What are the anesthetic considerations for ventriculoperitoneal shunt insertion?

Anesthetic Considerations for Ventriculoperitoneal Shunt Insertion

Pre-Induction Management

In pediatric patients with raised intracranial pressure (ICP), administer hypertonic saline (2.7-3%, 2-3 ml/kg) as a bolus before induction to prevent ICP spikes during laryngoscopy and apnea. 1

Critical Pre-Operative Assessment

• Measure and document baseline mean arterial pressure (MAP) targets specific to age in pediatric cases:

  • <3 months: 40-60 mmHg
  • 3 months-1 year: 45-75 mmHg
  • 1-5 years: 50-90 mmHg
  • 6-11 years: 60-90 mmHg
  • 12-14 years: 65-95 mmHg 1

• Check blood glucose in young children who are prone to rapid hypoglycemia; maintain normal range with isotonic saline containing 5-10% glucose at 50-60% of standard maintenance rates 1

• In obstructive hydrocephalus with blocked VP shunt, discuss with neurosurgery regarding sterile aspiration of the VP shunt reservoir (5-10 ml via butterfly needle) before transfer 1

• Ensure osmotherapy availability (hypertonic saline boluses or mannitol 20%) throughout the perioperative period, as children have less available intracranial space until age 20 and small volume changes cause dramatic clinical consequences 1

Induction Considerations

The tunneling phase of VP shunt insertion causes the most significant hemodynamic and ICP perturbations, requiring specific opioid management. 2, 3

Opioid Selection and Timing

• Administer fentanyl 1 mcg/kg at least 3-5 minutes before the tunneling phase to attenuate the hemodynamic response 2, 3

• Avoid butorphanol in neurosurgical patients, as it causes prolonged elevation of ICP and cerebral perfusion pressure changes during tunneling compared to fentanyl 2

• Despite fentanyl pretreatment, expect significant increases during tunneling:

  • MAP increases from ~81 to ~111 mmHg
  • ICP rises from ~21 to ~29 mmHg
  • Heart rate increases from ~74 to ~94 bpm
  • Hemodynamic changes persist for 3 minutes post-tunneling
  • ICP elevation lasts for 2 minutes 3

Induction Technique

• Use standard induction agents with awareness of their effects on blood pressure and ICP:

  • Fentanyl 2 mcg/kg
  • Thiopentone 4-5 mg/kg
  • Rocuronium 1 mg/kg for intubation 2

• Consider the potential fall in blood pressure related to opioids and induction agents when planning pre-induction hypertonic saline in children 1

Intraoperative Monitoring and Maintenance

Maintain end-tidal CO2 at 32 ± 2 mmHg through controlled mechanical ventilation to prevent ICP elevation from hypercarbia. 2

Essential Monitoring

• Standard monitoring includes heart rate, ECG, invasive arterial blood pressure, pulse oximetry, and capnography 2, 3

• Maintain capnography values at 4-5 kPa throughout the procedure 1

• In pediatric cases, avoid taping eyes closed to permit regular pupillary examination; use moisturizing eye drops or saline to prevent corneal drying 1

• Document pupillary size and reaction during the procedure 1

Anesthetic Maintenance

• Maintain anesthesia with isoflurane in N2O/O2 at MAC 1.0 ± 0.2 2

• Ensure adequate depth before tunneling despite prior fentanyl administration, as this phase remains intensely stimulating 3

Surgical Timing Considerations

Ideally, place the ventricular end of the shunt catheter before the tunneling phase to avoid ICP rises, as the catheter can serve as a pressure relief mechanism. 2

Special Populations

Neonates and Premature Infants

• Delay permanent shunt insertion until infant reaches approximately 2.5 kg, is infection-free, and CSF protein decreases to <1.5 g/L 1

• Consider antibiotic-impregnated shunt tubing or strict infection reduction protocols, as shunt infection rates are higher in preterm infants (13.8% vs 8.5% overall) 1

Patients with Existing Shunts Undergoing Other Procedures

• For laparoscopic procedures in patients with VP shunts, routine anesthetic monitoring is generally sufficient without shunt catheter clamping, as retrograde valve failure risk is minimal even with intraabdominal pressures up to 80 mmHg 4

Post-Operative Considerations

Structured post-operative monitoring is essential, including serial neurological assessments, monitoring for high-pressure symptoms (headache, nausea, vomiting, visual changes) or low-pressure symptoms (positional headache), and verification of adequate shunt function. 5, 6

Immediate Post-Operative Care

• Monitor for shunt malfunction signs including headache, nausea, vomiting, and visual disturbances 5, 6

• Assess surgical sites for infection or CSF leakage 6

• Document neurological status regularly including pupillary examination 6

• Maintain DVT prophylaxis and adequate pain control 5

Critical Pitfalls to Avoid

• Never assume standard opioid dosing is adequate for the tunneling phase; this is the most painful step and requires specific pre-emptive analgesia 2, 3

• Do not use butorphanol as the primary opioid in neurosurgical patients due to prolonged ICP elevation 2

• Avoid hyperventilation or hypoventilation; maintain strict normocapnia to prevent ICP fluctuations 2

• In children, do not overlook the rapid onset of hypoglycemia during prolonged procedures 1

• Remember that acceleration/deceleration during transport can cause systemic hypotension and ICP spikes in unstable patients 1