Neuro Anesthesia Part 2 Flashcards

Question

Induction of Anesthesia

Answer 1

STP, propofol, or etomidate **Prompt induction** without ICP elevation Muscle relaxant to facilitate endotracheal intubation & mechanical hyperventilation (BEWARE: coughing causes marked increases in ICP) Succinylcholine does not significantly alter CBF or ICP in patients with neurological injury…

Answer 2

**Elastance** = change in pressure / change in volume When intracranial compensatory mechanisms are exhausted, small changes in volume lead to dramatic changes in ICP

Answer 3

Goal: Not to have large hemodynamic swings in blood pressure. Increase with insertion & then decrease after due to the fact you administered a longer acting agent and now there is “down time”… No one way is “perfect” Know that your SBP will predictably **rise** ~40mmhg Therefore need to lower b/p… **Do NOT** let them start until you do this… AND do **NOT lower the b/p UNTIL they have pins in hand ready to go…** What does the evidence reveal & what do I do…

Answer 4

“The effect of skull-**pin** insertion on cerebros**pin**al fluid pressure and cerebral perfusion pressure: influence of sufentanil and fentanyl” Conclusion: In anesthetized patients, an intravenous bolus of fentanyl(4.5 mcg/kg) or sufentanil (0.8mcg/kg) prior to skull-**pin** insertion results in stable values of CSFP, CPP, BP, and HR... The b/p was modified with phenylephrine / atropine were indicated

Answer 5

Minimum of 4 mcg/kg Fentanyl Titrate Iso to **NO** more than **1.0 MAC** Propofol 1mg/kg, titrated to response Esmolol/Ntg – Only if necessary Lower SBP by ~40mmg Consider Lidocaine* **PIN Placement** Lower Iso, Propofol, NTG effects gone… B/P Normalizes

Answer 6

Positioning…100% fio2 Ett/IV can dislodge monitor vitals closely can take longer than you think... Position depends on tumor location Supratentorial: supine Infratentorial: prone or **sitting** (BEWARE: greatly increases risk of **venous air embolism) **

Answer 7

Mannitol reduces brain bulk by creating an osmotic gradient across the “**intact**” blood brain barrier causing water to flux from the extracellular extravascular to intravascular compartments. There also is evidence that mannitol improves deformability of red blood cells, thereby reducing viscosity promoting increased blood flow.

Answer 8

Mannitol is best given PRIOR to the time of skin incision (typically 0.5 mg/kg) so the peak effect becomes available upon dural opening. Additional mannitol may be of value if the brain is still "tight". Excessive use of Mannitol with serum osmolalities **> 320 mosms** may cause renal failure. Cumulative doses of Mannitol can exacerbate brain edema by leaking it to the brain interstitium. Adding Lasix is an option.

Answer 9

1. Rebound increase in ICP, if BBB not intact 2. Pulmonary Edema 3. Hypovolemia 4. Hyperkalemia (Transient-seen first) 5. Transient Hyponatremia & decrease in hgb concentration (acute hemodilution) VERY COMMON

Answer 10

I always see Hypokalemia? Acute increases in osmolaritity are reported to increase K by 0.6meq/L per 10 mOsm/L. The movement of water out of the cells is accompanied by movement of K out of cells The latter may be a result of “solvent drag” or the increase in intracellular K that follows cellular dehydration... If F & E are not repleted with diuresis Hypokalemia ensues…VERY COMMON in neurosurgery… Refer to Handout related to Mannitol

Answer 11

Discussion: mannitol versus hypertonic saline pharmacological principles of it use

Answer 12

Maintenance of anesthesia during craniotomy is usually uncomplicated & generic in many respects. There are two special considerations: 1. In patients with intracranial mass lesions, brain bulk can be a problem, particularly when the dura is being opened. 2. A swollen brain can herniate through the dural defect prohibiting further dural incision.... NOT GOOD!

Answer 13

* mannitol 0.25-1 Gm/kg IV * furosemide 0.5-1 mg/kg IV * thiopental * head up position (not >’er than 10-15 degrees) * hyperventilation * CSF Drain (Extremely effective) * Muscle Relaxants (Muscle activity -”light anesthesia’ contributes to cerebral swelling) * Discontinue N2O

Answer 14

EBL…Watch the clear plastic pouch Minimum: 1-3 ml/kg/hr Glucose NOT recommended - Discussed previously… - Hyperglycemia worsens cellular ischemic injury Isotonic crystalloids Hetastarch OK / Albumin better

Answer 15

Hetastarch decreases platelet aggregation… “Effect of delayed albumin hemodilution on infarction volume & brain edema after transient middle cerebral artery occlusion in rats” J Neurosurg 87: 595-601, 1997 **Conclusion**: Hemodilution with high-concentration albumin decreases focal cerebral ischemic injury

Answer 16

A human protein therefore: * Binds & inactivates toxic products * Regulation of plasma interstitial fluid concentrations of endogenous & exogenous administered substances & drugs * Maintenance of microvascular permeability to proteins * Scavenging of free radicals & prevention of lipid peroxidation

Answer 17

avoid coughing, straining thiopental or lidocaine BEWARE: N2O may cause tension pneumocephalus delayed return to consciousness or neurologic deterioration: CT or MRI

Answer 18

Brainstem Injury - Due to retraction, direct surgical trauma, or ischemia Positioning - VAE Pneumocephalus - Increased likelihood with sitting position Postural Hypotension

Answer 19

**Consider whenever head > 5 cm above heart ** - Air -> RV -> pulmonary circulation - Decreases pulmonary blood flow - pulmonary edema, bronchoconstriction, cardiovascular collapse, hypoxemia paradoxical (air) embolism * cerebral circulations * via patent foramen ovale (PFO) * 20-30% of adults have patent foramen ovale

Answer 20

Precordial Doppler ultrasound near right upper sternal border is **most sensitive non-invasive monitor** (**detects 0.25 m**l) trans-esophageal echocardiography is **most sensitive, but more invasive** and cumbersome then doppler, "mill-wheel" murmur sudden *decrease* in ETCO2, *increase* in ETN2 , *increase* in PAP’s hypoxemia, hypotension, dysrhythmias

Answer 21

* notify surgeon * irrigate operative site with fluid * apply occlusive material to bone edges * 100% O2, discontinue N2O * aspirate air through right atrial catheter (best if tip is at SVC-RA junction) * head down position * increase CVP, give fluids * inotropes, vasopressors may be needed * gently compress internal jugular veins * BEWARE of PEEP: - by reversing RA-LA pressure gradient, may lead to paradoxical air emboli via PFO * If the above measures fail, LLD with head slight down in attempt to dislodge air lock

Answer 22

A congenital malformation (although there have been some reported cases of an acquired form.) It is an anomaly in the posterior fossa A reduction in CSF pathways A protrusion of the **cerebellar tonsils** through the bottom of the skull **(foramen magnum)** into the spinal canal. The tonsils would normally be round -- often become elongated as they protrude down the spinal canal. Diagnosis can be difficult because not all patients will have the classical sign of deeply herniated tonsils.

Answer 23

Type I most common Characterized by downward displacement by > four millimeters, of the cerebellar tonsils beneath the foramen magnum into the cervical spinal canal.

Answer 24

Compression of the upper part of the spine into the base of the skull with resulting compression of the brainstem. Bony union of the first level of the spine (C1) to the base of the skull. Partial bony union of the first and second levels (C1 fusion to C2) of the spine.

Answer 25

Local decompression of the overlying bones Decompression of the bones Provides more space for the brainstem, spinal cord, and descended cerebellar components. A tissue graft is often spliced into this opening to provide even more room for the unimpeded passage of CSF. Removing the back of the foramen magnum and often the back of the first few vertebrae to the point where the cerebellar tonsils end Monitoring…SSEP/BAER/MEPS + Mannitol

Answer 26

Using the transsphenoidal route: Through the nose and across the sphenoid sinus of the face Result = no noticeable facial scar

Answer 27

In the United States, pituitary tumors represent 10% to 15% of all intracranial tumors diagnosed each year These benign lesions originate from the cells of the pituitary gland, which is located in the ***Sella turcica*** a rounded, bony structure behind the nose and ethmoid sinus of the face.

Answer 28

The pituitary gland is sometimes called the "master" gland of the endocrine system, because it controls the functions of the other endocrine glands The pituitary gland is no larger than a pea, and is located at the base of the brain The gland is attached to the hypothalumus (a part of the brain that affects the pituitary gland) by nerve fibers.

Answer 29

The pituitary gland itself consists of three sections: 1. the anterior lobe 2. the intermediate lobe 3. the posterior lobe

Answer 30

**Growth hormone ** **Prolactin** - to stimulate milk production after giving birth **ACTH** (adrenocorticotropic hormone) - to stimulate the adrenal glands **TSH** (thyroid-stimulating hormone) - to stimulate the thyroid gland **FSH** (follicle-stimulating hormone) - to stimulate the ovaries and testes **LH** (luteinizing hormone) - to stimulate the ovaries or testes

Answer 31

**Melanocyte**-stimulating hormone - to control skin pigmentation

Answer 32

**ADH** (antidiuretic hormone) - to increase absorption of water into the bloodby the kidneys **Oxytocin** - to contract the uterus during childbirth and stimulate milk production

Answer 33

A normal pituitary gland serves the vital function of producing hormones that interact with other parts of the body, such as the thyroid and adrenal glands, to regulate hormonal output Pituitary tumors can disrupt the output of hormones and are broadly categorized as either secreting or nonsecreting tumors.

Answer 34

Secreting tumors cause excess hormone production The most common type of secreting tumor is the **prolactin** tumor * In females, this tumor produces a classic combination of amenorrhea (infertility) and galactorrhea (lactating breasts) - These symptoms usually cause women to seek medical attention early, so the tumor is often detected while it is still small.

Answer 35

Prolactin tumors are less common in males, and are not usually detected until the tumors are larger in size This is because men tend to ignore the hormonal symptoms which occur as a result of the tumor, including fatigue and lack of sexual interest Patients with larger tumors that cause visual impairment due to compression of the optic chiasm

Answer 36

Other secreting tumors include the Growth Hormone and the Adrenocorticotropic Hormone (ACTH) types These tumors stimulate excessive adrenal function and can cause drastic medical issues such as hypertension and diabetes Most of these tumors are treated surgically, although adjunctive treatment with medication or radiation may be necessary for some in the postoperative period.

Answer 37

Cushing's syndrome is a debilitating endocrinopathy characterized by excessive cortisol levels in the blood which may be produced from tumors of the pituitary gland, adrenal glands or from tumors or cancer arising elsewhere in the body (ectopic ACTH producing tumors) Cushing's disease refers specifically to excessive ACTH secretion by a pituitary adenoma

Answer 38

The cause of Cushing's Syndrome is a pituitary adenoma in over 70% of adults and in approximately 60-70% of children and adolescents Most pituitary ACTH-secreting adenomas are small in size (microadenomas) Overall, Cushing's Disease is relatively rare, affecting 10 to 15 of every million people each year

Answer 39

* Change in body habitus: weight gain in face (moon face), above the collar bone (supraclavicular) and on back of neck (buffalo hump) * Skin changes with easy bruising, purplish stretch marks (stria) and red cheeks (plethora) * Excess hair growth (hirsutism) on face, neck, chest, abdomen, and thighs * Generalized weakness & fatigue/Wasting of musculature * Menstrual disorders in women (amenorrhea) * Decreased fertility and/or sex drive (libido)

Answer 40

Hypertension Diabetes mellitus Depression, mood and behavior disorders

Answer 41

Nonsecreting (nonfunctional) tumors are usually large when they are discovered due to the lack of hormonal side effects People with these tumors don’t realize there is a problem until the tumor begins to compress the optic chiasm, causing visual loss Patients with nonsecreting tumors usually respond well to surgical treatment, though improvement in visual function is dependent on the length of time vision is impaired prior to the procedure

Answer 42

TRANSSPENOIDAL RESECTION for pituitary tumors<10 cm Surgical approach is underneath the upper lip thru nasal septum and roof of sphenoid sinus to penetrate floor of sella turcica. Surgeon uses a microscope. Pituitary gland sits on top of the sella turcica. Tumors often hormone secreting. ANTERIOR: ACTH,GH,FSH,LH,PRL POSTERIOR: ADH (vasopressin)

Answer 43

**DO NOT** treat like other tumors (space occupying lesions) Normovolemic, normotensive, normocapnic **Do not shrink brain.** A full brain will push tumor down to surgeon-GOOD

Answer 44

Need for mucosal injection of epi-containing solutions Accumulation of blood & tissue debris in pharynx & stomach Risk of hemorrhage from inadvertent entry into the cavernous sinus or internal carotid artery

Answer 45

* Cranial nerve damage * Pituitary hypofunction - Prophylactic Decadron administration - Does not effect cortisol levels * Diabetes insipitus - 40 % chance postoperatively - < commonly intraoperatively - usually transient, U.O.>1L/hr - give DDAVP * Supine & slightly head up predisposes pt to VAE * CSF Leak

Answer 46

VEP may be employed with large tumors that involve the optic nerve +/- Precordial doppler 2 large bore IV’s If co-morbidity present, +/- A-line Many avoid N2O to prevent post op pneumocephalus Intense muscle paralysis Intrathecal CSF drain to facilitate surgical exposure May instill saline...