NeuroAnesthesia

Trauma

100

Fluid that may have increased mortality

What is albumin there are conflicting opinions and cross-currents in the literature. An analysis of the subset of patients in the SAFE (Saline versus Albumin Fluid Evaluation) trial with severe TBI (Glasgow Coma Scale [GCS] score, 3 to 8) revealed increased mortality among those who received albumin.

200

GCS score that requires intubation

What is 7-8 or less

300

Monitoring for TBI

What is SjvO2. This monitoring has been used to guide the management of patients with TBI.* The underlying concept is that a marginal or inadequate CBF results in an increasing oxygen extraction, a widening arteriovenous content difference, and reduction of SjvO2. Normal subjects have SjvO2 values between 60% and 75%. An SjvO2 less than 50% for 5 minutes is commonly accepted as constituting jugular desaturation.Brain tissue PO2 (PbtO2) has been used to guide the management of both TBI and SAH, and there have been limited reports of improvement in outcomes thereby.301-315 A PbtO2 equal to or more than 20 to 25 mm Hg is viewed as normal, and values equal to or less than 10 to 15 mm Hg are assumed to convey a substantial risk of hypoxic injury.

400

Optimal CPP in TBI

What is 60.The Brain Trauma Foundation’s most recent recommendations, however, give clinicians wide latitude in offering a recommendation of CPP targets “within the range of 50 to 70 mm Hg” in adults.68 Age-related CPP targets of 40 to 50 mm Hg have been recommended for children.

500

Role of hypothermia in TBI

What is None.Several local, prospective trials of hypothermia after TBI were performed. Because those trials appeared to indicate good patient tolerance of sustained mild hypothermia (32° C to 34° C) and improvement in ICP and outcome, a multicenter trial was performed. That trial, which required induction of hypothermia within 8 hours of injury, revealed no overall benefit. Because of concern that 8 hours was not sufficiently rapid, a second trial, which achieved the target temperature in 2.5 hours, was performed with no benifit.

Physiology

100

Cerebral Perfusion Equation

What is (CPP = MAP − ICP)

200

The single most important determinant of blood viscosity

What is HCT. Blood viscosity can influence CBF

300

Autoregulation likely occurs at MAP values of approximately

What is 70-150. Autoregulation refers to the capacity of the cerebral circulation to adjust its resistance to maintain CBF constant over a wide range of mean arterial pressure (MAP) values

400

Normal ICP

What is 8-12 mm Hg

500

Amount of CBF per minute

What is Global 45-55 mL/100 g/min, Cortical (mostly gray matter) 75-80 mL/100 g/min, Subcortical (mostly white matter, ≈20 mL/100 g/min

Medications

100

An intravenous agent that increases CBF and CMR

What is Ketamine. The anticipated ICP correlate of the increase in CBF and CBV has been confirmed to occur in humans. However, anesthetic drugs (e.g., diazepam, midazolam, isoflurane-N2O, propofol) blunt or eliminate the increases in ICP or CBF associated with ketamine.In fact, decreases in ICP occur when relatively large doses of ketamine (1.5 to 5 mg/kg) are administered to patients with head injuries who are sedated with propofol.

200

Inhalation Anesthetic that increases in CBF, CMR, and ICP

What is N2O. At least a portion of the increases in CBF and CMR may be the result of a sympathoadrenal-stimulating effect of N2O. The magnitude of the effect considerably varies according to the presence or absence of other anesthetic drugs

300

What happens to the CBF/CMR ratio with volatile anesthetics

What is Increased.This alteration is dose related, and, under steady-state conditions, increasing doses of volatile agents lead to greater CBF/CMRO2 that is, higher MAC levels cause more luxury perfusion

400

Can produce modest increases (∼5 mm Hg) in ICP in lightly anesthetized humans.

What is Succinylcholine.Although succinylcholine can produce increases in ICP, it can still be used for a rapid-sequence induction of anesthesia. Kovarik and coauthors205 observed no change in ICP after the administration of succinylcholine, 1 mg/kg, to 10 nonparalyzed, ventilated neurosurgical patients in the ICU, 6 of whom had sustained a head injury. Their observations are very relevant because it is in precisely this population of patients that the issue of the use of succinylcholine arises most frequently.

500

An osmotic diuretic that is used to lower ICP can exacerbate this cardiac condition if administered rapidly.

What is congestive heart failure? The purpose of diuretic therapy in intracranial procedures is to dehydrate the brain, thereby leading to a reduction in the volume of the fluid compartment. This facilitates surgical exposure and reduces the requirement for brain retraction. Because mannitol initially draws water into the vascular space before it is excreted, rapid dosing can cause a transient increase in ICP and can cause an acute CHF exacerbation. Administer over 20-30 minutes or alternatively, use Lasix. You may start with doses as small as 5 mg increments in a Lasix naïve person.

Anatomy

100

The adult human brain weighs approximately ?

What is 1350 Grams

200

How much Cardiac Output does the brain receive ?

What is 12-15%.

300

The brain consumes oxygen at an average rate of approximately ?

What is 3.5 mL of oxygen per 100 g of brain tissue per minute. Whole-brain oxygen consumption (50 mL/min) represents approximately 20% of total body oxygen utilization.

400

Arterial blood supply to the brain is composed of ?

What ispaired right and left internal carotid arteries, which give rise to the anterior circulation, and paired right and left vertebral arteries, which give rise to the posterior circulation. The connection of the two vertebral arteries forms the basilar artery. The internal carotid arteries and the basilar artery connect to form a vascular loop called the circle of Willis that permits collateral circulation between both the right and left and the anterior and posterior perfusing arteries. Three paired arteries that originate from the circle of Willis perfuse the brain: anterior, middle, and posterior cerebral arteries. The posterior communicating arteries and the anterior communicating artery complete the loop.

500

3 sets of Venous Drainage of the brain

What is the superficial cortical veins are within the pia mater on the brain surface. Deep cortical veins drain the deeper structures of the brain. These veins drain into dural sinuses, of which the superior and inferior sagittal sinuses and the straight, transverse and sigmoid sinuses are the major dural sinuses. These ultimately drain into the right and left internal jugular veins.

Mixed Bag

100

For controlling intracranial pressure (ICP), the clinician should consider the four subcompartments

What is cells, interstitial and intracellular fluid, cerebrospinal fluid (CSF), and blood. Blood compartment is most easily altered by the anestetist

200

Ways to rapidly decrease ICP

What is Reduction of PaCO2 (to not <23-25 mm Hg) CSF drainage (ventriculostomy, brain needle) Diuresis (usually mannitol) CMR suppression (barbiturates, propofol) MAP reduction (if dysautoregulation) Surgical control (i.e., lobectomy or removal of bone flap)

300

Dose of mannitol for reducing ICP

What is 0.25 g/kg to 100 g “for all comers”; 1.0 g/kg is the most common dose. However, a systematic study in TBI demonstrated that an equivalent initial ICP-reducing effect can be achieved with 0.25 g/kg, although that effect cannot be as sustained as when larger doses are used. Others use doses greater than 1.0 g/kg. Mannitol should be administered by infusion (e.g., over 10 to 15 minutes).

400

This is standard prophylactic therapy to prevent cerebral vasospasm. The mechanism of action is unknown however if given orally, it does improve outcomes.

What is Nimodipine? Patients given nimodipine have no change in overall incidence of vasospasm, but they have a lower incidence of severe narrowing. In addition, although no improvement is found in mortality, there is improvement in outcome for survivors.

500

The most sensitive monitor for venous air embolism.

What is TEE? VAE can potentially occur whenever there is an open venous channel beyond the venous fluid column to the heart. The sitting position confers the highest risk of VAE. The posterior fossa contains several major dural venous sinuses and their confluences, which are noncollapsible, drain into the internal jugular vein. Any posterior fossa craniotomy, regardless of position, should be considered for VAE monitoring. TEE is able to detect volumes of 0.02 mL per kg.