最佳方法,但下列标准被认为是除小儿外的各年龄组临床记录脑电图的最低要求。虽然这些最低标准下的记录不会使脑电图人员满足,也不能确保检测满意。但它仅仅是确保对患者和相关医生履行一定的责任。为此,我们认为这里特别推荐最低标准是为了改善操作的标准化,也只是为了促进北美各实验室之间记录和判定的交流。

    一,首先是设备,我们要在尽可能多的头皮同步记录,对于发现脑电活动是必须的。同步记录的导联太少,解释发生错误的机会就增加,相对地,使用越多导联,这种错误发生的可能性就会减少。对于短暂性的活动这点尤为突出。要显示大多正常和异常脑电图波形,至少需要16导联的记录。有些生理活动检测需要更多导联。交流电线路应该符合保险公司对于医院设备需要遵循的实验室标准。所有交流电插座必须提供合适的接地设施。在脑电图室,患者每一个部位的所有设备必须在一个公共接地点。一般的诊室环境,在患者和设备间不必设屏蔽,除非证明有必要。辅助设备应包括能对患者发出高频闪光刺激的装置。
    二,设备的电极,我们认为针电极是不推荐使用的,若环境所需不得不使用时,必须做好消毒工作或用完后直接抛弃。使用针电极的技术工作者应掌握好针电极的确切使用技术,并熟知使用针电极的缺点和危险性,校正针电极以保持前后平衡是重要的。若是针电极校正不到位,可能会引起波幅不一致或扭曲。使用针电极与实用其他任何形式的电极比,需要更多的专业知识和细心,但这一点往往很少引起大家的重视。然而,针电极可以更有效的用于昏迷的患者,后者对于痛觉的反应欠灵敏。同时针电极具有的最小时间延迟特性也能更有效的记录病人的脑电信号。在记录电极应注意避免噪音和移动。它们对0.5 ~ 70Hz间的信号不会产生明显衰减作用。实验证明火棉胶粘银-氯化银或金质盘状电极是最佳选择(编者注:标准发布时间为2006年,技术有进步,粉末银/氯化银电极粘医用导电膏是目前最佳选择),但若是联用一些具有高输入阻抗的增益装置,就可以由更多的有效的电极材料和电极粘附物可以选择。(一些制造商制造的高质量电极往往比资质的电极更为好用。减少噪音,保持电极的清洁,以及为由传染性疾病(病毒性肝炎、朊蛋白病、获得性免疫缺陷综合征)的患者进行记录后做好恰当的防护措施。并且每次进行检查前都需要检测电极间的阻抗,一般情况下,电极间阻抗应控制在5000欧姆(5KΩ)内。如果有任何图形出现伪迹,就必须在记录中重新检查电极间的阻抗。
    虽然,国际临床电生理学会(IFCN)所推荐的21个电极安放点都可以使用。10-20系统是IFCN唯一官方推荐系统,也是目前最常用的系统。“修订版10-20系统”是不合适的,因为它允许在不进行头部测量的情况就安置电极的位置,这样往往会产生误导的结果,称其为“估计10-20系统放置法”更为恰当。“10-10”系统应该适用于指南5所述的扩展组合系统中。足够数量的电极对于确保脑电活动的测量是非常重要的,只有用足够的点,才能记录到头皮最小代表区的电活动,这样更有利于准确分析复杂电活动的分布情况。在某些特殊情况下少量电极更为合适,但这种情况较少有。有时为了记录一些非常局限部位的电活动,我们会在标准电极放置部位的附近加放一些额外电极。除非像手术室这种地方,患者全身连有其他电子设备时可以不用接电电极,其他情况下往往需要使用接地电极。使用重复接地是不允许的,连载患者身上的接地电极必须只能直接连接在总的接地线上而不能间接连在其他任何设备的接地线上。
    三,然后是记录,对于记录出的图像必须符合指南6“临床脑电图学标准图像指南”要求,这样可以使每个实验室出来的图像更加一致以利于彼此间的交流与比较。数字系统能够让我们修改出更合适的反应患者病情的图像,即使可以进行这样的弹性改动,我们还是应该记录患者的原始图像以作参考。系统的参考值,本身是无法修正的,所以数字记录参考电极应该是一个额外的电极(或几个电极的联合),而不是10:10系统或10;20系统中某个电极,这种电极往往使安置在Cz和Pz间的,如果将双耳连接点作为参考电极的效果往往是不理想的。
    记录时应将患者的年龄、姓名、记录的数据、标识的数字、技术员的名字或名字的首字母标注在记录纸上。在记录的同时就应该标注好标识,否知容易导致医疗纠纷。每次记录都应该有一份基本的数据表。这份数据表包括记录的时间,最后一次痫间发作的时间及其他相关资料(如果有的话),患者的行为状态、患者所用药物的明细(这份明细也应该包括诱导睡眠而预先服用的药物)以及其他相关疾病的病史。
  每次EEG测量开始及完成时均应对仪器进行适当的校准,如果可能的话,应该在记录开始处标出全套电极连接的所有导联。然而,对这种全数字系统进行生物学校准是很难完成的。必要时,我们在开始测量时对所有导联进行校准,以使它们能与校准信号更为吻合。每次校正过放大器,我们都应该对仪器再进行一次新的校正。每次EEG测量时这种校正都是不可或缺的,这种校正对于操作者而言就好比一个用以平衡EEG灵敏度的尺度,这个尺度可以衡量高低频的反应,噪音的水平,记录笔尖的校直程度和润湿程度。反之,从这种校正中,我们也可以看出操作者的水平和细心程度。校正电压必须适合灵敏度所需。除了标准的方波之外,生物定标会对检测图形选择过程的错误或记录仪器的错误有所帮助,所以我们需要用前后起源(额枕起源)的概念,因为它包括快的α范围的必行,同时也包括θ范围内眼球运动的图像,数字系统不能完全自动化地完成仪器的校准和生物校准,所以操作者必须从最初的系统参数的图像中观察判断前30s记录过程中所记录图形的情况。
    1.在常规记录时,EEG仪器的灵敏性应设定在5~10μV/mm笔尖偏移距离。灵敏度被定义为输入电压后与笔尖偏移的距离的比率,单位为微伏每毫米(μV/mm)。常用的灵敏度为7μV/mm,它意味着50μV的校正信号会导致笔尖7.1mm的偏移。如果灵敏度下降(例如从7降至10μV/mm),EEG所做出的图像的振幅也会下降,相反地,若灵敏度上升(例如从7升至5μV/mm),图像的振幅也会加大。如果灵敏度低于10μV/mm(例如20μV/mm),振幅会低得难以识别。若灵敏度高于5μV/mm(例如3μV/mm)则会导致波峰过度以至于超出记录纸的边界或造成电脑显示屏的信号轨迹重叠。5μV/mm的灵敏度意味着若要使笔尖偏移仅1mm,就需要输入5μV的输入电压(相应地,若要使笔尖偏移仅10mm内的话,就需要50μV的输入电压)。若灵敏度降至10μV/mm,则若想笔尖偏移控制在1mm内就需要更大的输入电压。例如10μV就比5μV要大(也就是说10μV/mm意味着将笔尖偏移控制在10mm的话需要100μV的输入电压而不是50μV)。所以灵敏度增加的话,它的数值就会变小;相反地,灵敏度降低的话,它的数字值就会变大。这里表面看上去似乎是一个矛盾的关系,但实际上灵敏度定义为输入电压每笔尖偏移单位是一个逻辑结论。但在数字系统中,这种直接的物理关系就没有了,因为计算机显示器的空间维度是变化的,所以显示时应标上清晰的尺度标志。
    对脑电图仪放大器的操作可描述为增益,它定义为输出电压与输入电压的比率。例如,如果脑电图输入信号10μV被增益至1.0来趋动脑电图描记笔尖的移动,则它的增益就是1.0/0.00001=100 000,对于使用者而言,一个系统(模拟或数字)的增益,不会像灵敏度那样明显。在常规记录的校正期间,不能扭曲记录信号,但应使其扩大到足够大,以使得任何两个导联间的信号差异大于5%。不论记录前选择的哪个灵敏度(带有上述限制的),为了记录的准确性,不论脑电图形出现的是过高的振幅或过低的振幅,我们都应对灵敏度进行恰当的调整。
    2. 对于标准记录而言,低频滤波不应高于1Hz(3dB),对应时间常数至少需要0.16s。高频滤波不应低于70Hz(-3dB)。然后需要注意的是显示频率为70Hz时,计算机显示器在数据显示区域水平分辨率为至少1400,否则操作者会发现有高频信号的丢失和低频信号的失真。常规使用高于1Hz的低频滤波背景会减少记录的慢波伪迹,在δ范围内的病理活动容易丢失一些重要的信息,同样地,低于70Hz的高频背景滤波会扭曲或减少弱波的峰尖及其他的病理放电,使之不易辨认,或产生由于肌肉活动而出现的伪迹波形,而一份信息不全或不准确的记录往往会干扰医生的正确用药。值得强调的是,正确运用低频或高频滤波——需要在记录上标上正确的注释——能起到在记录上强调或清楚阐明图形模式的作用,所以对于滤波的选择我们必须谨慎。
  走纸速度为3cm/s或数据显示速度为10s/一张纸是常用的记录指标。走纸速度为1.5cm/s或显示速度为20s/一张纸,有时也会用于新生儿或其他特殊情况下的EEG测定。60Hz滤波会扭曲或减少图形的峰尖,所以出现这种设置我们往往只用于其他方法失效的情况下。
    注意:记录期间若仪器设定(灵敏度、滤波、走纸速度、图像)有改变,则应在改变时将之清楚地标注在记录上。如果技术上可行,则最终的标准应包括在记录中所用的每个灵敏度和滤波的设定。在高灵敏度时记下用过的校正信号是很重要的。对于一些数字系统,增益也许就是唯一能提供的评估手段,用以评估模拟系统的功能。在一些广泛使用的校正标准,诸如上述所提到的那些都是被鼓励使用的。基线记录应包含至少20min技术上令人满意的记录。记录越长久,其所包含的信息也越丰富。尽管重置数字脑电图可以让所有的记录都在一张纸上,但这种做法往往使不提倡的。仅仅只观察一幅图像往往不足以判断电极是否连接牢固,同时也会影响操作者对一些异常现象的评估,这些细微异常现象往往需要一些特殊的技术支持才能探测到(例如额外加装电极)。脑电图仅能记录患者生活中的一个小片段,在合理的限定下记录时间越长,越有可能记录到异常情况的异常状态。许多实验中心的经验显示20分钟的一段小小的无伪迹的记录对于评估脑电活动的基线状态是很有必要的。附加实验如闪光刺激、过度通气和特殊睡眠测定——如果有可能,这些均应完成并记录。
    记录应包含患者睁眼闭眼时的脑电活动,恰当的动态脑电图记录要求检查刺激对于脑电图的影响,睁闭眼试验时一种很重要的评估方法。正常情况下一些被α活动掩盖的脑电节律会在睁眼时α节律减弱的情况下显现出来。某些形式的眼动可能会表现为额叶的δ或θ活动,而睁眼试验有利于这种鉴别。一些阵发性的脑电活动可能仅在睁眼或闭眼时出现,也可能在睁闭眼交替时出现,所以,如果未将睁闭眼试验作为常规脑电图测定方法就有可能会错过一些有用的信息,这项检查非常简单,所以,只要病人可以合作都应该进行,或者若患者自身不能完成这项动作,我们可以手动帮助他们完成睁闭眼动作以利检查。
    除非用药的关系或有其他合理的原因而禁忌此项检查,否则过度通气也应作为一项常规的检测项目(特殊情况下例如近期有急性脑出血、明显的心肺疾病、镰刀状红细胞贫血,患者不能或不愿合作进行此项检查)。记录时间应不少于3min,且此中必须有至少1min的记录是在过度通气停止后记录的。有时为了获取更充分的脑电活动波形会需要患者进行一端长时间的过度通气。为了更好地评估过度通气的效果,常常需要在过度通气开始前有至少1min的脑电记录。记录中应包含有对患者过度通气努力程度评估。在记录的各个部分通过一个心电图导联记录心电活动是很有帮助的,特别是在波峰很高尖,或有脉冲波产生或有心电伪迹时,这种方法是很有帮助的。用一个额外的导联(例如第17导联),就可以继续监测心电图。
    如果可能的话应该同时记录做睡眠脑电图和清醒脑电图,越来越多的证据表明昏迷,昏昏沉沉状态下或睡眠时记录的脑电图能够提供更多的信息。一些实验室甚至将睡眠脑电图作为常规检查项目。对于可疑抽搐或已确定抽搐情况的患者,睡眠脑电图往往是不可或缺的。
    患者的意识水平(清醒、昏沉、睡眠或昏迷)和由此而来的一些改变,操作者都应记录在动态脑电图记录纸上,在记录的过程中我们要求患者做了什么动作,给了患者什么信号,以及患者有什么动作或临床痫间性活动或没有动作,我们都应在记录纸上有所记录。对患者细观察勤记录是很有必要的,特别是在有不常见的波形出现时,这种细微的工作就更为必要,缩写的使用必须规范化,以使用读者能很快明白它的含义。对于失去知觉或昏迷的病人或那些脑电图始终无变化的患者,我们应记录期间对之施之以视觉、听觉、感觉等各种刺激,这些加诸于患者的刺激以及患者对刺激的反应(无论是有还是无)均应记在脑电图记录单上尽可能近的标注刺激发生的位点上。识别出与不同意识状态相关的脑电图模式往往使脑电图仪操作者的责任,但这种操作员员对于患者临床状态的判断只能对医生提供参考,特别是当脑电图与临床情况出现矛盾或有异常相关性时,就更不能只依赖操作者的判断了。操作者确认患者处于非常清醒的状态或至少在记录时处于非常清醒的状态对于有效评价清醒的背景活动是非常重要的。在对患者实施一些有一定风险性操作时必须要有合格的内科医生在场,同时配备足够的复苏设施。当然,患者本人或重要亲属或法定监护人的知情同意也是不可或缺的。 脑电图对于脑功能中断的评价(“脑死亡”),要求一些特别的程序和准备(具体见指南3:脑电图用于可疑死亡患者的最低基数标准)。

 

1.Equipment

 

1.1 To find the distribution of EEG activity, it is necessary to record simultaneously from as many regions of the scalp as possible. When too few channels are used simultaneously, the chances of interpretive errors increase, and, conversely, when more channels are utilized, the likelihood of such errors decreases. This is particularly true for transient activity.


Sixteen channels of simultaneous recording are now considered the minimum number required to show the areas producing most normal and abnormal EEG patterns. Additional channels are often needed for monitoring other physiologic activities.


1.2 Alternating current (AC) wiring should meet the Underwriters Laboratories standards required for hospital service. Adequate grounding of the instrument must be provided by all AC receptacles. All equipment in each patient area in the EEG laboratory must be grounded to a common point.


1.3 In the usual clinical setting, electrical shielding of the patient and equipment is not necessary, and such shielding need not be installed unless proven necessary.


1.4 Ancillary equipment should include a device for delivering rhythmic, high-intensity flash stimuli to the patient.


1.5 Digital equipment should conform with the recommendations in Guideline 8.

 

2. Electrodes

 

2.1 Recording electrodes should be free of inherent noise and drift. They should not significantly attenuate signals between 0.5 and 70 Hz. Experimental evidence suggests that silver—silver chloride or gold disk electrodes held on by collodion are the best, but other electrode materials and electrode pastes have been effectively used especially with contemporary amplifiers having high input impedances. High-quality electrodes are available from several manufacturers and are generally preferable to homemade electrodes.

 

To decrease noise, electrodes must be kept clean, with appropriate precautions taken after recording from patients with contagious diseases (viral hepatitis, Creutzfeldt-Jakob disease, acquired immunodeficiency syndrome.) (AEEGS, 1994; ASET, 2000)

 

2.2 Needle electrodes are not recommended. If circumstances necessitate their use, they must be completely sterilized or discarded after use, and the technologist who em-ploys them should have been taught the exact techniques, as well as the disadvantages and hazards, of their use. Parallel anteroposterior alignment of the needles is important; misalignment may cause artifactual amplitude asymmetries or distortions.

 

It is rarely appreciated that proper use of needle electrodes requires more care and expertise than for any other type of electrode. However, needle electrodes can be effectively utilized in comatose patients, in whom pain responses are usually minimal or absent, and who are in medical settings requiring efficient recording with a minimum of delay.

 

2.3 All 21 electrodes and placements recommended by the International Federation of Clinical Neurophysiology (IFCN; Jasper HH, 1958, 1983) should be used. The 10-20 System is the only one officially recommended by the IFCN. It is the most commonly used existing system, and it should be used universally. The use of the term “modified 10-20 System” is undesirable and misleading when it means that head measurements have not been made and placements have been estimated. In this case, the term “estimated 10-20 placement” is more appropriate. The term “10-10 System” should be used for the extended combinatorial system described in Guideline 5. (For neonates, refer to Guideline 2.)

 

An adequate number of electrodes is essential to ensure that EEG activity having a small area of representation on the scalp is recorded and to analyze accurately the distribution of more diffuse activity. A smaller number of electrodes may be appropriate for special circumstances, but is not considered comprehensive. Occasionally, additional electrodes, placed between or below those representing the standard placements, are needed in order to record very localized activity.

 

A grounding electrode always should be used, except in situations (e.g., intensive care units, operating rooms) in which other electrical equipment is attached to the patient. In such cases, double grounding must be avoided. The ground electrode on the patient must be connected only to the appropriate jack of the input jackbox, and never to the equipment chassis or other earth ground.

 

2.4 Interelectrode impedances should be checked as a routine prerecording procedure. Ordinarily, electrode impedance should not exceed 5000 Ohms (5 KOhms.)

 

Electrode impedances should be rechecked during the recording when any pattern that might be artifactual appears.

 

3. Recordings

 

3.1 Montages should be designed in conformity with Guideline 6: A Proposal for Standard Montages to Be Used in Clinical Electroencephalography. It is desirable that at least some montages in all laboratories be uniform to facilitate communication and comparison. Digital systems allow reformatting of montages to provide optimal display of activity at the time of interpretation. To permit this flexibility, initial recording must be made from a referential montage; but the system reference itself cannot easily be reformatted. For this reason the digital recording reference should be an additional electrode (or combination of electrodes), and not one of those in the 10:10 or 10:20 system. An additional electrode between Cz and Pz is commonly used. The use of linked ears as a digital recording reference is specifically discouraged.

 

3.2 The record should have written on it as a minimum the name and age of the patient, the date of the recording, an identification number, and the name or initials of the technologist.

 

Identifications should be made at the time of recording. Failure to do so may result in errors that have adverse medical and legal consequences. A Basic Data Sheet, attached to every record, should include the time of the recording, the time and date of the last seizure (if any), the behavioral state of the patient, a list of all medications that the patient has been taking, including premedication given to induce sleep during EEG, and any relevant additional medical history.

 

3.3 Appropriate calibrations should be made at the beginning and end of every EEG re-cording. If feasible, a recording with all channels connected to the same pair of electrodes should follow at the beginning. However, this biological calibration may not be possible with all digital systems. At the outset, all channels should be adjusted, if necessary, so that they respond equally and correctly to the calibration signal. When doubt as to correct functioning of any amplifier exists, a repeat calibration run should be made.

 

The calibration is an integral part of every EEG recording. It gives a scaling factor for the interpreter, and tests the EEG machine for sensitivity, high and low-frequency response, noise level, and pen alignment and damping. It also gives information about the competence and care of the technologist. Calibration voltages must be appropriate for the sensitivities used.

 

In addition to the standard square-wave calibration, the biologic calibration (“bio-cal”) may at times be of additional help in detecting errors in the montage selection process or in the pen-writing mechanism. For this purpose, an anteroposterior (fron to occipital) derivation should be used, since it can include fast and alpha range patterns as well as eye movement activity in the delta range. In digital systems that lack full provision for instrumental and biological calibration, the first 30 seconds of recording should be observed by the technologist from the primary system-reference montage.

 

3.4 The sensitivity of the EEG equipment for routine recording should be set in the range of 5—10 μV/ mm of pen deflection.

 

Sensitivity is defined as the ratio of input voltage to pen deflection. It is expressed in microvolts per millimeter (μV/mm). A commonly used sensitivity is 7 μV/mm, which, for a calibration signal of 50 μV, results in a deflection of 7.1 mm.

 

If the sensitivity is decreased (for example, from 7 to 10 μV/mm), the amplitude of the writeout of a given EEG on the paper also decreases. Conversely, if the sensitivity is increased (for example, from 7 to 5 μV/ mm), the amplitude of the writeout of a given EEG increases.

 

When the sensitivity is less than 10 μV/mm (for example, 20 μV/mm), significant low-amplitude activity may become indiscernible. If the sensitivity is greater than 5 μV/mm (for example, 3 μV/mm), normal EEG activity may overload the system, causing a squaring off of the peaks of the writeout onto the paper or overlapping of traces on the computer monitor.

 

Note that a sensitivity of 5 μV/mm means that, to obtain a pen deflection of 1 mm, a 5-uV input voltage is required (and correspondingly, to obtain a 10-mm deflection, an input of 50 μV is required). If the sensitivity is decreased to 10 μV/mm, the same 1-mm pen deflection now requires a larger input, i.e., 10 μV rather than 5 μV (and correspondingly, a 10-mm pen deflection now requires an input of 100 uV rather than 50 μV). Thus, as the sensitivity is increased, its numerical value becomes smaller. Conversely, as the sensitivity is decreased, its numerical value becomes larger. This perhaps seemingly paradoxical relationship is actually a logical consequence of the definition of sensitivity as input voltage per unit of pen deflection. With digital systems, this straightforward physical relationship is lost. Because the dimensions of computer monitors will vary, clear scale markers must be available as part of the display.

 

The operation of EEG amplifiers can also be expressed as gain, defined as the ratio of the output voltage to the input voltage. For example, if an EEG input signal of 10 μV is amplified to 1.0 V in order to move the mechanical pens of an electroencephalograph, then the gain is 1.0/.00001 = 100,000. The gain of an analog or digital system is not as obvious to the user as the sensitivity.

 

During calibration for routine recordings, the recorded signals should not be distorted but should be large enough to permit measurement to better than ±5% between any of the signals on the different channels.

 

No matter which sensitivity (within the above limits) is chosen prior to the recording, appropriate adjustments should be made whenever EEG activity encountered is of too high or low amplitude to be recorded properly.

 

3.5 For standard recordings, the low-frequency filter should be no higher than 1 Hz (—3 dB) corresponding to a time constant of at least 0.16 s. The high-frequency filter should be no lower than 70 Hz (-3 dB). Note, however, that to display frequencies as high as 70 Hz, a computer monitor would need a horizontal resolution of at least 1400 pixels in the data display area. Interpreters should be aware that some loss of high-frequency resolution will otherwise occur, along with the possibility of lower-frequency distortion due to spatial aliasing.

 

A low-frequency filter setting higher than 1 Hz should not be used routinely to attenuate slow-wave artifacts in the record. Vital information may be lost when pathologic activity in the delta range is present. Similarly, a setting lower than 70 Hz for the high-frequency filters can distort or attenuate spikes and other pathologic discharges into unrecognizable forms and can cause muscle artifact to resemble spikes. Production of a record with lost or inaccurate information is poor medical practice.

 

It must be emphasized, however, that judicious use of the low- or high-frequency filters—with appropriate annotation on the record—can emphasize or clarify certain types of patterns in the record. These filter controls, therefore, should be used selectively and carefully.

 

3.6 The 60-Hz (notch) filter can distort or attenuate spikes; it therefore should be used only when other measures against 60 Hz interference fail.

 

3.7 A paper speed of 3 cm/s, or digital display of 10 seconds/page, should be utilized for routine recordings. A paper speed of 1.5 cm/s, or 20 seconds/page, is sometimes used for EEG recordings in newborns or in other special situations.

 

3.8 When instrument settings (sensitivities, filters, paper speed, montage) are changed during the recording, the settings should be clearly identified on the record at the time of the change. If technologically feasible, the final calibration(s) should include each sensitivity and filter settings used in the recording, and should include calibration voltages appropriate to the sensitivities actually used. It is especially important to record calibration signals at very high sensitivities when these settings have been used. With some digital systems, a gain factor display may be the only available assessment for function of the analog system. More comprehensive calibrations, such as those described above, are encouraged.

 

3.9 The baseline record should contain at least 20 min of technically satisfactory recording. Longer recordings are often more informative. Although the possibility of reformatting digital EEG allows the entire recording to be performed in a single montage, this is not acceptable practice. Observing only one montage may prevent recognition of poor connections in electrodes that happen not to be included, and also prevent appreciation of subtle abnormalities that require special technical maneuvers (such as placement of additional electrodes.)

 

The EEG is a short sample in time from the patient’s life. Within reasonable limits, the longer the recording, the better the chance of recording an abnormality or abnormalities demonstrating the variability of these. Experience in many centers shows that a very minimum of 20 min of artifact-free recording is necessary to assess baseline waking EEG activity. The addition of photic stimulation, hyperventilation, and especially sleep—which should be recorded whenever possible—often requires an increase of recording time.

 

3.10 The recordings should include periods when the eyes are open and when they are closed.

 

Proper EEG recordings requires examining the effect of stimuli upon the EEG. A comparison between the eyes-open and eyes-closed condition constitutes one important means for assessment. Some rhythms can be masked by the alpha activity and are visible only when the alpha rhythm has been attenuated by eye-opening. Certain forms of eye movement may appear to be frontal delta or theta activity but eye-opening and closing helps in differentiation. Finally, paroxysmal activity may appear only when the eyes are opened or only when the eyes are closed or at the times these conditions change. Thus, failure to record with eye-opening and closing as a routine procedure can reduce chances of obtaining potentially important information. This procedure is so simple that it is unjustifiable not to request eye-opening and closure whenever patient cooperation per-mits, or to manually open and close the eyes when it does not.

 

3.11 Hyperventilation should be used routinely unless medical or other justifiable reasons (e.g., a recent intracranial hemorrhage, significant cardiopulmonary disease, sickle cell disease or trait, or patient inability or unwillingness to cooperate) contraindi-cate it. It should be performed for a minimum of 3 min with continued recording for at least 1 min after cessation of overbreathing. At times, hyperventilation must be performed for a longer period in order to obtain adequate activation of the EEG. To evaluate the effects of this activation technique, at least 1 min of recording with the same montage should be obtained before overbreathing begins. The record should contain an assessment of the quality of patient effort during hyperventilation. It is often helpful to record electrocardiographic (ECG) activity directly on one EEG channel during this and other parts of the recording, particularly if spikes and sharp waves, or pulse or ECG artifact, are in question. With an additional (e.g., 17th) channel, the ECG can be monitored continuously.

 

3.12 Sleep recordings should be taken whenever possible but not to the exclusion of the waking record.

 

It is increasingly evident that considerable additional information can be obtained by recording during drowsiness and sleep. Some laboratories use sleep recording routinely. Sleep recording is usually essential for patients with suspected or known convulsive disorders.

 

3.13 The patient’s level of consciousness (awake, drowsy, sleeping, or comatose), and any change thereof, should be noted by the technologist on the EEG recording. Any commands or signals to the patient, and any movement or clinical seizure activity or absence thereof, should also be noted on the recording. Careful observation of the patient with frequent notations is often essential, particularly when unusual waveforms are observed in the tracing. Abbreviations used should be standardized, with their definitions readily available to the reader.

 

In stuporous or comatose patients and those showing invariant EEG patterns of any kind, visual, auditory, and somatosensory stimuli should be applied systematically during recording. The stimuli and the patient’s responses or failure to respond should be noted on the recording paper as near as possible to their point of the occurrence.

 

It is the responsibility of the electroencephalographer to recognize the patterns usually associated with different states of consciousness. However, observations by the technologist about the patient’s clinical status can be of considerable interpretative value, particularly when discrepancies or unusual correlations occur.

 

To facilitate assessing awake background activity, it is important for the technologist to ascertain that the patient is maximally alert for at least a portion of the record.

 

3.14 Special procedures that are of some risk to the patient should be carried out only in the presence of a qualified physician, only in an environment with adequate resuscitating equipment, and with the informed consent of the patient or responsible relative or legal guardian.

 

3.15 EEGs for the evaluation of cessation of cerebral function (“cerebral death”) require special procedures and extraordinary precautions (see Guideline 3: Minimum Technical Standards for EEG Recording in Suspected Cerebral Death).