The purpose of implementing devastating brain injury guidelines is to promote physiologic stability in order to support potential for neurological improvement, allow time for family presence, and preserve the opportunity for organ donation
Oxygenation and ventilation: maintain PaO2 > 100 and pH 7.35–7.45
1. Adjust ventilator as appropriate
2. Maintain pulmonary hygiene interventions (turn q 2 h, suction)
Blood pressure: maintain MAP >60 mm Hg and SBP > 100 mm Hg
1. Administer IV fluids (NS or LR unless lab values indicate otherwise) to maintain euvolemia. Adequate intravascular volume is critical to hemodynamic stability
2. Vasopressor support: if patient remains hypotensive once euvolemic, start vasopressors and titrate to keep MAP >60 mm Hg and SBP > 100 mm Hg
Note: tachycardia and hypertension may be seen immediately prior to brainstem herniation. If treatment is desired, use only short-acting medications
Temperature: maintain normothermia. (Note: for some populations, hypothermia may be used as a therapeutic measure)
1. Monitor temperature at least q 1 h
2. Maintain temperature 36 °C–37.5 °C using cooling devices as needed. In general, active rewarming of neurologic patients is not recommended, but may be necessary prior to assessment of death by neurologic criteria
Urine output: maintain urine output >0.5 ml/kg/h and <400 ml/h
1. If <0.5 ml/kg/h, reassess hydration and need for BP support
2. If >400 ml/h, consider diabetes insipidus and check serum sodium. Treat DI with desmopressin (DDAVP) 1–2 mcg IVP or an infusion of vasopressin 1–2.5 units/h, and replace urine output ml for ml with 0.45% saline
Labs: monitor labs and treat as appropriate
1. BMP, Mg, Phos, CBC, PT/PTT, blood bank sample for ABO typing initially and PRN
2. Maintain Hgb > 8 g/dL and HCT > 24%.
3. Replete electrolytes as needed
4. Maintain blood glucose between 80 and 180 mg/dL
In some cases, the injury to the brain is so severe that compression of the brain stem occurs, or loss of perfusion to the entire brain occurs due to highly elevated ICP, resulting in loss of function of the entire brain, including the brain stem. These patients can be declared dead by neurologic criteria (DNC). Clinical or imaging findings must reveal a reason for the patient to be unresponsive; examples include but are not limited to large SAH or ICH, traumatic injury, or diffuse cerebral edema. Potential confounders that must be excluded include the effects of CNS depressant drugs; neuromuscular blockade; and severe electrolyte, acid-base, or endocrine disturbance . Body temperature must be normal, with a lower limit of 36 °C recommended by the AAN practice parameters. Blood pressure must also be adequate, defined by the AAN practice parameter as ≥100 mmHg, with or without vasopressor support. Once the cause of unresponsiveness has been identified and possible confounders have been eliminated, testing for DNC can proceed. Examination for DNC encompasses three cardinal features: coma, absence of brainstem reflexes, and apnea. One examination, performed according to the AAN guidelines, is clinically sufficient to declare DNC in adults , but a period of observation and a second exam is sometimes required by state law or organizational policy.
Assessing for response to noxious stimulus is the first part of the clinical exam for DNC. Patients who are DNC exhibit no eye opening or movement and no body movement in response to central and peripheral pain stimulus, except for reflexes mediated by the spinal cord. One of the most common reflexes mediated by the spinal cord is triple flexion, characterized by stereotypical flexion at the hip, knee, and ankle. Other movements that may be observed after DNC include toe movements, finger movements, and the Lazarus signs, characterized by a rising up motion with the torso and arms [2, 8]. Spinally mediated movements can occur in response to stimulation and are most common in the first 24 h after DNC . Any movement, even spinal reflexes, can be very disconcerting to the patient’s family and to the staff, and a clear explanation of the nature of the movement should be provided. If there is any question about whether or not a movement is initiated by the brain, ancillary testing is recommended (see below).
18.4.2 Brainstem Areflexia
The next step in the evaluation of DNC is assessment of brainstem reflexes and cranial nerve function, as outlined in the AAN guidelines (see Table 18.2) .
Brainstem reflexes and cranial nerve function in DNC evaluation
Pupillary light reflex
Pupils are nonreactive to bright light. Size varies from mid-position to dilated. Smaller pupils should alert the clinician to the possibility of drug effect
The head of bed is elevated to 30°, and the integrity of the tympanic membrane and auditory canal is confirmed. Ice water is instilled into the external auditory canal for 60 s continuously, one ear at a time, while observing for eye movement with the patients’ eyelids held open. In patients with DNC, no movement is seen. An interval of 5 min should transpire before testing the contralateral ear
Except in cases where cervical spine instability cannot be ruled out, the oculocephalic reflex is tested by rotating the patient’s head rapidly side to side, while holding the eyelids open and observing for eye movement. Movement in response to rapid vertical head movement may also be tested. Any eye movement precludes the declaration of DNC
No eyelid movement is seen when the cornea is stimulated. For brain death determination, an adequate stimulus must be provided, such as pressing with a sterile cotton swab on the cornea adjacent to the iris. Care must be taken not to injure the cornea to maintain the option of subsequent donation
Facial movement to noxious stimulation
No grimacing or other facial movement is observed in response to deep pressure on the supraorbital ridge and temporomandibular joint.
Pharyngeal (gag) reflex
The posterior pharynx is stimulated, most often with a rigid suction catheter or tongue blade. There is no response in patients who are DNC.
Tracheal (cough) reflex
No cough reflex is noted in response to insertion of a suction catheter down the endotracheal tube to the level of the carina
The final step in the clinical exam is apnea testing, which assesses for spontaneous respirations in response to an elevated carbon dioxide level and acidosis. There are several acceptable methods for completing the apnea test [2, 9]. The most common and validated is apneic oxygenation, in which oxygen is provided through a cannula inserted to the level of the carina or via a T-piece, but the patient is not ventilated. The patient is observed for spontaneous respirations, and reconnected to the ventilator if any respirations are noted. The test is also aborted if the patient’s oxygen saturation or blood pressure drops below established limits, defined in the AAN practice parameters as an oxygen saturation of less than 85% for more than 30 s or a systolic blood pressure less than 90 mmHg . If no spontaneous respirations are observed with the patient disconnected from the ventilator, a blood gas is drawn, typically 8–10 min after the test is initiated. A PaCO2 of >60 mmHg, or a rise in PaCO2 of >20 mmHg in a patient with baseline elevations in PaCO2 due to COPD or OSA, is consistent with DNC . The patient is reconnected to the ventilator while results are reviewed and shared with the family. The patient’s time of death is the time the blood gas result consistent with DNC is reported. Transcutaneous CO2 monitoring may be a useful adjunct to guide the timing of blood gas measurements, but arterial blood gas measurements are still required .
The APC has a key role in preparing the patient for apnea testing and maintaining patient stability during the test. Hypovolemia is common in brain death due to the development of diabetes insipidus, and will increase the likelihood of hypotension during apnea testing. Careful attention to fluid balance is paramount. Many patients undergoing apnea testing will be on vasopressors, and upward titration may be required. If not already in use, vasopressors and/or intravenous fluids should be made available during apnea testing. Prior to starting apnea testing, the patient’s systolic blood pressure should be >100 mmHg, and a buffer of at least 110–120 mmHg is recommended. Careful adjustment of ventilator settings in preparation for apnea testing is needed. Prior to starting the apnea test, the patient’s CO2 should be normal (35–45 mmHg) and preoxygenation is mandatory to a PaO2 of >200 mmHg. At no point during the apnea test should the patient become hypoxic, and hypoxia is not the stimulus for respiration (hypercarbia, and more importantly, acidosis is what simulates the medullary respiratory centers). As outlined in the AAN practice parameters, body temperature should be ≥36 °C; CO2 is produced more slowly at lower temperatures, which could potentially lengthen the amount of time required to complete apnea testing. Close collaboration with the patient’s bedside nurse is essential to optimize the patient’s physiologic stability prior to and during apnea testing. With adequate preparation (especially preoxygenation) and careful management, apnea testing can be safely completed in most patients .
Of note, it is common practice at some institutions to complete apnea testing with the patient attached to the ventilator but placed on CPAP with a pressure trigger of −2 cm H2O. Use of this method is not recommended because the cardiac cycle may be enough to trigger a ventilator breath in some patients.