Delirium is characterized by a severe degree of confusion with disorientation to time, place, and/or person. The patient may be restless and hyperkinetic with psychic symptoms including incoherence, hallucinations, and delusion.
Confusion is a state in which there is a mild reduction in the level of consciousness. The patient with a defect in attention span reacts normally to ordinary stimulation but is disoriented to time, place, and/or person.
Lethargy or hypersomnia is a severe degree of drowsiness in which the patient can be awakened with ordinary stimulation but may fall back to sleep as soon as the stimulus is removed.
Stupor or semicoma is a state of partial loss of response in which the patient can be temporarily aroused with vigorous stimulation but lapses into an unresponsive state when not stimulated.
Coma is defined as a state of complete or almost complete loss of consciousness from which the patient cannot be aroused, even by powerful stimuli.
Background slowing without accompanying theta or delta slow waves (Fig. 11-1)
Diffuse theta and delta activity associated with normal background activity (Fig. 11-2)
Slow background activity along with diffuse theta and delta activity (Fig. 11-3)
FIGURE 11-1 | An example of slight slowing of waking background activity (7 to 8 Hz) without significant increase of delta-theta slow waves. This is grade IA abnormality.
FIGURE 11-2 | An example of excessive irregular diffuse delta slow waves associated with normal 9- to 10-Hz alpha rhythm. This is grade IIA abnormality.
FIGURE 11-3 | An example of slow background activity (5 to 7 Hz) associated with diffuse delta-theta slow waves. This is grade IIB abnormality.
FIGURE 11-4 | A: Grade IA with slight slowing of background activity (7 to 8 Hz) without significant delta-theta slow waves. B: Grade IB with moderate slowing of background activity (6 to 7 Hz) without significant delta-theta slow waves.
FIGURE 11-5 | A: Grade IIA with background activity of mostly alpha rhythm associated with interspersed theta-delta slow waves. B: Grade IIB with background activity of 5 to 6 Hz associated with mixture of theta-delta slow waves.
FIGURE 11-6 | A: Grade IIIA with irregular delta slow waves, associated with a fair amount of alpha background activity. B: Grade IIIB with irregular delta slow waves, associated with slow background activity consisting of 5- to 7-Hz theta activity.
FIGURE 11-7 | A: Grade IVA with high-amplitude prominent, irregular delta slow waves with minimal alpha or theta background activity. B: Grade IVB low-amplitude irregular delta slow waves with minimal or no alpha or theta background activity.
FIGURE 11-8 | A: Grade VA EEG represents burst suppression pattern with burst duration of 1 to 2 seconds and suppression period of 0.5 to 1 seconds. B: Grade VB EEG with prolonged suppression period of more than 5 seconds and short burst duration.
a mild to moderate impairment of consciousness but may also be seen in fully awake patients. Some triphasic discharges secondary to encephalopathy are difficult to differentiate from nonconvulsive status epilepticus (see Figs. 8-17 and 10-33B; see also Fig. 13-1B and C).
FIGURE 11-12 | A 49-year-old patient with chronic uremic encephalopathy. EEG shows slow background activity consisting of 4- to 6-Hz theta background activity and irregular delta slow waves. Note intermittent triphasic waves (shown by circles) that were less stereotypical and less rhythmic as compared to those seen in hepatic encephalopathy (see Fig. 11-11).
FIGURE 11-13 | A 52-year-old comatose patient after anoxic cerebral injury. EEG showed diffuse and bianterior dominant 10- to 11-Hz alpha activity, representing alpha-coma pattern. Some underlying delta slow waves are also seen.
FIGURE 11-14 | A 65-year-old male with postanoxic cerebral insult after cardiac arrest. The first EEG at 8 hours after cardiac arrest showed intermittent diffuse low-voltage theta interrupted by some brief suppression periods (A). EEG then showed progressively faster frequency (B) and background activity reaching alpha frequency, that is, alpha-coma state (C and D), which seemingly was improving from the earlier EEG despite Glasgow Coma state remained the same.6 EEG then changed to the low-voltage pattern when Glasgow Come Scale changed from 6 to 3 (D). The patient expired several hours after this EEG.
FIGURE 11-15 | A 45-year-old comatose patient following a cardiac arrest. Diffuse theta activity, representing theta-coma pattern.
A full set of scalp electrodes should be utilized: the electrodes should include Fz, Cz, and Pz. Additionally, a ground electrode is required, though double grounding should be avoided.
Interelectrode impedance should be under 10,000 Ω but over 100 Ω: extremely high- and extremely low-electrode impedance attenuates the potential. Extreme low impedance (<100 Ω) suggests shorting (electrodes “salt bridge”) of two electrodes.
The integrity of the entire recording system should be tested: this can be accomplished by observing artifacts introduced by touching each electrode.
Interelectrode distance should be at least 10 cm: this is to avoid a cancellation effect of short interelectrode distance, especially when dealing with extremely lowamplitude activity. Double interelectrode distances compared to routine electrode placement, for example, Fp1 to C3 (instead of Fp1-F3) are commonly used. The longest interelectrodes (Fp1-O2 or Fp2-O1) may also be included.
Sensitivity must be increased from 7 µV/mm to at least 2 µV/mm for at least 30 minutes of the recording, with inclusion of appropriate calibration. This is necessary to delineate low-voltage activity (Fig. 11-9C and D). A calibration signal of 10 to 20 µV is appropriate for a sensitivity of 2 µV/mm.
Filter setting should be appropriate for assessment of ECS: the high filter (low-pass filter) should not be below 30 Hz and the low filter (high-pass filter) should not be higher than 1 Hz. The use of the 60-Hz notch filter is allowed if necessary. One may include a low filter (highpass filter) setting of 0.3 Hz for part of the recording to enhance slow waves, but that filter is not required.
Additional monitoring techniques should be employed when necessary to clarify the record: this include EKG and respiration monitoring. Additional electrodes placed over the dorsum of the hand may help to monitor
environmental electrical artifacts. If excessive EMG (muscle tone) artifacts interfere with a reliable interpretation of the EEG, the use of a short-acting muscle relaxant is allowed.
There should be no EEG reactivity to intense somatosensory, auditory, or visual stimuli: this can be accomplished by calling the patient’s name, pinching the nail bed, and/or delivering photic stimulation. Photic stimulation may elicit ERG (electroretinogram) at Fp1 or Fp2 but should not yield photic evoked response or driving response at occipital electrodes.
Recording should be made only by a qualified technologist: because ECI is recorded in an “electrically hostile” ICU setting where many electrical and mechanical pieces of equipment are attached to the patient, the EEG is often contaminated by a variety of artifacts. This is further aggravated by the increased sensitivity (gain) required for ECS determination. Identifying and eliminating artifacts that interfere with the accurate interpretation depends on the skill, knowledge, and experience of the technologist (R. EEG T.) and also of the interpreting EEGer (Electroencephalographer or clinical neurophysiologist).
A repeat EEG should be performed when ECI is in doubt. Before 1980, repeating the EEG 24 h after the first ECS recording was mandatory in order to determine brain death. However, accumulated evidence indicates that no patients survived for more than a short period after one EEG showed ECI.35 Therefore, a repeat EEG is no longer required for adult patients. Although this can apply to term neonates and children, an EEG cannot substitute for a neurological examination in brain death evaluation. If there is any doubt, question, or uncertainty from either a technical or clinical perspective, the EEG should be repeated after an interval, for example, of 6 hours.
Physiological variables and medication should be documented. This is because severe hypothermia, low blood pressure, or low oxygen saturation can cause cerebral inactivity or severe suppression EEG activity, which may be reversible by correcting these variables. Also, it is important to record all medications, especially sedative or anesthetic drugs such as barbiturates, benzodiazepine, propofol, or narcotics.
TABLE 11-1 Slowing and/or Paroxysmal Discharge in Different Cerebral Disorders