Page 1167 - Hall et al (2015) Principles of Critical Care-McGraw-Hill

806 PART 6: Neurologic Disorders

optodes placed 4 to 6 cm apart on the forehead. Light waves in the 700 to suspected elevated ICP is outlined in Table 86-10. Once the patient
1000 nm range are emitted from one optode and received by the adjacent is adequately resuscitated and stabilized, attention is directed to the
optode after penetrating the scalp, skull, and brain to a depth of a few clinical evaluation for signs and symptoms of uncontrolled ICP and
centimeters. These light waves are differentially absorbed by oxygenated the detection of brain herniation. The need for CSF drainage via EVD
hemoglobin, deoxygenated hemoglobin, and cytochrome aa3. Recent should be quickly identified based on the imaging and clinical findings.
developments in NIRS technology have resulted in the availability of If intracranial hypertension and brain herniation are suspected or diag-
single, easy-to-use values for measuring cerebral tissue oxygenation and nosed, medical measures should be implemented while preparing for
monitoring the tissue oxygenation index, defined as the ratio of oxygen- more definitive interventions such as an EVD or operative evacuation
ated to total tissue hemoglobin, which provides estimates of regional of a space-occupying lesion. These interventions include head of the
cerebral oxygen saturation. 58 bed elevation, mannitol or other hyperosmolar therapy, and intuba-
Continuous video EEG (cvEEG) monitoring allows for noninvasive tion with temporary hyperventilation. Electrolyte analysis and blad-
evaluation of electrical brain activity, which is used to identify possible der catheterization are necessary prior to hyperosmolar therapy. Until
subclinical or nonconvulsive status in patients with acute brain injury. ICP monitoring is available, we recommend maintenance of a MAP of
Depressed mental status or intermittent neurological deficits without 70 to 80 mm Hg. Once ICP readings are available, the CPP should be
an appropriate explanation on imaging or by clinical presentation and optimized at around 60 mm Hg.
history may be explained by clinically silent seizures. This is an impor- If no acute herniation syndrome is clinically evident and the patient
tant distinction to make, as nonconvulsive status does not require ICP has an acute change in neurological examination or an acute brain
monitoring in most cases while a similar clinical examination in the injury, immediate imaging of the head (noncontrast head CT) is
absence of seizures would provide an indication for ICP monitoring. Up performed. With suspected ischemic syndromes and normal renal
to one-third of patients in specialized neurocritical care settings may function, CT angiography of the head and neck is commonly performed
have nonconvulsive seizures and generally, the longer the cvEEG studies simultaneously in order to delineate the arterial anatomy and any exist-
are performed, the higher the yield of identifying abnormalities. Most ing abnormalities. Reconstructed images of the cervical spine together
physicians employ cvEEG for 24 to 72 hours in the acute setting to rule with the clinical injury mechanism allow for early c-spine evaluation.
66
out abnormal electrical activity. 63 MR imaging of acute brain injuries represents a potential alternative
Transcranial Doppler (TCD) allows deriving the pulsatility index (PI), with higher diagnostic yield for cranial and spinal injuries. In the spine
which compares the changing relationships of systolic to diastolic flow it is the preferred imaging modality. However, MR imaging comes with
patterns. A low resistance vessel waveform will have continuous forward a distinct time demand for completion and minimal accessibility to the
flow throughout systole and diastole while a high resistance vessel will patient during scanning; therefore, only hemodynamically and neuro-
show a sharp systolic upstroke, a narrow peak in systole and much less logically stable patients should be referred for MRI in the setting of a
flow during diastole. The underlying principle is that under constant primary survey for the etiology of brain dysfunction.
blood pressure and carbon dioxide tension, the pulsatility of blood flow Once the primary survey is complete and ICP, MAP, and CPP moni-
through the basal cranial arteries (ie, middle cerebral artery, MCA) toring implemented, basic principles of ICP management should con-
reflects distal cerebrovascular resistance and the arteries themselves pro- tinue to be followed. The head and upper body should be kept 30° to
vide only very minimal flow resistance. Several studies have suggested 45° elevated at all times, and the head stabilized in midposition
that the PI is a helpful, noninvasive estimate of ICP and CPP and a cor- (straight forward) avoiding head rotations or lateral flexions, which
relation between PI and ICP exists. The trend of the numerical values of risk jugular venous outflow obstruction. Accordingly, subclavian
PI and its corresponding waveform analysis may be useful as a clinical rather than internal jugular catheters are preferred. Patients with labile
guide for ICP changes (Fig. 86-6). or increased ICP should initially be sedated with short-acting agents
Brain temperature probing presents another monitoring parameter (eg, propofol) to minimize obscuration of the clinical examination.
in the brain injured patient to help avoid secondary injury. It may be Any sedative should ideally be titrated to light sedation with eye open-
used alone or in combination with other intraparenchymal sensors ing and awakening to voice (Richmond Agitation Scale, RASS -2).
(ie, LICOX™, Camino™ ICP monitor). Measured brain temperature is Interventions, procedures, cleaning, mobilization (eg, x-rays, transport,
normally 0.5°C to 2°C higher than core temperature, and temperature etc), and airway manipulations (suctioning, bronchoscopy, etc) in
gradients of 0.5°C to 1°C can be detected between different brain areas patients with labile ICP should be performed with sedative, analgesic,
with standard temperature probes. Cerebral metabolic rate oxygenation and occasionally even paralytic premedication. Airway manipulations
(CMRO ) can increase 10% for every °C above euthermia and decrease may be additionally pretreated with 1 mg/kg of intravenous lidocaine
2
5% for temperatures below normal. This metabolic relationship serves bolus to attenuate coughing.
as the basis for the implementation of early hypothermia after traumatic Most patients will benefit from generous intravascular volume
brain injury. Hypothermia is proposed to improve outcome in brain resuscitation to maintain cerebral perfusion, and there is no role for
64
injury by decreasing metabolic demand, thereby decreasing oxygen con- fluid deprivation in acute brain injury. The method of volume resus-
sumption and alleviating the risk for ischemia. Fever is associated con- citation should be carefully monitored to avoid serum hypotonicity.
sistently with worse outcomes across all categories of acute brain injury. Hyponatremia is a significant risk for increasing ICP as intravascular
Accurately and continuously monitoring brain temperature may assist volume is drawn into brain cells, therefore, intravenous saline solutions
in the management of intracranial hypertension to maintain normother- should consist of at least 0.9% sodium chloride. For the same reason,
mia or to induce hypothermia to decrease cerebral metabolic demand. we avoid correction of hypernatremic states with larger hypotonic fluid
(IV or enteric) boluses as measured ICP may transiently and suddenly
increase in response to such infusions. During large volume infusions,
MANAGEMENT OF INCREASED the serum sodium should be monitored closely and maintained in the
INTRACRANIAL PRESSURE mid-140s as brain injured patients may develop an unexpected, sudden
■ GENERAL APPROACH TO PATIENTS WITH ABNORMAL ICP sodium drop and intracranial hypertension.
Bedside examination of hydration status, pulse contour cardiac output
All patients experiencing acute injury to the neuraxis must be stabilized (PiCCO), monitoring inferior vena cava by ultrasound and other modal-
with respect to circulation, airway, and breathing (CAB) In addi- ities can be used to evaluate hydration status and guide fluid therapy.
65
tion, acute trauma life support (ATLS) provides special attention in Because of the frequent coexistence of myocardial injury, patients with
stabilizing and clearing the cervical spine in patients with suspected acute brain injury, especially the elderly, undergo echocardiography in
or verified trauma. Suggested airway management in patients with addition to ECG and troponin assessment. Serum glucose should be
7

section06.indd 806 1/23/2015 12:56:06 PM