Which physiological criteria would exclude a patient from brainstem death testing?
Factor
Lower Limit
Upper Limits
Comments
Temperature Disturbance
34°c
-
Impaired consciousness can occur below 34°c
Biochemistry Disturbance
-
-
Derangements clearly the result of brainstem death (e.g. hyponatraemia of DI) may not require correction prior to testing
Sodium
115 mmol/l
160 mmol/l
-
Potassium
2 mmol/l
-
-
Magnesium
0.5 mmol/l
3.0 mmol/l
-
Phosphate
0.5 mmol/l
3.0 mmol/l
-
Glucose
3 mmol/l
20 mmol/l
-
Endocrine Disturbance
-
-
If there is any clinical reason to expect endocrine disturbances, hormonal assays should be undertaken.
Respiratory and Haemodynamic Disturbance
-
-
Requirement for cardiorespiratory stability is an important new prerequisite
pH
7.35
7.45
-
pCO2
-
6.0 kPa
-
pO2
10 kPa
-
-
MAP
60 mmHg
-
How are tests for brainstem reflex activity performed and what does each test check?
Test
Sensory Nerve
(Afferent Pathway)
Motor Nerve
(Efferent Pathway)
Brainstem Level
Pupillary Reflex
Optic nerve (II)
Oculomotor nerve (III)
Midbrain, pretectal olivary and Erdinger-Westphall nuclei
Corneal Reflex
Ophthalmic branch of trigeminal nerve (V)
Facial nerve (VII)
Pons, trigeminal and facial nuclei
Caloric (Oculo-vestibular) Reflex
Vestibulocochlear nerve (VIII)
Oculomotor nerve (III) & abducens nerve (VI)
Pons, nucleus vestibularus, nucleus abducens
Painful Stimulation (Brow)
Ophthalmic branch of trigeminal nerve (V)
Facial nerve (VII)
Pons, trigeminal and facial nuclei
Painful Stimulation (Limb)
Lateral spinothalamic tract
Facial nerve (VII)
Pons, trigeminal and facial nuclei
Gag Reflex
Glossopharyngeal nerve (IX)
Vagus nerve (X)
Medulla, nucleus tractus solitarius
Cough Reflex
Vagus nerve (X)
Vagus nerve (X)
Phrenic & intercostal nerves
Phrenic & intercostal nerves
Medulla, nucleus tractus solitarius
How is the apnoea test performed?
Preparation
- Only be performed once the absence of brainstem reflex activity has been confirmed
- Ensure cardiovascular stability maintained
- Ensure utilization of end tidal carbon dioxide (EtCO2) monitoring, pulse oximetry, blood pressure monitoring and blood gas analysis:
- Prevents the development of significant hypoxia
- Prevents the development of excessive hypercarbia
- Minimizes the development of hypotension which could risk further injury to potentially recoverable brain tissue
- Preoxygenate with an FiO2 1.0.
- Ensure mild hypercarbia (PaCO2 >6.0 kPa) and acidosis (pH <7.4) prior to testing:
- Reduce the minute ventilation to allow PaCO2 to rise
- A PaCO2 >6.5 kPa should be targeted in:
- Patients with chronic CO2 retention
- Patients receiving intravenous bicarbonate
Performance
- Remove patient from ventilator - cardiac pulsation may be sufficient to trigger supportive breaths
- Ensure oxygenation - options include:
- Connect the patient to CPAP circuit (e.g. Mapleson C)
- Administer oxygen via a catheter in the trachea at a rate of >6L/minute
- Perform a pre-test arterial blood gas to confirm PaCO2 is at least 6.0 kPa and pH <7.4
- Observe for respiratory activity for 5 min, confirming the start time
- Perform a confirmatory blood test to ensure an increase in PaCO2 of more than 0.5 kPa
- After completion of the apnoea, test reconnect the ventilator