9 | Appendices

Use of CTA to demonstrate absent brain perfusion

ANZICS recommendation:

1. When imaging to demonstrate absence of brain perfusion is required, it must be preceded by performance of those parts of the clinical examination that are possible. Responsiveness, all testable brainstem reflexes and breathing effort must be absent.
2. If assessment of brain perfusion is required, three- or four-vessel angiography or radionuclide imaging are preferred. Computed tomography angiography is acceptable if recommended radiological diagnostic guidelines are followed. Magnetic resonance imaging or angiography and transcranial Doppler should not be used.

Computed tomography angiography

Computed tomography angiography (CTA) to demonstrate absent brain perfusion is not recommended where intra-arterial catheter angiography or radionuclide imaging is available, because contrast enhancement of more proximal intracranial arteries (Circle of Willis, A1, M1, P1) and other veins and dural sinuses may occur when there is permanent loss of brain function. This enhancement is a reflection of the high sensitivity of CTA to small amounts of contrast that may admix within the Circle of Willis in the absence of brain perfusion.

If CTA is performed, ANZICS recommends the use of a four-point scale^1,2 , to assess absent enhancement of peripheral intracranial arteries at 20 seconds and central veins at 60 seconds after an intravenous bolus injection of 120 mL of >300 mg/mL non-ionic contrast injected at 3 mL/sec via a power injector through at least an 18 g intravenous catheter.

Before assessing brain perfusion with the four-point scale, the presence of contrast enhancement of external carotid artery branches is required to confirm that the study is technically adequate.

Criteria for absent brain perfusion under the four-point scale are:

• absent enhancement of both middle cerebral artery (MCA) cortical branches (i.e. beyond the Sylvian branches) and
• absent enhancement of both internal cerebral veins.

The four-point scale has demonstrated 100% specificity and 85.7% sensitivity.¹ A subsequent meta- analysis of CTA in 322 patients with permanent loss of brain function using the four-point scale showed a sensitivity of 87%.² Specificity was not assessed in the meta-analysis. A seven-point scale (based on absence of opacification in the cortical segments of bilateral MCAs, bilateral internal cerebral veins, bilateral pericallosal arteries and the great cerebral vein) used in France since 1998 has a demonstrated specificity of 100% but a sensitivity of only 68.2%.³

Cautionary notes

Solely relying on absent enhancement of the bilateral internal cerebral veins, while sensitive, is of questionable specificity given the possibility of venous sinus thrombosis in a patient without permanent loss of brain function.

Assessment of the specificity of CTA has been limited by the small number of normal controls in the published literature.

Recommended language to be used when reporting on a CTA performed for the determination of cerebral blood flow

It is recommended that unambiguous descriptions are used such as:

• “intracranial blood flow is absent”
• “intracranial blood flow is present”
• “there is no cerebral perfusion”

Do not use terms such as “ineffective” or “minimal”.

Please note, brain death is determined by two doctors in the ICU who know the patient’s history and who have examined the patient. It is not diagnosed by the reporting radiologist. The role of the reporting radiologist is to report if blood flow is present or absent.

References:

1. Frampas E, Videcoq M, de Kerviler E et al. CT angiography for brain death diagnosis. AJNR Am J Neuroradiol. 2009; 30(8): 1566-70.
2. Brasil S, Bor-Seng-Shu E, de-Lima-Oliveira M et al. Role of computed tomography angiography and perfusion tomography in diagnosing brain death: A systematic review. J Neuroradiol. 2016; 43(2): 133-40.
3. Dupas B, Gayet-Delacroix M, Villers D et al. Diagnosis of brain death using two-phase spiral CT. AMJR Am J Neuroradiol. 1998; 19(4):

95th percentile for age

Acceptable plasma concentrations:

Severe endocrine abnormalities that prevent clinical examination for the neurological determination of death include severe untreated hypothyroidism and severe hypoadrenalism.

Apnoea testing in patients with severely impaired oxygenation may lead to desaturation and circulatory instability. 

The following process of apnoea testing is recommended in these patients.

1. Ventilate the patients with 100% oxygen for at least 10 minutes.
2. Adjust the ventilation to allow mild hypercarbia PaCO₂ (~45mmHg) prior to disconnecting the patient from the ventilator for apnoea testing.
3. While mechanical ventilation is temporarily stopped, supply oxygen via a self-inflating bag (eg AmbuBag®) with a positive end-expiratory pressure (PEEP) valve to prevent atelectasis. Set the PEEP level to equal to the mean airway pressure the person was receiving on the ventilator.
4. Observe the patient for desaturation or haemodynamic instability and breathing.
5. Measure a PaCO₂ after 5 minutes of apnoea (CO₂ rises by 3mmHg – 0.4kPa every minute). PaCO₂ should be >60mmHg or 8kPa.
6. If the noradrenaline needs to be increased (in the absence of hypoxaemia) this is likely due to a respiratory acidosis and an ABG should be taken as sufficient hypercarbia may have been achieved (PaCO₂ of 60mmHg and pH<7.3) to maximally stimulate the ventilatory centre.  
7. If hypoxia occurs (SpO₂ <88%) 1 – 2 manual breaths may be delivered. Although this will reduce the PaCO₂, it may allow sufficient oxygenation for the apnoea test to be continued.
8. If despite these measures the apnoea test cannot be performed, please contact the ODNZ medical specialist via the donor coordinator.