POVZETEK

Možganska smrt je ireverzibilna izguba možganskih funkcij, vključno s funkcijo možganskega debla. Diagnoza možganske smrti dovoljuje darovanje organov ali opustitev podpore življenjskih funkcij, za kar so dodatno potrebna natančna merila za diagnozo možganske smrti. Po hrvaških predpisih o presaditvi organov morajo ponovljeni testi možganske smrti pokazati izgubo refleksov možganskega debla, poleg tega pa mora biti smrt dokazana tudi z enim od dodatnih testov. Danes uporabljamo različne dodatne teste za diagnozo možganske smrti, ki izkažejo prenehanje delovanja možganov ali možganskega debla, oziroma potrdijo cirkulacijsko odpoved. Obpostelnjo testiranje možganske smrti omogočajo elektroencefalografija (EEG) in nevrosonološki testi. Običajno ali digitalno subtrakcijsko angiografijo je treba izvajati v radioloških laboratorijih, izotopno angiografijo s tehnecijevim 99m heksametilpropileneaminovim oksimom (^99mTc-HMPAO) pa na oddelkih nuklearne medicine. Teste mora opraviti izurjeno medicinsko osebje ob doslednem upoštevanju protokolov, ki se razlikujejo od rutinskih preiskav. V članku predstavljamo teste za potrditev možganske smrti, tehnike, kriterije in razlago rezultatov, ki jih uporabljamo na Hrvaškem.

Ključne besede: diagnoza možganske smrti, Hrvaške smernice, ultrasonografija, zakonodaja in sodna praksa o možganski smrti

SUMMARY

Brain death is the irreversible loss of all brain functions, including functions of the brainstem. The diagnosis of brain death allows organ donation or withdrawal of support, which additionaly supports the need for following exact criteria in diagnosing brain death. In the Croatian Act on Transplantation, repeated neurologic examination must show loss of brainstem reflexes, and one confirmation test must be done. Several tests are available, showing the cessation of brain or brainstem activity, or confirming the cerebral circulatory arrest. Bedside evaluation is possible through electroencephysiologic and neurosonologic tests. Conventional or digital subtraction angiography is done in radiology suite, and isotope angiography and technetium 99m hexamethylpropyleneamine oxime (^99mTc-HMPAO) at the Department of Nuclear Medicine. All tests require trained personel and strict protocols, which differ from routine investigations. Here, we present an outline of confirmatory tests used in Croatia for brain death confirmation, techniques, criteria, results interpretation.

Key words: brain death diagnosis, Croatian Guidelines, brain death legislation and jurisprudence, ultrasonography

INTRODUCTION

Brain death in a normothermic, nondrug comatose patient with a known irreversible massive brain lesion and no contributing metabolic or hormonal derangement, is declared when brainstem reflexes, motor responses and respiratory drive are absent. The first observation was documented in 1959 by Mollaret and Goulon (1). The use of mechanical ventilation and intensive care unit setting have prevented respiratory arrest and transformed the course of terminal neurologic disorder. Vital functions could since then be maintained artificially after the brain has ceased to function. The definition using neurologic criteria became formalized after a report of the Harvard Medical School Ad Hoc Committee in 1968 (2). The definition of irreversible coma or brain death was defined as unresponsiveness and lack of receptivity, the absence of movement and breathing, the absence of brainstem reflexes, and coma, the cause of which was identified. Over years, the Committee has been a target of criticism.

In 1971, Mohandas and Chou (3) described damage to the brainstem as a critical component of severe brain damage.

A STATEMENT ON THE DIAGNOSIS OF BRAIN DEATH

The Conference of the Medical Royal Colleges and their faculties in the United Kingdom published a statement on the diagnosis of brain death in 1976 (4). Brain death was defined as complete, irreversible loss of brainstem function. This statement provided guidelines that included a refinement of apnea testing and pointed to the brainstem as the center of brain function, with no life existing without its function. In 1981, the President’s Commission for the Study of Ethical Problems in Medicine and Biomedical and Behavioral Research published its guidelines (5). This document recommended the use of confirmatory tests to shorten the duration of the required observational period and recommended a period of 24 hours for patients with anoxic damage. It ruled out shock as a requirement for determination of brain death.

In 1995, brain death was selected as a topic for practice parameters (6) because of the perceived need of standardized clinical examination criteria for the diagnosis of brain death in adults, large differences in practice in performing the apnea test, and controversies over appropriate utilization of confirmatory tests.

The Committee defined practice parameters that should serve as guidelines in the management of patients with brain death (7). For the first time brain death patients were separated from persisting vegetative state. With this document (7), diagnostic criteria for the clinical diagnosis of brain death were defined, as well as pitfalls in its diagnosis and clinical observations compatible with the diagnosis of brain death. A practical description of apnea testing was addressed. Optional confirmatory laboratory tests and standard medical record documentation were listed. Despite such definition, the criteria varied between countries.

A survey on brain death criteria (8) throughout the world revealed uniform agreement on the neurologic examination with the exception of apnea test. Major differences between countries were related to the presence of legal standards on organ transplantation, presence of practice guidelines for brain death in adults, number of physicians required to declare brain death, observational period, or presence of required expertise of examining physicians. Only 28 of 70 (40 %) national practice guidelines require confirmatory testing.

CLINICAL NEUROLOGIC EXAMINATION

In Croatian legislature (9–12), clinical neurologic examination remains the standard for the determination of brain death. Clinical examination of patients who are presumed to be brain dead must be performed with precision (7, 13). To declare brain death requires not only a series of careful neurologic tests but also the establishement of the cause of coma, the ascertainment of irreversibility, the resolution of any misleading clinical neurologic signs, the recognition of possible confounding factors, the interpretation of the findings on neuroimaging, and the performance of one confirmatory laboratory test are mandatory. At least two physicians are involved in the clinical diagnosis, one should be anesthesiologist and the other anesthesiologist, neurologist or neurosurgeon. The observational period is at least 6 hours, and in anoxic brain damage 24 hours or 48 hours in children.

Before clinical examination in brain death determination, clinical conditions that may confound clinical assessment must be ruled out. These include severe acid-base or endocrine disturbances, hypothermia defined as core temperature of 32 °C or lower, and according to Croatian legislature 35 °C or lower (9), hypotension (systolic blood pressure < 90 mm Hg), drug or alcohol intoxication, poisoning or neuromuscular blocking agents.

Neuroimaging must show evidence of an acute central nervous system (CNS) catastrophe that is compatible with the clinical diagnosis of brain death. Usually, computed tomography (CT) scanning documents a mass or massive hemorrhage with brain herniation, multiple hemispheric lesions with edema, or edema alone. The confounders must be carefully searched for. The CT scan can be normal in the early period after cardiorespiratory arrest and in patients with fulminant meningitis or encephalitis. Examination of the cerebrospinal fluid should reveal diagnostic findings in circumstances of CNS infection.

Complete clinical neurologic examination includes documentation of coma, absence of brainstem reflexes, and apnea test (6, 7) (Table 1). As brain death occurs, patients lose their reflexes in a rostral to caudal direction. Therefore, the cessation of medulla oblongata reflexes occurs last. The brainstem destruction may last for hours to be complete, and during that period medullary functions are present (14), so normal blood pressure is obtained as well as cough response after tracheal suctioning and tachycardia after the administration of 1 mg of atropine.

The depth of coma is assessed by documentation of the presence or absence of motor responses to a standardized painful stimulus such as nail-bed pressure or pressing on the supraorbital nerve or temporomandibular joint (Table 2). Motor response known as Lazarus sign (15) may occur spontaneously during apnea testing, often during hypoxic or hypotensive episodes, and is of spinal origin. Neuromuscular blocking agents can produce prolonged weakness. If neuromuscular blocking agents have recently been administered, examination with a bedside peripheral nerve stimulator is needed.

Table 2. Diagnostic procedure for clinical diagnosis of brain death

• A.Diagnostic criteria for clinical diagnosis of brain death
  Prerequisites. Brain death is the absence of clinical brain function when the proximate cause is known and demonstrably irreversible:
  • 1.presence of clinical or neuroimaging evidence of an acute central nervous system catastrophe that is compatible with the clinical diagnosis of brain death
  • 2.exclusion of complicating medical conditions that may confound clinical assessment (no severe electrolyte, acid-base or endocrine disturbance)
  • 3.no drug intoxication or poisoning
  • 4.core temperature > 32 °C
• B.Clinical findings
  • 1)coma or unresponsiveness: absent motor response to pain in all extremities (nail-bed pressure and supraorbital pressure)
  • 2)absence of brainstem reflexes
    • a)Pupils:
      • i.midposition (4 mm) to dilated (9 mm)
      • ii.no response to bright light
    • b)Ocular movement:
      • i.no oculocephalic reflex (testing only when no fracture or instability of the cervical spine is apparent)
      • ii.no deviation of the eyes to irrigation in each ear with 50 ml of cold water (allow 1 minute after injection and at least 5 minutes between testing on each side)
    • c)Facial sensation and facial motor response:
      • i.no corneal reflex to touch with a throat swab
      • ii.no jaw reflex
      • iii.no grimacing to deep pressure on nail bed, supraorbital ridge or temporomandibular joint
    • d)Pharyngeal and tracheal reflexes:
      • i.no response after stimulation of the posterior pharynx with tongue blade
      • ii.no cough response to bronchial suctioning
  • 3)Apnea testing performed as follows
    • a)Prerequisites:
      • i.Core temperature > 36 °C
      • ii.Systolic blood pressure > 90 mm Hg
      • iii.Euvolemia. Option: positive fluid balance in the previous 6 hours
      • iv.Normal PCO₂. Option: arterial PCO₂ > 40 mm Hg
      • v.Normal PO₂. Option: preoxygenation to obtain arterial PO₂ > 200 mm Hg
    • b)connect pulse oximeter and disconnect the ventilator
    • c)deliver 100 % O₂, 6 l/min, into the trachea. Option: place a cannula at the level of the carina
    • d)look closely for respiratory movements (abdominal or chest excursions that produce adequate tidal volumes)
    • e)measure arterial PO₂, PCO₂ and pH after approximately 8 minutes and reconnect the ventilator
    • f)if respiratory movements are absent and arterial PCO₂ is > 60 mm Hg (option: 20 mm Hg increase in PCO₂ over a baseline normal PCO₂), the apnea test result is positive (i.e. it supports the diagnosis of brain death)
    • g)if respiratory movements are observed, the apnea test result is negative (i.e. it does not support the clinical diagnosis of brain death), and the test should be repeated
    • h)connect the ventilator if, during testing, the systolic blood pressure becomes < 90 mm Hg or the pulse oximeter indicates significant oxygen desaturation and cardiac arrhythmias are present; immediately draw an arterial blood sample and analyze arterial blood gas. If PCO₂ is > 60 mm Hg or PCO₂ increase is > 20 mm Hg over baseline normal PCO₂, the apnea test result is positive (it supports the clinical diagnosis of brain death); if PCO₂ is < 60 mm Hg or PCO₂ increase is < 20 mm Hg over baseline normal PCO₂, the result is indeterminate
  • 4)Clinical conditions that may interfere with the clinical diagnosis of brain death, and the diagnosis cannot be made with certainty on clinical grounds alone
    • a)severe facial trauma
    • b)pre-existing pupillary abnormalities
    • c)toxic levels of any sedative drugs, aminoglycosides, tricyclic antidepressants, anticholinergics, antiepileptic drugs, chemotherapeutic agents or neuromuscular blocking agents
    • d)sleep apnea or severe pulmonary disease resulting in chronic retention of CO₂
  • 5)Confirmatory laboratory tests
    After repeat clinical evaluation of 6 hours or 24 hours after anoxic injury, the confirmatory test must be done. It should be emphasized that any of the suggested confirmatory tests may produce similar results in patients with catastrophic brain damage who do not (yet) fulfill the clinical criteria of brain death.
    • a)conventional or digital subtraction angiography: no intracerebral filling at the level of carotid bifurcation or circle of Willis, patent external carotid circulation
    • b)electroencephalography: electrical silence during at least 30 min of recording in 16-channel EEG instruments
    • c)transcranial Doppler ultrasonography: two times performed, recording reverberating flow pattern or one reverberating flow pattern followed by small systolic spikes, at least one arterial segment per window through three bone windows, documentation of similar flow patterns in both common and internal carotid and vertebral arteries extracranially
    • d)^99mTc-HMPAO: no uptake of isotope in brain parenchyma (“hollow skull phenomenon”)
    • e)isotope angiography with the injection of serum albumin labeled with technetium 99m is followed by bedside imaging with a portable gamma camera, and intracranial radioisotope activity is absent
    • f)evoked potentials: bilateral absence of N20-P22 response with median nerve stimulation in somatosensory evoked potential
    • g)CT or MRI absence of brain blood flow

Certain clinical observations are compatible with the diagnosis of brain death. Respiratory acidosis, hypoxia or brisk neck flexion may generate spinal cord responses (15–18). Spontaneous movements of the limbs from spinal mechanisms can occasionally occur and are more frequent in young adults. These spinal reflexes include rapid flexion in arms, raising of all limbs off the bed, grasping movements, spontaneous jerking of one leg, walking-like movements, and movements of the arms up to the point of reaching the endotracheal tube (15). Respiratory-like movements may also occur and are typical agonal breathing patterns. They are characterized by shoulder elevation and adduction, back arching and intercostal expansion without any significant tidal volume. Profuse sweating, blushing, tachycardia and sudden increases in blood pressure may be observed, but are compatible with the diagnosis of brain death (19). Such observations may be elicited by brain death testing or apnea testing. Normal blood pressure and absence of diabetes insipidus without pharmacologic support are also compatible with brain death. Muscle stretch reflexes, superficial abdominal reflexes and Babinski reflexes are of spinal origin and do not invalidate the diagnosis of brain death. Patients may have initial plantar flexion of the great toe followed by sequential brief plantar flexion of the second, third, fourth and fifth toes after snapping off one of the toes (“undulating toe flexion sign”) (17) (Table 3).

There are several neurologic states that can mimic brain death, so careful history should be taken and thorough examination should be performed, with relevant imaging procedures. Still, these states should be kept in mind. A locked-in syndrome (20), especially in early phase, hypothermia or drug intoxication may be misdiagnosed. The locked-in syndrome is usually a consequence of destruction of the base of the pons. The patient cannot move the limbs, grimace, or swallow, but the upper rostral mesencephalic structures involved in voluntary blinking and vertical eye movements remain intact. During the early phase patient may be comatose due to edema, and later is conscious because the tegmentum with the reticular formation is not affected. This condition is most often caused by an acute embolus to the basilar artery. Even more dramatic is the Guillain-Barre syndrome, which involves all the peripheral and cranial nerves (21). The progression usually occurs over a period of days, but may be fulminant developing in one day. The precise history should prevent this reversible disease. Accidental hypothermia from prolonged environmental exposure may mimic loss of brain function, and alcohol and drug intoxication and head injury are often major confounders (22). Hypothermia causes a downward spiral of loss of brainstem reflexes and pupillary dilatation. The response to light is lost at core temperatures of 28 °C to 32 °C, and brainstem reflexes disappear when the core temperature drops below 28 °C (22). These deficits are all potentially reversible.

The effects of many sedative and anesthetic agents can closely mimic brain death, but aspects of brainstem function, particularly the pupillary responses to light, remain intact. In large quantities ingested, many drugs can cause partial loss of brainstem reflexes. Formal determinations of brain death documenting conditions that are entirely similar to those caused by structural lesions are exceptional but have been reported in cases of intoxication with tricyclic antidepressants and barbiturates (23, 24). Even a more complex problem is the possible confounding of the clinical determination of brain death by metabolites or traces of circulating pharmaceutical agents. Screening test for drugs may be helpful but some toxins like cyanide, lithium or fentanyl may not be detected by routine screening tests (23). According to Croatian legislature (9), the clinical diagnosis of brain death should not be started before drugs like sedatives, anesthetics, narcotics, muscle relaxants, antiepileptics, or antidepressants are present. Alcohol should not be present in the blood. If the drug of poisoning is known but the substance cannot be quantified, the observation time for five elimination half-life of the substance would ensure its almost complete elimination.

THE CONFIRMATORY TESTS OF BRAIN DEATH

Brain death is a clinical diagnosis. According to Croatian legislature (9), repeat clinical evaluation after a 6-hour observational period, or after 24 hours in anoxic brain damage, is required. Also, according to Croatian legal provisions, a confirmatory test is mandatory for confirmation of brain death. The tests that are accepted are conventional angiography, electroencephalography, evoked potentials, transcranial Doppler sonography, isotope angiography, and technetium-99m hexamethylpropyleneamine oxime brain scan (^99mTc-HMPAO). After confirming the clinical diagnosis with one of the tests, the examined brain death person is declared dead.

Some of the tests are more convenient to use for technical reasons such as bedside evaluation of unstable brain death patients. Therefore, transcranial Doppler and electroencephalographic tests are preferable, although technical or patient contraindications may present a problem. Conventional or isotope angiography or ^99mTc-HMPAO brain scan require special settings that are not available in all hospitals, although they have little technical or patient contraindications. The application of contrast medium in angiography is potentially harmful for the residual organ functions, so noninvasive tests are preferred.

Transcranial Doppler sonography

Oscillating flow or systolic spikes are typical Doppler sonography flow signals found in the presence of cerebral circulatory arrest, which results in brain death (25). The Neurosonology Research Group (NSRG) of the World Federation of Neurology (WFN) has established a Task Force Group in order to evaluate the role of Doppler sonography as a confirmatory test for determining brain death, and has defined criteria and guidelines for the use of Doppler sonography in this setting (26).

Soon after Doppler sonography had been introduced for cerebrovascular evaluation, typical findings for cerebral circulatory arrest were described (27). The reliability of the method increased with the introduction of transcranial Doppler sonography (TCD) (28) and standardization of the insonating protocol (29). Extensive death of brain tissue causes extreme increase of intracranial pressure (ICP). When the ICP equals the diastolic arterial pressure, the brain is perfused only in the systole and with further increase of ICP over the systolic arterial pressure cerebral perfusion will cease (30). Due to elasticity of the arterial wall and the compliance of the vasculature distal to the recording site, such cerebral circulatory arrest is associated with Doppler evidence of oscillatory movement of blood in the large arteries at the base of the brain. However, the net forward flow volume is zero. With time the oscillations become low amplitude spectral spikes until no pulsations are detectable. This development correlates with a more proximal demonstration of the angiographic flow arrest (31). At the time of angiographic flow arrest at the internal carotid artery (ICA), Doppler sonography shows an oscillating flow pattern in the middle cerebral artery (MCA), because the contrast medium progresses slowly toward the brain. From the clinical experience in cardiac arrest, such cerebral ischemia of about 10–15 minutes in vivo at normal body temperature leads to irreversible total loss of brain function (32).

TCD actually evaluates blood flow velocities from basal cerebral arteries, depending on the systemic blood pressure (BP) and ICP. Figure 1 shows time course of flow velocities in MCA from normal condition up to cerebral circulatory arrest. The relation of ICP with BP is presented. With the increase of ICP, a higher pulsatility in basal cerebral arteries can be recorded, and with further increase of ICP over diastolic BP only forward flow persists in the systole. With further increase of ICP that equals systolic BP, reverberating flow with forward and reverse flow are nearly equal and cerebral perfusion ceases. Net flow is zero when the equality of both flow components is present and if the area under the envelope of the positive and negative deflection is the same. This finding correlates with the angiographic appearance of cerebral circulatory arrest (31). With further increase of ICP over systolic BP, only systolic spikes can be recorded, and the amplitude becomes ever lower. Such systolic spikes are a characteristic pattern for cerebral circulatory arrest, but may resemble high resistance pattern with reduction of diastolic flow, a phase before the developement of reverberating flow. Due to the usage of high pass filters for elimination of artifacts from wall movement, reverberating flow can be missed. Therefore, the filters must be set at lowest level, i.e. 50 Hz. With further reduction of blood movement, further reduction of amplitude is recorded until complete cessation of signals occurs. A failure to detect flow signals alone as the first finding may also result from ultrasonic transmission problems. In such cases, extracranial findings show typical hemodynamic spectra in common carotid arteries, ICAs and vertebral arteries (VA), representing an important criterion. At the same time, the flow in the external carotid arteries remains patent, with normal hemodynamic spectrum. The flow in the ICA can be influenced by flow through the ophthalmic artery, although the volume of the ophthalmic artery flow plays a minor portion of the ICA flow. According to the aforementioned findings, the Task Force Group of the NSRG WFN (26) has set guidelines for the use of Doppler sonography as a confirmatory test for cerebral circulatory arrest, which are presented in Table 4 (33–39).

The greatest advantage of Doppler sonography is the possibility of bedside evaluation, which enables close monitoring and intervention in unstable patient. No contrast agents are applied, preserving the residual organ function. A disadvantage of TCD is that in up to 20 % of individuals the insonation is not possible due to bone hyperostosis. In patients with skull defects or drainage, false results can be produced due to inappropriate ICP recording, and therefore TCD in not the method of choice for brain death confirmation. The blood flow velocities can be affected by marked changes in PCO₂, hematocrit and cardiac output. It cannot be performed in hypotensive patients. TCD ultrasonography requires considerable practice and skill.

Conventional angiography or digital subtraction angiography

A selective four-vessel angiogram is done in the radiology suite. Iodinated contrast medium is injected under high pressure in both the anterior and posterior circulation. Intracerebral filling is absent at the level of carotid bifurcation or circle of Willis (40, 41). The external carotid circulation is patent, and time delayed filling of the superior longitudinal sinus may be seen. Interobserver studies have not been published, and no guidelines for interpretation have been developed. Repeat contrast injections may increase the risk of nephrotoxicity and decrease the acceptance rate in organ recipients.

Electroencephalography

A 16- or 18-channel instrument is used with guidelines developed by the American Electroencephalographic Society for Recording Brain Death (42, 43). No electrical activity occurs above 2 µV at a sensitivity of 2 µV/mm with filter setting at 0.1 or 0.3 s and 70 Hz. Recording should continue for at least 30 min. However, according to Croatian legislature (44), electroencephalography (EEG) must be performed three times for at least 15 min, and absent electrical activity must be recorded. Most patients meeting the clinical criteria for brain death have isoelectric EEGs. Nevertheless, in one consecutive series of patients fulfilling the clinical diagnosis of brain death, 20 % of 56 patients had residual EEG activity that lasted up to 168 hours (45). Such activity may be the consequence of autolytic process. A major disadvantage are considerable artifacts in the intensive care unit settings that can limit interpretation (46).

Isotope angiography – radionuclide cerebral angiography

Nondiffusible radioisotopes have been used for the determination of brain death as early as the late 1960s and their use has been well documented and accepted (47–51). Any of hydrophilic radiopharmaceutical agents (^99mTc-pertechnetate, ^99mTc-glucoheptonate, ^99mTc-DTPA) can be used and they are readily available at nuclear medicine departments. Confirmation of brain death with this method relies primarily on the absence of cerebral flow on anterior-projection rapid sequence angiography, obtained for up to 1 min following intravenous bolus injection of the radiopharmaceutical. The method is highly sensitive (98 %) and although the dynamic imaging technique is technically demanding, it has the advantages of speed, noninvasiveness, performance without moving the patient from the bed, freedom from electrical interference, and avoidance of iodinated contrast media. A confounding finding is faint visualization of dural sinuses, reported in small numbers of patients, due to external carotid filling of intracranial venous sinuses via supplying vessels to the falx and tentorium. Those patients otherwise had no evidence of cerebral flow on dynamic images, therefore it does not contradict the diagnosis of brain death.

Scintigraphy with lipophilic agents – ^99mTc-HMPAO

Agents that cross the blood-brain barrier can overpass the concerns over the significance of sinus activity. Studies with ^99mTc-HMPAO are insensitive to intravenous bolus techniques, allow for assessment of individual brain regions, and they readily distinguish between low and absent flow (52, 53). Lipophilic tracers such as ^99mTc-HMPAO cross the blood-brain barrier and after extraction by brain cells convert to hydrophilic form and remain trapped in cell. The accumulation is not affected by metabolic disturbances, pharmacologic intoxicants or hypothermia. Reconstitution of ^99mTc-HMPAO within nuclear medicine “hot-labs” requires strict adherence to the instructions of the manufacturer. If stabilized with methylene blue it can be used within the subsequent 4 hours, otherwise ^99mTc-HMPAO must be administered within 30 minutes of reconstitution. Planar static images obtained immediately and between 30–60 minutes show absence of brain uptake and provide straightforward confirmation of brain death, with nearly 100 % sensitivity. Dynamic study is an optional procedure and absence of flow on cerebral angiogram is a supportive information.

Both cerebral scintigraphic methods are noninvasive, safe, rapid and highly sensitive confirmatory methods, without deleterious effects on donor organs. Metabolic aberrations, pharmacologic intoxicants, hypothermia, and the presence of skull defects or scalp trauma do not preclude its performance. The main disadvantage is inaccessibility and also dislocation of nuclear medicine departments, which requires transport of patients.

Somatosensory and brainstem evoked potentials

A portable instrument can be used at the bedside. According to the Croatian legislature (9), somatosensory evoked potentials can be used. Cables and contacts should be shielded from the external electromagnetic influences. The results should be confirmed in at least two consequent testings.

In somatosensory evoked potentials testing, median nerve stimulation is performed on both sides. N13-P14 response (Fz-Pgz) or N18-20 response (Cz-NC or C2), with positivity measured at the peak, upwards from the baseline, is expected to be bilaterally absent (54, 55). In brainstem auditory evoked potential testing, both flat auditory responses (I-V) are expected (56). The major disadvantage of the technique is that it is nonspecific, so deaf patients may also have a flat auditory response.

Other Tests

CT or magnetic resonance imaging showing cessation of blood brain perfusion can be used (57). Contrast CT with a bolus of meglumine diatrizoate, 1 ml/kg body weight, followed by drip infusion of 0.02 ml/kg per minute, does not visualize intracranial vessels (58). A good correlation with cerebral angiography has been demonstrated.

CONCLUSION

In comatose patients with absent motor and brainstem reflexes, and evidence of brain damage compatible with the diagnosis, brain death is suspected. An observational period of at least 6 hours is mandatory according to the Croatian legislature, and repeat examination should be perfomed according to the protocol. Apnea testing and one of the confirmatory test should be performed. Noninvasive, bedside evaluation is preferable.

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