Obj. 12-17 Flashcards
What is the preferred method of anesthesia with Evoked Potentials?
Narcotics-they cause little change
In what order are Evoked Potentials adversely affected by anesthetic agents? (greatest to least)
VEP > SSEP/MEP > BAEP
What are Visual Evoked Responses used for?
Visual Evoked Responses:
- evaluate the optic nerve
- used for tumor surgery that may effect the optic chiasm, pituitary or anterior cerebral vasculature
What are Brainstem Auditory Evoked Responses used for?
Brainstem Auditory Evoked Responses:
- monitor the function of the auditory pathway between CN VIII and the brainstem and cortex
- Used in pts with increased risk for brain injury during intracranial surgery
What are Motor Evoked Potentials used for?
Motor Evoked Potentials:
-monitor ischemia in the anterior (ventral) columns by stimulating the motor cortex to elicit movement
How do IV and inhalational agents effect Motor Evoked Potentials?
Motor Evoked Potentials:
- are very sensitive to anesthetics (particularly VAs. N2O is < depressing than equivalent MACs of other VAs)
- TIVA works well: narcotics, propofol. Propofol causes MEP suppression, but < than VAs
- NDMR weaken MEPs! (Avoid during critical parts of surgery)
What are Somatosensory Evoked Potentials (SSEPs) used for?
SSEPs:
- monitor sensory pathways (DORSAL COLUMN, brainstem, subcortex, and sensory cortex). Used during spine surgery& intracranial vascular surgery
- the response of peripheral nerve stimulation to CONTRALATERAL somatosensory cortex
- SSEPs are derived from EEG waves, just significantly less.
How do IV and inhalational agents effect SSEPs?
- All VAs:dose-dependent increase in SSEP latency/decrease in amplitude
- Adding N2O potentiates these responses of VAs & IV AGENTS (fentanyl) when used with GA, but N2O alone effects SSEPs LESS than equivalent MAC levels of gases
- NDMRs do not hinder SSEPs & may improve waveform quality
Which two IV agents dramatically increase ampitude?
Etomidate & Ketamine
What is the suggestion for titration of VAs with any mode of Evoked Potentials?
Use < .5 MAC (.5-1) & avoid rapid changes in anesthetic depth (Find a good plane & keep them there!)
What is Electromyography (EMG) used for?
EMG:
- assesses cranial and peripheral motor nerves with electrodes placed into or near specific muscles
- used during spine surgery or to look at specific cranial nerves
How do IV and inhalational agents effect EMGs?
- VAs do not affect EMGs
- AVOID MUSCLE RELAXANTS
What are the indications for cerebral oximetry monitoring?
- mostly used in CEAs
- intracranial surgery where a change in the patient’s neuro status may occur
- shoulder surgeries and other sitting cases
How is cerebral oximetry used to monitor the neurosurgical patient?
- Obtain baseline cerebral oximetry reading pre-induction
- Monitor and keep it within 20% of baseline (more than that correlates with a change in neuro status)
- Notify surgeon of sudden, drastic changes. Benefits are controversial.
How should fluids be managed in neurosurgery?
- AVOID glucose-containing solutions
- Keep the pt ISOvolemic, ISOtonic, & ISOoncotic. If dehydrated, restore volume
- Give hourly maintenance & replace U/O
- Replace blood when Hct 25-30% (depending on status & hx)
- Mannitol may be given after the dura is opened
Discuss positioning in neurosurgery (in general).
- Most common: supine, semi-sitting, lateral & prone
- 100%O2 prior to turn & remember to reconnect all monitors!
- Watch for hypoTN with sicker pts. Possibly turn agent down/off
If neurosurgery in the supine position, use caution to…
Avoid extreme head rotation that can obstruct jugulars or vertebrals
If neurosurgery in the prone position, one should…
- watch eyes for risk of BLINDNESS
- Check ALL pressure points
What are the relative contraindications to the sitting position?
- pt with ventriculo-atrial shunt
- an awake, un-anesthetized pt demonstrating cerebral ischemia in the upright pstn (cerebral vascular dx, coronary dx)
- CAD with CHF with Right atrial P> Left atrial P, or patent foramen ovale
What are the complications of sitting pstn?
- Circulatory instability
- VAE
- Quadriplegia
- Head, neck, and tongue edema
- Compressive peripheral neuropathy
How is ventilation managed during neurosurgery?
- Obtain baseline ABG to aproximate PaCO2 with etCO2 readings
- Routine hyperventilation is NO LONGER recommended
- Maintain PaCO2 30-32 mmHg
Which drugs treat “tight brain?”
- Boluses or transfusions of thiopental, etomidate, propofol, or narcotic
- Diuretics
What is the most sensitive NON-invasive monitor for VAE?
Precordial Doppler (still a standard modality)
What are the anesthetic implications of stereotactic -assisted procedures?
- Pts are often sedated & local anesthesia is used to apply the localizing frame
- Sedation is omitted if IICP or altered LOC
- Awake FOB may be safest, intubation is hard with frame in place
- Avoid hypocapnea during GA to prevent shifting of the brain
