I. Prerequisites
(A) Clarify the cause of coma
Primary brain injury includes craniocerebral trauma, cerebrovascular disease, etc.; secondary brain injury mainly refers to hypoxic encephalopathy, such as cardiac arrest, drowning, asphyxia, etc. The cause of coma is not clear can not be implemented to determine brain death.
(II) Exclude reversible coma of various causes
Such as acute poisoning (carbon monoxide, sedative sleeping drugs, narcotics, psychotropic drugs, muscle relaxants, etc.), hypothermia (anal temperature ≤ 32℃), serious electrolyte and acid-base balance disorders, metabolic and endocrine disorders (such as hepatic encephalopathy, uremic encephalopathy, non-ketotic hyperglycemic hyperosmolar coma), etc.
Second, clinical determination
(A) Deep coma
1. Examination method and determination of results
Use the thumb to strongly compress the supraorbital notch or pin the face on both sides of the patient respectively, there should not be any facial muscle activity.
Use Glasgow Coma Scale (GCS) to determine the coma score of 3.
2. Precautions
(1) Any stimulation must be confined to the head and face.
(2) Spinal reflexes can be elicited during stimulation below the neck. The spinal cord below the foramen magnum may survive brain death and still have spinal reflexes and spinal automatic reflexes. Spinal cord reflexes include various deep reflexes and pathological reflexes. Most of the spinal automatic reflexes are related to the site of stimulation. Stimulation of the neck can cause head rotation; stimulation of the upper limbs can cause upper limbs to flex, extend, lift, rotate forward and rotate backward; stimulation of the abdomen can cause abdominal wall muscle contraction; stimulation of the lower limbs can cause lower limbs to flex and extend; involuntary limb movements can occasionally occur during the autonomic respiratory excitation test.
(3) Spinal automatic reflexes must be distinguished from spontaneous movements, which usually occur in the absence of stimulation and are mostly one-sided, while spinal automatic reflexes appear fixed at the site related to a specific stimulus.
(2) Loss of brainstem reflexes
1. Pupil-to-light reflex
(1) Examination method
Irradiate the pupil with a bright light and observe whether there is a constricted pupil response. Irradiate one side of the pupil with light from the side and observe whether the pupil on the same side shrinks (direct-to-light reflex), check one side and then the other. Shine light on one pupil and observe the pupil on the opposite side for constriction (indirect reflex to light), check one side and then the other. These tests should be repeated.
(2) Determination of results
The pupil’s reflex to light is judged to have disappeared if there is no pupillary constriction on the opposite side, both directly and indirectly.
(3) Precautions
Most brain-dead patients have dilated pupils (>4 mm) bilaterally, but a few pupils may be narrowed or unequal in size. Therefore, pupil size should not be used as a necessary condition for determining brain death.
②Ocular trauma can affect the observation of light reflex.
2. Corneal reflex
(1) Inspection method
Lift the upper eyelid on one side to expose the cornea, touch the peripheral part of the cornea with a cotton wool, and observe whether there is a bilateral blinking movement. Do the same for both sides.
(2) Determination of results
The corneal reflex can only be judged to be absent if there is no blinking movement on both sides.
(3) Precautions
(1) Even if there is no clear blink, but there is a weak contraction of the upper and lower eyelids and periocular muscles, it cannot be judged as a loss of corneal reflex.
(2) Bleeding from eye trauma, bulbar conjunctival edema, peripheral facial nerve palsy or trigeminal nerve damage can affect the judgment of corneal reflex.
3.Head-eye reflex
(1) Examination method
Hold the head up with your hand, hold the eyelids open, turn the head quickly from one side to the other and observe whether the eye turns in the opposite direction, and check the opposite side after checking one side.
(2) Determination of results
When the head is turned to the left or to the right, the eyeballs are fixed and there is no movement in the opposite direction, the head-eye reflex is judged to be absent (except for those with extraocular muscle paralysis).
(3) Precautions
This test is prohibited when there is trauma to the cervical spine to avoid damage to the spinal cord.
4.Vestibulo-ocular reflex (temperature test)
(1)Examination method
Raise the head 30 degrees, and use a curved disk close to the external auditory canal for irrigation outflow. Use a syringe to draw 20ml of ice water at 0~4℃ and inject it into the external auditory canal on one side for 20~30 seconds, while holding up the eyelids on both sides and observing whether there is nystagmus. After completing the examination on one side, test the other side in the same way.
(2) Result determination
If there is no nystagmus, the vestibulo-ocular reflex disappears.
(3) Precautions
(1) Before the test, the tympanic membrane on both sides must be checked for damage with an otoscope. If there is a blood clot or blockage in the external auditory canal, treat it and then perform the test.
②Even if there is no obvious nystagmus, but there is weak eye movement, it cannot be judged that the vestibulo-ocular reflex is gone.
③Ocular hemorrhage and edema caused by head and facial trauma can affect the observation of ocular activity.
④This test method is different from the temperature test used in otorhinolaryngology, which alternately stimulates with cold water at 20℃ or hot and cold water at body temperature ±7℃, and cannot be used for the determination of brain death.
5.Cough reflex
(1) Examination method
Stimulate the tracheal mucosa with a suction tube longer than the length of the artificial airway to cause a cough reflex.
(2) Judgment of results
If there is no coughing movement by stimulating the tracheal mucosa, the cough reflex is judged to have disappeared.
(3) Precautions
If there are chest and abdominal movements during stimulation, the cough reflex should be considered to exist.
(3) Absence of spontaneous respiration
All brain dead people have no voluntary breathing and must rely on ventilator to maintain ventilation. However, to determine the cessation of voluntary breathing, in addition to observing the presence or absence of respiratory movements in the chest and abdomen according to visual judgment, it must also be determined by the voluntary respiratory excitation test and must be performed in strict accordance with the following steps and methods.
1.Prerequisites
Autonomic respiratory excitation test must meet the following conditions.
(1) anal temperature ≥ 36.5 ℃ (such as hypothermia, can be warmed).
(2) systolic blood pressure ≥ 90 mmHg or mean arterial pressure ≥ 60 mmHg (if blood pressure is falling, available drugs to raise pressure).
(3) Arterial partial pressure of carbon dioxide (PaCO2) 35~45 mmHg.
(4) arterial partial pressure of oxygen (PaO2) ≥ 200 mmHg (when insufficient, should be sucked 100% O210 ~ 15 minutes).
2, test methods and procedures
(1) 8 minutes off the ventilator.
(2) The oxygen catheter must be inserted through the tracheal cannula to the level of the rongeur and input 100% O26L/min.
(3) Closely observe the abdomen and chest for respiratory movements.
(4)Measure PaCO2 at 8 minutes.
3.Result determination
If PaCO2≥60 mmHg or PaCO2 exceeds the original level by 20 mmHg in patients with chronic carbon dioxide retention and there is still no respiratory movement, it can be determined that there is no spontaneous breathing.
4.Caution
If cyanosis, oxygen saturation ≤ 90%, hypotension, arrhythmia or other dangers occur during the spontaneous respiratory excitation test, the test should be terminated immediately.
III. Laboratory tests
(A) Electroencephalogram (EEG)
1.Environmental conditions
(1) Use independent power supply with resistance to ground <4Ω, with voltage regulator if necessary.
(2) If necessary, suspend the use of other medical instruments that may interfere with the EEG instrument during EEG tracing.
2.EEG instrument parameter setting
(1) Place electrodes according to the international 10~20 system, only 8 recording electrodes (frontal Fp1, Fp2; central C3, C4; occipital O1, O2; middle temporal T3, T4). The grounding electrode was in the frontal midline (Fz).
(2) The distance between electrodes should not be <10 cm.
(3) Degrease with acetone or 75% alcohol before placing electrodes.
(4) Fix the electrode on the marked electrode position on the scalp with disc electrode or needle electrode.
(5)The impedance between electrodes scalp 0.1~10KΩ, the impedance of each electrode on both sides should be matched basically.
(6) High frequency filtering 75Hz; time constant 0.3 seconds.
(7) Sensitivity 2μV/mm.
(8) Bilateral earlobes or bilateral mastoids as reference electrodes.
3.EEG tracing
(1)Do 10 seconds instrument calibration before tracing, input 10μV square wave into each amplifier, and observe whether the sensitivity of 8 channels amplifier is consistent.
(2) Trace the reference leads for 30 minutes.
(3) During the tracing, both upper extremities were stimulated with pain and bright light was shone on both pupils respectively to observe any changes in EEG.
(4) Any changes in the patient’s condition during the tracing and any manipulation of the patient (pain stimulation, bright light stimulation of the pupils, etc.) should be recorded in real time.
(5) The electrocardiogram should be recorded at the same time.
(6) All information recorded at 30 minutes must be kept intact.
(7) Repeat 1 time in 12 hours under the same conditions.
4.Result judgment
EEG is flat and no brain wave activity >2μV, i.e., electroencephalographic rest.
(II) Transcranial Doppler ultrasound (TCD)
1.Environmental conditions
No special requirements.
2.Probe
2MHz pulsed wave Doppler ultrasound probe.
3.Parameter setting
(1) Gain adjustment. Adjust the intensity of the gain according to the clarity of the spectrum display.
(2) Doppler frequency filtering. Set to low filter state, not higher than 50 Hz.
4.Checking site and blood vessels
(1) Temporal window. Bilateral middle cerebral artery (MCA), anterior cerebral artery (ACA) and posterior cerebral artery (PCA) are detected in the area of the horizontal line between the arch of the eyebrow and above the ear margin.
(2) Occipital window or parieto-occipital window. The vertebral artery (VA) and basilar artery (BA) are detected in the foramen magnum or parietal foramen magnum below the occipital ridge.
5. Identification of vessels
(1)MCA via temporal window, depth 40~65mm, systolic flow direction towards the probe, confirm the detected vessels by common carotid artery compression test if necessary; or via contralateral eye window, depth 70mm or more, systolic flow direction back from the probe.
(2)ACA1 via temporal window, depth 55~75mm, systolic flow direction is away from the probe; or via contralateral eye window, depth 70mm or more, systolic flow direction is towards the probe.
(3) PCA via temporal window, depth 55~70mm, systolic flow direction of P1 segment facing the probe; systolic flow direction of P2 segment is away from the probe.
(4)VA via occipital or parieto-occipital window, depth 55~80mm, systolic flow direction is backward to the probe.
(5) BA via occipital window or parietal occipital window, depth 90~120mm, systolic blood flow direction away from the probe.
6.Results determination
(1)Blood flow spectrum
①Shock wave Systolic forward (F) and diastolic reverse (R) flow signals in one cardiac cycle, direction of flowing index (DFI) ≤ 0.8, DFI=1-R/F
② small systolic wave (spike wave) unidirectional positive flow signal in early systole, duration less than 200ms, flow velocity less than 50cm/s.
③The blood flow signal disappears.
(2) Determination of vessels
①The anterior circulation is mainly determined by bilateral MCA.
②The BA is the main vessel in the posterior circulation.
(3) Determination of results
If one of the above-mentioned blood flow spectral phenomena occurs in both the anterior and posterior cranial circulation, it can be judged as positive.
7.Cautions
(1) If no clear or completely undetectable blood flow signal is detected through the temporal window, artifacts caused by poor temporal window or operating techniques must be excluded. When testing patients, the temporal and occipital windows should be tested simultaneously, and the depth of the temporal window vessel detection should be adjusted appropriately according to the size of the patient’s biparietal diameter.
(2) In the case of poor transillumination of the temporal window, the segments of the ipsilateral internal carotid artery siphon, the contralateral MCA and ACA1 are detected on the closed eyelid.
(3) Repeated testing (at intervals of not less than 2 hours) all detected one of the above spectral phenomenon changes.
(4) Certain factors, such as ventricular drainage, craniotomy decompression and peripheral artery systolic pressure <90 mmHg, may affect the determination of the results.
(C) Short latency somatosensory evoked potential (SLSEP) of median nerve
1.Environmental conditions: same as electroencephalography (EEG)
2.Basic requirements of evoked potential instrumentation.
(1) Amplifier
①Low noise 0.5~0.6μV r.m.s
② sensitivity 0.5~2μV/mm
③Input resistance ≥ 100MΩ
④Common mode rejection ≥100dB
⑤ gain 120dB
(2) signal averager: digital-to-analog converter (ADC) 16-bit (16bit), sampling interval (dwell time) 0.2ms.
3.Stimulation techniques
(1) Stimulation site 2 cm above the midpoint of the transverse wrist on the median nerve path
(2) Reduce the impedance between the stimulating electrode and the skin (degrease with 75% alcohol)
(3) Split-lateral stimulation
(4)Stimulation parameters
①Stimulation square wave time range: 0.1~0.2ms, up to 0.5ms if necessary (pay attention to prevent burns);
②Stimulation intensity: the intensity index is about 1cm of thumb flexion, and the intensity index should be consistent during each test;
③Stimulation frequency: 1~5Hz;
4, recording technology
(1) Number of channels There should be at least 4 channels
(2) electrodes Usually use disk electrodes, if necessary, also available needle electrodes
(3)Electrode placement Refer to EEG International 10~20 system, electrode parts are as follows.
①C3, and C4, respectively, are 2 cm after C3 and C4 of the international 10-20 system, and C3, or C4, is called Cc, when stimulating the opposite side, and Ci, when stimulating the same side,
②Fz (same as EEG)
③C6S that Cv6 is located in the spine of the cervical vertebra 6, C2S is located in the spine of the cervical vertebra 2
④CLi and CLc are 1 cm above the ipsilateral or contralateral midclavicular point, respectively
(4) Electrode lead combinations.
First channel: CLi-CLc (N9)
Second channel: C6S-CLc (N13)
Third channel: Cc,-Fz or FPz (N20)
Fourth channel: Ci,-C2S or Fz-C2S (N18)
(5) each electrode impedance: record, reference electrode impedance ≤ 5KΩ
(6) the placement of the ground and impedance 5 cm above the stimulation point, impedance ≤ 7KΩ
(7) analysis time 50ms, 100ms if necessary
(8) bandpass 10Hz~2000Hz
(9)Average number of times 1000~4000 times
(10) observe repeatability Each side at least 2 ~ 3 times to test the average value of the measured value
5.Result judgment
(1)N9 and (or) N13 exist
(2)N20 disappeared
(3) P14 and N18 disappeared
If the above three points are met, it can be judged as positive.
6. Precautions.
Keep the patient’s skin temperature of the tested limb normal, and raise the temperature if necessary.
IV. Precautions
1, in the brainstem reflex examination, all five reflexes disappear, the brainstem reflex can be judged to disappear; if one to two of the five reflexes cannot be examined, another laboratory test should be added.
2.When there is trigeminal neuropathy or peripheral facial nerve palsy, brain death should not be judged lightly.
3, Brain dead people should not have decerebrate tonicity, decortical tonicity or spasticity.
4.Brain death should be strictly differentiated from the vegetative state.