In most scenarios, death remains a clear-cut event. However, with progressively advanced degrees of organ support and medical intervention, scenarios can arise which are more challenging. As such, critical care has brought about a revision of the definitions of death, with greater clarification on what it actually ‘is’.
These notes are a discussion about the medical perspective on death, but this is far from the only viewpoint. There are a variety of different philosophical and religious interpretations, and these will often have importance to our patients and their families.
What is Death?
The guidance from the Academy of Medical Royal Colleges and the President’s Council on Bioethics recognise death as a discrete event with two key features:
An irreversible loss of consciousness
An irreversible loss of the capacity to breath
These are recognised as the essential features needed for an organism to be ‘alive’ and therefore their absence (irreversibly so) constitutes death. This unification of the definition of death helps us understand how we can confirm it clinically.
Thus there can be considered to be 3 criteria for determining death:
Cardiorespiratory criteria - no cardiorespiratory activity
Somatic criteria - clearly visible death e.g. decapitation
Neurological criteria - the diagnosis of brain death.
The confirmation of death remains the legal responsibility of medical practitioners, and acts as a clear point for certain legal and religious processes e.g. triggering of a will. This is a major reason why the concept of live and death is a binary state. However, any medical practitioner will clearly recognise that dying is usually a process, and this has to be borne in mind too.
Death by Neurological Criteria
This refers to the concept of brain death. In the UK, the concept of brainstem death is used, as brainstem function is essential to the criteria for life. However, it is useful to know that this isn’t an international definition, with ‘whole brain death’ being used as the criteria in North America.
The UK code for confirming death by neurological criteria has 3 essential components:
Fulfillment of essential preconditions
Exclusion of potentially reversible causes of apnoeic coma
The formal demonstration of coma, apnoea and absence of brainstem reflex activity
The tests should should be carried out:
By 2 doctors (at least one a consultant) of at least 5 years registration
On 2 separate occasions
After completion of the second set of tests, the patient is confirmed as dead. The time of death is noted as the time of completion of the first set of tests.
The patient should be deeply unconscious, apnoeic and mechanically ventilated. There should be no doubt that the patient has suffered irreversible brain damage of known aetiology.
The doctors must be sure that the current clinical condition is not due to the effects of any reversible causes:
Depressant drugs As these are a common cause of coma, confidence that they have been fully eliminated is necessary. This can be challenging when the dose or even nature of the drug is unknown (e.g. overdose). Impaired renal and hepatic function can also pose a challenge to confidence in the elimination of a drug. Some options to consider include:
Testing of drug levels e.g. thiopental
A trial of specific antagonists e.g. naloxone
A period of observation of four times the half life
Physiological Parameters There are strict physiological criteria for being able to conduct brainstem death testing, to ensure that these factors aren’t interfering.
Temperature >34 degrees celsius
Sodium 115 - 160 mmol/l
Potassium > 2 mmol/l
Magnesium 0.5 - 3.0 mmol/l
Phosphate 0.5 - 3.0 mmol/l
Glucose 3 - 20 mmol/l
pH 7.35 - 7.45
MAP 60 mmHg
There must be a consideration of profound thyroid or adrenal disease.
These are only performed after the first two steps are completed. They consist of two component:
Assessment of brainstem reflexes
The apnoea test
Brainstem reflexes These formal tests assess the brainstem reflexes through the testing of several cranial nerves looking for a normal reflex response. The normal response (which won’t be present in brainstem death) and pathways are described:
Pupillary response - direct and consensual constriction to light should be sought (Sensory CNII, Motor CNIII)
Corneal reflex - swabbing of the cornea should result in blinking (Sensory CNV, Motor CNVII)
Pain - Painful pressure is applied to the supraorbital ridge and also peripherally, looking for a motor response of the cranial nerves (Sensory CNV, Motor CNVII)
Oculovestibular reflex - visualisation of the tympanic beforehand. Instilation of 50ml of ice cold saline into the ear canal. Looking for nystagmus. Both sides should be tested if possible, though not essential. (Sensory CNVIII, Motor CNIII, CNIV, CNVI)
Gag reflex - stimulation of the pharynx looking for a gag response (Sensory CNIX, Motor CNX
Cough reflex - passage of a suction catheter to the carina, looking for a cough response (Sensory CNX, Motor CNX)
Apnoea test This should be performed as the final test. The aim is to produce a respiratory acidosis that should stimulate respiration (in a normally functioning brain stem) but without hypoxia or cardiovascular disturbance.
Increase FiO2 to 100%
Measure a baseline ABG to allow calibration of ETCO2 with pCO2
Reduce minute ventilation to achieve an ETCO2 of 6 kPa.
Stop ventilation and observe for 5 minutes for any signs of respiratory effort
Confirm an increase in pCO2 of at least 0.5 kPa with a repeat ABG.
Restart ventilation at this point
Oxygenation should be maintained with apnoeic oxygenation throughout the test. This can be done either via CPAP via a Mapleson C circuit, or installation of O2 into the lungs via a suction catheter.
This term refers to other investigations that can aid with the diagnosis of death. The diagnosis of death by neurological criteria is perfect if done correctly and completely, but there may be cases where some of the preconditions cannot be met. Examples include a high cervical spinal injury, potentially impacting on apnoea assessment, or the inability to rule out a metabolic cause.
Confirmatory tests may help provide evidence that the brain stem is indeed dead e.g. evidence of no blood flow. They include:
Four vessel cerebral angiography - the gold standard
It is important to be aware that even in the context of death by neurological criteria, spinal reflexes can still be preserved. These can be relatively complex in their nature, including motor reflexes and autonomic reflexes. This is important to communicate to relatives (and staff) in that they don’t represent consciousness (but can look like it). It is also important to consider as part of anaesthesia for DBD. Here the ‘anaesthesia’ is not for the patient, who is dead, but to obtund the physiological reflexes (autonomic and motor) that may impair the donation process.
These are criteria where brief external inspection confirms, beyond doubt, that a person is dead. Paramedic crews can use these to identify when not to commence CPR, and have been termed ‘Recognition of Life Extinct’:
Massive cranial and cerebral destruction
Massive truncal injury incompatible with life e.g. decapitation.
Incineration (full thickness burning with charing of over 95% of the body)
Hypostasis (pooling of blood in congested vessels in the dependent poition)
As can be well appreciated, these conditions will meet the definitions of death, as they indicate the irreversible loss of consciousness and capacity to breath.
Although these may appear to be well known, the unification of a definition of death means that some changes to the criteria have been made compared to previous methods. They have become similar to those of diagnosing death by neurological criteria in some ways. They again aim to demonstrate the definition of death has been obtained.
It is well known that loss of cerebral circulation (as evidenced by loss of cardiac output) will result in a loss of capacity for consciousness because of the effect of ischaemia on the brain. However, the challenges have arisen because of the increase in donation of organs after cardiac death. In this scenario, the aim is to minimise the time between loss of cardiac output and the cooling of the organs (the warm ischaemia time). The question is therefore how long is necessary to confirm that this loss of function is irreversible (some people may therefore prefer the term permanent)? There is some variability internationally about this length of time, but in the UK it is 5 minutes. This is based on evidence that the minimal time for irreversibility (without intervention) is 65 seconds, and there is a subsequent increased window of confidence to confirm that the patient is indeed dead. This window of observation is higher and lower in other countries.
The diagnosis of death by cardiorespiratory criteria in the UK therefore involves:
Confirmation of absence of cardiorespiratory effort (demonstration of loss of capacity to breath)
No central pulse
Can be supplemented by:
Asystole on ECG
No arterial waveform on invasive monitoring
Absence of cardiac activity on echocardiography
Demonstration of the loss of capacity for consciousness
No pupillary reflexes
No corneal reflexes
No response to painful stimuli
This observation for absence of cardiorespiratory effort must occur over a minimum period of 5 minutes, after which there is confirmation with the tests of consciousness. If there is any brief spontaneous return of cardiorespiratory activity, the 5 minute period must be started again.
As with the neurological criteria, there are some essential preconditions for using these criteria. This can be summarised that there must be a clear intention not to start CPR and restore cerebral perfusion. This may be because of recognised futility, or because it has already failed. This is because such a restoration of perfusion may invalidate the definition of death based on the concept of irreversibility. As such, this decision to not instigate any measures which might produce cerebral perfusion is essential, particularly for DCD patients, where it could otherwise be argued that the patient isn’t truly defined as dead at the time of donation.
Last updated 12th April 2017 Tom Heaton
Links & References
Oram, J. Murphy, P. Diagnosis of death. CEACCP. 2011. 11(3):77-81