Death by Neurological Criteria

Death by Neurological Criteria (DNC) — 2023 Guidelines. A reference covering terminology, physician requirements, prerequisites, the neurologic examination, the apnea test, ancillary testing, and special situations.

Terminology

• DNC “Death by Neurological Criteria” is the new term to replace “Brain Death”, to clearly indicate death using neurological criteria as opposed to cardiopulmonary criteria.
• Death by Neurological Criteria indicates permanent loss of the function of the brain as a whole including the brainstem resulting in coma, brainstem areflexia and apnea.

Physician Requirements

• Adult DNC: the guidelines didn’t address special qualifications
• Pediatric DNC: DNC should be performed by 2 attendings, either pediatric intensivists, neonatologist, pediatric neurologist, neurosurgeon, trauma surgeon or anesthesiologist with critical care training or adult specialist trained in neurology or critical care.
• Clinician involved in DNC should avoid any direct involvement in organ donation decision making to avoid conflict of interest

Prerequisites

Patient Selection

• DNC evaluation is indicated in patient who is comatose, apneic with absent brain stem reflexes with identifiable cause of brain injury that is known to cause brain death
• Consent is NOT needed to proceed with DNC evaluation; however clinician should inform the family the plan to perform DNC.

Imaging

• Clinician should determine that neuroimaging is consistent with the mechanism and severity of brain injury

Timing

• Clinician must wait sufficient amount of time after brain injury to ensure there no potential for recovery.
• Wait at least 24h after hypoxic brain injury in patients 24 months and older
• Wait at least 48h for infants less than 24 months
• Wait sufficient amount of time after surgical/medical interventions to treat increased ICP

Vital Signs

• Temperature: Maintain body temperature ≥36°C for at least 24h before proceeding with DNC evaluation.
• Blood Pressure:
  • Adults: SBP > 100mmHg and MAP ≥ 75mmHg
  • Children: SBP and MAP ≥ 5th percentile for age
  • ECMO patients: same above SBP & MAP values for VV ECMO, use only MAP for VA ECMO
  • Chronic low BP: for patients with a baseline BP that varies from the normal range, target SBP and MAP close to their chronic baseline.

Metabolic Derangements

• Toxicology: Negative toxicology screen if indicated
• Alcohol: level <80mg/dL if indicated
• CNS depressant medications: ensure that blood levels are therapeutic or subtherapeutic, if levels are not available:
  • Wait at least 5 half-lives, and longer if there is renal/hepatic dysfunction
  • For pentobarbital, level must be <5 microgram/ml
• Exclude effect of paralytic agents, use train of 4 if suspected.
• If metabolic derangements are unable to be corrected, but exam and apnea are consistent with DNC, you must use an additional ancillary test.

Neurologic Examination

• In adults, at least 1 neurological examination must be performed for DNC, a second clinician may perform a separate examination in adults
• In Children, at least 2 separate neurological examinations must be performed with at least 12h in-between.
• If a component of the examination can’t be assessed, you must use ancillary test.
• Component of Neurologic Examination:
  • Mental status: Comatose, unresponsive to auditory, visual or tactile stimulation
  • Motor response: No motor response other than spinally mediated reflexes with noxious stimuli
    • If it is unclear whether observed limb movements are spinally mediated reflexes, you should use an additional ancillary test.
  • Pupillary reflex: No response to light bilaterally
  • Oculocephalic reflex: absent
    • IF can’t be performed due to spine injury, OVR test (caloric test) must be performed bilaterally
  • Corneal reflex: absent bilaterally
  • Cough and gag reflexes: absent
  • Sucking and rooting reflex in infants < 6 month: absent

Apnea Test

Number of Tests

At least 1 in adults and 2 in children

Preparation Before the Test

• Risk of cardiopulmonary decompensation during the test must be acceptable
• Baseline PaCO2 and PH: must be at normal levels (PaCO2 35–45, PH 7.35–7.45).
  • If patient is a chronic hypercarbic, PaCO2 should be at patient’s chronic baseline if known, if chronic baseline is not known, clinician should perform ancillary test
• Preoxygenation: use 100% oxygen for at least 10 minutes to achieve PaO2 > 200mmHg
• Arterial line: needed to allow for multiple ABG measurement and reliable BP monitoring.
• ABG: obtain ABG after preoxygenation to determine baseline PaO2 and PaCO2

Perform the Apnea Test

• Ensure adequate oxygenation by either:
  • Disconnect the ventilator from ETT, and deliver 100% oxygen at a 4–6L/m rate through:
    • Catheter in the ETT/tracheostomy just above the level of carina
    • Flow-inflating resuscitation bag with a PEEP valve
  • Stop mechanical ventilation and deliver 100% through CPAP mode on the ventilator
• ABG: Obtain an ABG every 2 minutes
• Duration: 10 minutes, however if ABG parameters were not reached, you may continue longer.

Abortion

• Abort the test if:
  • SBP < 100 or MAP < 75 mmHg in adults or < 5th percentile for age in children despite pressors.
  • SaO2 < 85%
  • Cardiac arrythmia with hemodynamic instability
• If you decide to abort, obtain ABG before placing patient back on the ventilator

Positive Test (Patient is Apneic) if:

• No respiration occurs and
• PH < 7.3 and
• PaCO2:
  • Non chronic retainers: PaCO2 ≥60 and ≥20 mmHg above the test baseline.
  • Chronic CO2 retainers with known PaCO2 baseline: PaCO2 ≥60 and ≥20 mmHg above the patient’s chronic baseline.
  • Chronic CO2 retainers with unknown PaCO2 baseline: PaCO2 ≥60 and ≥20 mmHg above the test baseline. In addition, ancillary test must be done

Negative Test (Patient is Able to Breath)

If patient was able to take a breath, DNC should be aborted.

Aborted Test

• If test was aborted for hypoxemia, the test may be repeated using an alternative apneic oxygenation (CPAP or resuscitation bag) or perform ancillary test.
• If test was aborted for hypotension, the test may be repeated after augmenting blood pressure or perform ancillary test.
• If test was aborted for cardiac arrythmia, the test may be repeated when it can be safely performed or perform ancillary test.

Apnea Test in ECMO Patients

• Use SBP and MAP for VV ECMO, and MAP only for VA ECMO
• Pre-oxygenate by using 100% oxygen on the ventilator and also on the membrane lung
• CO2: To achieve adequate increase in PaCO2, either titrate exogenous CO2 in ECMO circuit or adjust sweep gas flow rate to 0.2–1 L/min
• ABG sampling:
  • VV ECMO: from distal arterial line
  • VA ECMO: From both distal arterial line and ECMO circuit post-oxygenator
  • Patients cannulated through Rt carotid or axillary a: from distal arterial sample on left upper or either lower extremity.
  • Patients cannulated through femoral line: from right upper extremity
• Site of obtaining ABG is critical in VA ECMO patients with cardiac contractility (gas tension in peripheral arteries may not represent cerebral circulation)

Ancillary Testing

Indications

• If neurological exam or apnea test can’t be performed or interpreted adequately
  • Component of the neurological exam can’t be performed (ex; facial trauma, orbit trauma)
  • Unclear if motor response is a spinal reflex or not
  • Metabolic derangement can’t be corrected
  • Apnea test can’t be completed due to hypotension, hypoxia or arrythmia
  • Chronic CO2 retainers with unknown baseline PaCO2

Types

• 4-vessel catheter angiography: Flow arrest at the point of entry of vessels into the dura
• Radionuclide Perfusion Scintigraphy: Hollow-skull sign
• Transcranial doppler: Oscillating flow or Systolic spikes in large arteries, only in adults, not validated for children

Don’t Use

• EEG, Evoked potentials: AEP, SEP
• CTA or MRA

Time of Death

• No ancillary test: time of the last ABG results reported during apnea test
• Ancillary test was done: time ancillary test results were reported in the chart (radiology, TCD or angiography report time)

Special Situations

• Pregnancy: Is not a contraindication to proceed with DNC evaluation if clinically indicated
• Posterior Fossa Injury: Ensure that posterior fossa process has led to catastrophic supratentorial injury, demonstrated on imaging before proceeding with DNC evaluation, even if patient is comatose with brainstem areflexia.

DNC Ancillary Tests Images

• Cerebral Angiography: No intracranial filling
• Scintigraphy/SPECT: Hollow Skull sign
• TCD:
  • Systolic peaks without diastolic flow
  • Oscillating flow
  • Systolic spike

Summary: DNC Evaluation in non-CO2 retainers (COPD) and non-ECMO Adults

Ahmed Koriesh, MD