Diagnosis of DeathTop
Death is defined as the irreversible loss of bodily functions that support a living organism. In the majority of cases (when respiratory and circulatory functions are not artificially supported), the traditional criteria of death apply.
Brain death is defined as the irreversible loss of brain stem functions needed to support a living organism. Brain death is important in the setting of organ donation and when artificial ventilation is used.
The traditional criterion for the diagnosis of death involves identification of:
1) Cessation of circulatory function: Absence of pulse on large arteries (carotid arteries) and no heart sounds on auscultation for ≥2 minutes. Difficulties in palpating the pulse may be caused by advanced atherosclerosis or presence of stents in the carotid arteries. If the examination of pulse or auscultation of heart sounds is too short, it is possible to overlook preserved cardiac function in patients with profound bradycardia.
2) Cessation of spontaneous respiratory function: Auscultate and observe the chest for 1 minute. An insufficiently long observation of breathing in patients with irregular and slow respirations in the course of acid-base disturbances, drug poisoning, encephalitis, brain tumors, and brain edema can miss extreme bradypnea. Contractions of the neck and chest muscles can imitate breathing even for several minutes after cessation of circulatory function; thus, observation must be combined with auscultation.
3) Dilated pupils unresponsive to light: Assess both eyes, as the lack of pupillary response to light may be a result of iris trauma, diseases of the retina and optic nerve, treatment with mydriatics, and presence of ocular prosthesis.
This requires more rigorous testing than determination of death. It is usually done in the setting of anticipated organ donation. In Canada, criteria for determination of clinical brain death in the adult patient include:
1) Cause of death that is capable of causing brain death.
2) Absence of reversible causes of coma:
a) Untreated shock.
b) Hypothermia (<34 degrees Celsius).
c) Untreated metabolic disturbances.
d) Peripheral nerve or muscle dysfunction due to disease or neuromuscular blocking agents.
e) Central nervous system depressants.
3) Absence of brain stem reflexes:
a) Pupillary response to light.
b) Corneal reflex.
c) Gag reflex.
d) Cough reflex (use bronchial suctioning to try to elicit the reflex).
e) Oculovestibular reflex (cold calorics): With the head of the bed at 30 degrees, 50 mL ice cold water is syringed into the patient’s ear canal. Any movement of the eyes excludes neurologic death. Repeat in both ears.
4) Absence of response to stimuli in all extremities and above clavicles.
5) Absence of respiratory effort: Apnea testing: In the setting of normal arterial blood gas values the patient is preoxygenated with 100% oxygen. The ventilator is disconnected but oxygen is delivered to the patient (through an endotracheal tube or tracheostomy). The patient is monitored continuously for respirations. Arterial blood gas measurement is repeated at 10 to 15 minutes, and the patient is reconnected to the ventilator. Apnea is confirmed if partial pressure of carbon dioxide in arterial blood (PaCO2) is >60 mm Hg, has risen >20 mm Hg above baseline, and pH is ≤7.28. Testing is aborted if the patient becomes hemodynamically unstable.
6) Two physicians who are fully licensed for independent practice must confirm that the above criteria are met. These physicians must not have a relationship with the potential organ recipients. They may perform the examination simultaneously or separately, although the apnea test is usually only done once with both physicians present.
7) Ancillary testing to confirm the lack of cerebral blood flow is necessary only when any of the above physical examination steps cannot be completed or interpreted. Radionucleotide imaging, 4-vessel cerebral angiography, computed tomography (CT), and magnetic resonance angiography (MRA) are acceptable modalities of ancillary testing.
A pacemaker may continue to provide electrical stimulation for a short time after death. This ongoing electrical activity will be detected on electrocardiography (ECG) but will not create a systemic pulse or systemic circulation.
Death can be diagnosed in a cadaver at subzero temperatures in the presence of postmortem lividity, rigor mortis, and body decomposition. If you approach a hypothermic person without circulatory function and cannot confirm the above criteria, start and continue resuscitation (see Cardiac Arrest) while warming the patient. Death can be diagnosed when resuscitation is ineffective in spite of normalizing the body temperature. In some situations achieving normothermia is impossible and death will have to be declared despite ongoing low core body temperatures.
When diagnosing death on the basis of postmortem lividity, it is important to remember that cyanotic discoloration of the skin, which develops in advanced congestive heart failure, may be mistaken for postmortem lividity (cyanotic areas blanch under pressure, postmortem lividity does not).