FOR OTOLARYNGOLOGY SURGERY, NEURORADIOLOGY, AND ECT


Intracranial Pressure (ICP)


ICP = cranial (closed space) pressure on brain, CSF, & blood components


•  Brain components: Brain mass/cells (80%); blood (10%); CSF (10%)


•  Normal range: 0–10 mm Hg; CSF: 150 mL normal volume; 450 mL/d


•  Increased ICP can lead to herniation & severe neurologic sequelae


• Acute ↑—shunting of CSF to spinal canal; ventricular compression


• Further ↑—compress brain tissue, mass effect, neuro deterioration


• Severe ↑—Cushing’s triad (↑↑ BP + ↓↓ HR + irreg. resp.)
Herniation—pupil asymmetry, ocular paresis, obtundation, nausea, decerebrate posturing, hemiplegia


Figure 20-1. Relationship between cerebral blood flow in response to changes in PaCO2 and PaO2.





CRANIOTOMY


Anesthetic Management




General Features


•  Mayfield pins & horseshoe headrest both commonly used


• Pinning is highly stimulating


• Anesthesiologist must anticipate (rather than react to) stimulation


• Best to place invasive arterial monitoring before pinning


• May inject pin sites with local anesthetic before pinning


• May need to deepen anesthesia/control BP in anticipation of pinning (may give IV, propofol, nicardipine, or opioid 30 sec prior)


•  Airway may be rotated away from anesthesiologist


•  Soft bite block should be placed immediately after induction between molars


• Tissue edema from tongue biting can form during surgery


• Can prevent tube kinking from biting or positioning


•  Eye protection


• Secure taping of the closed eyelids


• Careful application of ophthalmic ointment recommended to avoid physical & chemical injury of the cornea


•  Plan early for IV access (arms out or tucked)


• Decide early on need & site for intraop infusions


• Infuse via visible IV (if possible) to ↓ unnoticed infiltration


•  Main times of stimulation: Intubation/pinning/incision/drilling/dural incision


•  Avoid coughing/bucking/movement at any time


•  Rapid blood loss is possible during any craniotomy


•  Immediate postop assessment of neurologic function is crucial


• Inability to perform neuro exam → immediate postop CT imaging


• Avoid routine use of sedative medications (confound postop assessment)


•  Opioids: Often used as part of a balanced-anesthesia technique


• Aggressive use of narcotics may lead to delayed emergence


• Give opioid dose early (i.e., induction, pinning, incision)


• Fentanyl = short-acting & titratable (5–10 mcg/kg total dose)


• Hydromorphone = longer-acting, give for postop analgesia


• Morphine = sedating, slow emergence; avoid in intracranial proc.


(Morphine metabolites may accumulate in renal failure)


• Remifentanil (0.1–0.5 mcg/kg/min) & sufentanil (0.1–0.2 mcg/kg/hr can be used as infusions


• Consider intravenous acetaminophen (1 g/6 hrs) for adjunctive analgesia


•  Tight control of BP via invasive monitoring


•  Fluid resuscitation


• Normal saline is usually the crystalloid solution of choice (can ↑↑ CI → metabolic acidosis)


• Avoid hypotonic or glucose containing fluids (can inc. brain swelling/injury)


• Colloid used as indicated by clinical context


•  Periop antibiotics usually indicated


•  Anticonvulsant therapy


• Indications for anticonvulsant & steroids vary with each pt


• May potentiate neuromuscular blockers (acute) or antagonize NMB (chronic)


• Anticonvulsant often used if contact with cortical tissue anticipated


• IV phenytoin (dilantin) loading dose: 18 mg/kg in 250 mL NSS at 25 mg/min)


Caution: Rapid bolus dosing of phenytoin may cause significant cardiac arrhythmia, hypotension, & cardiovascular collapse


• Fosphenytoin (a phenytoin prodrug with ↓ side effects) loading dose: 15–20 phenytoin equivalent mg/kg in 250 mL NSS @ 50–100 PE mg/min


• IV levetiracetam (keppra) loading dose: 1000 mg in 100 mL of normal saline over 15–30 min


Underlying renal failure, metabolic syndrome, & baseline meds should be considered prior to anticonvulsant admin


•  IV dexamethasone (10 mg bolus, repeat 4 mg q6h) for edema when indicated


• Usually reserved for cases with intracranial lesion, elevated ICP, edema


Induction


•  Controlled induction with hemodynamic stability


•  Moderate hyperventilation in setting of ↑ ICP


•  Combination of propofol 1–2 mg/kg, fentanyl 2–4 mcg/kg & nondepolarizing muscle relaxant is one approach


•  Rapid, short-acting anti-HTN agents (esmolol, nicardipine) should be available


•  Succinylcholine associated muscle fasciculation may result in transient ↑ ICP


•  Coughing, bucking, or sympathetic surge during laryngoscopy with ↑ BP may cause sudden & untoward ↑ ICP (can use lidocaine 1 mg/kg to prevent)


•  Physiologic manifestations of light anesthesia may be devastating in pts with intracranial aneurysm susceptible to rupture


Maintenance


•  May use amnestic dose (0.5–1.0 MAC) of inhalational agent to ↓ brain volume


•  Narcotic bolus as needed up to a predetermined estimate of total dose


•  Consider TIVA if monitoring evoked potentials or if need to ↓ brain volume


• Consider using a processed EEG monitor to guide TIVA dose


•  Common strategy


• Propofol infusion for amnesia & brain relaxation


(Stop infusion once 1° resection complete to expedite emergence)


• Narcotic infusion for analgesia & immobility


(If muscle relaxation contraindicated because of monitoring)


•  Provided an appropriate anesthetic depth has been reached, HTN should be liberally treated with labetatol or nicardipine to decrease likelihood for emergence hypertension


•  Closely monitor urine output & resuscitate with normal saline


•  Monitor glucose & treat glucose >160 mg/dL with insulin


• Hyperglycemia may predispose to or exacerbate neurologic injury


•  If not contraindicated by monitoring requirements, maintain muscle relaxation to one twitch with bolus or infusion of nondepolarizing muscle relaxant


•  Maintain MAP within 20% of baseline


•  N2O may be used with several caveats:


• May complicate EEG or potential monitoring if level not constant


• May ↑ cerebral blood flow & contribute to brain swelling/↑ ICP


• May contribute to pneumocephalus (particularly in posterior fossa proc.) or pneumothorax expansion (esp. in trauma)


• May have deleterious effects on neuronal cells (under investigation)


Emergence


•  BP control is critical


• HTN episodes at emergence & postop may cause ↑ bleeding or edema


• Treat with labetalol or nicardipine


•  Prophylaxis for nausea/vomiting recommended (ondansetron)


• Avoid promethazine, droperidol, diphenhydramine (can be sedating)


•  Emergence should begin after Mayfield pins have been removed


•  Time should be allowed (5 min) for head wrapping before extubation


•  Extubation: Reaches baseline mental status


•  Small boluses of propofol (10–40 mg) or remifentanil (0.2–0.5 mcg/kg) can smooth emergence as can a dexmedetomidine infusion


•  Continuous vital sign monitoring during transport


Special Features of Operations Involving the Posterior Fossa


•  ↑ ICP commonly a concern (due to obstruction by a posterior fossa mass)


• Consider aggressive treatment of ICP prior to induction


• In severe cases, consider ventriculostomy under local anesthesia


• ↑ ICP may occur if head down during positioning/surgical prep


•  Prone, head-up position—concern for air embolus


•  Potential for postop, compressive pneumocephalus


•  Kinking of ETT with neck flexion in pins (MUST place bite block)


• Postextubation macroglossia, tongue ischemia/injury


•  Proximity to critical neurologic structures involving regulatory centers


• Brainstem/medulla/pons regulatory centers


• Bradycardia, apnea, rapid swings in BP may occur


• Possibility for new postop deficits


•  Small operative window may lead to inc. brain swelling


• Jugular venous drainage/head position



Awake Craniotomy


•  Used for resection of tumors (motor or speech cortex) & epileptic foci


•  Team approach with emphasis on communication, patience, & experience


•  Critical to set pt & surgeon expectations


•  Awake with variable sedation versus “asleep → awake → asleep” with LMA/ETT


• Preference varies by center & experience


• Simplest method is to avoid airway instrumentation


• Only period of intense stimulation is opening/drilling/dural incision


•  Patient comfort


• Positioning with padding/pillows for optimal comfort


• Vasoactive substances (nitroglycerin) may cause profound headache


• Warming blanket as needed for patient comfort


• Placement of Mayo stand over head to lift drapes off of the awake patient


•  Preparation


• IV access, monitors, & arterial line prior to blocks


• Consider bilateral nasal trumpets (28–34 Fr) connected to O2 for airway management


Topical anesthetic & vasoconstrictors to nares prior to placement


•  Consider peripheral nerve blocks


• CNV1—supraorbital, supratrochlear n.


• CNV2—auriculotemporal, zygomaticotemporal n.


• Cervical branches—posterior auricular, greater & lesser occipital n.


• Remifentanil infusion for analgesia during block placement; PONV prophylaxis at start


• Choice of local: Use long-acting ropivicaine 0.375% with 1:200,000 epi


• Bupivicaine in large volume may have increased risk of cardiac toxicity


• Allow for additional local to be infiltrated by surgeons


• Metoprolol prior to block to blunt tachycardia


•  Maintenance


• Deeper sedation only during drilling & opening of bone flap


• Minimize sedation just before dural incision


• Monitor CO2—hypercarbia can contribute to brain swelling


• Propofol/remifentanil with spontaneous ventilation


• Dexmedetomidine infusion is a useful adjunct


Minimal resp. depression, can cause hypotension/bradycardia


Treat with glycopyrrolate (0.2 mg) if bradycardia is clinically significant


Load 1 mcg/kg over 15 min & infuse 0.3–1 mcg/kg/hr


• Neuromonitoring


Map functional cortex—usually speech area


Requires continuous patient feedback, communication, contact


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Aug 28, 2016 | Posted by in ANESTHESIA | Comments Off on FOR OTOLARYNGOLOGY SURGERY, NEURORADIOLOGY, AND ECT

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