169. Central Nervous System Procedures and Devices

Lumbar Puncture

C/I: skin infection, increased ICP, platelets <20k, >50k are safe, INR > 1.5, heparin/lovenox <24hrs, hemophilia, vW dx, other coagulopathies, trauma to lumbar vertebrae.

Transverse line thru iliac crests is L4 spinous process. Go above (L3-L4) or below (L4-L5). Direct needle toward umbilicus. The ‘pop’ is usually the ligamentum flavum.

US used to identify interspace; not to guide the procedure (basically better able to see midline of spinous processes and where they are in obese patient).

Opening pressure (normal 50-170mmH20) must be measured with patient in lying in extended position; not curled position or it could be artifically elevated. Careful repositiong (straightening of curled patient vs helping the seated patient to a lying position on his side) can be safely performed with the needle in place.

Complications: Post-LP headache (continuous CSF leakage from dural puncture site) – begins 24-48 hrs after procedure – usually frontal or occipital; pressure-like. Worse with patient sitting/standing upright and with Valsalva/coughing. Improves with patient supine. IV caffeine (500mg IV of caffeine sodium benzoate) is common tx. Persistent headache can be treated with epidural blood patch.

CSF Shunts

Silastic tube passed into ventricle via burr hole – tunnels to valve chamber (establishes pressure gradient that allows drainage away from ventricle) – distal tubing goes to drainage point. MC site peritoneal cavity. Can also be right atrium, gallbladder, pleural cavity, ureter. Dials on valve are usually radiopaque can pressure settings can sometimes be seen. MRI can sometimes adjust the valve so settings need to be verified afterward.

Complications: Obstruction (MC proximal tubing), usually within first year. Distal obstruction more common after >2y since placement. Present with increased ICP: headache, lethargy, nausea/vomiting, CN palsies.Fracture (of tubing) – occurs usually over clavicle or distal ribs.

Slit Ventricle Syndrome: overdrainage where elevated ICP eventually leads to drainage again until it hits a point. Will be cyclical – waxing/waning.

Decreased LOC is usually MC sign for malfunction. As ICP increases, paralysis of upward gaze (sundowning), dilated pupils, papilledema.

For simple device, pressing on chamber and observing refill is normal. Difficulty compressing might mean distal flow obstruction whereas slow refill > 3s might indicate prox obstruction. 40$ of obstructed shunts though can have normal refill during manual palpation.

Shunt series: AP/lateral skull, AP chest/abdomen looking for kinking/migration.

CT: ventricular size – need to compare priors since baseline ventricular size is usually abnormal. 24% of documented shunt malformation showed no evidence of malfunction on CT. CT/xray can not be relied on to rule out malfunction in the appropriate clinical setting. Basically always call NSGY, particularly if you are really suspecting it.

Do tap shunt unless life threatening ICP situation. Measure pressure with LP manometer sterilly. Should be 12 +- 2.  Distal obstruction = high H20, proximal obstruction = low H20. Remove slowly to prevent choroid plexus bleeding.

Shunt Infection: 50% occur within first 2 weeks after revision/placement, 70% within 2 months. Usually in very young/old. Higher incidence of meningitis (similiar bugs: Strep pneumo, N.meningitidis). Usual shunt infections caused by staph epidermidis; also Staph aureus and propionibacterium acnes. GN have high risk mortality.

Nonspecific symptoms: headache, AMS, n/v, neck stiffness, fever. Rule out with shunt tap. LP misses shunt infections. Cultures still grow in 1/5 of patient despite normal initial CSF analysis. Treat early with typical meningitis coverage (Vancomycin + Rocephin).

Halo Devices

Rigid cervical immobilization. Used for stabilization of unstable cervical spine fractures/dislocations/subluxations. Not used when distal sensory deficit (unable to detect skin breakdown). 4 pins usually placed in thick portions of skull.

Complications: pin loosening – check for infection; if there is movement of cervical spine, need to apply alternative measure (aspen collar) while waiting on NSGY consult and xrays. Pin site infections occur 50% within first month. Typical pin site infections require typical wound care, treatment for staph/strep if warranted. Pain with mastication usually due to too lateral placement of pins into the temporalis muscle. Dysphagia due to extreme extension of neck. Can also occur with anterior displacement of bone graft.

Intrathecal Baclofen Infusion Devices

Baclofen: GAMA agonist that acts on level of spinal cord to decrease spasticity, improves gait, sitting ability and upper extremity function. Withdrawal symptoms: extreme hypertonicity and spasma which can lead to rhabdo. Treat with oral baclofen, oral or IV benzos.

Implantable CNS Stimulators

Help with Parkinsons resistant to medications. High frequency stimulation in the subthalamic and globus pallidus interna. Consider lead displacement or migration. Consider turning off the stimulator to sort of acute CNS abnormalities.

Spinal Cord Stimulation

Treatment for chronic back pain. Multiple contact points are placed in epidural space and hooked up to pulse generator. Complications include dura puncture, spinal cord compression, CSF leak. MC complication is device failure.

References

Tintinalli, Seventh Edition, Chapter 169: Central Nervous System Procedures and Devices

169. Central Nervous System Procedures and Devices

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